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

Cell Death Differ. 2014 May;21(5):797-810. doi: 10.1038/cdd.2014.3. Epub 2014 Jan 24.


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 αvβ5 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 (Kd=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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Angiogenesis Inhibitors / metabolism*
  • Animals
  • Apoptosis / physiology
  • Cell Fractionation
  • Cell Growth Processes / physiology
  • Cell Line, Tumor
  • Endoplasmic Reticulum Chaperone BiP
  • Female
  • HEK293 Cells
  • Heat-Shock Proteins / genetics
  • Heat-Shock Proteins / metabolism*
  • Human Umbilical Vein Endothelial Cells
  • Humans
  • Intercellular Signaling Peptides and Proteins
  • Mice
  • Mice, Inbred BALB C
  • Mitochondria / metabolism
  • Mitochondria / physiology*
  • NIH 3T3 Cells
  • Neovascularization, Pathologic / metabolism
  • Proteins / genetics
  • Proteins / metabolism
  • Swiss 3T3 Cells
  • Transfection


  • Angiogenesis Inhibitors
  • Endoplasmic Reticulum Chaperone BiP
  • HSPA5 protein, human
  • Heat-Shock Proteins
  • Hspa5 protein, mouse
  • Intercellular Signaling Peptides and Proteins
  • Proteins
  • isthmin protein, mouse