Extracellular matrix modulates enterocyte growth via downregulation of c-jun but is independent of p21 and p27 expression

Regulation of the intestinal crypt-villus axis is multifactorial and involv es growth factors and extracellular matrix composition. Laminin, a componen t of the enterocyte basement membrane, induces enterocyte differentiation a nd inhibits proliferation. To investigate the mechanism of this observation , we examined the expression of cell cycle modulators in enterocytes cultur ed on laminin. IEC-6 enterocytes were cultured on collagen I or laminin for 24 hours in media with serum followed by 48 hours of culture in serum-free media. Cells were then stimulated with epidermal growth factor, and RNA an d protein were extracted before and up to 18 hours after stimulation. c-jun mRNA expression and p21 and p27 protein expression were analyzed. Expressi on of c-jun was inhibited in cells grown on laminin as compared to collagen I. Expression of p21 and p27 was no different between cells grown on lamin in or collagen I. The mechanism of enterocyte growth inhibition mediated by laminin involves downregulation of c-jun expression. In contrast, p21 and p27 levels were unaffected by extracellular matrix indicating that the chan ges in expression of these cyclin-dependent kinase inhibitors do not contri bute to the effect of laminin on enterocyte proliferation.