The genetic basis for inactivation of Wnt pathway in human osteosarcoma

BMC Cancer201414:450

DOI: 10.1186/1471-2407-14-450

Received: 27 December 2013

Accepted: 5 June 2014

Published: 18 June 2014

Abstract

Background

Osteosarcoma is a highly genetically unstable tumor with poor prognosis. We performed microarray-based comparative genomic hybridization (aCGH), transcriptome sequencing (RNA-seq), and pathway analysis to gain a systemic view of the pathway alterations of osteosarcoma.

Methods

aCGH experiments were carried out on 10 fresh osteosarcoma samples. The output data (Gene Expression Omnibus Series accession number GSE19180) were pooled with published aCGH raw data (GSE9654) to determine recurrent copy number changes. These were analyzed using Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis to identify altered pathways in osteosarcoma. Transcriptome sequencing of six osteosarcomas was performed to detect the expression profile of Wnt signaling pathway genes. Protein expression of WNT1, β-catenin, c-myc, and cyclin D1 in the Wnt pathway was detected by immunohistochemistry (IHC) in an independent group of 46 osteosarcoma samples.

Results

KEGG pathway analysis identified frequent deletions of Wnt and other Wnt signaling pathway genes. At the mRNA level, transcriptome sequencing found reduced levels of mRNA expression of Wnt signaling pathway transcripts. While WNT1 protein expression was detected by IHC in 69.6% (32/46) of the osteosarcomas, no β-catenin protein was detected in the nucleus. β-catenin protein expression was, however, detected in the membrane and cytoplasm of 69.6% (32/46) of the osteosarcomas. c-myc protein expression was detected in only 47.8% (22/46) and cyclin D1 protein expression in 52.2% (24/46) of osteosarcoma samples. Kaplan-Meier survival analysis showed that WNT1-negative patients had a trend towards longer disease free survival than WNT1-positive patients. Interestingly, in WNT1-negative patients, those who were also cyclin D1-negative had significantly longer disease free survival than cyclin D1-positive patients. However, there was no significant association between any of the investigated proteins and overall survival of human osteosarcoma patients.

Conclusions

Frequent deletions of Wnt and other Wnt signaling pathway genes suggest that the Wnt signaling pathway is genetically inactivated in human osteosarcoma.

Keywords

Osteosarcoma Wnt signal pathway Genetic aberration Microarray-based comparative genomic hybridization

Background

Osteosarcoma is a malignant bone tumor, often associated with copy number alterations, that most commonly arises in the metaphyseal ends of long bones [13]. The survival of patients with osteosarcoma has not improved significantly in recent years and the prognosis of patients with metastatic osteosarcoma is especially poor [1]. Identification of prognosis markers and key genetic and molecular events for osteosarcoma is critical for development of effective therapeutics [2, 3].

Fortunately, the discovery of signal transduction pathways and their importance in a variety of cancers has led to the development of many new targeted agents. With regard to osteosarcoma, preclinical investigations targeting the rapamycin (mTOR) pathway, as well as the VEGF pathway showed promising results [2, 4]. The Wnt pathway is clearly important in many forms of human cancer, particularly in epithelial cancer types where gain- or loss-of-function events appear to contribute to both inherited cancer risk and somatic carcinogenesis [5]. In human osteosarcoma, most previous studies have suggested that active Wnt signaling contributes to osteosarcoma development, evidenced by cytoplasmic and/or membranous β-catenin staining or detection of Wnt pathway components [6, 7]. However, Cai and colleagues recently reported that the Wnt pathway is inactivated in osteosarcomas [8]. These contradictory findings provoke debate and stimulate further research into the role of Wnt signaling in osteosarcoma [5].

In this study, we sought to gain a comprehensive understanding of the key driving pathways for osteosarcoma by performing pathway analysis of recurring gene copy number aberrations using array comparative genomic hybridization (aCGH) analysis. Transcriptome sequencing (RNA-seq) and immunohistochemistry (IHC) were used to explore the expression level of key signaling pathways affected by these genetic aberrations. The most surprising and intriguing finding was the deletion of Wnt pathway genes, suggesting the genetic inactivation of the Wnt signaling pathway, in human osteosarcoma.

Methods

Osteosarcoma tissues and clinical information

Ten frozen osteosarcoma biopsy samples, all with at least 90% tumor content, were obtained from the Tissue Bank of the Tianjin Medical University Cancer Institute & Hospital (TMUCIH) for aCGH and RNA-Seq analysis as described below. Tumor samples were snap frozen in liquid nitrogen. In addition, an independent group of 46 primary osteosarcoma cases with formalin-fixed and paraffin-embedded (FFPE) tissues and clinicopathologic data were collected. All of the tissues and information collection took place at Tianjin Medical University Cancer Institute & Hospital (TMUCIH) with Institutional Review Board (IRB) approved protocols and the patients’ consent. The clinical and pathological parameters included age, gender, locations, Enneking staging, and follow-up data (Table 1). All neoadjuvant and adjuvant chemotherapy had been administered according to the Rosen T10 regimen [9, 10]. Disease-free and overall survival time ranged from 0 to 94 months, with medians of 9 and 13 months, respectively.
Table 1

The clinical and pathological features in 46 human conventional osteosarcomas

 

N

Disease free survival

Overall survival

P

HR

95.0% CI

P

HR

95.0% CI

L

U

L

U

Sex

Male

29

0.86

   

0.07*

   

Female

29

0.86

1.11

0.36

3.44

0.08

3.49

0.86

14.28

Age group

<=15 y

14

0.76

   

0.79

   

15-20 y

23

0.94

1.10E + 04

0

1.40E + 116

0.5

1.82

0.32

10.42

21-30 y

11

0.94

3.70E + 04

0

4.40E + 116

0.72

0.73

0.13

4.05

31-40 y

1

0.93

5.30E + 04

0

6.40E + 116

0.97

0

0

1.90E + 282

>40 y

9

1

1.02

0

3.90E + 225

0.99

0

0

 

Tumor location

limbs

51

0.28

   

0.97

   

Others

7

0.48

23.34

0.004

1.60E + 05

0.97

0.97

0.12

7.72

Enneking stage

I

4

0.96

   

0.43

   

IIA

19

0.78

0.71

0.06

7.88

0.17

0.1

0.004

2.74

IIB

2

0.631

0.59

0.07

5.01

0.1

0.09

0.01

1.61

III

1

0.897

0.83

0.05

13.39

0.99

0

0

 

Neoadjuvant chemotherapy

No

10

0.51

   

1.5E-4*

   

Yes

30

0.51

1.51

0.44

5.15

0.003

11.85

2.36

59.45

Adjuvant chemotherapy

No

3

0.21

   

0.41

   

Yes

19

0.43

0.04

0

129.34

0.61

0.04

0

1.20E + 04

Recurrence

No

50

    

0.49

   

Yes

8

    

0.49

2.05

0.26

16.26

Metastasis

No

38

    

0.045*

   

Yes

11

    

0.436

0.01

0

2.40E + 03

*Significantly different; L: lower; U: upper.

Array comparative genomic hybridization and pathway enrichment analysis

The aCGH data analysis was performed as previously described [2, 3]. aCGH data in this publication have been deposited in NCBI’s Gene Expression Omnibus (GEO) and are accessible through GEO Series accession number GSE19180. In addition, we obtained the raw aCGH data of another 10 osteosarcoma biopsy samples from the GEO database (GSE9654) [11] and pooled the two datasets for analysis. Briefly, the median-normalized log-2 ratio data were first subjected to a circular binary segmentation (CBS) algorithm to reduce the effect of noise [12]. Then, the CGHcall algorithm was used to call segments of DNA sequences as amplified or deleted in each sample [13]. A permutation analysis was further applied to call recurrent copy number aberration in osteosarcoma [2]. As a result of this procedure, each target was given a label of “normal”, “deletion” or “amplification” as previously described [2, 3, 13]. A bacterial artificial chromosome (BAC) clone–based CGH array dataset from 36 cases of osteosarcoma was also analyzed to confirm the overall recurrent gene copy alteration patterns [2, 3, 14].

Pathway enrichment analysis was performed separately on the recurrent amplified and deleted gene lists from gene sets GSE19180 and GSE9654 as previously reported [2, 3]. Here, we used the gene annotations data in the Kyoto Encyclopedia of Genes and Genomes (KEGG). Pathways with more annotations in our gene list than expected by random (hypergeometric model, P < 0.05) were considered to be significantly enriched with amplified or deleted genes [2, 3].

RNA-seq analysis

Frozen tumors were crushed, then total RNA was isolated using TRIzol reagent (Invitrogen, Grand Island, NY). RNA was quantified by Qubit (Invitrogen, Grand Island, NY) and Nanodrop ND1000 (ThermoFisher Scientific, Waltham, MA) before quality assessment with the Agilent 2100 Bioanalyzer. Six of the 10 samples with high quality RNA were used for RNA library construction, followed by emulsion PCR and whole transcriptome 90 bp paired-end sequencing on Illumina HiSeq™ 2000 instruments at the Beijing Genomics Institute (BGI, Shenzhen, China). Each sequencing run produced approximately 50 million paired end reads.

Whole transcriptome sequencing reads were aligned against the GRCh37 human reference genome using Tophat version 2.0.4 [15]. The number of overlapping reads was calculated for all exons and then for all genes annotated in Ensembl 67. Gene expression values were normalized across samples using median-of-ratios normalization [16]. Briefly, an expression ratio between two samples for every gene (or exon) with > 500 reads is calculated, and the median of those ratios is determined. All gene expression values are then multiplied by the median-of-ratios.

Immunohistochemical analysis of WNT1, β-catenin, c-myc, and cyclin D1 expression

The 46 FFPE tissues were sectioned at 4 μm and mounted onto charged glass slides (ProbeOn Plus, Fisher Scientific, Pittsburgh, PA, USA) for immunohistochemical staining as described previously [2]. Briefly, tissues were deparaffinized with xylene and ethanol, endogenous peroxidase activity was blocked with 0.3% H2O2 (Fisher Scientific, Fair Lawn, NJ, USA). Tissues were blocked for 30 min with normal serum (Vector Laboratories, Burlingame, CA, USA) and then incubated overnight at 4°C with appropriate antibodies. Antibodies for WNT1, β-catenin, c-myc, and cyclin D1 (Abcam, Cambridge, UK) were used at a dilution of 1:200, 1:100, 1:100, and 1:100, respectively. The same concentrations of non-immune rabbit serum were used as negative controls. Signal was detected using biotinylated anti-rabbit antibodies, followed by avidin, biotinylated enzyme and colorimetric detection using 3,3′-diaminobenzidine tetrahydrachloride (DAB) (DAKO Corporation, Carpinteria, CA, USA). Samples were then counterstained with Mayer’s hematoxylin (Polyscientific, Bay Shore, NY, USA).

Two pathologists, blinded to clinical information, evaluated and scored the immunohistochemical staining for WNT1, β-catenin, c-myc, and cyclin D1 in osteosarcoma tissues based on the overall intensity of membranous, cytoplasmic, and nuclear staining within the tumor cells and the percentage of cells stained [8, 1720]. WNT1 and β-catenin staining were scored as described in [8, 17]. Specifically, intensity of staining was graded as follows: lost (score 0); weak (“+”, score 1); moderate (“++”, score 2); and strong (“+++”, score 3). Extent of staining was evaluated as the percentage of positive cells per 100 or more cells (at least 100 cells in 10 high-power fields) in each evaluated compartment and was graded into five classes as follows: < 5% (score 0); 6% to 25% (score 1); 26% to 50% (score 2); 51% to 75% (score 3); > 75% (score 4). A final staining score was calculated by adding intensity score and extent score for each compartment, and the expression was categorized into two classes based on the final score: positive (final score 2–7) and negative (final score 0–1) expression. For β-catenin staining evaluation, any intensity and extent of staining found in the nucleus was considered positive. The staining of c-myc and cyclin D1 was assessed on the basis of published data: negative (< 10% of the cells), and positive (> 10% of the cells) [1820].

Statistics

Student’s t-test, ANOVA, Chi-square, Fisher’s exact test, Kaplan-Meier, and Mantel-Cox survival analysis were performed using SPSS software 16.0 version when necessary. A P value of less than 0.05 was considered statistically significant in multivariate analysis.

Results

Several signaling pathways are genetically altered in osteosarcoma

As presented in our previous reports, high-density genome-wide aCGH profiling (GSE19180) of 10 osteosarcoma tissues identified several major regions with significant genetic alterations. This pattern of copy number alterations was strikingly similar to that from an independent aCGH dataset (GSE9654) of osteosarcoma samples obtained from Canadian patients [2, 3, 11]. It was therefore reasonable to pool the two aCGH datasets (GSE19180 and GSE 9654) for further pathway analysis. Analysis of the combined dataset led to the identification of the amplification of 2,519 genes and deletion of 1,276 genes among the 20 osteosarcoma samples (Figure 1A). We also analyzed a BAC clone-based, aCGH dataset from 36 Norwegian osteosarcoma samples (Figure 1B) [14]. The analysis of this third dataset showed similar results to the first 20 aCGH osteosarcomas, suggesting consistent genetic alterations underlying the pathogenesis of osteosarcoma.
http://static-content.springer.com/image/art%3A10.1186%2F1471-2407-14-450/MediaObjects/12885_2013_4628_Fig1_HTML.jpg
Figure 1

Genetic aberrations in human osteosarcoma samples. The x-axis numbered with 1–22 denotes chromosome numbers. The y-axis denotes log-ratio for every aCGH probe (scatter plot). The y-axis shows recurrence of gains (positive axis) and losses (negative axis) for each measured sequence aligned evenly in chromosomal order on the x-axis. Recurrence rates that exceed the threshold are color-coded to emphasize the locations of significantly recurrent aberrations. Red denotes significantly recurrent amplifications and green denotes significantly recurrent deletions. Gray represents nonsignificant recurrence of aberrations. A. Genetic aberrations of 20 osteosarcomas (GSE19180 and GSE9654). B. Genetic aberrations of 36 Norwegian osteosarcoma samples.

The GSE19180 and GSE9654 datasets were measured on Agilent Human Genome CGH Microarrays, while the third aCGH dataset was BAC clone-based. Therefore the KEGG pathway enrichment analysis was only performed on dataset GSE19180 and GSE9654. In the KEGG pathway enrichment analysis, significant genetic amplifications were identified in the component genes of 20 signaling pathways including the VEGF, mTOR, CAMs, and adherens junction signaling pathways. Significant genetic deletions were identified in the component genes of 11 signaling pathways including the Wnt and Hedgehog signaling pathways (Tables 2 and 3). In our previous studies, the integrated methods of aCGH, fluorescent in situ hybridization (FISH), and IHC has led to validation of the genetic amplification of VEGF pathway genes [2].
Table 2

Genetic amplifications of key pathway genes in osteosarcoma

KEEG pathways

P-value

Gene name cohort

VEGF signaling pathway

0.000611811

MAPK14, AKT1, PLA2G2D, PLA2G2E, NFATC4, PIK3CD, PLA2G2A, PLA2G5, MAPK1, MAPK13, PTK2, RAC1, RAC3, PLA2G2F, VEGFA, CASP9, PIK3R3, SPHK1, SH2D2A, CDC42P2, CDC42

mTOR signaling pathway

0.024894273

AKT1, MTOR, RICTOR, PIK3CD, PRKAA1, PRKAA2, MAPK1, RPTOR, RPS6KA1, VEGFA, PIK3R3, ULK2

Tight junction

0.044332801

INADL, EXOC3, CSNK2B, CLDN19, AKT1, CLDN14, CLDN17, LLGL2, LLGL1, MYH6, MYH7, F11R, ASH1L, PRKCZ, CGN, JAM2, RAB3B, RAB13, ACTB, ACTG1, CLDN5, CLDN8, CRB3, TJAP1, CDC42P2, CDC42

Synthesis and degradation of ketone bodies

0.019871373

HMGCL, HMGCS1, HMGCS2, OXCT1

C21-Steroid hormone metabolism

0.04221587

CYP11B1, CYP11B2, HSD3B1, HSD3B2

Peptidoglycan biosynthesis

0.017208179

PGLYRP2, PGLYRP3, PGLYRP4

Ether lipid metabolism

0.006547877

AGPAT1, PLA2G2D, PLA2G2E, PAFAH2, ENPP2, PLA2G2A, PLA2G5, AGPAT3, PLA2G2F, PPAP2B

Arachidonic acid metabolism

0.02227667

CYP2J2, CYP4A11, GPX6, PLA2G2D, GPX5, GPX7, PLA2G2E, CYP4F3, PLA2G2A, PLA2G5, PLA2G2F, CYP4F2, CBR3

Alpha-Linolenic acid metabolism

0.003362937

PLA2G2D, PLA2G2E, ACOX1, PLA2G2A, PLA2G5, PLA2G2F, FADS2

Nitrogen metabolism

0.007842327

CTH, CA14, CA1, CA2, CA3, CA6, CA8, ASRGL1

Glycan structures-biosynthesis 2

0.025972282

PIGK, B3GALT5, ST6GALNAC3, PIGP, PIGV, ST3GAL1, ST3GAL3, ST6GALNAC5, B4GALT3, B4GALT2, B3GALT4, GPAA1, PIGM, PIGL

Biosynthesis of unsaturated fatty acids

0.021314211

ACOT7, FASN, ACOT11, FADS1, ACOX1, FADS2, TECR

Antigen processing and presentation

0.028228218

CTSS, HLA-DMA, HLA-DMB, HLA-DOA, HLA-DOB, HLA-DPA1, HLA-DQA2, HLA-DRB5, HLA-F, HSPA1B, HSPA1A, HSPA1L, HSP90AB1, NFYA, NFYC, RFX5, TAP1, TAP2, CALR

Fc epsilon RI signaling pathway

0.000481297

MAPK14, AKT1, FCER1A, FCER1G, PLA2G2D, GRB2, PLA2G2E, LYN, PIK3CD, PLA2G2A, PLA2G5, MAPK1, MAPK13, MAP2K3, MAP2K7, RAC1, RAC3, PLA2G2F, TNF, VAV1, PIK3R3

Insulin signaling pathway

0.047775005

FLOT1, CRKL, AKT1, FASN, EXOC7, MTOR, GRB2, INSR, PFKL, PIK3CD, PKLR, PRKAA1, PRKAA2, PRKAB2, PRKACA, PRKACB, PRKCZ, MAPK1, RPTOR, PTPRF, SHC1, SREBF1, PIK3R3, MKNK1, TRIP10

GnRH signaling pathway

0.04873803

ADCY8, MAPK14, ADCY4, PLA2G2D, GRB2, PLA2G2E, ITPR3, JUN, PLA2G2A, PLA2G5, PRKACA, PRKACB, MAPK1, MAPK7, MAPK13, MAP2K3, MAP2K7, PLA2G2F, CDC42P2, CDC42

Alzheimer’s disease

0.020850782

NCSTN, BACE2, APP, APH1A, C1QA, TNF, C1QB, C1QC

Asthma

0.003038215

FCER1A, FCER1G, HLA-DMA, HLA-DMB, HLA-DOA, HLA-DOB, HLA-DPA1, HLA-DQA2, HLA-DRB5, TNF

Systemic lupus erythematosus

2.49E-06

FCGR1A, FCGR2A, FCGR2B, FCGR3A, HIST1H2AB, HIST1H2AE, HIST1H2BD, H3F3B, H3F3A, HLA-DMA, HLA-DMB, HLA-DOA, HLA-DOB, HLA-DPA1, HLA-DQA2, HLA-DRB5, HIST2H2AB, C1QA, TNF, C1QB, C1QC, C2, C3, C6, C7, C8A, C8B, C9, HIST1H2AG, SMCHD1, HIST1H2AI, HIST1H2AK, HIST1H2AL, HIST1H2AM, HIST1H2AJ, HIST1H2AC, HIST2H2AC, HIST1H2BC, HIST1H2BE, HIST1H2BF, HIST1H2BG, HIST1H2BI, HIST1H2BO, HIST2H2BE, HIST1H3A, HIST1H3B, HIST1H3C, HIST1H3D, HIST1H3E, HIST1H3F, HIST1H3G, HIST1H3H, HIST1H3I, HIST1H3J, HIST4H4, HIST1H4A, HIST1H4B, HIST1H4C, HIST1H4D, HIST1H4E, HIST1H4F, HIST1H4H, HIST1H4I, HIST1H4J, HIST1H4K, HIST1H4L, HIST2H4A, HIST2H4B, HIST1H4G, HIST1H2AH, HIST1H2BK, HIST1H2BJ

Allograft rejection

0.046891168

HLA-DMA, HLA-DMB, HLA-DOA, HLA-DOB, HLA-DPA1, HLA-DQA2, HLA-DRB5, HLA-F, TNF

Table 3

Genetic deletions of key pathway genes in osteosarcoma

KEEG pathways

P value

Gene name cohort

Wnt signaling pathway

0.01039

FRAT1, CSNK1A1L, CTBP2, PRICKLE2, FRAT2, GSK3B, PLCB2, SFRP5, MAP3K7, TCF7L2, WNT5A, WNT6, WNT8B, FZD5, WNT10A, FZD7, FZD8, BTRC

Hedgehog signaling pathway

0.012811

CSNK1A1L, STK36, GSK3B, SUFU, WNT5A, WNT6, WNT8B, WNT10A, BTRC

Adherens junction

0.014329

SORBS1, WASF3, FER, FYN, PVRL3, MLLT4, PARD3, MAP3K7, TCF7L2, VCL, WASF1

Metabolism of xenobiotics by cytochrome P450

0.006437

AKR1C4, GSTO2, CYP2C19, CYP2C8, CYP2C9, CYP2C18, AKR1C1, AKR1C2, UGT1A8, AKR1C3, GSTO1

PPAR signaling pathway

0.039963

SORBS1, CYP27A1, FABP7, ACSL3, ACADL, ME1, ACSL5, SCD, ACOX2

Non-homologous end-joining

0.001607

DNTT, POLL, DCLRE1C, XRCC5, NHEJ1

Phosphatidylinositol signaling system

0.040426

DGKH, INPP5D, PLCE1, CALML5, PIK3R1, GNG7, PIP4K2A, PLCB2, PTEN, PLCD4, DGKD

ECM-receptor interaction

0.032505

COL6A3, FNDC3A, SV2C, FN1, ITGA1, ITGB1, LAMA4, THBS1, THBS2, ITGA8, CD47

T cell receptor signaling pathway

0.020903

RASGRP1, CHUK, MAP3K8, CTLA4, FYN, ICOS, NFKB2, PIK3R1, PRKCQ, PAK6, CBLB, CD28

Melanogenesis

0.007761

ADCY5, CREB1, GSK3B, MITF, CALML5, PLCB2, TCF7L2, WNT5A, WNT6, WNT8B, FZD5, WNT10A, FZD7, FZD8

Basal cell carcinoma

0.00088

STK36, GSK3B, SUFU, TCF7L2, WNT5A, WNT6, WNT8B, FZD5, WNT10A, FZD7, FZD8

Wnt pathway genes are deleted in human osteosarcomas

In contrast to the amplification of VEGF pathway genes, we detected significant over-representation of deleted genes in 11 pathways. Among these pathways, the Wnt signaling pathway was most highly affected (Table 3). This is the first description of this genetic aberration in human osteosarcoma. As controversy exists in the field as to whether the Wnt signaling pathway is inactivated or not in osteosarcoma [8, 21], we further investigated copy number alterations of individual genes in the Wnt signaling pathway. In the canonical Wnt signaling pathway, the following genes were significantly deleted across the osteosarcoma dataset: WNT, FRP, Frizzled, GBP, GSK-3β, TCF/LET, TAK1, CK1, CtBP, and B-TrCP (Figure 2). Specifically, the WNT1 gene was deleted in 10 cases of the 20 human osteosarcomas with a deletion frequency of 50%.
http://static-content.springer.com/image/art%3A10.1186%2F1471-2407-14-450/MediaObjects/12885_2013_4628_Fig2_HTML.jpg
Figure 2

Visualization of the location of altered genes in the Wnt pathway. Pink indicates genes with significantly recurrent amplification, and green denotes genes with significantly recurrent deletion. White indicates genes with no significant aberrations.

Reduced transcript and protein expression of Wnt signaling pathway components suggests the Wnt signaling pathway is inactivated in human osteosarcomas

To determine whether there was an association between gene copy number and mRNA expression of Wnt pathway genes, we compared transcriptome sequencing data of six osteosarcoma samples (Additional file 1) with aCGH analysis performed on their genomic DNA (Additional file 2). We found that the deletion of certain genes was associated with low mRNA expression, such as NLK, SOX1, MAPK8, MAP1B, and FZD7 genes (Figure 3).To further explore the expression level of Wnt signaling pathways and its effect on the downstream signaling, WNT1, β-catenin, c-myc, and cyclin D1 protein expression was measured by IHC in 46 osteosarcoma samples (Figure 4A-D). WNT1 protein expression was detected predominantly in cytoplasm. β-catenin protein expression was observed in the membrane and cytoplasm but not in the nucleus. c-myc and cyclin D1 protein expression were detected in the nucleus. No protein expression was detected in negative control samples.
http://static-content.springer.com/image/art%3A10.1186%2F1471-2407-14-450/MediaObjects/12885_2013_4628_Fig3_HTML.jpg
Figure 3

mRNA expression of genes in the Wnt signaling pathway. Circle color indicates copy number (red are amplified, blue are deleted). Circle size indicates mRNA expression level calculated based on RNA-seq reads. Absolute expression: the size of circles is based on the absolute read count (Left panel). Normalized expression: the size of circles is relative to the average expression (Right panel). Primary data for aCGH and RNA-seq can be found in Additional files 1 and 2.

http://static-content.springer.com/image/art%3A10.1186%2F1471-2407-14-450/MediaObjects/12885_2013_4628_Fig4_HTML.jpg
Figure 4

Protein expression of the Wnt signaling pathway and its role in survival. A. WNT1 protein expression (IHC, 10 × 40). B. β-catenin protein expression (IHC, 10 × 40). C. c-myc protein expression (IHC, 10 × 40). D. Cyclin D1 protein expression (IHC, 10 × 40). E. Disease free time of WNT1-negative patients was not significantly longer than WNT1-positive patients. F. K-M survival analysis showed that patients negative for both WNT1 and cyclin D1 expression had significantly longer disease free survival time.

WNT1 protein expression was detected in 69.6% (32/46) of the osteosarcomas (Figure 4A), however no β-catenin protein expression was observed in the nucleus (Figure 4B). β-catenin protein expression was detected in the membrane and cytoplasm of 69.6% (32/46) of the osteosarcomas (Figure 4B), negative c-myc protein expression was recorded for 52.2% (24/46) of osteosarcomas and negative cyclin D1 protein expression was recorded for 47.8% (22/46) of osteosarcomas (Figure 4C-D). Compared with previously published reports of c-myc and cyclin D1 expression frequencies in other tumors, such as endometrial carcinoma [22, 23], these detection frequencies (47.8% (22/46) c-myc-positive and 52.2% (24/46) cyclin D1-positive) are low. Combined with the low levels of mRNA expression for Wnt pathway genes, these data, especially the lack of β-catenin protein expression in the nucleus, suggest that the Wnt signaling pathway may be inactive.

Negative expression of WNT1 and cyclin D1 is associated with longer disease-free survival

While the expression of WNT1, β-catenin, c-myc, and cyclin D1 had no correlation with clinicopathological factors, WNT1 expression had significant positive correlation with β-catenin (χ2 = 15.97, P = 0.001, Pearson’s R = 0.59), c-myc (χ2 = 5.62, P = 0.018, Pearson’s R = 0.35), and cyclin D1 expression (χ2 = 11.58, P = 0.001, Pearson’s R = 0.50). β-catenin protein expression had significant positive correlation with c-myc (χ2 = 5.62, p = 0.018, Pearson’s R = 0.35) and cyclin D1 (χ2 = 16.36, p = 5.25E-5, Pearson’s R = 0.6). Because β-catenin is a key mediating factor and c-myc/cyclin D1 are key targets regulated by the Wnt signaling pathway, these consistent relationships suggest that the initial signal, mediating factor, and downstream events of the Wnt signaling pathway may all be inactivated in human osteosarcoma.

To detect the effect of the Wnt signaling pathway on survival, the disease-free and total survival of patients were analyzed. Even though single protein expression of β-catenin, c-myc and cyclin D1 showed no significant effect on disease-free survival, K-M survival analysis showed that WNT1-negative patients had a trend towards longer disease-free survival than WNT1-positive patients, although this was not statistically significant (Log Rank = 2.452, P = 0.117) (Figure 4E).Patients negative for all of WNT1, β-catenin and cyclin D1/c-myc protein expression might be considered to have an inactivated Wnt signaling pathway. Therefore, the survival of such patients will reflect the effect of inactivation of the Wnt signaling pathway on survival. Indeed, our data showed that in the patients who were negative for WNT1 protein expression, those who were also negative for cyclin D1 expression had significantly longer disease-free survival than patients with positive cyclin D1 expression (Log Rank = 3.884, P = 0.049) (Figure 4F). However, expression of none of the proteins examined had significant correlation with the overall survival of human osteosarcoma patients.

Discussion

In this study we describe, for the first time, significant deletion of genes involved in the Wnt signaling pathway, implying genetic inactivation of this important signaling pathway, in human osteosarcoma. Supporting this, transcriptome analysis determined that mRNA expression of genes in the Wnt signaling pathway was reduced. In addition, at the protein level, nuclear β-catenin expression was not observed and c-myc/cyclin D1 protein were detected at lower frequencies compared with the frequencies observed in other tumors. Our results are in agreement with published data from Cai and colleagues, who reported that the Wnt pathway is inactivated in bone cancers [8]. Furthermore, similar results were reported by Matushansky and Gregory, indicating that inactivation of the Wnt pathway contributes to tumorigenesis in so-called malignant fibrous histiocytoma and melanoma [17, 21, 24]. In contrast to these results, most previous studies have suggested that active Wnt signaling contributes to osteosarcoma development [6, 7]. Furthermore, it is reported that the Wnt pathway is transcriptionally active in radiation-induced rat osteosarcomas [25], and that the Wnt/β-catenin pathway antagonists, curcumin and PKF118-310, demonstrate anti-tumor activity against human osteosarcoma cells [26]. These seemingly conflicting results suggest that the complexity of this important signaling pathway is still poorly understood in human osteosarcoma [5].

An interesting but unanswered question raised in the present study is: at which time during osteosarcoma progression is the Wnt signaling pathway inactivated. As inactivation of the Wnt signaling pathway is associated with longer disease-free survival, it suggests that this inactivation may occur at an early time point in osteosarcoma progression. However, more investigations in vivo and in vitro are required before this question can be answered.

Conclusions

Based on evidence at the genomic, our data suggest that the Wnt signaling pathway may be genetically inactivated in osteosarcoma. These results remind us of the complexity of this important signaling pathway.

Declarations

Acknowledgments

This work was partly supported by the National Nature Science Foundation of China (81372872 to JY and 81320108022 to KC), the funds from the University Cancer Foundation via the Sister Institution Network Fund (SINF) at the Tianjin Medical University Cancer Institute & Hospital (TMUCIH), Fudan University Shanghai Cancer Center (FUSCC), and University of Texas MD Anderson Cancer Center (UT MDACC), program for Changjiang Scholars and Innovative Research Team in University (PCSIRT) in China (IRT1076), and National Key Scientific and Technological Project (2011ZX09307-001-04) (K. Chen).

The genomic studies were supported by Dr. Wei Zhang (wzhang@mdanderson.org) and the Cancer Genomics Core Laboratory. We would like to thank Limei Hu and David Cogdell for performing the aCGH experiments.

Authors’ Affiliations

(1)
Department of Diagnostics, Tianjin Medical University
(2)
Department of Bone and Soft Tissue Tumors, Tianjin Medical University Cancer Institute & Hospital, National Clinical Research Center for Cancer
(3)
Department of Pathology, The University of Texas MD Anderson Cancer Center
(4)
Department of Medical Microbiology, Tianjin Medical University

References

  1. Picci P, Mercuri M, Ferrari S, Alberghini M, Briccoli A, Ferrari C, Pignotti E, Bacci G: Survival in high-grade osteosarcoma: improvement over 21 years at a single institution. Ann Oncol 2010,21(6):1366–1373.PubMedView Article
  2. Yang J, Yang D, Sun Y, Sun B, Wang G, Trent JC, Araujo DM, Chen K, Zhang W: Genetic amplification of the vascular endothelial growth factor (VEGF) pathway genes, including VEGFA, in human osteosarcoma. Cancer 2011,117(21):4925–4938.PubMed CentralPubMedView Article
  3. Yang J, Cogdell D, Yang D, Hu L, Li H, Zheng H, Du X, Pang Y, Trent J, Chen K, Zhang W: Deletion of the WWOX gene and frequent loss of its protein expression in human osteosarcoma. Cancer Lett 2010,291(1):31–38.PubMedView Article
  4. Bjornsti MA, Houghton PJ: The TOR pathway: a target for cancer therapy. Nat Rev Cancer 2004,4(5):335–348.PubMedView Article
  5. Thomas DM: Wnts, bone and cancer. J Pathol 2010,220(1):1–4.PubMedView Article
  6. Iwaya K, Ogawa H, Kuroda M, Izumi M, Ishida T, Mukai K: Cytoplasmic and/or nuclear staining of beta-catenin is associated with lung metastasis. Clin Exp Metastasis 2003,20(6):525–529.PubMedView Article
  7. Kansara M, Tsang M, Kodjabachian L, Sims NA, Trivett MK, Ehrich M, Dobrovic A, Slavin J, Choong PF, Simmons PJ, Dawid IB, Thomas DM: Wnt inhibitory factor 1 is epigenetically silenced in human osteosarcoma, and targeted disruption accelerates osteosarcomagenesis in mice. J Clin Invest 2009,119(4):837–851.PubMed CentralPubMedView Article
  8. Cai Y, Mohseny AB, Karperien M, Hogendoorn PC, Zhou G, Cleton-Jansen AM: Inactive Wnt/beta-catenin pathway in conventional high-grade osteosarcoma. J Pathol 2010,220(1):24–33.PubMedView Article
  9. Meyers PA, Heller G, Healey J, Huvos A, Lane J, Marcove R, Applewhite A, Vlamis V, Rosen G: Chemotherapy for nonmetastatic osteogenic sarcoma: the Memorial Sloan-Kettering experience. J Clin Oncol 1992,10(1):5–15.PubMed
  10. Boussen H, Mezzi F, Gamoudi A, Daldoul O, Ben Hamida H, Mezlini A, Khalfallah S, Karray S, Ben Romdhane K, Ben Ghachem M, Ben Abdallah M, Douik M, Saadi A, Ben Ayed F, Ben Hassine H: [Primary chemotherapy with the Rosen T10 protocol before conservative surgery in limb primitive osteosarcomas: results about 56 cases]. Bull Cancer 2000,87(2):183–188.PubMed
  11. Squire JA, Pei J, Marrano P, Beheshti B, Bayani J, Lim G, Moldovan L, Zielenska M: High-resolution mapping of amplifications and deletions in pediatric osteosarcoma by use of CGH analysis of cDNA microarrays. Genes Chromosomes Cancer 2003,38(3):215–225.PubMedView Article
  12. Olshen AB, Venkatraman ES, Lucito R, Wigler M: Circular binary segmentation for the analysis of array-based DNA copy number data. Biostatistics 2004,5(4):557–572.PubMedView Article
  13. Van Wieringen WN, Van De Wiel MA, Ylstra B: Weighted clustering of called array CGH data. Biostatistics 2008,9(3):484–500.PubMedView Article
  14. Kresse SH, Ohnstad HO, Paulsen EB, Bjerkehagen B, Szuhai K, Serra M, Schaefer KL, Myklebost O, Meza-Zepeda LA: LSAMP, a novel candidate tumor suppressor gene in human osteosarcomas, identified by array comparative genomic hybridization. Genes Chromosomes Cancer 2009,48(8):679–693.PubMedView Article
  15. Kim D, Pertea G, Trapnell C, Pimentel H, Kelley R, Salzberg SL: TopHat2: accurate alignment of transcriptomes in the presence of insertions, deletions and gene fusions. Genome Biol 2013,14(4):R36.PubMed CentralPubMedView Article
  16. Mortazavi A, Williams BA, McCue K, Schaeffer L, Wold B: Mapping and quantifying mammalian transcriptomes by RNA-Seq. Nat Methods 2008,5(7):621–628.PubMedView Article
  17. Chien AJ, Moore EC, Lonsdorf AS, Kulikauskas RM, Rothberg BG, Berger AJ, Major MB, Hwang ST, Rimm DL, Moon RT: Activated Wnt/beta-catenin signaling in melanoma is associated with decreased proliferation in patient tumors and a murine melanoma model. Proc Natl Acad Sci U S A 2009,106(4):1193–1198.PubMed CentralPubMedView Article
  18. De Blasio A, Messina C, Santulli A, Mangano V, Di Leonardo E, D’Anneo A, Tesoriere G, Vento R: Differentiative pathway activated by 3-aminobenzamide, an inhibitor of PARP, in human osteosarcoma MG-63 cells. FEBS Lett 2005,579(3):615–620.PubMedView Article
  19. Gazitt Y, Kolaparthi V, Moncada K, Thomas C, Freeman J: Targeted therapy of human osteosarcoma with 17AAG or rapamycin: characterization of induced apoptosis and inhibition of mTOR and Akt/MAPK/Wnt pathways. Int J Oncol 2009,34(2):551–561.PubMed
  20. Takayama S, Rogatsky I, Schwarcz LE, Darimont BD: The glucocorticoid receptor represses cyclin D1 by targeting the Tcf-beta-catenin complex. J Biol Chem 2006,281(26):17856–17863.PubMedView Article
  21. Matushansky I, Hernando E, Socci ND, Mills JE, Matos TA, Edgar MA, Singer S, Maki RG, Cordon-Cardo C: Derivation of sarcomas from mesenchymal stem cells via inactivation of the Wnt pathway. J Clin Invest 2007,117(11):3248–3257.PubMed CentralPubMedView Article
  22. Gu Y, Pan Y, Meng B, Guan B, Fu K, Sun B, Zheng F: High levels of bcl-2 protein expression do not correlate with genetic abnormalities but predict worse prognosis in patients with lymphoblastic lymphoma. Tumour Biol 2013,34(3):1441–1450.PubMedView Article
  23. Liang S, Mu K, Wang Y, Zhou Z, Zhang J, Sheng Y, Zhang T: CyclinD1, a prominent prognostic marker for endometrial diseases. Diagn Pathol 2013, 8:138.PubMed CentralPubMedView Article
  24. Gregory CA, Singh H, Perry AS, Prockop DJ: The Wnt signaling inhibitor dickkopf-1 is required for reentry into the cell cycle of human adult stem cells from bone marrow. J Biol Chem 2003,278(30):28067–28078.PubMedView Article
  25. Daino K, Ugolin N, Altmeyer-Morel S, Guilly MN, Chevillard S: Gene expression profiling of alpha-radiation-induced rat osteosarcomas: identification of dysregulated genes involved in radiation-induced tumorigenesis of bone. Int J Cancer 2009,125(3):612–620.PubMedView Article
  26. Leow PCTQ, Ong ZY, Yang Z, Ee PL: Antitumor activity of natural compounds, curcumin and p KF118–310, as Wnt/β-catenin antagonists against human osteosarcoma cells. Invest New Drugs 2010,28(6):766–782.PubMedView Article
  27. Pre-publication history

    1. The pre-publication history for this paper can be accessed here: http://​www.​biomedcentral.​com/​1471-2407/​14/​450/​prepub

Copyright

© Du et al.; licensee BioMed Central Ltd. 2014

This article is published under license to BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://​creativecommons.​org/​licenses/​by/​2.​0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly credited. The Creative Commons Public Domain Dedication waiver (http://​creativecommons.​org/​publicdomain/​zero/​1.​0/​) applies to the data made available in this article, unless otherwise stated.