Ligation of cancer cell surface GRP78 with antibodies directed against its COOH-terminal domain up-regulates p53 activity and promotes apoptosis

Abstract

Binding of activated α 2 -macroglobulin to GRP78 on the surface of human prostate cancer cells promotes proliferation by activating signaling cascades. Autoantibodies directed against the activated α 2 -macroglobulin binding site in the NH 2 -terminal domain of GRP78 are receptor agonists, and their presence in the sera of cancer patients is a poor prognostic indicator. We now show that antibodies directed against the GRP78 COOH-terminal domain inhibit [3 H]thymidine uptake and cellular proliferation while promoting apoptosis as measured by DNA fragmentation, Annexin V assay, and clonogenic assay. These antibodies are receptor antagonists blocking autophosphorylation and activation of GRP78. Using 1-LN and DU145 prostate cancer cell lines and A375 melanoma cells, which express GRP78 on their cell surface, we show that antibodies directed against the COOH-terminal domain of GRP78 up-regulate the tumor suppressor protein p53. By contrast, antibody directed against the NH 2

GRP78 Secreted by Colon Cancer Cells Facilitates Cell Proliferation via PI3K/Akt Signaling

“…For example, ligation of surface GRP78 by α2-M* activates MAPK and Akt-dependent signaling and promotes cellular proliferation (Misra et al, 2006), while ligation of surface GRP78 with antibodies against the C-terminal domain of GRP78 result in suppression of cell growth and induction of apoptosis (Misra et al, 2009;Misra and Pizzo, 2010a;Misra and Pizzo, 2010b). Studies have actually shown that the PI3K/Akt signaling plays a significant role in the promotion of tumor cell proliferation and colon tumorigenesis (Zheng et al, 2012).…”

Targeting plasma membrane GRP78 for cancer growth inhibition

“…15,16 It has been demonstrated in several manuscripts, including the study described in this issue, that C-terminal antibodies lead to numerous molecular changes central to proliferation, survival and apoptosis. 13,22 The variety and degree of these molecular alterations upon GRP78 ligation with C-terminal antibodies would be consistent with supraphysiologic responses, such as lipid accumulation, however to our knowledge this has not been examined to date.…”

“…mediated death. 13,17 How then would GRP78 ligation lead to cell death? Use of the SAM-6 antibody resulted in a marked non-physiologic accumulation of intracellular lipids prior to apoptosis induction.…”

“…Although there is at least one instance of a C-terminal GRP78 antibody that does not elicit cell death, 21 those that have cytotoxic activity are exclusively localized to the C-terminus. 13 One explanation is that instead of acting in an antagonistic manner, binding to the C-terminus leads to a novel agonistic activity. Evidence for this hypothesis is derived from experiments demonstrating that GRP78 downregulation actually rescues cells from antibodyexist, but there is no definitive experimental data to support this model as of yet.…”

“…A second approach reported earlier this year was to target GRP78 with antibodies specifically against the carboxy-terminal region. 13 The antibody approach resulted in a marked reduction in total GRP78 expression, decreased cellular proliferation and apoptosis induction. In this issue of Cancer Biology & Therapy, the Pizzo laboratory has extended these findings to address the molecular mechanisms underlying the anti-growth and pro-death effects elicited by GRP78 C-terminal antisera.…”