Mucormycosis is a fungal infection of the sinuses, brain, or lungs that causes a mortality rate of at least 50% despite first-line therapy. Because angioinvasion is a hallmark of mucormycosis infections, we sought to define the endothelial cell receptor(s) for fungi of the order Mucorales (the fungi that cause mucormycosis). Furthermore, since patients with elevated available serum iron, including those with diabetic ketoacidosis (DKA), are uniquely susceptible to mucormycosis, we sought to define the role of iron and glucose in regulating the expression of such a receptor. Here, we have identified glucose-regulated protein 78 (GRP78) as what we believe to be a novel host receptor that mediates invasion and damage of human endothelial cells by Rhizopus oryzae, the most common etiologic species of Mucorales, but not Candida albicans or Aspergillus fumigatus. Elevated concentrations of glucose and iron, consistent with those seen during DKA, enhanced GRP78 expression and the resulting R. oryzae invasion and damage of endothelial cells in a receptor-dependent manner. Mice with DKA, which have enhanced susceptibility to mucormycosis, exhibited increased expression of GRP78 in sinus, lungs, and brain compared with normal mice. Finally, GRP78-specific immune serum protected mice with DKA from mucormycosis. These results suggest a unique susceptibility of patients with DKA to mucormycosis and provide a foundation for the development of new therapeutic interventions for these deadly infections.

The recent development of hormonal therapy that blocks estrogen synthesis represents a major advance in the treatment of estrogen receptor-positive breast cancer. However, cancer cells often acquire adaptations resulting in resistance. A recent report reveals that estrogen starvationinduced apoptosis of breast cancer cells requires BIK, an apoptotic BH3-only protein located primarily at the endoplasmic reticulum (ER). Searching for novel partners that interact with BIK at the ER, we discovered that BIK selectively forms complex with the glucose-regulated protein GRP78/BiP, a major ER chaperone with prosurvival properties naturally induced in the tumor microenvironment. GRP78 overexpression decreases apoptosis of 293T cells induced by ER-targeted BIK. For estrogen-dependent MCF-7/BUS breast cancer cells, overexpression of GRP78 inhibits estrogen starvation-induced BAX activation, mitochondrial permeability transition, and consequent apoptosis. Further, knockdown of endogenous GRP78 by small interfering RNA (siRNA) sensitizes MCF-7/BUS cells to estrogen starvation-induced apoptosis. This effect was substantially reduced when the expression of BIK was also reduced by siRNA. Our results provide the first evidence that GRP78 confers resistance to estrogen starvation-induced apoptosis in human breast cancer cells via a novel mechanism mediated by BIK. These results further suggest that GRP78 expression level in the tumor cells may serve as a prognostic marker for responsiveness to hormonal therapy based on estrogen starvation and that combination therapy targeting GRP78 may enhance efficacy and reduce resistance. [Cancer Res 2007;67(8):3734-40]

GRP78/BiP has recently emerged as a novel biomarker for aggressive prostate cancer. Here, we report that homozygous deletion of Grp78 specifically in mouse prostate epithelium suppresses prostate tumorigenesis without affecting postnatal prostate development and growth. Mouse prostates with double conditional knockout of Grp78 and Pten exhibit normal histology and cytology, in contrast to the invasive adenocarcinoma in mouse prostates with Pten inactivation. AKT activation in Pten null prostate epithelium is inhibited by Grp78 homozygous deletion, corresponding with suppression of AKT phosphorylation by GRP78 knockdown in prostate cancer cell line. Thus, inactivation of GRP78 may represent a previously undescribed approach to stop prostate cancer and potentially other cancers resulting from the loss of PTEN tumor suppression and/or activation of the oncogenic AKT.cancer suppressor ͉ chaperone gene ͉ inactivation P rostate cancer is the most common cancer in men and develops through successive stages including prostatic intraepithelial neoplasia (PIN), carcinoma in situ, invasive adenocarcinoma, and metastatic disease. Although local surgery, radiation, or hormonal ablation provide initial response at early stages of the disease, tumor cells often develop resistance and relapse. Thus, the identification of new therapeutic targets for prostate cancer is of critical importance. The 78-kDa glucose regulated protein (GRP78) was initially linked to prostate cancer progression and metastasis through epitope mapping of humoral immune response from cancer patients, and identified as a functional molecular target for circulating ligands (1). Recent studies further revealed that Ϸ2/3 of human prostate cancers expressed high level of GRP78, associating with recurrence, development of castration-resistance, and poor survival (2, 3). These studies provide the first hints that GRP78 may have a critical role in prostate cancer development and therapeutic resistance.GRP78, also referred to as BiP or HSPA5, is a member of the HSP70 protein family. As a major endoplasmic reticulum (ER) chaperone, GRP78 facilitates protein folding and assembly, protein quality control, ER-associated protein degradation, Ca 2ϩ binding, and regulation of transmembrane ER stress inducers (4, 5). GRP78 is encoded by a single copy gene in rodents and humans. It is expressed as early as at the 2-cell stage of embryonic development, and is essential for proliferation and survival of embryonic cells (6). GRP78 is highly induced in a wide range of tumors through intrinsic factors such as altered glucose metabolism of cancer cells, compounded by extrinsic factors such as glucose deprivation, hypoxia, and acidosis in the microenvironment of poorly-perfused solid tumor (7). In a wide variety of cancer cell lines and xenograft models, GRP78 has emerged as having a critical role in cancer cell survival, tumor progression, and resistance to therapy (7-10). Despite these advances, it remains unknown whether GRP78 could also be essential for the genesis of tumor. I...

It has been established that as molecular chaperones, the glucose-regulated proteins (GRPs) play an important role in maintaining cellular homeostasis. This conventional concept of GRPs as protein folding chaperones is updated by discoveries that GRPs promote tumor proliferation, metastasis, drug resistance, immunotherapy, which have major clinical implications in the prognosis and treatment of cancer. Further, the localization of GRPs on the cell surface of certain cell types suggests that they serve new functions as cell surface receptors for signaling. These and other new developments on the role of GRP78, GRP94 and GRP170 in cancer progression and therapy are discussed in this review.

Neurodegenerative diseases are often associated with dysfunction in protein quality control. The endoplasmic reticulum (ER), a key site for protein synthesis, senses stressful conditions by activating the unfolded protein response (UPR). Here we report the creation of a novel mouse model where GRP78/BiP, a major ER chaperone and master regulator of UPR, is specifically eliminated in the Purkinje cells (PCs). GRP78 depleted PCs activate UPR including induction of GRP94, PDI, CHOP and GADD34, feedback suppression of eIF2α phosphorylation and apoptotic cell death. In contrast to current models of protein misfolding where abnormal accumulation of ubiquitinated protein is prominent, cytosolic ubiquitin staining is dramatically reduced in GRP78 null PCs. Ultrastructural evaluation reveals that the ER shows prominent dilatation with focal accumulation of electron-dense material within the ER. The mice show retarded growth and severe motor coordination defect by week 5 and cerebellar atrophy by week 13. Our studies uncover a novel link between GRP78 depletion and reduction in cytosolic ubiquitination and establish a novel mouse model of accelerated cerebellar degeneration with basic and clinical applications.