Isthmin targets cell-surface GRP78 and triggers apoptosis via induction of mitochondrial dysfunction

Abstract

Isthmin (ISM) is a secreted 60-kDa protein that potently induces endothelial cell (EC) apoptosis. It suppresses tumor growth and angiogenesis in mice when stably overexpressed in cancer cells. Although avb5 integrin serves as a low-affinity receptor for ISM, the mechanism by which ISM mediates antiangiogenesis and apoptosis in ECs remain to be fully resolved. In this work, we report the identification of cell-surface glucose-regulated protein 78 kDa (GRP78) as a high-affinity receptor for ISM (K d ¼ 8.6 nM). We demonstrated that ISM-GRP78 interaction triggers apoptosis not only in activated ECs but also in cancer cells expressing high level of cell-surface GRP78. Normal cells and benign tumor cells tend to express low level of cell-surface GRP78 and are resistant to ISM-induced apoptosis. Upon binding to GRP78, ISM is internalized into ECs through clathrin-dependent endocytosis that is essential for its proapoptotic activity. Once inside the cell, ISM co-targets with GRP78 to mitochondria where it interacts with ADP/ATP carriers on the inner membrane and blocks ATP transport from mitochondria to cytosol, thereby causing apoptosis. Hence, ISM is a novel proapoptotic ligand that targets cell-surface GRP78 to trigger apoptosis by inducing mitochondrial dysfunction. The restricted and high-level expression of cell-surface GRP78 on cancer cells and cancer ECs make them uniquely susceptible to ISM-targeted apoptosis. Indeed, systemic delivery of recombinant ISM potently suppressed subcutaneous 4T1 breast carcinoma and B16 melanoma growth in mice by eliciting apoptosis selectively in the cancer cells and cancer ECs. Together, this work reveals a novel ISM-GRP78 apoptosis pathway and demonstrates the potential of ISM as a cancer-specific and dual-targeting anticancer agent.

Refuting the hypothesis that semaphorin‐3f/neuropilin‐2 exclude blood vessels from the cap mesenchyme in the developing kidney

“…Consequently, the receptors for Ism1 and Sema3f would need to be expressed in the plexus endothelia for them to transduce their signals. The receptors for Ism1 are integrin alpha-V (Itgav; Zhang et al, 2011) and 78 kDa glucose-regulated protein homolog (Grp78) (Chen et al, 2014), and, based on microarray data, they were expressed weakly in renal endothelia (Fig. 1E).…”

Nanoparticles inhibit cancer cell invasion and enhance antitumor efficiency by targeted drug delivery via cell surface-related GRP78

“…[28][29][30] Nowadays, cell surface GRP78 is regarded as a potential target for the targeted therapy of many human cancers. [31][32][33] In this paper, we show that bovine serum albumin (BSA) NPs conjugated with the monoclonal antibody against GRP78 (mAb GRP78) could inhibit the adhesion, invasion, and metastasis of hepatocellular carcinoma SMMC-7721, in which GRP78 is overexpressed. The mAb GRP78-NPs combined with GRP78 receptors situated at the surface of cancer cells and were internalized to intracellular compartments to form endosomes.…”

Targeting the unfolded protein response in cancer

“…Conversely, in response to TRAIL-mediated ER stress, GRP78 binds with Prostate apoptosis response-4 (Par4), translocates to the cell surface and leads to the activation of extrinsic apoptotic pathway (43). Additionally, cell surface GRP78 may also serve as a receptor for the angiogenesis inhibitor Kringle 5 (K5) and may act as a pro-apoptotic factor in stressed tumor cells (44). GRP78 and Bcl2 have been shown to form a complex which binds with separate domain of BIK, a pro-apoptotic protein.…”