Matrix Attachment Regulates FAS-Induced Apoptosis in Endothelial Cells

Abstract

Survival of endothelial cells is critical for cellular processes such as angiogenesis. Cell attachment to extracellular matrix inhibits apoptosis in endothelial cells both in vitro and in vivo, but the molecular mechanisms underlying matrix-induced survival signals or detachment-induced apoptotic signals are unknown. We demonstrate here that matrix attachment is an efficient regulator of Fas-mediated apoptosis in endothelial cells. Thus, matrix attachment protects cells from Fas-induced apoptosis, whereas matrix detachment results in susceptibility to Fas-mediated cell death. Matrix attachment modulates Fas-mediated apoptosis at two different levels: by regulating the expression level of Fas, and by regulating the expression level of c-Flip, an endogenous antagonist of caspase-8. The extracellular signal–regulated kinase (Erk) cascade functions as a survival pathway in adherent cells by regulating c-Flip expression. We further show that detachment-induced cell death, or anoikis, itself results from activation of the Fas pathway by its ligand, Fas-L. Fas-L/Fas interaction, Fas–FADD complex formation, and caspase-8 activation precede the bulk of anoikis in endothelial cells, and inhibition of any of these events blocks anoikis. These studies identify matrix attachment as a survival factor against death receptor–mediated apoptosis and provide a molecular mechanism for anoikis and previously observed Fas resistance in endothelial cells.

Anoikis: an emerging hallmark in health and diseases

“…Loss of anchorage to the ECM leads to increase in Fas expression and Fas-L expression and to a decreased expression of FLIP, an endogenous inhibitor of Fasmediated signalling [37]. Furthermore, also changes in cell shape during detachment (cell rounding) can induce extrinsic anoikis [38], mainly through membrane relocalization and activation of Fas [39].…”

Angiostatin's molecular mechanism: Aspects of specificity and regulation elucidated

“…In the tumor microenvironment, there are several parameters that are different. The matrix is higher in collagens, laminin, and certain other proteins relative to normal stroma [Canfield et al, 1986;Baatout and Cheta, 1996;Grant and Kleinman, 1997;Aoudjit and Vuori, 2001]. The pH and the oxygen levels are low, and the degree of attachment is compromised because cells are rapidly dividing and often motile, and the NHE is more active.…”

Integrins as a distinct subtype of dependence receptors

“…Aside from immediate effects on cytosolic and cytoskeletal elements, these signaling cascades also regulate transcription events in the cell nucleus, 40 and have profound effects upon cell viability. Integrin-mediated signaling has been linked to a number of factors directly governing cell resistance to apoptosis, including cell cycle progression 10 and p53 activation, 35 Bcl-2 family protein expression, 34 death receptor and death ligand expression 41,42 and regulation of the PI3K/Akt/ GSKb axis. 43 Moreover, these signaling events also influence cellular production of extracellular proteins, such as osteopontin 44 and intracellular adaptors, such as osteoprotegerin 45 and c-flip, 42 which themselves act directly or indirectly to regulate cell survival.…”