Intestinal epithelial cell differentiation involves activation of p38 mitogen-activated protein kinase that regulates the homeobox transcription factor CDX2

The intracellular signaling pathways responsible for cell cycle arrest and differentiation along the crypt-villus axis of the human small intestine re main largely unknown. p38 mitogen-activated protein kinases (MAPKs) have re cently emerged as key modulators of various vertebrate cell differentiation processes. In order to elucidate further the mechanism(s) responsible for the loss of proliferative potential once committed intestinal cells begin t o differentiate, the role and regulation of p38 MAPK with regard to differe ntiation were analyzed in both intact epithelium as well as in well establi shed intestinal cell models recapitulating the crypt-villus axis in vitro. Results show that phosphorylated and active forms of p38 were detected prim arily in the nuclei of differentiated villus cells. Inhibition of p38 MAPK signaling by 2-20 muM SB203580 did not affect E2F-dependent transcriptional activity in subconfluent Caco-2/15 or HIEC cells. p38 MAPK activity dramat ically increased as soon as Caco-2/15 cells reached confluence, whereas add ition of SB203580 during differentiation of Caco-2/15 cells strongly attenu ated sucrase-isomaltase gene and protein expression as well as protein expr ession of villin and alkaline phosphatase. The binding of CDX2 to the sucra se-isomaltase promoter and its transcriptional activity were significantly reduced by SB203580. Pull-down glutathione S-transferase and immunoprecipit ation experiments demonstrated a direct interaction of CDX3 with p38, Final ly, p38-dependent phosphorylation of CDX3 was observed in differentiating C aco-2/15 cells. Taken together, our results indicate that p38 MAPK may be i nvolved in the regulation of CDX2/3 function and intestinal cell differenti ation.