Abstracts
1998 Digestive Disease Week

#1065

EXTRACELLULAR MATRIX MODULATES ENTEROCYTE GROWTH VIA DOWN REGULATION OF c-jun BUT IS INDEPENDENT OF p21 AND p27 EXPRESSION. S.I. Wolpert, K.M. Lally, J. Li J-Y Wang, B.L. Bass. The Department of Surgery, The University of Maryland and the Baltimore VAMC; Baltimore, MD.

Introduction: The intestinal epithelium undergoes rapid turnover with intestinal crypt cells proliferating to yield the terminally differentiated cells of the villus tip. The mechanisms regulating the growth and differentiation of enterocytes is poorly understood and likely multifactorial. We have previously demonstrated that enterocytes grown on laminin, a component of the intestinal basement membrane, have an impaired growth response to the peptide growth factors. To investigate the mechanism of this observation, we examined the expression of modulators of the cell cycle in enterocytes cultured on laminin. Specifically, we compared the expression of c-jun, p21 and p27 in synchronized epidermal growth factor (EGF) stimulated enterocytes grown on laminin or collagen IV. c-jun is an early gene product required for initiation of the cell cycle while p21 and p27 inhibit cell cycle progression. Method: IEC-6 cells were plated on dishes coated with laminin or collagen IV. The cells were synchronized through serum starvation for 48 hours and then stimulated with EGF (20ng/ml). Cells were lysed at intervals prior to and following EGF stimulation and underwent extraction of RNA and protein. c-jun expression was evaluated by Northern blot while p21 and p27 expression was measured by Western blot. Results: c-jun was decreased basally in IEC-6 cells grown on laminin relative to cells grown on collagen IV. With EGF stimulation, c-jun levels peaked at 1/2 hour in both groups and incrementally declined at 1,2 and 4 hours post stimulation. c-jun levels in cells grown on laminin were decreased at 1/2, 2 and 4 hours post EGF stimulation relative to cells cultured on collagen IV. p21 and p27 levels were measured pre EGF stimulation and 4,6,8,10, and 18 hours post EGF stimulation. p21 and p27 levels in enterocytes cultured on laminin were equivalent to those in cells grown on collagen IV at all time points. Summary: IEC-6 cells cultured on laminin responded to EGF stimulation with increased c-jun expression. However, in cells cultured on laminin, basal c-jun expression was decreased and the response to EGF was blunted relative to cells grown on collagen IV. p21 and p27 levels were unaffected by extracellular matrix composition. Conclusion: The mechanism of enterocyte growth inhibition mediated by laminin involves down regulation of c-jun expression. In contrast, p21 and p27 levels were unaffected by extracellular matrix suggesting that laminin inhibition of enterocyte growth is independent of this major regulatory pathway. Laminin appears to interrupt cell cycle progression at an early stage. These data suggest that multiple factors may influence cell cycle regulation in proliferating enterocytes through separate pathways.

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