Fak/Src signaling in human intestinal epithelial cell survival and anoikis:: Differentiation State-specific uncouplin with the P13-K/Akt-1 ang MEK/Erk pathways

Human intestinal epithelial cell survival and anoikis are distinctively regulated according to the state of differentiation. In the present study, we analyzed the roles of focal adhesion kinase (Fak)/Src signaling to the P13-K/Akt- I and mitogen -activated protein kinase (MEK)/ extracellular regulated kinases (Erk) pathways, within the context of such differentiation -state distinctions. Anoikis was induced by inhibition of beta I integrins (antibody blocking), inhibition of Fak (pharmacologic inhibition or overexpression of dominant negative mutants), or by maintaining cells in suspension. Activation parameters of Fak, Src, Akt- 1, and Erk 1 /2 were analyzed. Activities of Src, Akt- 1, or Erk 1 /2 were also blocked by pharmacological inhibition or by overexpression of dominant-negative mutants. We report that: (1) the loss or inhibition of P I integrin binding activity causes anoikis and results in a down-activation of Fak, Src, Akt- 1, and Erk 1 /2 in both undifferentiated, and differentiated cells; (2) the inhibition of Fak likewise causes anoikis and a down-activation of Src, Akt- 1, and Erk 1 /2, regardless of the differentiation state; (3) Src, P]3-K/Akt- 1, and MEK/Erk contribute to the survival of differentiated cells, whereas MEK/ Erk does not play a role in the survival of undifferentiated ones; (4) the inhibition/loss of P I integrin binding and/or Fak activity results in a loss of Src engagement with Fak, regardless of the state of differentiation; and (5) Src contributes to the activation of both the P13-K/Akt- I and MEK/Erk pathways in undifferentiated cells, but does not influence P13-K/Akt- I in differentiated ones. Hence, Fak/Src signaling to the P13-K/Akt- I and MEK/Erk pathways undergoes a differentiation state-specific uncoupling which ultimately reflects upon the selective engagement of these same pathways in the mediation of intestinal epithelial cell survival.