Physiological Roles of the Autoantibodies to the 78-Kilodalton Glucose-Regulated Protein (GRP78) in Cancer and Autoimmune Diseases.

The 78 kDa glucose-regulated protein (GRP78), a member of the 70 kDa heat-shock family of molecular chaperones (HSP70), is essential for the regulation of the unfolded protein response (UPR) resulting from cellular endoplasmic reticulum (ER) stress. During ER stress, GRP78 evades retention mechanisms and is translocated to the cell surface (csGRP78) where it functions as an autoantigen. Autoantibodies to GRP78 appear in prostate, ovarian, gastric, malignant melanoma, and colorectal cancers.

Glucose-regulated protein (GRP78) is an important cell surface receptor for viral invasion, cancers, and neurological disorders.

The 78 kDa glucose-regulated protein (GRP78) is an endoplasmic reticulum (ER)-resident molecular chaperone. GRP78 is a member of the 70 kDa heat shock family of proteins involved in correcting and clearing misfolded proteins in the ER. In response to cellular stress, GRP78 escapes from the ER and moves to the plasma membrane where it (a) functions as a receptor for many ligands, and (b) behaves as an autoantigen for autoantibodies that contribute to human disease and cancer.

Autoantibodies against the cell surface-associated chaperone GRP78 stimulate tumor growth via tissue factor.

Tumor cells display on their surface several molecular chaperones that normally reside in the endoplasmic reticulum. Because this display is unique to cancer cells, these chaperones are attractive targets for drug development. Previous epitope-mapping of autoantibodies (AutoAbs) from prostate cancer patients identified the 78-kDa glucose-regulated protein (GRP78) as one such target.

Myelin basic protein stimulates plasminogen activation via tissue plasminogen activator following binding to independent l-lysine-containing domains.

Myelin basic protein (MBP) is a key component of myelin, the specialized lipid membrane that encases the axons of all neurons. Both plasminogen (Pg) and tissue-type plasminogen activator (t-PA) bind to MBP with high affinity. We investigated the kinetics and mechanisms involved in this process using immobilized MBP and found that Pg activation by t-PA is significantly stimulated by MBP.

Activated α2-Macroglobulin Regulates Transcriptional Activation of c-MYC Target Genes through Cell Surface GRP78 Protein.

Activated α2-macroglobulin (α2M*) signals predominantly through cell surface GRP78 (CS-GRP78) to promote proliferation and survival of cancer cells; however, the molecular mechanism remains obscure. c-MYC is an essential transcriptional regulator that controls cell proliferation. We hypothesize that α2M*/CS-GRP78-evoked key signaling events are required for transcriptional activation of c-MYC target genes.

Catalytic autoantibodies against myelin basic protein (MBP) isolated from serum of autistic children impair in vitro models of synaptic plasticity in rat hippocampus.

Autoantibodies from autistic spectrum disorder (ASD) patients react with multiple proteins expressed in the brain. One such autoantibody targets myelin basic protein (MBP). ASD patients have autoantibodies to MBP of both the IgG and IgA classes in high titers, but no autoantibodies of the IgM class.

Adult-Onset Ligneous Conjunctivitis with Detection of a Novel Plasminogen Gene Mutation and Anti-Plasminogen IgA Antibody: A Clinicopathologic Study and Review of Literature.

Purpose: To report a novel plasminogen gene mutation and detection of anti-plasminogen antibodies in a patient with ligneous conjunctivitis successfully treated with 60% fresh frozen plasma (FFP).

Methods: Retrospective data collected on a 45-year-old Caucasian female presenting with unilateral chronic membranous lesions.

Results: Laboratory investigation demonstrated decreased plasminogen antigen level, plasminogen activity, and rate of plasminogen activation by u-PA or t-PA, and elevated plasminogen activator inhibitor-1.

Binding of tissue-type plasminogen activator to the glucose-regulated protein 78 (GRP78) modulates plasminogen activation and promotes human neuroblastoma cell proliferation in vitro.

The glucose-regulated protein 78 (GRP78) is a plasminogen (Pg) receptor on the cell surface. In this study, we demonstrate that GRP78 also binds the tissue-type plasminogen activator (t-PA), which results in a decrease in K(m) and an increase in the V(max) for both its amidolytic activity and activation of its substrate, Pg. This results in accelerated Pg activation when GRP78, t-PA, and Pg are bound together.

The voltage-dependent anion channel (VDAC) binds tissue-type plasminogen activator and promotes activation of plasminogen on the cell surface.

The voltage-dependent anion channel (VDAC), a major pore-forming protein in the outer membrane of mitochondria, is also found in the plasma membrane of a large number of cells where in addition to its role in regulating cellular ATP release and volume control it is important for maintaining redox homeostasis. Cell surface VDAC is a receptor for plasminogen kringle 5, which promotes partial closure of the channel. In this study, we demonstrate that VDAC binds tissue-type plasminogen activator (t-PA) on human neuroblastoma SK-N-SH cells.

Changes in oligosaccharide chains of autoantibodies to GRP78 expressed during progression of malignant melanoma stimulate melanoma cell growth and survival.

A correlation between expression of the glucose-regulated protein of 78 kDa (GRP78) in malignant melanoma tumors and poor patient survival is well established. In this study, in addition to demonstrating the expression of GRP78 in tumor tissue, we investigated the immune response against GRP78 in a group of patients with different progression stages of malignant melanoma. Furthermore, we analyzed the glycosylation status of GRP78 immunoglobulin (Ig) G autoantibodies at these stages and evaluated their capacities to affect the protein B-dependent protein kinase signaling pathway and unfolded protein response signaling mechanisms, all known to promote malignant melanoma cell proliferation and survival.

Autoantibodies against cell surface GRP78 promote tumor growth in a murine model of melanoma.

Autoantibodies that react with GRP78 expressed on the cell-surface of many tumor cell lines occur in the sera of patients with prostate cancer, melanoma, and ovarian cancer. These autoantibodies are a negative prognostic factor in prostate cancer and, when purified, stimulate tumor cell proliferation in vitro. It is unclear, however, whether these immunoglobulin Gs are merely a biomarker, or whether they actually promote the tumor growth in vivo.

Binding of anti-GRP78 autoantibodies to cell surface GRP78 increases tissue factor procoagulant activity via the release of calcium from endoplasmic reticulum stores.

The increased risk of venous thromboembolism in cancer patients has been attributed to enhanced tissue factor (TF) procoagulant activity (PCA) on the surface of cancer cells. Recent studies have shown that TF PCA can be modulated by GRP78, an endoplasmic reticulum (ER)-resident molecular chaperone. In this study, we investigated the role of cell surface GRP78 in modulating TF PCA in several human cancer cell lines.

Antibodies against the voltage-dependent anion channel (VDAC) and its protective ligand hexokinase-I in children with autism.

Autistic children show elevated serum levels of autoantibodies to several proteins essential for the function of normal brains. The voltage-dependent anion channel (VDAC) and hexokinase-I, a VDAC protective ligand, were identified as targets of this autoimmunity in autistic children. These autoantibodies were purified using immunoaffinity chromatographic techniques.

Patterns of GRP78 and MTJ1 expression in primary cutaneous malignant melanoma.

Cell surface expression of glucose-regulated protein 78 (GRP78) occurs in several types of cancer; however, its role in the behavior of primary cutaneous melanoma is not well studied. The association of cell surface GRP78 with other proteins such as MTJ1 stimulates cell proliferation. In this study, we characterized the pattern of expression of GRP78 and MTJ1 in invasive primary cutaneous melanomas and analyzed the relationships between the pattern of expression and various clinicopathological parameters.

GRP78: a multifunctional receptor on the cell surface.

The 78 kDa glucose-regulated protein (GRP78) is an endoplasmic reticulum chaperone, whose function is generally thought to be restricted to controlling the structural maturation of nascent glycoproteins. However, GRP78 also is expressed on the cell surface where it functions as a receptor for a wide variety of ligands, behaving as an autoantigen for several classes of autoantibodies. GRP78 is a signaling receptor for activated alpha2-macroglobulin, plasminogen kringle 5, and microplasminogen, and it plays a critical role in viral entry of coxsackie B, and dengue fever viruses.

Dipeptidyl peptidase IV (DPP IV/CD26) is a cell-surface plasminogen receptor.

Binding of plasminogen (Pg) to cell-surface receptors colocalized with plasminogen activators promotes Pg activation and enables cells to utilize the proteolytic activity of plasmin (Pm). Proteolysis by Pm is necessary in several physiological and pathological processes requiring extracellular matrix degradation including cell migration, tumor cell invasion and metastasis. The binding of Pg to cell-surface receptors is regulated by two major structural features: L-lysine binding sites (LBS) and negatively charged sialic acid residues located on its carbohydrate chains.

Plasminogen structural domains exhibit different functions when associated with cell surface GRP78 or the voltage-dependent anion channel.

Both the voltage-dependent anion channel and the glucose-regulated protein 78 have been identified as plasminogen kringle 5 receptors on endothelial cells. In this study, we demonstrate that kringle 5 binds to a region localized in the N-terminal domain of the glucose-regulated protein 78, whereas microplasminogen does so through the C-terminal domain of the glucose-regulated protein 78. Both plasminogen fragments induce Ca(2+) signaling cascades; however, kringle 5 acts through voltage-dependent anion channel and microplasminogen does so via the glucose-regulated protein 78.

Prostate cancer cell proliferation in vitro is modulated by antibodies against glucose-regulated protein 78 isolated from patient serum.

Circulating autoantibodies against the glucose-regulated protein of 78 kDa (GRP78) are present at high levels in prostate cancer patients and are a biomarker of aggressive tumor behavior. We purified the anti-GRP78 IgGs and examined their effect on 1-LN, PC-3, DU145, and LnCap human prostate cancer cells. We also evaluated its effects on the breast cancer MDA-MB231 and melanoma DM413 cell lines.

Anti-tumor necrosis factor-alpha therapy augments dipeptidyl peptidase IV activity and decreases autoantibodies to GRP78/BIP and phosphoglucose isomerase in patients with rheumatoid arthritis.

Objective: To assess the enzymatic activity and biochemical status of dipeptidyl peptidase IV (DPP IV), an enzyme that participates in the degradation of proinflammatory molecules, in sera from a group of patients with rheumatoid arthritis (RA; n = 15) treated with a human anti-tumor necrosis factor-a (anti-TNF-alpha) antibody (adalimumab) for 32 weeks. IgG antibody titers against chaperone Bip (GRP78), phosphoglucose isomerase (PGI), lactate dehydrogenase (LDH), fibronectin (FN), and actin were also studied.

Methods: DPP IV activity was measured in sera using Gly-Pro-p-nitroanilide as substrate.

Angiostatin's molecular mechanism: aspects of specificity and regulation elucidated.

Tumor growth requires the development of new vessels that sprout from pre-existing normal vessels in a process known as "angiogenesis" [Folkman (1971) N Engl J Med 285:1182-1186]. These new vessels arise from local capillaries, arteries, and veins in response to the release of soluble growth factors from the tumor mass, enabling these tumors to grow beyond the diffusion-limited size of approximately 2 mm diameter. Angiostatin, a naturally occurring inhibitor of angiogenesis, was discovered based on its ability to block tumor growth in vivo by inhibiting the formation of new tumor blood vessels [O'Reilly et al.

Association of plasminogen with dipeptidyl peptidase IV and Na+/H+ exchanger isoform NHE3 regulates invasion of human 1-LN prostate tumor cells.

Binding of plasminogen type II (Pg 2) to dipeptidyl peptidase IV (DPP IV) on the surface of the highly invasive 1-LN human prostate tumor cell line induces an intracellular Ca2+ ([Ca2+]i) signaling cascade accompanied by a rise in intracellular pH (pHi). In endothelial cells, Pg 2 regulates intracellular pH via Na+/H+ exchange (NHE) antiporters; however, this mechanism has not been demonstrated in any other cell type including prostate cancer cells. Because the Pg 2 receptor DPP IV is associated with NHE3 in kidney cell plasma membranes, we investigated a similar association in 1-LN human prostate cancer cells and a mechanistic explanation for changes in [Ca2+]i or pHi induced by Pg 2 in these cells.

The role of MTJ-1 in cell surface translocation of GRP78, a receptor for alpha 2-macroglobulin-dependent signaling.

MTJ-1 associates with a glucose-regulated protein of Mr approximately 78,000(GRP78) in the endoplasmic reticulum and modulates GRP78 activity as a chaperone. GRP78 also exists on the cell surface membrane, where it is associated with a number of functions. MHC class I Ags on the cell surface are complexed to GRP78.

Angiostatin directly inhibits human prostate tumor cell invasion by blocking plasminogen binding to its cellular receptor, CD26.

Previous studies demonstrate that one of the six plasminogen type 2 glycoforms, plasminogen 2epsilon, enhances invasiveness of the 1-LN human prostate tumor cell line in an in vitro model. Binding of plasminogen 2epsilon to CD26 on the cell surface induces a Ca(2+) signaling cascade which stimulates the expression of matrix metalloproteinase-9, required by these cells to invade Matrigel. We now report that angiostatin, a fragment derived from plasminogen which prevents endothelial cell proliferation, is also a potent, direct inhibitor of 1-LN tumor cell invasiveness.

A novel receptor function for the heat shock protein Grp78: silencing of Grp78 gene expression attenuates alpha2M*-induced signalling.

The activated proteinase inhibitor alpha2-macroglobulin (alpha2M*) binds to two receptors, the low density lipoprotein receptor-related protein (LRP-1) and the alpha2M* signalling receptor (alpha2MSR). Silencing LRP-1 gene expression in macrophages by RNA interference does not block alpha2M* activation of signalling cascades. We now demonstrate that transfection of macrophages with a double-stranded RNA homologous in sequence to the Grp78 gene markedly decreased induction of inositol 1,4,5-trisphosphate (IP3) and subsequent IP3-dependent elevation of [Ca2+]i induced by alpha2M*.