Cell-Cell Contacts Prevent Anoikis in Primary Human Colonic Epithelial Cells

Background & Aims: Colonic epithelial cells (CECs) receive important survival signals from the extracellular matrix and undergo detachment-induced apoptosis (anoikis) as soon as they lose their cell-matrix anchorage. In contrast to the established role of cell-matrix contact, the role of cell-cell contacts as a physiologic survival factor for CECs is less clear. Methods: Intact CEC crypts gently centrifuged to form a cell aggregate in which cell-cell contacts were maintained. Induction of apoptosis was assessed by Western Blot analysis, colorimetric assays, DNA electrophoresis, 4′,6-diamidino-2-phenylindole staining, and flow cytometry. Activation of survival pathways was analyzed by Western blot. The role of mitogen-activated protein kinase/extracellular signal–regulated kinase (MEK)/extracellular signal–regulated kinase (Erk)1/2, epidermal growth factor receptor, phosphatidylinositol 3-kinase (PI3-K), and Src signaling was investigated using specific inhibitors. Results: Despite a complete loss of cell-matrix adhesion after CEC isolation, activation of caspases was blocked and anoikis was prevented when cell-cell contacts were preserved. CECs with preserved cell-cell contacts exhibited a rapid dephosphorylation of focal adhesion kinase. Aggregated CECs had stable levels of active β-catenin and phosphorylated Akt, Erk1/2, and epidermal growth factor receptor, but CECs undergoing anoikis rapidly degraded β-catenin and dephosphorylated Akt. Inhibition of Src- and PI3-K–dependent signaling reversed the antiapoptotic effect of cell-cell contact preservation, while inhibition of the MEK pathway had no effect. Conclusions: Integrity of cell-cell contacts compensates for the loss of cell-matrix contact-mediated survival signals in CECs and prevents apoptosis. Cell-cell contact-triggered CEC survival involves antiapoptotic signaling through β-catenin-, Src-, and PI3-K/Akt- but not through MEK- and focal adhesion kinase–dependent pathways.

Abbreviations used in this paper: CEC, colonic epithelial cell, ECM, extracellular matrix, EGFR, epidermal growth factor receptor, Erk, extracellular signal–regulated kinase, FAK, focal adhesion kinase, IEC, intestinal epithelial cell, MAPK, mitogen-activated protein kinase, MEK, mitogen-activated protein kinase/extracellular signal–regulated kinase, P-CEC, colonic epithelial cell cultured in pellets, PI3-K, phosphatidylinositol 3-kinase, S-CEC, colonic epithelial cell cultured in suspension