Role of p27(Kip1) in human intestinal cell differentiation

Growth arrest and differentiation are generally considered to be temporally and functionally linked phenomena in the intestinal epithelium. To delineate the mechanism(s) responsible for the loss of proliferative potential as committed intestinal cells start to differentiate, we have analyzed the regulation of G(1)-phase regulatory proteins in relation to differentiation in the intact epithelium as well as in well-established intestinal cell models that allow the recapitulation of the crypt-villus axis in vitro. With intestinal cell differentiation, we have observed an induction of the cell cycle inhibitors p21(Cip), p27(Kip1), and p57(Kip2) expression with an increased association of p27(Kip1) and p57(Kip2) with cyclin-dependent kinase 2 (Cdk2). At the same time, there was an accumulation of the hypophosphorylated form of the pRb proteins and a strong decline in Cdk2 activity. Stable expression of a p27(Kip1) antisense complementary DNA in Caco-2/15 cells did not prevent growth arrest induced by confluence, but repressed villin, sucrase-isomaltase, and alkaline phosphatase expression. Our results indicate that the growth arrest that precedes differentiation involves the activation of Rb proteins and the inhibition of Cdk2. Furthermore, intestinal cell differentiation apparently requires a function of p27(Kip1) other than that which leads to inhibition of Cdks.