Resveratrol is pro-apoptotic and thyroid hormone is anti-apoptotic in glioma cells: Both actions are integrin and ERK mediated

The stilbene resveratrol (RV) initiates p53-dependent apoptosis via plasma membrane integrin αVβ3 in human cancer cells. A thyroid hormone (L-thyroxine, T₄) membrane receptor also exists on αVβ3. Stilbene and T₄ signals are both transduced by extracellular-regulated kinases 1 and 2 (ERK1/2); however, T₄ promotes cell proliferation in cancer cells, whereas RV is pro-apoptotic. Thyroid hormone has been shown to interfere with RV-induced apoptosis. However, the mechanisms involved are not fully understood. In this study, we examined the mechanism whereby T₄ inhibits RV-induced apoptosis in glioma cells. RV activated conventional protein kinase C and ERK1/2 and caused nuclear localization of cyclooxygenase-2 (COX-2), consequent p53 phosphorylation and apoptosis. RV-induced ERK1/2 activation is involved in not only COX-2 expression but also nuclear COX-2 accumulation. NS-398, a COX-2 inhibitor, did not affect ERK1/2 activation, but reduced the nuclear abundance of COX-2 protein and the formation of complexes of nuclear COX-2 and activated ERK1/2 that are required for p53-dependent apoptosis in RV-treated cells. T₄ inhibited RV-induced nuclear COX-2 and cytosolic pro-apoptotic protein, BcLx-s, accumulation. Furthermore, T₄ inhibited RV-induced apoptosis by interfering with the interaction of nuclear COX-2 and ERK1/2. This effect of T₄ was prevented by tetraiodothyroacetic acid (tetrac), an inhibitor of the binding of thyroid hormone to its integrin receptor. Tetrac did not, in the absence of T₄, affect induction of apoptosis by RV. Thus, the receptor sites on αVβ3 for RV and thyroid hormone are discrete and activate ERK1/2-dependent downstream effects on apoptosis that are distinctive.