Our results indicate that disturbed THOC1 and ALY expression are associated with tumorogenesis. Overexpression of THOC1 has previously been correlated to the grade of invasiveness in breast tumor, and also a relationship between the levels of this protein in non-small lung cancers has been suggested [12, 15]. This study shows that not only the expression of THOC1, but also that of THO/TREX complex is upregulated in breast cancer cells. Moreover, new links between the expression of THOC1 and different tumors were found. THOC1 mRNA and protein levels are up-regulated in ovarian, and lung tumors and down-regulated in those of testis and skin. Interestingly, we show that ALY, another mRNP biogenesis factor is highly detected in proliferative cells and overexpressed in a broad range of tumors. The different pattern of expression of THOC1 and ALY in tumors could indicate a different relevance for each factor in tumorogenesis. Nevertheless, since many genes are differentially expressed in cancer tissues and cancerous cell populations are highly heterogeneous, any intent of associating a specific expression profile with tumorogenesis needs further studies and confirmations with additional tumor banks .
Our data indicates that overexpression of THOC1 and ALY is specifically associated with tumors, and not a consequence of high metabolism and proliferation of tumor cells, since an altered pattern of expression of transcription factors, such as hSpt4 in the cDNA tumor array, was not observed. At the same time, the different expression pattern of THOC1, as representative of THO, and ALY in normal and tumor tissues, indicates a different relevance of these factors in the tumorogenisis process. In fact, altered expression or dysfunction of other RNA binding proteins involved in different pre-mRNA metabolic steps such as splicing, 3'-end formation are implicated in various diseases including cancer, supporting the physiological relevance of mRNP biogenesis control . High levels of the THOC1 protein were observed in the nuclei of ovarian, and lung cancer tumors in comparison with normal tissues. As a reduction of THOC1 was also associated with some cancers such as those of skin and testis, these results argue against the idea that THOC1 expression would be required for proliferation and survival of oncogene-transformed cells . As THO has a role in mRNP biogenesis, likely general among eukaryotes, it is possible that changes in THOC1 expression could affect mRNP formation as previously reported in yeast [9, 22]. However, we cannot exclude that the pattern of expression of THOC1 in some tumors could also be related to a specific physiological role of THO in different tissues. It is not clear yet whether the physiological relevance is the same in the different tissues and at different stages of development and differentiation. In this sense, it has recently been shown that THOC1 conditional knockout mice affects testis development , and that THOC5 function is critical in bone marrow and hematopoiesis . Therefore THOC1 expression levels might potentially be used as a prognostic indicator in specific tumors, but not a general biomarker.
We provide evidence that high expression levels of ALY are connected to normal proliferative tissues and with a wide variety of tumors. This is in agreement with the proposed role of ALY in cell cycle progression and proliferation . It has been suggested that ALY could be a physiological target of nuclear PI3K signaling, which regulates ALY's subnuclear residency in speckles, as well as, cell proliferation and mRNA export activities through nuclear Akt phosphorylation and phosphoinositide association . Despite this link between mRNA export function and proliferation, other activities of ALY could contribute to tumorogenesis. Thus, ALY has also been proposed as a transcriptional coactivator important for c-myc expression in virally induced leukemias and lymphomas , and the yeast homolog Yra1 has been shown to be required for S phase entry .
It is particularly interesting that high ALY mRNA levels are found in tumor tissues (see cDNA arrays results), whereas low ALY protein levels are associated with high-grade tumors. It is possible that a post-transcriptional regulation of ALY protein occurs in advanced steps of tumorogenesis. Indeed, ALY is regulated by the AKT kinase, and inhibition of ALY phosphorylation substantially decreases cell proliferation and mRNA export . Interestingly, other proteins involved in mRNA export, such as the yeast THOC1 ortholog Hpr1, have been shown to be a target of ubiquitination  and phosphorylation .
Interestingly, the expression profile of ALY seems to be similar to that of other related mRNP-export factors, such as UAP56/Sub2 and NXF1/Mex67, which interact physically and functionally with THO. Human protein atlas IHCs for these factors (CAB034012 and CAB016327) show that normal tissues display a strong nuclear signal and tumor cells exhibited moderate to strong nuclear immunoreactivity. Instead, approximately 40% and 65% of the tumor samples showed a lower staining than the normal tissues in the UAP56 and NXF1 IHC reports respectively. The significant association between altered ALY expression and tumors open the possibility that ALY could be considered as a possible tumor prognostic marker.
We can conclude that an alteration in THOC1 and ALY expression is associated with tumorogenesis. Given the small size of samples available it is possible that for some tests a sizeable true effect may not have been detected in this study, which could explain some of the apparent inconsistencies with other studies. However, the different patterns of expression of the proteins in tumors could indicate a different relevance of each factor in tumorogenesis. Importantly, however, their different pattern of expression would be consistent with a different functional role of these proteins in mRNP biogenesis and export. Despite the physical and functional interactions between these factors, THO behaves as a stable structural core in eukaryotic cells . In fact, Sub2/UAP56 and Yra1/ALY have not been found or are only detected in substoichiometric amounts in chromatography purifications of the THO complex under high salt conditions from yeast, Drosophila and human cell extracts [6, 7, 12]. ALY is not stably associated with THO, and this interaction is mediated by UAP56 and THOC5 [30, 19]. Moreover, although ALY/Yra1 recruitment to chromatin was first shown to be dependent on THO and UAP56/Sub2 factors in yeast , other factors such as the cap-binding protein CBP80 and the transcription elongation factor Spt6 also contribute to the cotranscriptional loading of ALY protein [32, 33]. It seems, therefore, that Yra1/ALY could serve as a bridge between RNA-binding proteins early during mRNP biogenesis, acting upstream during transcription and downstream at mRNA export. The different pattern of expression of THO and ALY in tumors is consistent with a differentiated role of both factors in gene expression, for the correct proliferation of the cell and developmental changes that could take place in tumors.