Cholesterol depletion induces anoikis-like apoptosis via FAK down-regulation and caveolae internalization.

Caveolae (lipid rafts), microdomains of the plasma membrane, are known to contain various signalling molecules and consequently are involved in the regulation of many biological functions. To investigate the role of the caveolae in cell survival and adhesion, we disrupted the caveolae by depletion of cholesterol, a major lipid component of the caveolae, with methyl-beta cyclodextrin (MbetaCD) treatment of A431 cells. We found that cholesterol depletion induced an anoikis-like cell death involving actin reorganization, resulting in a decrease in cell spreading and an increase in cell detachment, which was reversed by cholesterol addition. Disruption of caveolae led to the down-regulation of FAK, Src activation, tyrosine phosphorylation of caveolin-1 and mobilization of caveolae markers, GM1 and caveolin-1, from the cell surface to the cytoplasm, which were also recovered by cholesterol addition. The expression of dominant-active FAK was able to delay caveolae internalization and apoptosis and attenuated Akt inactivation by MbetaCD, whereas dominant-negative FAK expression resulted in enhanced apoptosis. Moreover, FAK down-regulation by si-RNA resulted in Akt inactivation and thus increased cell death by MbetaCD treatment. Our results suggest that the cholesterol content and/or surface levels of the caveolae affect the activity of FAK, which in turn regulates caveolae internalization and cell survival.