Apoptosis induced by interferon-alpha and antagonized by EGF is regulated by caspase-3-mediated cleavage of gelsolin in human epidermoid cancer cells.

We have previously reported that interferon-alpha (IFNa) induces apoptosis and EGF can antagonize this effect in human epidermoid cancer KB cells. Since apoptosis occurs together with cytoskeleton reorganization we have evaluated if IFNa and EGF could modulate cell remodeling in our experimental conditions. We have found that 48 h 1,000 IU/ml IFNa induced structural reorganization of stress fibers and membrane delocalization and partial capping of the actin severing protein gelsolin. The transfection of KB cells with both a wild type (WT) or a C-terminal truncated form of gelsolin caused overexpression of the protein and an increase of both the spontaneous and IFNa-induced apoptosis and cell cytoskeletal modifications. In fact, after 48 h of treatment IFNa induced 45% of apoptotic cell death in parental cells while an approximately 80% of cell population was apoptotic in transfected cells. These effects occurred together with an increase of the expression and consequent degradation of gelsolin. Again the addition of EGF to IFNa-treated transfected cells caused a recovery of the apoptosis. Notably, IFNa and EGF did not modify the expression of other molecules associated to cytoskeleton such as focal adhesion kinase and vinculin. In the same experimental conditions IFNa induced also gelsolin cleavage that occurred together with caspase-3 activation and release of cytochrome c. All these effects were antagonized by the exposure of IFNa-treated KB to 10 nM EGF for the last 12 h. Moreover, the specific inhibition of caspase-3 with 20 mM DEVD completely abrogated apoptosis and gelsolin cleavage induced by IFNa. In conclusion, our data are the first demonstration that IFNa can induce morphological cell changes that are peculiar of apoptosis onset through the caspase-3-mediated cleavage of gelsolin. Furthermore, we have demonstrated that EGF is able to antagonize these effects through the inhibition of caspase-3 activation.