Epidermal growth factor receptor-mediated proliferation of enterocytes requires p21waf1/cip1 expression.
ABSTRACT Epidermal growth factor receptor (EGFR)-mediated increase in enterocyte proliferation following massive resection is a major mechanism by which the small intestine adapts to the loss of its mucosal surface area. In addition, expression of the cyclin-dependent kinase inhibitor p21(waf1/cip1) is required for resection-induced enterocyte proliferation. This study sought to establish a mechanistic link between EGFR-mediated intestinal epithelial cell proliferation and p21(waf1/cip1) expression.
EGF was used to stimulate IEC-6 and HCA-7 cells. P21(waf1/cip1) messenger RNA (mRNA) and protein expression were measured by real-time polymerase chain reaction and Western blot, respectively. P21(waf1/cip1) promoter studies were performed using p21(waf1/cip1) promoter-driven luciferase assay. Pharmacologic inhibitors of PI3-kinase and mitogen activated protein kinase (MAPK) were used to block these pathways downstream of the activated EGFR. Constitutively active Ras, Raf, or MEK-1 constructs were transfected into cells for overexpression studies. Cell proliferation was measured by bromodeoxyuridine incorporation following p21(waf1/cip1) silencing with RNAi. Finally, Cyclin D(1)/Cdk interaction was evaluated by immunoprecipitation.
EGFR activation in intestinal epithelial cells induced the expression of p21(waf1/cip1) mRNA and protein This event was transcriptionally regulated via a 50-bp segment of the p21(waf1/cip1) promoter as a result of MAPK activation. Exogenous EGF failed to induce proliferation in p21(waf1/cip1)-silenced cells and adaptive proliferation after intestinal resection in p21(waf1/cip1)-null mice. Functionally, p21(waf1/cip1) up-regulation was required for stabilizing Cyclin D/Cdk 4 complexes and intestinal cell proliferation.
EGFR-mediated induction of enterocyte proliferation requires MAPK-dependent increase in p21(waf1/cip1) expression in intestinal epithelial cells. These studies elucidate an important mechanism for resection-induced enterocyte proliferation during intestinal adaptation.
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ABSTRACT: Necrotizing enterocolitis (NEC) is a devastating disease of premature infants and is associated with significant morbidity and mortality. While the pathogenesis of NEC remains incompletely understood, it is well established that the risk of disease is increased by the administration of infant formula and decreased by the administration of breast milk. This review will focus on the mechanisms by which breast milk may serve to protect against NEC, and will review the evidence regarding various feeding strategies that may be utilized before and after an episode of NEC.Expert Review of Clinical Immunology 06/2014; DOI:10.1586/1744666X.2014.913481 · 3.34 Impact Factor
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ABSTRACT: Necrotizing enterocolitis (NEC) is a challenging disease to treat, and caring for patients afflicted by it remains both frustrating and difficult. While NEC may develop quickly and without warning, it may also develop slowly, insidiously, and appear to take the caregiver by surprise. In seeking to understand the molecular and cellular processes that lead to NEC development, we have identified a critical role for the receptor for bacterial lipopolysaccharide (LPS) toll like receptor 4 (TLR4) in the pathogenesis of NEC, as its activation within the intestinal epithelium of the premature infant leads to mucosal injury and reduced epithelial repair. The expression and function of TLR4 were found to be particularly elevated within the intestinal mucosa of the premature as compared with the full-term infant, predisposing to NEC development. Importantly, factors within both the enterocyte itself, such as heat shock protein 70 (Hsp70), and in the extracellular environment, such as amniotic fluid, can curtail the extent of TLR4 signaling and reduce the propensity for NEC development. This review will highlight the critical TLR4-mediated steps that lead to NEC development, with a focus on the proinflammatory responses of TLR4 signaling that have such devastating consequences in the premature host.Clinical and Developmental Immunology 05/2013; 2013:475415. DOI:10.1155/2013/475415 · 2.93 Impact Factor