Human intestinal epithelial crypt cell survival and death: Complex modulations of Bcl‐2 homologs by Fak, PI3‐K/Akt‐1, MEK/Erk, and p38 signaling pathways

Abstract

To investigate the mechanisms responsible for survival and apoptosis/anoikis in normal human intestinal epithelial crypt cells, we analyzed the roles of various signaling pathways and cell adhesion on the expression of six Bcl‐2 homologs (Bcl‐2, Bcl‐X_L, Mcl‐1, Bax, Bak, Bad) in the well established HIEC‐6 cell model. Pharmacological inhibitors and/or dominant‐negative constructs were used to inhibit focal adhesion kinase (Fak) and p38 isoforms, as well as the phosphatidylinositol 3′‐kinase (PI3‐K)/Akt‐1 and mitogen‐activated protein kinase [MAPK] kinase (MEK)/extracellular regulated kinases (Erk) pathways. Cell adhesion was disrupted by antibody‐inhibition of integrin binding or forced cell suspension. The activation levels of studied kinase pathways were also analyzed. Herein, we report that β1 integrins, Fak, and the PI3‐K/Akt‐1 pathway, but not β4 integrins or the MEK/Erk pathway, are crucial for the survival of HIEC‐6 cells. Conversely, p38β, but not p38α or γ, is required for the induction of apoptosis/anoikis in HIEC‐6 cells. However, each of the signaling molecules/pathways analyzed were found to affect distinctively the individual expression of the Bcl‐2 homologs studied. For example, the inhibition of the PI3‐K/Akt‐1 pathway down‐regulated Bcl‐X_L, Mcl‐1, and Bad, while at the same time up‐regulating Bax, whereas the inhibition of Fak up‐regulated both Bax and Bak, down‐regulated Bad, and did not affect the other Bcl‐2 homologs analyzed. These results indicate that integrins, Fak, PI3‐K/Akt‐1, MEK/Erk, and p38 isoforms perform distinct roles in the regulation of HIEC‐6 cell survival and/or death. In addition, our data show that the functions performed by these molecules/pathways in promoting cell survival or apoptosis/anoikis translate into complex, differential modulations of individual Bcl‐2 homologs. J. Cell. Physiol. 198: 209–222, 2004