Differentiation state-selective roles of p38 isoforms in human intestinal epithelial cell anoikis

Abstract

Background & Aims: Little is known of the signaling events implicated in the induction of human enterocytic anoikis. In the present study, we analyzed the role of the stress-activated protein kinase p38 in this process. Methods: Anoikis was induced in undifferentiated and differentiated enterocytes by inhibition of focal adhesion kinase (Fak; pharmacologic inhibition or overexpression of a dominant negative form) or β1 integrins (antibody blocking), or by maintaining cells in suspension. Expression/activation parameters of p38 (isoforms α, β, γ, δ) and of the Fak/phosphatidylinositol-3-kinase (PI3-K)/Akt anoikis-suppressing pathways were analyzed. Kinase activities of p38 isoforms also were blocked by pharmacologic inhibitors or by overexpression of dominant-negative forms. Results: (1) p38 activation is sustained transiently after induction of anoikis in both undifferentiated and differentiated enterocytes; (2) such sustenance of p38 activation is associated with a downregulation of the Fak/PI3-K/Akt pathway; (3) distinct profiles of p38 isoform expression are exhibited by undifferentiated (α, β, γ) and differentiated (α, γ, δ) enterocytes; (4) none of the 4 known p38 isoforms was found to promote cell survival in either differentiation state; and (5) only p38β and p38δ are required specifically for anoikis in undifferentiated and differentiated cells, respectively. Conclusions: Distinct p38 isoforms play a major role in the induction of enterocytic anoikis and the regulation of such selective p38 isoform-mediated anoikis is linked with the state of cell differentiation. These data provide novel insights into the synchronized regulation of cell survival/death required in the epithelial renewal process along the human intestinal crypt-villus axis.