Endometrial cancer is the most common invasive gynecologic malignancy but the molecular mechanisms underlying its onset and progression are poorly understood. Paradoxically, endometrial tumors exhibit increased apoptosis, correlating with disease progression and poor patient prognosis. Endometrial tumors also show altered activity and expression of protein kinase C (PKC) isoforms, implicated in the regulation of programmed cell death; however, PKC modulation of apoptosis in endometrial cancer cells has not been investigated. We detected nine out of ten PKC isoforms in Ishikawa endometrial cancer cell lines, and demonstrated expression of both PKCα and δ in human endometrial tumors. To determine the functional roles of PKCα and δ in apoptosis in endometrial cancer, Ishikawa cells were treated with selective PKC inhibitors or adenoviral constructs encoding wild-type or isoform-specific, dominant-negative mutants. Apoptosis was assessed by DNA fragmentation and caspase-mediated poly-(ADP-ribose)-polymerase cleavage. The inhibition of PKCδ suppressed etoposide-induced apoptosis, while overexpression of PKCδ enhanced it. In contrast, inhibition of PKCα elevated basal levels of apoptosis and potentiated etoposide-induced cell death. Etoposide treatment also selectively activated PKCδ, but resulted in both cytosolic translocation and decreased activity of PKCα. A fraction of PKCδ also underwent caspase-dependent cleavage, in response to etoposide. Our results suggest that changes in apoptosis and PKC expression in endometrial cancer are mechanistically linked, such that PKCδ is required for DNA damage-induced apoptosis, while PKCα mediates a survival response. Thus, PKCα and δ expression and signaling may be important in endometrial tumorigenesis and could serve as potential prognostic indicators and/or novel targets for therapeutic intervention.
Activation of Stress-activated Protein Kinase/c-Jun NH2-terminal Kinase and p38 Kinase in Calphostin C-induced Apoptosis Requires Caspase-3-like Proteases but Is Dispensable for Cell Death
