Ligation of cell surface GRP78 with antibody directed against the COOH-terminal domain of GRP78 suppresses Ras/MAPK and PI 3-kinase/AKT signaling while promoting caspase activation in human prostate cancer cells

We have previously shown that treatment of prostate cancer and melanoma cells expressing GRP78 2 on their cell surface with antibody directed against the COOH-terminal domain of GRP78 up-regulates and activates p53 causing decreased cell proliferation and up-regulated apoptosis. In this report, we demonstrate that treatment of 1-LN prostate cancer cells with this antibody decreases cell surface expression of GRP78, Akt Thr308 and Akt Ser473 kinase activities and reduces phosphorylation of FOXO, and GSK3β. This treatment also suppresses activation of ERK1/2, p38 MAPK, and MKK3/6; however, it up-regulates MKK4 activity. JNK, as determined by its phosphorylation state, is subsequently activated, triggering apoptosis. Incubation of cells with antibody reduced levels of anti-apoptotic Bcl-2, while elevating pro-apoptotic BAD, BAX, and BAK expression as well as cleaved caspases-3, -7, -8, and -9. Silencing GRP78 or p53 gene expression by RNAi prior to antibody treatment abrogated these effects. We conclude that antibody directed against the COOH-terminal domain of GRP78 may prove useful as a pan suppressor of proliferative/survival signaling in cancer cells expressing GRP78 on their cell surface.