Opposing roles for p21^waf1/cip1 and p27^kip1 in enterocyte differentiation, proliferation, and migration

Background. Originating from proliferating stem cells of the intestinal crypt, enterocytes differentiate as they migrate up the crypt-villus axis. A regulatory role of the cyclin-dependent kinase inhibitors p21 ^waf1/cip1 and p27^kip1 in these processes has been suggested by in vitro models. We sought to determine the effect of p21 ^waf1/cip1 and p27^kip1 deficiency on enterocyte differentiation, proliferation and migration. Methods. Three strains of mice including control (C57Bl/6), p27^kip1-null, and p21 ^waf1/cip1-null were studied. Enterocyte differentiation was evaluated by immunostaining for intestinal alkaline phosphatase, by colorimetric assaying for intestinal alkaline phosphatase and sucrase enzyme activity, and by polymerase chain reaction for intestinal fatty acid-binding protein and villin-messenger RNA in enterocytes extracted by laser capture microdissection. Rates of enterocyte proliferation and migration were determined by 5-bromo 2-deoxyuridine immunostaining after a 50% small-bowel resection (SBR). Results. Compared with controls, p27^kip1-null mice demonstrated minimal differentiation but maintained a normal proliferative response to SBR. Contrarily, p21^waf1/cip1-null mice demonstrated greater enterocyte differentiation without significant increases in enterocyte proliferation after SBR. Conclusions. These findings suggest that p21^waf1/cip1 and p27^kip1 have distinctive and opposing roles in the pathogenesis of enterocyte differentiation, proliferation, and migration.