Background. Intestinal mucosal turnover is a process of proliferation, differentiation, and apoptosis; the mechanisms remain largely undefined. The purpose of our study was to (I) assess the relationship between apoptosis and enterocyte differentiation and (2) determine whether the cell-cycle inhibitors, p21(Wafl/cip1) and p27(Kip1), or the apoptosis inhibitors, Bcl-2 and Bcl-X(L), may be involved. Methods. Gut-derived Caco-2 cells were treated with sodium butyrate. Apoptosis was assessed by Hoechst stain, DNA laddering, and annexin V assay; differentiation was determined by alkaline phosphatase and sucrase activity. RNA and protein were analyzed for expression of p21(Waf1/Cip1), p27(Kip1), and members of the Bcl-2 family. Results. Treatment of Caco-2 cells with sodium butyrate resulted in the concomitant induction of both differentiation (increased alkaline phosphatase and sucrase activity) and apoptosis. Increased levels of p21(Waf1/Cip1) and p27(Kip1) mRNA and protein were detected at 24 hours, occurring before apoptosis or differentiation; decreased mRNA levels of Bcl-2 and Bcl-X(L) were noted at 24 hours. Conclusions. Differentiation and apoptosis occurred simultaneously in Caco-2 cells, suggesting that apoptosis may be linked to enterocyte differentiation. The induction of p21(Waf1/cip1) and p27(KiP1) and the down- regulation of Bcl-2 and Bcl-X(L) further suggest a link between the cell- cycle mechanisms regulating enterocyte differentiation and apoptosis.
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