Oxidative Stress Stimulates Apoptosis and Activates NF-κB in Osteoblastic Cells via a PKCβ/p66shc Signaling Cascade: Counter Regulation by Estrogens or Androgens

Aging or acute loss of estrogens or androgens increases the levels of reactive oxygen species, activates nuclear factor-kappa B (NF-kappa B), and promotes the phosphorylation of p66(shc), a redox enzyme that amplifies mitochondrial reactive oxygen species generation and stimulates apoptosis. We report that in mesenchymal progenitor and osteoblastic cell models, H2O2 activated a protein kinase C (PKC)beta/p66(shc)/NF-kappa B signaling cascade and that p66(shc) was an essential mediator of the stimulating effects of H2O2 on the apoptosis of osteoblastic cells as well as their ability to activate NF-kappa B. 17 beta-Estradiol (E-2) or the nonaromatizable androgen dihydrotestosterone abrogated the effects of H2O2 on p66(shc) and NF-kappa B activation by attenuating the phosphorylation of the redox-sensitive cytoplasmic kinase PKC beta. Additionally, both E-2 and dihydrotestosterone prevented H2O2-induced apoptosis by a mechanism that involved attenuation of p66(shc) resulting from decreased phosphorylation of PKC beta. Consistent with a kinase-mediated mechanism of sex steroid action, the effects of E-2 were reproduced by a polymeric form of estradiol that is not capable of stimulating the nuclear-initiated actions of ER alpha. These results demonstrate that p66(shc) is an essential mediator of the effects of oxidative stress on osteoblastic cell apoptosis, NF-kappa B activation, and cytokine production. The ability of either estrogen or androgen to attenuate the effects of oxidative stress on osteoblastic cell apoptosis, NF-kappa B activation, and cytokine production results from their common property to suppress PKC beta-induced p66(shc) phosphorylation via a mechanism that does not require stimulation of the nuclear-initiated actions of sex steroids. (Molecular Endocrinology 24: 2030-2037, 2010)