Contribution of caveolin-1α and Akt to TNF-α-induced cell death

We used retrovirus insertion-mediated random mutagenesis to generate tumor necrosis factor-alpha (TNF-alpha)-resistant lines from L929 cells. Using this approach, we discovered that caveolin-1alpha is required for TNF-alpha-induced cell death in L929 cells. The need for caveolin-1alpha in TNF-alpha-induced cell death was confirmed by the restoration of sensitivity to TNF-alpha after ectopic reconstitution of caveolin-1alpha/beta expression. This caveolin-1alpha-mutated line was also resistant to H2O2 and staurosporine, but not to lonidamine. HepG2 cells are known to lack endogenous caveolins. HepG2 cells stably transfected with caveolin-1alpha/beta were found to be much more sensitive to TNF-alpha than either parental cells transfected with caveolin-1alpha or parental cells transfected with an empty vector. In contrast to its extensively documented antiapoptotic effect, the elevated activity of Akt appears to be important in sensitizing caveolin-1-expressing cells to TNF-alpha, since pretreatment of cells with the phosphatidylinositide 3-kinase (PI3K) inhibitor LY-294002 or wortmannin completely blocked PI3K activation and markedly improved the survival of TNF-alpha-treated L929 cells. The survival rates of caveolin-1alpha-normal and caveolin-1alpha-deficient L929 cells were comparable after treatment with PI3K inhibitor and TNF-alpha. Similar results were obtained with HepG2 cells that stably expressed caveolin-1alpha/beta or -beta and parental cells transfected with an empty vector. In summary, our results indicate that caveolin-1alpha preferentially sensitizes L929 cells to TNF-alpha through the activation of a PI3K/Akt signaling pathway.