The pro-apoptotic actions of 2-methoxyestradiol against ovarian cancer involve catalytic activation of PKCδ signaling

Background: 2-methoxyestradiol (2MeOE(2)) is a natural metabolite of estradiol, which is generated by the action of CYP1A1 enzyme in the liver. We have previously shown that a flaxseed-supplemented diet decreases both the incidence and severity of ovarian cancer in laying hens, also induces CYP1A1 expression in liver. Recently, we have shown that as a biologically derived active component of flax diet, 2MeOE(2) induces apoptosis in ovarian cancer cells which is partially dependent on p38 MAPK. The objective of this study was to elucidate the molecular mechanism of actions of 2MeOE(2), a known microtubule disrupting agent, in inducing apoptosis in ovarian tumors. Results: 2MeOE(2) induces γH2Ax expression and apoptotic histone modifications in ovarian cancer cells, which are predicted downstream targets of protein kinase Cδ (PKCδ) during apoptosis. Overexpressing full length PKCδ alone does not induce apoptosis but potentiates 2MeOE(2)-mediated apoptosis. C3-domain mutated dominant-negative PKCδ (PKCδ(DN)) significantly reduces 2MeOE(2)-induced caspase-3 cleavage and apoptotic histone modification. Silencing PKCδ diminishes 2MeOE(2)-mediated apoptosis. The catalytic fragment of PKCδ (PKCδ(CAT)) evokes pro-apoptotic effects which are principally dependent on p38 MAPK phosphorylation. Conclusions: The pro-apoptotic actions of 2MeOE(2) are in part dependent on catalytic activation of PKCδ. Catalytic activation of PKCδ accelerates the 2MeOE(2)-induced apoptotic cascade. This study describes a novel molecular action of flaxseed diet in ovarian cancer.