In the intestinal epithelium, the Cdx, GATA, and HNF transcription factor families are responsible for the expression of differentiation markers such as sucrase-isomaltase. Although previous studies have shown that Cdx2 can induce differentiation in rat intestinal IEC-6 cells, no data are available concerning the direct implication of transcription factors on differentiation in human normal intestinal epithelial cell types. We investigated the role of Cdx2, GATA-4, and HNF-1α using the undifferentiated human intestinal epithelial crypt cell line HIEC. These transcription factors were tested on proliferation and expression of polarization and differentiation markers. Ectopic expression of Cdx2 or HNF-1α, alone or in combination, altered cell proliferation abilities through the regulation of cyclin D1 and p27 expression. HNF-1α and GATA-4 together induced morphological modifications of the cells toward polarization, resulting in the appearance of functional features such as microvilli. HNF-1α was also sufficient to induce the expression of cadherins and dipeptidylpeptidase, whereas in combination with Cdx2 it allowed the expression of the late differentiation marker sucrase-isomaltase. Large-scale analysis of gene expression confirmed the cooperative effect of these factors. Finally, although DcamKL1 and Musashi-1 expression were downregulated in differentiated HIEC, other intestinal stem cell markers, such as Bmi1, were unaffected. These observations show that, in cooperation with Cdx2, HNF-1α acts as a key factor on human intestinal cells to trigger the onset of their functional differentiation program whereas GATA-4 appears to promote morphological changes.

BackgroundIntegrins are known to be important contributors to cancer progression. We have previously shown that the integrin β4 subunit is up-regulated in primary colon cancer. Its partner, the integrin α6 subunit, exists as two different mRNA splice variants, α6A and α6B, that differ in their cytoplasmic domains but evidence for distinct biological functions of these α6 splice variants is still lacking.MethodsIn this work, we first analyzed the expression of integrin α6A and α6B at the protein and transcript levels in normal human colonic cells as well as colorectal adenocarcinoma cells from both primary tumors and established cell lines. Then, using forced expression experiments, we investigated the effect of α6A and α6B on the regulation of cell proliferation in a colon cancer cell line.ResultsUsing variant-specific antibodies, we observed that α6A and α6B are differentially expressed both within the normal adult colonic epithelium and between normal and diseased colonic tissues. Proliferative cells located in the lower half of the glands were found to predominantly express α6A, while the differentiated and quiescent colonocytes in the upper half of the glands and surface epithelium expressed α6B. A relative decrease of α6B expression was also identified in primary colon tumors and adenocarcinoma cell lines suggesting that the α6A/α6B ratios may be linked to the proliferative status of colonic cells. Additional studies in colon cancer cells showed that experimentally restoring the α6A/α6B balance in favor of α6B caused a decrease in cellular S-phase entry and repressed the activity of c-Myc.ConclusionThe findings that the α6Bβ4 integrin is expressed in quiescent normal colonic cells and is significantly down-regulated in colon cancer cells relative to its α6Aβ4 counterpart are consistent with the anti-proliferative influence and inhibitory effect on c-Myc activity identified for this α6Bβ4 integrin. Taken together, these findings point out the importance of integrin variant expression in colon cancer cell biology.

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The integrin 6 subunit exists as two diVerent variants, termed 6A and 6B. These two variants have been shown to harbor potentially distinct biochemical properties but little is known about their cellular function. The aim of this work was to characterize the expression of the integrin 6A and B variants in relation to cell proliferation and diVerentiation in the human small intestinal epithelium. The results showed distinct expression patterns for the two variants along the crypt-villus axis. Indeed, proliferative cells of the crypt were found to predominantly express 6A, while diVerentiated enterocytes and Paneth cells expressed the 6B variant. A similar relationship was observed in intestinal cell models by competitive RT-PCR. Further studies in the Caco-2 cell model showed that manipulating the cellular balance of the two 6 variants can inXuence transcriptional activities related to cell proliferation but not diVerentiation. This suggests that diVerential expression of the 6 subunits is involved in the intestinal epithelial cell renewal process. Further studies will be needed to substantiate this hypothesis.