Deregulation of E2F1 activity and resistance to TGFbeta are hallmarks of gastric cancer. MicroRNAs (miRNAs) are small noncoding RNAs frequently misregulated in human malignancies. Here we provide evidence that the miR-106b-25 cluster, upregulated in a subset of human gastric tumors, is activated by E2F1 in parallel with its host gene, Mcm7. In turn, miR-106b and miR-93 regulate E2F1 expression, establishing a miRNA-directed negative feedback loop. Furthermore, upregulation of these miRNAs impairs the TGFbeta tumor suppressor pathway, interfering with the expression of CDKN1A (p21(Waf1/Cip1)) and BCL2L11 (Bim). Together, these results suggest that the miR-106b-25 cluster is involved in E2F1 posttranscriptional regulation and may play a key role in the development of TGFbeta resistance in gastric cancer.

The CDX1 homeobox gene encodes a transcription factor specifically expressed in normal intestinal and colonic epithelia, and CDX1 gene expression is affected during colorectal tumour progression. In this study, real-time quantitative RT-PCR was used to investigate CDX1 expression in 26 colorectal carcinomas. Reduced expression of CDX1 was observed in 19 of 26 colon carcinomas compared to matched normal colonic mucosa: the decrease in CDX1 expression ranged between 0.10 and 0.79 (21-90% decrease; mean 64.75% +/-22; p = 0.001). Mutation and loss of heterozygosity (LOH) analyses were then used to determine if reduced CDX1 expression was due to genetic alteration. No CDX1 gene mutations, but two known polymorphisms in exon 1, were observed. LOH was observed in 33% of the tumours investigated but this was not related to CDX1 expression. Since aberrant promoter methylation is a well-known mechanism that participates in gene silencing, the methylation status of the CDX1 5' CpG island promoter was also investigated. PCR amplification of bisulphite-treated DNA followed by cloning was performed in 7 carcinomas that showed low expression of CDX1 and in 1 colonic carcinoma without reduced expression. Promoter hypermethylation occurred in carcinomas in which CDX1 reduced expression was present. These results suggest that CDX1 promoter hypermethylation is one of the molecular mechanisms that accounts for reduced CDX1 gene expression in colorectal carcinoma.

According to our results the MSI-H status was associated with particular features (right locations/locally advanced tumors). The results of a long-term follow-up indicate a trend for better survival in MSI-H vs MSS patients. Notably, an increased LNR is associated with worse survivals, both at the univariate and multivariate analysis, displaying this ratio as the strongest prognostic factor of cancer-related survival.

Identification of molecular alterations with implication for prognosis and sensibility to chemotherapeutic agents represents a great challenge in colorectal carcinoma treatment. Controversial results have been reported on prognostic value of chromosome 18q loss. Ninety-seven unselected patients with sporadic colorectal carcinoma Stage II and III were investigated for loss of heterozygosity at 18q D18S58 and D18S61 loci. Molecular alterations were correlated with clinicopathological data and survival. 18q loss of heterozygosity (LOH) was present in 56 per cent cases of carcinoma and was not related either to the clinicopathological characteristics of the patients or to prognosis. However, patients with LOH at locus D18S61 showed a more favorable prognosis. This finding was especially true for Stage II and untreated carcinoma. Survival was not influenced by the status of D18S58 locus. In our series, LOH at chromosome 18q does not seem to predict an unfavorable outcome. It seems of special interest the benefit that D18S61 loss of heterozygosity confers to untreated patients and patients with Stage II colon carcinoma.