Upregulation of LncRNA SNHG15 indicates an unfavourable prognosis and clinical features of patients in multiple malignancies: a meta-analysis and bioinformatics

Background: A snoRNA host gene named SNHG15 which produces a short half-lived lncRNA has been reported to be dysregulated in multiple cancers and correlated with tumor progression in published researches recently. So this meta-analysis was performed to evaluate the generalized prognostic effect of SNHG15 on malignancies because of the discrepant data amongst different studies. Methods: Four public databases were utilized for identifying eligible studies. The association between prognostic indicators and clinical features were extracted and pooled for estimation of the hazard ratios (HRs) or odds ratios (ORs) with 95% condence intervals (CIs). Publication bias and the stability of pooled results were measured by Begg’s test, Egger’s test and sensitivity analysis respectively. Additionally, Online database based on The Cancer Genome Atlas (TCGA) was screened and further validate our results. Results: Totally eleven studies including 1087 patients were ultimately enrolled in our paper. Promoted SNHG15 expression was associted with worse OS and DFS.Moreover, increased SNHG15 expression suggested advanced TNM stage and LNM but not correlated with age, gender and tumor size. No publication bias and instability of result were observed. SNHG15 was signicantly upregulated in seven cancers and elevated expression of SNHG15 indicated shorter OS and DFS in ve malignancies according to the validation using GEPIA (Gene Expression Proling Interactive Analysis). Conclusions: Promoted expression of lncRNA SNHG15 was markedly related to worse prognosis and clinical features, suggesting that SNHG15 might serve as a novel factor in various cancers.

interacting protein 5 antisense RNA 1) have been identi ed as potential prognostic biomarkers which were involved in modulation of tumor-related genes and molecular mechanism in human cancers [6][7][8].
However,owing to inconsistence existed amongst those published studies, small number of patient samples and different detection methods, the prognostic value of SNHG15 remains discrepant and inde nite.Therefore,we conducted this meta-analysis and bioinformatic validation to identify whether SNHG15 could characterize as a noninvasive predictor of tumors and tried to reach consensus on the prognostic value of this gene.

Search strategies for eligible literatures
Potential relevant articles that investigate the association between SNHG15 expression and clinical outcomes of cancers were thorough searched using PubMed, Web of science, Embase and the Cochrane Library up to February 26, 2020. There domains of keywords in multiple combinations were utilized as searched subjects as follows: ("long noncoding RNA" OR "lncRNA") AND ("SNHG15" OR "small nucleolar RNA host gene 15") AND ("Cancer" OR "Cancers" OR "Tumors" OR "Tumor" OR "Malignancy" OR "Malignancies" OR "Neoplasia" OR "Neoplasias" OR "Neoplasm" OR "Malignant Neoplasms" OR "Malignant Neoplasm" OR "Neoplasm, Malignant" OR "Neoplasms, Benign" OR "Benign Neoplasm" OR "Neoplasms, Malignant" OR "Benign Neoplasms" OR "Neoplasm, Benign"). Further manual search was conducted to avoid the ellipsis of eligible papers by screening the title and abstracts of references list in pertinent articles.

Inclusion and exclusion criteria
All enrolled researches were assessed by two independent investigators and disagreements were solved by reaching a consensus after discussing with the third author. Articles that met the following criterias would be enrolled in our study:(1) original articles investigated the roles of SNHG15 in cancers which were de nitively diagnosed by histopathology;(2) samples were cancer tissue and adjacent normal tissue; (3)Detection method was qRT-PCR;(4)clinical features including age,gender,tumor size,TNM stage, lymph node metastasis or distant metastasis and prognosic indicators like OS,DFS or PFS were both reported in paper.(5) patients were categorized into promoted SNHG15 expression group and decreased SNHG15 expression group on the basis of the cut-off value and the number of these two groups was illustrated explicitly. (6) HRs and 95% CIs were reported by multivariate analysis from the articles or were available to be calculated via the Kaplans-Meier curves indirectly. (7)The language of articles was English.
Exclusion criteria:(1)studies explored other lncRNAs or were not related to cancers;(2)duplicate articles; (3)other literature type like review,letter,conference abstract,meta-analysis, case report,retraction; (4)articles focused on biological functions;(5)lack of su cient data for HR and 95% CI extraction.

Data extraction and quality evaluation
The main informations from eligible studies were extracted as follows: rst author, publication year, country, cancer type,sample type,sample size(high/low),cut-off value of SNHG15 expression, assay method, survival(OS/RFS/PFS), HR availability, HR (95%CI) with its P value,follow-up months and NOS scores. If survival rates were not obtained from multivariate analysis, the survival HR (95%CI) were indirectly retrieved from K-M curves via Engauge Digitiser software.The quality of enrolled studies was assessed by Newcastle-Ottawa Scale (NOS) with a range from 0 to 9 and a score more than 6 was considered as quali ed literature.

Validation of bioinformatics database
Gene Expression Pro ling Interactive Analysis (GEPIA), which is based on The Cancer Genome Atlas (TCGA), was performed to further verify the abnormal expression of SNHG15 between cancer tissues and match TCGA normal and GTEx data amongst various neoplasms, using p<0.01 as cut-off value.Moreover, survival plots of the correlation between SNHG15 expression and overall survival (OS) and disease-free survival (DFS) were retrieved as Kaplan-Meier (K-M) curves on the basis of different cancer datasets online.

Statistical analysis
Stata (Version 12.0) was employed to analyze all the datas extracted from articles included and P value < 0.05 indicated the existence of signi cant difference. The hazard ratio(HR) and odds ratio (OR) with their corresponding 95% CIs were utilized to analyse the association between SNHG15 expression and prognosic indicators(OS/DFS),clinical features respectively.And when HR/OR > 1 and 95% CI did not include 1 were observed in the results, it implied that patients with promoted SNHG15 expression had the worse prognosis and advanced clinicopathological parameters.Cochran's Q and I 2 statistics were carried out to measure the heterogeneity across all enrolled studied. A random-effect model was applied with the existence of markedly heterogeneity as I 2 > 50% and P < 0.10 otherwise adopting the x-effect model. Begg's and Egger's tests were quantitatively conducted for detection of underlying publication bias.
Accordingly,sensitivity analysis was used to evaluate the stability of results.

Screening process of publication literatures
The systematically databases search of literatures including initially pertinent publication about the correlation between SNHG15 and cancers in PubMed (n=36), Web of science (n=35), Embase(n=75) and the Cochrane Library(n=0).After originally removing the duplications(n=49),the remained studies(n=97) were browsed for titles and abstracts.72 studies were removed due to irrelvant topics,reviews,case reports,conference abstracts.Next, 25 full-text articles were assessed for eligibility.Among them,nine were removed owing to only focusing on functional exploration of SNHG15,two were excluded for lacking of prognosic data and three articles were precluded due to unclear group number. Ultimately,11 articles containing su cient datas of both survivals and clinical features were enrolled in our metaanalysis. Figure 1 presented the detailed selection process for quali ed publications.

Characteristic description of enrolled studies
Eleven studies with a total of 1087 patients were all performed in China and the published year was from 2016 to 2019.With respect to cancer types,three studies explored lung carcinoma including one lung cancer and two NSCLC, others were respectively gastric cancer, hepatocellular carcinoma, renal cell carcinoma, pancreatic ductal adenocarcinoma, breast cancer, papillary thyroid cancer, colorectal cancer, epithelial ovarian cancer.All samples were cancer tissues and adjacent normal tissues and the detection assay was qRT-PCR.Patients were classi ed as high SNHG15 expression group and low SNHG15 expression group and most studies used median value for cut-off values except one utilizing mean value and one missing. All studies reported overall survival while only two referred to disease-free survival and one mentioned progression-free survival.In terms of HR with 95% CI availability, ve studies could obtain from papers directly and the remaining cohorts were retrieved from K-M curves via Engauge Digitiser software.The follow-up time was ranged from 40 to 180 months. The quality of involved studies was assessed by NOS with a range from 6 to 8 scores. The main features of enrolled studies were listed in Table 1.
To further demonstrate whether SNHG15 could act as a prognostic predictor of cancers, we explore the association between elevated SNHG15 expression and survival indicators (OS/DFS).All enrolled studies reported the overall survival and forest plot revealed that the pooled HR and 95% CI was 1.  Figure3(b)).Because no obvious heterogeneity was observed in the results so we didn't performed subgroup analysis. Additionally,we only conducted publication bias for OS due to only two studies reporting DFS.More detailed informations were integrated in Table 2.

Publication bias and sensitivity analysis for prognosis
The pooled HR for OS and DFS was not in uenced after removing any study one by one in sensitivity analysis,which meant the reliability and stability of our results (Figure4(a-b)). Furthermore, Begg's and Egger's test(P=0.938 and P=0.970) both quantitatively revealed that there was no signi cant publication bias of OS (Figure4(c-d)).
Validation of the results in GEPIA database GEPIA database was utilized to further validate our results. In terms of SNHG15 dysregulation, promoted  (Figure6-7). These results certi ed our conclusions in our paper and indicated that SNHG15 could characterized as a novel prognostic biomarker for cancers.

Discussion
LncRNAs were primitively acknowledged as "transcriptional noise" or "junk DNA" and did not draw investigates' attention in the last few decades [32]. However, research results suggests that aberrant lncRNAs expression may emerge tumor promoting or suppressing e cacy leading to carcinogenesis and cancer progression owing to next-generation genome wide sequencing and microarray widely applying in clinic in recent years [33,34]. For instance, some lncRNAs like NOC2L-4.1, TUG1, MALAT1 are well established as tumor promotors [35][36][37], while other lncRNAs including ASMTL-AS1,LINC02381 LINC02499 could inhibit tumor progression [38][39][40]. Accordingly,the potential molecular modulation participated in the tumor progression may be throughout investigate to better understand the interaction between altered SNHG15 expression and poor prognosis (Table 3). In gastric cancer, SNHG15 upregulation promoted cell proliferation and invasion via modulating the expression of MMP2/MMP9 [21].In terms of lung cancer, the research of Cui et al reported that promoted SNHG15 expression enhanced tumor occurrence and development by targeting miRNA-211-3p via regulating proliferation and migration in vitro [23].Similarly in non-small cell lung cancer,two studies demonstrated that knockdown of SNHG15 could suppress tumorigenesis via inhibiting the expression of EMT,MMP2,MMP9 and regulating the miR-486/CDK14 axis [24,25]. Meanwhile, Du et al identi ed that SNHG15 facilitated renal cell carcinoma invasion and migration through involving NF-κB signaling pathway and inducing EMT process [26].With respect to breast cancer, Kong et al acknowledged that SNHG15 served as a ceRNA to sponge miR-211-3p contributing to the promotion of proliferation, migration and invasion and the inhibition of apoptosis [28].Besides, SNHG15 acted as a ceRNA to modulate miR-200a-3p/YAP1-Hippo molecular mechanism in papillary thyroid carcinoma according to the study of Wu et al [29]. Consistently, function assays revealed that upregulation of SNHG15 facilitated migration, invasion, proliferation, and chemoresistance of epithelial ovarian cancer [31].However,the throughout investigation of the signaling pathways were still insu cient in HCC,PDAC and colorectal cancer so more studies should be performed to explore the potential mechanisms of SNHG15 expression in predicting survival in diverse malignancies [22,27,30] Several highlights should be mentioned in our paper,Firstly, our meta-analysis was the rst study exhaustively investigated the association between SNHG15 expression and clinical outcomes so far.Secondly,only one random-effect model was employed in most of our analysis so the results were quite credible and accurate.Thirdly,we formulated the rigorous inclusion and exclusion criteria to select the enrolled studies for the high-quality of literatures.
Nonetheless, few limitations which should be taken into consideration still exist in our study.First, the region of included subjects were all from China with the small cases of cancer types and sample size,which led to our results only applying in Asia. So we further validated these results via GEPIA database to support our conclusion as far as possible. Second,HR with its 95%Cis were retrived from K-M curves in six studies which may inevitably exaggerate the prognosic value of SNGH15 and produce bias.Third, lack of articles with negative results may overestimate the clinical value of this gene.Fourth,the inconsistent cut-off values may introduce heterogeneity amongst the studies.

Conclusions
Taken together, in spite of above limitations,our study initial indicated that promoted SNHG15 expression was signi cantly associated with unfavorable prognsis and advanced clinical features. However, highquality researches with standardized methods and larger sample size from different country are still in need to further certify our results.

Declarations
Ethics approval and consent to participate Not applicable.

Consent for publication
Not applicable.

Availability of data and materials
All datas are included in our paper.

Competing interests
The authors declare no potential con icts of interest.

Funding
The authors declare that our study is not supported by any fundings.

Author Contributions
WZ designed the concept of study. YL collected and analyzed the data. CZC wrote the manuscript and arranged the tables and gures; JJW and YQF revised the paper. All authors reviewed and approved the nal manuscript.   Figure 1 Flow diagram of this meta-analysis.