Distinct patterns of alterations between intestinal and diffuse types of gastric tumors support the hypothesis that these types follow different genetic pathways.

Our study investigated the relationship between MYC alterations and clinicopathological features in gastric cancers. We evaluated the effect of MYC mRNA expression and its protein immunoreactivity, as well as copy number variation, promoter DNA methylation, and point mutations, in 125 gastric adenocarcinoma and 67 paried non-neoplastic tissues. We observed that 77% of the tumors presented MYC immunoreactivity which was significantly associated with increased mRNA expression (p<0.05). These observations were associated with deeper tumor extension and the presence of metastasis (p<0.05). MYC protein expression was also more frequently observed in intestinal-type than in diffuse-type tumors (p<0.001). Additionally, MYC mRNA and protein expression were significantly associated with its copy number (p<0.05). The gain of MYC copies was associated with late-onset, intestinal-type, advanced tumor stage, and the presence of distant metastasis (p<0.05). A hypomethylated MYC promoter was detected in 86.4% of tumor samples. MYC hypomethylation was associated with diffuse-type, advanced tumor stage, deeper tumor extension, and the presence of lymph node metastasis (p<0.05). Moreover, eighteen tumor samples presented at least one known mutation. The presence of MYC mutations was associated with diffuse-type tumor (p<0.001). Our results showed that MYC deregulation was mainly associated with poor prognostic features and also reinforced the presence of different pathways involved in intestinal-type and diffuse-type gastric carcinogenesis. Thus, our findings suggest that MYC may be a useful marker for clinical stratification and prognosis.

MYC is an oncogene involved in cell cycle regulation, cell growth arrest, cell adhesion, metabolism, ribosome biogenesis, protein synthesis, and mitochondrial function. It has been described as a key element of several carcinogenesis processes in humans. Many studies have shown an association between MYC deregulation and gastric cancer. MYC deregulation is also seen in gastric preneoplastic lesions and thus it may have a role in early gastric carcinogenesis. Several studies have suggested that amplification is the main mechanism of MYC deregulation in gastric cancer.In the present review, we focus on the deregulation of the MYC oncogene in gastric adenocarcinoma c a r c i n o g e n e s i s , i n c l u d i n g i t s a s s o c i a t i o n w i t h Helicobacter pylori (H pylori ) MYC AND CANCERMYC gene was found to be the cellular homolog of retroviral v-myc oncogene about 30 years ago [12][13][14] . It is located on chromosomal region 8q24.1, has 3 exons [15,16] and encodes a nuclear phosphoprotein [17] . MYC has to heteromerize with MAX, a protein expressed constitutively, to acquire DNA-binding activity. MYC/MAX dimmers are made viable by a basic region helix-loop-helix leucine-zipper motif (bHLHZip), conserved sequences in the carboxyl terminus of both proteins. MYC/MAX dimmers bind to E-box sequence CACGTG in the promoters of specific target genes and stimulate their transcription [18] . MYC has an effect on up to about 15% of genes in genomes of many organisms, from flies to humans [19] . Groups of genes involved in cell cycle regulation, metabolism, ribosome biogenesis, protein synthesis, and mitochondrial function are over-represented in the Myc target gene network.MYC also consistently represses genes involved in cell growth arrest and cell adhesion [20] . Dominguez-Sola et al [21] recently showed that Myc interacts with the prereplicative complex and localizes to early sites of DNA synthesis. Thus, it also has a direct role in the control of DNA replication.MYC regulates transcription from its targets through several mechanisms, including recruitment of histone acetylases, chromatin modulating proteins, basal transcription factors and DNA methyltransferase [22][23][24][25][26] . Protein products of MYC target genes g o on to mediate the downstream effects of MYC on cell biology. MYC is then rapidly degraded, and the pathway switches to a transcriptionally repressive state when MAX dimerizes with a group of related bHLH-Zip proteins, the MAD family, that act as MYC antagonists [27] ( Figure 1).MYC expression might be regulated transcriptionally (initiation and elongation), post-transcriptionally (mRNA stability and translation) or post-translationally (protein stability) [28] . MYC is generally recognized as an important regulator of proliferation, growth, differentiation and apoptosis [29,30] . Therefore, it is also accepted that the deregulation of MYC expression is a major event in cancer pathogenesis or progression. Deregulated expression of a wild-type MYC protein is suff...

BackgroundMYC deregulation is a common event in gastric carcinogenesis, usually as a consequence of gene amplification, chromosomal translocations, or posttranslational mechanisms. FBXW7 is a p53-controlled tumor-suppressor that plays a role in the regulation of cell cycle exit and reentry via MYC degradation.MethodsWe evaluated MYC, FBXW7, and TP53 copy number, mRNA levels, and protein expression in gastric cancer and paired non-neoplastic specimens from 33 patients and also in gastric adenocarcinoma cell lines. We also determined the invasion potential of the gastric cancer cell lines.ResultsMYC amplification was observed in 51.5% of gastric tumor samples. Deletion of one copy of FBXW7 and TP53 was observed in 45.5% and 21.2% of gastric tumors, respectively. MYC mRNA expression was significantly higher in tumors than in non-neoplastic samples. FBXW7 and TP53 mRNA expression was markedly lower in tumors than in paired non-neoplastic specimens. Moreover, deregulated MYC and FBXW7 mRNA expression was associated with the presence of lymph node metastasis and tumor stage III-IV. Additionally, MYC immunostaining was more frequently observed in intestinal-type than diffuse-type gastric cancers and was associated with MYC mRNA expression. In vitro studies showed that increased MYC and reduced FBXW7 expression is associated with a more invasive phenotype in gastric cancer cell lines. This result encouraged us to investigate the activity of the gelatinases MMP-2 and MMP-9 in both cell lines. Both gelatinases are synthesized predominantly by stromal cells rather than cancer cells, and it has been proposed that both contribute to cancer progression. We observed a significant increase in MMP-9 activity in ACP02 compared with ACP03 cells. These results confirmed that ACP02 cells have greater invasion capability than ACP03 cells.ConclusionIn conclusion, FBXW7 and MYC mRNA may play a role in aggressive biologic behavior of gastric cancer cells and may be a useful indicator of poor prognosis. Furthermore, MYC is a candidate target for new therapies against gastric cancer.