Role of p27(Kip1) in human intestinal cell differentiation

Background & Aims: Growth arrest and differentiation ave generally consider ed to be temporally and functionally linked phenomena in the intestinal epi thelium. Methods: To delineate the mechanism(s) responsible for the loss of proliferative potential as committed intestinal cells start to differentia te, we have analyzed the regulation of G(1)-phase regulatory proteins in re lation to differentiation in the intact epithelium as well as in well-estab lished intestinal cell models that allow the recapitulation of the crypt-vi llus axis in vitro. Results: With intestinal cell differentiation, we have observed an induction of the cell cycle inhibitors p21(Cip), P27(Klp1) and p57(Klp2) expression with an increased association of p27(Kip1) and p57(Kip 2) with cyclin-dependent kinase 2 (Cdk2). At the same time, there was an ac cumulation of the hypophosphorylated form of the pRb proteins and a strong decline in Cdk2 activity. Stable expression of a p27(Kip1) antisense comple mentary DNA in Caco-2/15 cells did not prevent growth arrest induced by con fluence, but repressed villin, sucrase-isomaltase, and alkaline phosphatase expression. Conclusions: Our results indicate that the growth arrest that precedes differentiation involves the activation of Rb proteins and the inh ibition of Cdk2. Furthermore, intestinal cell differentiation apparently re quires a function of p27(Kip1) Other than that which leads to inhibition of Cdks.