Exploring the contribution of ARMS2 and HTRA1 genetic risk factors in age-related macular degeneration

Age-related macular degeneration (AMD) is the leading cause of severe irreversible central vision loss in individuals over 65 years old. Genome-wide association studies (GWASs) have shown that the region at chromosome 10q26, where the age-related maculopathy susceptibility (ARMS2/LOC387715) and HtrA serine peptidase 1 (HTRA1) genes are located, represents one of the strongest associated loci for AMD. However, the underlying biological mechanism of this genetic association has remained elusive. In this article, we extensively review the literature by us and others regarding the ARMS2/HTRA1 risk alleles and their functional significance. We also review the literature regarding the presumed function of the ARMS2 protein and the molecular processes of the HTRA1 protein in AMD pathogenesis in vitro and in vivo, including those of transgenic mice overexpressing HtrA1/HTRA1 which developed Bruch's membrane (BM) damage, choroidal neovascularization (CNV), and polypoidal choroidal vasculopathy (PCV), similar to human AMD patients. The elucidation of the molecular mechanisms of the ARMS2 and HTRA1 susceptibility loci has begun to untangle the complex biological pathways underlying AMD pathophysiology, pointing to new testable paradigms for treatment.

Alpha-2-Macroglobulin in Inflammation, Immunity and Infections

Alpha-2-macroglobulin is an extracellular macromolecule mainly known for its role as a broad-spectrum protease inhibitor. By presenting itself as an optimal substrate for endopeptidases of all catalytic types, alpha-2-macroglobulin lures active proteases into its molecular cage and subsequently ‘flags’ their complex for elimination. In addition to its role as a regulator of extracellular proteolysis, alpha-2-macroglobulin also has other functions such as switching proteolysis towards small substrates, facilitating cell migration and the binding of cytokines, growth factors and damaged extracellular proteins. These functions appear particularly important in the context of immune-cell function. In this review manuscript, we provide an overview of all functions of alpha-2-macroglobulin and place these in the context of inflammation, immunity and infections.

Dermatan Sulfate Is a Potential Regulator of IgH via Interactions With Pre-BCR, GTF2I, and BiP ER Complex in Pre-B Lymphoblasts

Dermatan sulfate (DS) and autoantigen (autoAg) complexes are capable of stimulating autoreactive CD5+ B1 cells. We examined the activity of DS on CD5+ pre-B lymphoblast NFS-25 cells. CD19, CD5, CD72, PI3K, and Fas possess varying degrees of DS affinity. The three pre-BCR components, Ig heavy chain mu (IgH), VpreB, and lambda 5, display differential DS affinities, with IgH having the strongest affinity. DS attaches to NFS-25 cells, gradually accumulates in the ER, and eventually localizes to the nucleus. DS and IgH co-localize on the cell surface and in the ER. DS associates strongly with 17 ER proteins (e.g., BiP/Grp78, Grp94, Hsp90ab1, Ganab, Vcp, Canx, Kpnb1, Prkcsh, Pdia3), which points to an IgH-associated multiprotein complex in the ER. In addition, DS interacts with nuclear proteins (Ncl, Xrcc6, Prmt5, Eftud2, Supt16h) and Lck. We also discovered that DS binds GTF2I, a required gene transcription factor at the IgH locus. These findings support DS as a potential regulator of IgH in pre-B cells at protein and gene levels. We propose a (DS•autoAg)-autoBCR dual signal model in which an autoBCR is engaged by both autoAg and DS, and, once internalized, DS recruits a cascade of molecules that may help avert apoptosis and steer autoreactive B cell fate. Through its affinity with autoAgs and its control of IgH, DS emerges as a potential key player in the development of autoreactive B cells and autoimmunity.

Die Wechselwirkung mit ribosomalen Proteinen begleitet die Stressinduktion des Wirkstoffkandidaten BOLD-100/KP1339 im endoplasmatischen Retikulum

Der metallhaltige Wirkstoff BOLD‐100/KP1339 zeigte bereits vielversprechende Resultate in verschiedenen In vitro‐ und In vivo‐Tumormodellen sowie in klinischen Studien. Der detaillierte Wirkmechanismus wurde jedoch noch nicht komplett aufgeklärt. Als entscheidende Wirkstoffeffekte kristallisierten sich kürzlich die Stressinduktion im endoplasmatischen Retikulum (ER) und die damit einhergehende Modulierung von HSPA5 (GRP78) heraus. Das spontane und stabile Addukt zwischen BOLD‐100 und menschlichem Serumalbumin wurde als Immobilisierungsstrategie ausgewählt, um einen chemoproteomischen Ansatz auszuführen, der die ribosomalen Proteine RPL10, RPL24 und den Transkriptionsfaktor GTF2I als potentielle Interaktoren dieser Ru(III)‐Verbindung identifizierten. Dieses Ergebnis wurde mit proteomischen und transkriptomischen Profiling‐Experimenten kombiniert, was die Interpretation einer ribosomalen Beeinträchtigung sowie der Induktion von ER‐Stress unterstützte. Die Bildung von Polyribosomen und begleitende ER‐Schwellungen in behandelten Krebszellen wurden zudem durch TEM‐Messungen bestätigt. Somit scheint eine direkte Wechselwirkung von BOLD‐100 mit ribosomalen Proteinen die ER‐Stressinduktion und die Modulierung von GRP78 in Krebszellen zu begleiten.

Interaction with Ribosomal Proteins Accompanies Stress Induction of the Anticancer Metallodrug BOLD-100/KP1339 in the Endoplasmic Reticulum

The ruthenium-based anticancer agent BOLD-100/KP1339 has shown promising results in several in vitro and in vivo tumour models as well as in early clinical trials. However, its mode of action remains to be fully elucidated. Recent evidence identified stress induction in the endoplasmic reticulum (ER) and concomitant down-modulation of HSPA5 (GRP78) as key drug effects. By exploiting the naturally formed adduct between BOLD-100 and human serum albumin as an immobilization strategy, we were able to perform target-profiling experiments that revealed the ribosomal proteins RPL10, RPL24, and the transcription factor GTF2I as potential interactors of this ruthenium(III) anticancer agent. Integrating these findings with proteomic profiling and transcriptomic experiments supported ribosomal disturbance and concomitant induction of ER stress. The formation of polyribosomes and ER swelling of treated cancer cells revealed by TEM validated this finding. Thus, the direct interaction of BOLD-100 with ribosomal proteins seems to accompany ER stress-induction and modulation of GRP78 in cancer cells.

Binding of Gtf2i-β/δ transcription factors to the ARMS2 gene leads to increased circulating HTRA1 in AMD patients and in vitro

The disease-initiating molecular events for age-related macular degeneration (AMD), a multifactorial retinal disease affecting many millions of elderly individuals worldwide, are still unknown. Of the over 30 risk and protective loci so far associated with AMD through whole genome-wide association studies (GWAS), the Age-Related Maculopathy Susceptibility 2 (ARMS2) gene locus represents one of the most highly associated risk regions for AMD. A unique insertion/deletion (in/del) sequence located immediately upstream of the High Temperature Requirement A1 (HTRA1) gene in this region confers high risk for AMD. Using electrophoretic mobility shift assay (EMSA), we identified that two Gtf2i-β/δ transcription factor isoforms bind to the cis-element 5'- ATTAATAACC-3' contained in this in/del sequence. The binding of these transcription factors leads to enhanced upregulation of transcription of the secretory serine protease HTRA1 in transfected cells and AMD patient-derived induced pluripotent stem cells (iPSCs). Overexpression of Htra1 in mice using a CAG-promoter demonstrated increased blood concentration of Htra1 protein, caused upregulation of vascular endothelial growth factor (VEGF), and produced a choroidal neovascularization (CNV)-like phenotype. Finally, a comparison of 478 AMD patients to 481 healthy, age-matched controls from Japan, India, Australia, and the USA showed a statistically increased level of secreted HTRA1 blood concentration in AMD patients compared with age-matched controls. Taken together, these results suggest a common mechanism across ethnicities whereby increased systemic blood circulation of secreted serine protease HTRA1 leads to subsequent degradation of Bruch's membrane and eventual CNV in AMD.

Cell surface GRP78 signaling: An emerging role as a transcriptional modulator in cancer

Cancer cells acquire dysregulated gene expression to establish specific transcriptional dependencies and their underlying mechanisms that are ultimately responsible for this addictions have not been fully elucidated. Glucose-regulated protein 78 (GRP78) is a stress-inducible, multifunctional, prosurvival, endoplasmic reticulum chaperone in the heat shock protein 70 family. Expression of cell surface GRP78 (CS-GRP78) is associated with increased malignant behavior and resistance to chemotherapy and radiotherapy by endowing various cancer cells with increased proliferative ability, altered metabolism, improved survival, and augmented invasive and metastatic potential. Emerging evidence has highlighted an unusual role of CS-GRP78 in regulating transcription factors (TFs) by mediating various signaling pathways involved in malignant transformation, metabolic reprogramming, and tumor progression. During the last decade, we targeted CS-GRP78 with C38 monoclonal antibody (C38 Mab) in numerous studies, which have highlighted the epigenetic interplay between CS-GRP78 and various TFs including c-MYC, Yes-associated protein/transcriptional coactivator with PDZ-binding motif, c-Fos, and histone acetylation to potentiate subsequent modulation of tumorigenesis, invasion, and metastasis. Here, we summarize the current state of knowledge about the role of CS-GRP78 in cancer development and progression, including epigenetic regulation and sheds light on CS-GRP78 as vulnerable target for cancer therapy. Overall, this review focuses on the mechanisms of TFs that are behind the transcriptional dysregulation in cancer and lays the groundwork for rational therapeutic use of C38 Mab based on CS-GRP78 biology.

The Unfolded Protein Response in Breast Cancer

In 2018, in the US alone, it is estimated that 268,670 people will be diagnosed with breast cancer, and that 41,400 will die from it. Since breast cancers often become resistant to therapies, and certain breast cancers lack therapeutic targets, new approaches are urgently required. A cell-stress response pathway, the unfolded protein response (UPR), has emerged as a promising target for the development of novel breast cancer treatments. This pathway is activated in response to a disturbance in endoplasmic reticulum (ER) homeostasis but has diverse physiological and disease-specific functions. In breast cancer, UPR signalling promotes a malignant phenotype and can confer tumours with resistance to widely used therapies. Here, we review several roles for UPR signalling in breast cancer, highlighting UPR-mediated therapy resistance and the potential for targeting the UPR alone or in combination with existing therapies.

The contribution of GTF2I haploinsufficiency to Williams syndrome

Williams syndrome (WS) is a neurodevelopmental disorder involving hemideletion of as many as 26-28 genes, resulting in a constellation of unique physical, cognitive and behavior phenotypes. The haploinsufficiency effect of each gene has been studied and correlated with phenotype(s) using several models including WS subjects, animal models, and peripheral cell lines. However, links for most of the genes to WS phenotypes remains unclear. Among those genes, general transcription factor 2I (GTF2I) is of particular interest as its haploinsufficiency is possibly associated with hypersociability in WS. Here, we describe studies of atypical WS cases as well as mouse models focusing on GTF2I that support a role for this protein in the neurocognitive and behavioral profiles of WS individuals. We also review collective studies on diverse molecular functions of GTF2I that may provide mechanistic explanation for phenotypes recently reported in our relevant cellular model, namely WS induced pluripotent stem cell (iPSC)-derived neurons. Finally, in light of the progress in gene-manipulating approaches, we suggest their uses in revealing the neural functions of GTF2I in the context of WS.

Lifetime Genistein Intake Increases the Response of Mammary Tumors to Tamoxifen in Rats

PURPOSE

Whether it is safe for estrogen receptor-positive (ER+) patients with breast cancer to consume soy isoflavone genistein remains controversial. We compared the effects of genistein intake mimicking either Asian (lifetime) or Caucasian (adulthood) intake patterns to that of starting its intake during tamoxifen therapy using a preclinical model.

EXPERIMENTAL DESIGN

Female Sprague-Dawley rats were fed an AIN93G diet supplemented with 0 (control diet) or 500 ppm genistein from postnatal day 15 onward (lifetime genistein). Mammary tumors were induced with 7,12-dimethylbenz(a)anthracene (DMBA), after which a group of control diet-fed rats were switched to genistein diet (adult genistein). When the first tumor in a rat reached 1.4 cm in diameter, tamoxifen was added to the diet and a subset of previously only control diet-fed rats also started genistein intake (post-diagnosis genistein).

RESULTS

Lifetime genistein intake reduced de novo resistance to tamoxifen, compared with post-diagnosis genistein groups. Risk of recurrence was lower both in the lifetime and in the adult genistein groups than in the post-diagnosis genistein group. We observed downregulation of unfolded protein response (UPR) and autophagy-related genes (GRP78, IRE1α, ATF4, and Beclin-1) and genes linked to immunosuppression (TGFβ and Foxp3) and upregulation of cytotoxic T-cell marker CD8a in the tumors of the lifetime genistein group, compared with controls, post-diagnosis, and/or adult genistein groups.

CONCLUSIONS

Genistein intake mimicking Asian consumption patterns improved response of mammary tumors to tamoxifen therapy, and this effect was linked to reduced activity of UPR and prosurvival autophagy signaling and increased antitumor immunity. Clin Cancer Res; 23(3); 814-24. ©2017 AACR.

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. Activation of CS-GRP78 by α2M* requires ligation of the GRP78 primary amino acid sequence (Leu(98)-Leu(115)). After stimulation with α2M*, CS-GRP78 signaling activates 3-phosphoinositide-dependent protein kinase-1 (PDK1) to induce phosphorylation of PLK1, which in turn induces c-MYC transcription. We demonstrate that PLK1 binds directly to c-MYC and promotes its transcriptional activity by phosphorylating Ser(62) Moreover, activated c-MYC is recruited to the E-boxes of target genes FOSL1 and ID2 by phosphorylating histone H3 at Ser(10) In addition, targeting the carboxyl-terminal domain of CS-GRP78 with a mAb suppresses transcriptional activation of c-MYC target genes and impairs cell proliferation. This work demonstrates that α2M*/CS-GRP78 acts as an upstream regulator of the PDK1/PLK1 signaling axis to modulate c-MYC transcription and its target genes, suggesting a therapeutic strategy for targeting c-MYC-associated malignant progression.

Cross-talk between endoplasmic reticulum (ER) stress and the MEK/ERK pathway potentiates apoptosis in human triple negative breast carcinoma cells: role of a dihydropyrimidone, nifetepimine

Triple negative breast cancers (TNBC) are among the most aggressive and therapy-resistant breast tumors and currently possess almost no molecular targets for therapeutic options in this horizon. In the present study we discerned the molecular mechanisms of potential interaction between the endoplasmic reticulum (ER) stress response and the MEK/ERK pathway in inducing apoptosis in TNBC cells. Here we observed that induction of ER stress alone was not sufficient to trigger significant apoptosis but simultaneous inhibition of the MEK/ERK pathway enhanced ER stress-induced apoptosis via a caspase-dependent mechanism. Our study also demonstrated nifetepimine, a dihydropyrimidone derivative as a potent anti-cancer agent in TNBC cells. Nifetepimine down-regulated the MEK/ERK pathway in MDAMB-231 and MDAMB-468 cells and resulted in blockage of ER stress-mediated GRP78 up-regulation. Detailed mechanistic studies also revealed that nifetepimine by down-regulating pERK expression also declined the promoter binding activity of TFII-I to the GRP78 promoter and in turn regulated GRP78 transcription. Studies further extended to in vivo Swiss albino and SCID mice models also revalidated the anti-carcinogenic property of nifetepimine. Thus our findings cumulatively suggest that nifetepimine couples two distinct signaling pathways to induce the apoptotic death cascade in TNBC cells and raises the possibility for the use of nifetepimine as a potent anti-cancer agent with strong immune-restoring properties for therapeutic intervention for this group of cancer bearers.

Knockdown of glucose-regulated protein 78/binding immunoglobulin heavy chain protein expression by asymmetric small interfering RNA induces apoptosis in prostate cancer cells and attenuates migratory capability

Glucose-regulated protein 78 [GRP78, also termed binding immunoglobulin heavy chain protein (Bip)] may be involved in cancer progression and metastasis. However, to date there has been minimal investigation into its potential role in human prostate cancer cells. Recent studies have demonstrated that asymmetric small interfering RNA (asiRNA)-mediated gene silencing is more effective and longer-lasting than conventional symmetric siRNA. Thus, the current study aimed to investigate the effects of GRP78-specific asiRNA on human prostate cancer cells. A series of asiRNAs was synthesized and their efficiency in silencing GRP78 expression in PC-3 human prostate cancer cells was evaluated. The effects of knockdown using asiRNAs were compared to those of knockdown using symmetric siRNAs. The effect of GRP78 silencing on PC-3 cell apoptosis and migration, and the possible mechanisms governing these biological processes were examined. Compared with the symmetric siRNA, transfection with the 15 base pair asiRNA (asiGRP78-3) resulted in greater downregulation of GRP78 expression. GRP78 depletion in PC-3 cells resulted in increased apoptosis and decreased migration of these cells. Experiments investigating the underlying mechanisms of these effects revealed that knockdown of GRP78 attenuated protein kinase B activation and decreased the expression of pro-caspase 9, pro-caspase 3 and vimentin. In conclusion, knockdown of GRP78/Bip expression with asymmetric siRNA led to increased prostate cancer cell apoptosis and reduced cellular migration.

E1A-mediated inhibition of HSPA5 suppresses cell migration and invasion in triple-negative breast cancer

BACKGROUND

Triple-negative breast cancer (TNBC) is defined by reduced expression of the estrogen receptor, progesterone receptor, and HER2. TNBC is an especially aggressive group of breast cancers with poor prognosis. There are currently no validated molecular targets to effectively treat this disease. Thus, it is necessary to identify effective molecular targets and therapeutic strategies for TNBC patients.

METHODS

The expression of HSPA5 in patients with breast cancer was examined by immunohistochemistry. The association of HSPA5 expression with tumor grade and metastatic events in TNBC patients was analyzed using the Oncomine database. The knockdown and overexpression of HSPA5 protein were performed to investigate the effects on E1A-suppressed cell migration/invasion of TNBC using in vitro transwell assays and tumor growth/experimental metastasis studies in animal models.

RESULTS

The expression of HSPA5 was positively correlated with high-grade tumors, metastatic events, and poor overall survival in breast cancer patients with TNBC. E1A-inhibited HSPA5 expression suppressed cell migration/invasive ability of TNBC cell lines. Moreover, E1A significantly abolished lung metastases from breast cancer cells by inhibiting HSPA5 expression in a xenograft tumor model.

CONCLUSIONS

The overexpression of HSPA5 is critical for high-risk metastasis of breast cancer and TNBC. The results of our study suggest that HSPA5 may be a crucial mediator of E1A-suppressed metastatic ability of breast cancer cells. Thus, E1A may be a potential target for diagnosis and individualized treatment in clinical practice.

Role of endoplasmic reticulum stress in rheumatoid arthritis pathogenesis

Rheumatoid arthritis (RA) is a chronic inflammatory disease characterized by abnormal proliferation of synoviocytes, leukocyte infiltration, and angiogenesis. The endoplasmic reticulum (ER) is the site of biosynthesis for all secreted and membrane proteins. The accumulation of unfolded proteins in the ER leads to a condition known as ER stress. Failure of the ER's adaptive capacity results in abnormal activation of the unfolded protein response. Recently, we have demonstrated that ER stress-associated gene signatures are highly expressed in RA synovium and synovial cells. Mice with Grp78 haploinsufficiency exhibit the suppression of experimentally induced arthritis, suggesting that the ER chaperone GRP78 is crucial for RA pathogenesis. Moreover, increasing evidence has suggested that GRP78 participates in antibody generation, T cell proliferation, and pro-inflammatory cytokine production, and is therefore one of the potential therapeutic targets for RA. In this review, we discuss the putative, pathophysiological roles of ER stress and GRP78 in RA pathogenesis.

Endoplasmic reticulum stress: its role in disease and novel prospects for therapy

The endoplasmic reticulum (ER) is a multifunctional organelle required for lipid biosynthesis, calcium storage, and protein folding and processing. A number of physiological and pathological conditions, as well as a variety of pharmacological agents, are able to disturb proper ER function and thereby cause ER stress, which severely impairs protein folding and therefore poses the risk of proteotoxicity. Specific triggers for ER stress include, for example, particular intracellular alterations (e.g., calcium or redox imbalances), certain microenvironmental conditions (e.g., hypoglycemia, hypoxia, and acidosis), high-fat and high-sugar diet, a variety of natural compounds (e.g., thapsigargin, tunicamycin, and geldanamycin), and several prescription drugs (e.g., bortezomib/Velcade, celecoxib/Celebrex, and nelfinavir/Viracept). The cell reacts to ER stress by initiating a defensive process, called the unfolded protein response (UPR), which is comprised of cellular mechanisms aimed at adaptation and safeguarding cellular survival or, in cases of excessively severe stress, at initiation of apoptosis and elimination of the faulty cell. In recent years, this dichotomic stress response system has been linked to several human diseases, and efforts are underway to develop approaches to exploit ER stress mechanisms for therapy. For example, obesity and type 2 diabetes have been linked to ER stress-induced failure of insulin-producing pancreatic beta cells, and current research efforts are aimed at developing drugs that ameliorate cellular stress and thereby protect beta cell function. Other studies seek to pharmacologically aggravate chronic ER stress in cancer cells in order to enhance apoptosis and achieve tumor cell death. In the following, these principles will be presented and discussed.

Receptor-recognized α₂-macroglobulin binds to cell surface-associated GRP78 and activates mTORC1 and mTORC2 signaling in prostate cancer cells

OBJECTIVE

Tetrameric α(2)-macroglobulin (α(2)M), a plasma panproteinase inhibitor, is activated upon interaction with a proteinase, and undergoes a major conformational change exposing a receptor recognition site in each of its subunits. Activated α(2)M (α(2)M*) binds to cancer cell surface GRP78 and triggers proliferative and antiapoptotic signaling. We have studied the role of α(2)M* in the regulation of mTORC1 and TORC2 signaling in the growth of human prostate cancer cells.

METHODS

Employing immunoprecipitation techniques and Western blotting as well as kinase assays, activation of the mTORC1 and mTORC2 complexes, as well as down stream targets were studied. RNAi was also employed to silence expression of Raptor, Rictor, or GRP78 in parallel studies.

RESULTS

Stimulation of cells with α(2)M* promotes phosphorylation of mTOR, TSC2, S6-Kinase, 4EBP, Akt(T308), and Akt(S473) in a concentration and time-dependent manner. Rheb, Raptor, and Rictor also increased. α(2)M* treatment of cells elevated mTORC1 kinase activity as determined by kinase assays of mTOR or Raptor immunoprecipitates. mTORC1 activity was sensitive to LY294002 and rapamycin or transfection of cells with GRP78 dsRNA. Down regulation of Raptor expression by RNAi significantly reduced α(2)M*-induced S6-Kinase phosphorylation at T389 and kinase activity in Raptor immunoprecipitates. α(2)M*-treated cells demonstrate about a twofold increase in mTORC2 kinase activity as determined by kinase assay of Akt(S473) phosphorylation and levels of p-Akt(S473) in mTOR and Rictor immunoprecipitates. mTORC2 activity was sensitive to LY294002 and transfection of cells with GRP78 dsRNA, but insensitive to rapamycin. Down regulation of Rictor expression by RNAi significantly reduces α(2)M*-induced phosphorylation of Akt(S473) phosphorylation in Rictor immunoprecipitates.

CONCLUSION

Binding of α(2)M* to prostate cancer cell surface GRP78 upregulates mTORC1 and mTORC2 activation and promotes protein synthesis in the prostate cancer cells.

[Macroglobulin signaling system]

This review will focus on the systematization of knowledge about structure of macroglobulin signaling system, which includes macroglobulin family proteins (alpha-2-macroglobulin, alpha-2-glycoprotein, pregnancy associated plasma protein A), their receptors (LRP, grp78), ligands (proteinases, cytokines, hormones, lipids, et al.) transforming and transcriptional factors for regulation of macroglobulins synthesis. After reviewing the functions of macroglobulin signaling system, and mechanisms of their realization, we discuss the complex and significant role of this system in different physiological and pathological processes.

Glucose regulated protein 78: a critical link between tumor microenvironment and cancer hallmarks

Glucose regulated protein 78 (GRP78) has long been recognized as a molecular chaperone in the endoplasmic reticulum (ER) and can be induced by the ER stress response. Besides its location in the ER, GRP78 has been found to be present in cell plasma membrane, cytoplasm, mitochondria, nucleus as well as cellular secretions. GRP78 is implicated in tumor cell proliferation, apoptosis resistance, immune escape, metastasis and angiogenesis, and its elevated expression usually correlates with a variety of tumor microenvironmental stresses, including hypoxia, glucose deprivation, lactic acidosis and inflammatory response. GRP78 protein acts as a centrally located sensor of stress, which feels and adapts to the alteration in the tumor microenvironment. This article reviews the potential contributions of GRP78 to the acquisition of cancer hallmarks based on intervening in stress responses caused by tumor niche alterations. The paper also introduces several potential GRP78 relevant targeted therapies.

Biochemistry and biology of the inducible multifunctional transcription factor TFII-I: 10 years later

Exactly twenty years ago TFII-I was discovered as a biochemical entity that was able to bind to and function via a core promoter element called the Initiator (Inr). Since then several different properties of this signal-induced multifunctional factor were discovered. Here I update these ever expanding functions of TFII-I--focusing primarily on the last ten years since the first review appeared in this journal.

Loss of cell surface TFII-I promotes apoptosis in prostate cancer cells stimulated with activated α₂ -macroglobulin

Receptor-recognized forms of α₂ -macroglobulin (α₂ M) bind to cell surface-associated GRP78 and initiate pro-proliferative and anti-apoptotic signaling. Ligation of GRP78 with α₂ M also upregulates TFII-I, which binds to the GRP78 promoter and enhances GRP78 synthesis. In addition to its transcriptional functions, cytosolic TFII-I regulates agonist-induced Ca(2+) entry. In this study we show that down regulation of TFII-I gene expression by RNAi profoundly impairs its cell surface expression and anti-apoptotic signaling as measured by significant reduction of GRP78, Bcl-2, and cyclin D1 in 1-Ln and DU-145 human prostate cancer cells stimulated with α₂ M. In contrast, this treatment significantly increases levels of the pro-apoptotic proteins p53, p27, Bax, and Bak and causes DNA fragmentation. Furthermore, down regulation of TFII-I expression activates agonist-induced Ca(2+) entry. In plasma membrane lysates p-PLCγ1, TRPC3, GRP78, MTJ1, and caveolin co-immunoprecipitate with TFII-I suggesting multimeric complexes of these proteins. Consistent with this hypothesis, down regulating TFII-I, MTJ1, or GRP78 expression by RNAi greatly attenuates cell surface expression of TFII-I. In conclusion, we demonstrate that not only does cell surface GRP78 regulate apoptosis, but it also regulates Ca(2+) homeostasis by controlling cell surface localization of TFII-I.

Ligation of prostate cancer cell surface GRP78 activates a proproliferative and antiapoptotic feedback loop: a role for secreted prostate-specific antigen

GRP78, a well characterized chaperone in the endoplasmic reticulum, is critical to the unfolded protein response. More recently, it has been identified on the cell surface, where it has many roles. On cancer cells, it functions as a signaling receptor coupled to proproliferative/antiapoptotic and promigratory mechanisms. In the current study, we demonstrate that ligation of prostate cancer cell surface GRP78 by its natural ligand, activated α(2)-macroglobulin (α(2)M*), results in a 2-3-fold up-regulation in the synthesis of prostate-specific antigen (PSA). The PSA is secreted into the medium as an active proteinase, where it binds to native α(2)M. The resultant α(2)M·PSA complexes bind to GRP78, causing a 1.5-2-fold increase in the activation of MEK1/2, ERK1/2, S6K, and Akt, which is coupled with a 2-3-fold increase in DNA and protein synthesis. PSA is a marker for the progression of prostate cancer, but its mechanistic role in the disease is unclear. The present studies suggest that PSA may be involved in a signal transduction-dependent feedback loop, whereby it promotes a more aggressive behavior by human prostate cancer cells.

Roles of GRP78 in physiology and cancer

As one member of 70 kDa heat shock proteins, glucose-regulated protein 78 (GRP78) participates in protein folding, transportation and degradation. This sort of capacity can be enhanced by stresses under which GRP78 is induced rapidly. Unlike its homologues, GRP78 presents multifaceted subcellular position: When ER retention, it serves as the switch of unfolded protein response; When mitochondrial binding, it directly interacts with apoptotic executors; When cell surface residing, it recognizes extracellular ligands, transducing proliferative signals, especially in certain tumors. The close correlation between GRP78 and neoplasm provides us further insight into the event of carcinogenesis and cancer cell chemoresistance, indicating its prognostic predicting significance and validating potential therapeutics for clinical usage, especially because its small molecular inhibitors are emerging quickly these years. What's more, GRP78-related signaling may be helpful for clearer understanding of its biological mechanisms.

Protection of pancreatic beta-cells from various stress conditions is mediated by DJ-1

Pancreatic beta-cells are vulnerable to multiple stresses, leading to dysfunction and apoptotic death. Deterioration in beta-cells function and mass is associated with type 2 diabetes. Comparative two-dimensional gel electrophoresis from pancreatic MIN6 cells that were maintained at varying glucose concentrations was carried out. An induced expression of a protein spot, detected in MIN6 cells experiencing high glucose concentration, was identified by mass spectrometry as the oxidized form of DJ-1. DJ-1 (park7) is a multifunctional protein implicated in familial Parkinsonism and neuroprotection in response to oxidative damage. The DJ-1 protein and its oxidized form were also induced following exposure to oxidative and endoplasmic reticulum stress in MIN6 and betaTC-6 cells and also in mouse pancreatic islets. Suppression of DJ-1 levels by small interfering RNA led to an accelerated cell death, whereas an increase in DJ-1 levels by adenovirus-based infection attenuated cell death induced by H(2)O(2) and thapsigargin in beta-cell lines and mouse pancreatic islets. Furthermore, DJ-1 improved regulated insulin secretion under basal as well as oxidative and endoplasmic reticulum stress conditions in a dose-dependent manner. We identified TFII-I (Gtf2i) as DJ-1 partner in the cytosol, whereas the binding of TFII-I to DJ-1 prevented TFII-I translocation to the nucleus. The outcome was attenuation of the stress response. Our results suggest that DJ-1 together with TFII-I operate in concert to cope with various insults and to sustain pancreatic beta-cell function.

Modulation of the unfolded protein response in prostate cancer cells by antibody-directed against the carboxyl-terminal domain of GRP78

Receptor-recognized forms of alpha(2)-macroglobulin (alpha(2)M*) bind to cancer cell surface GRP78, which functions as a signaling receptor promoting proliferation and survival. Patients with prostate, ovary, and skin cancer may develop auto-antibodies to the alpha(2)M* binding site which are receptor agonists whose presence indicates a poor prognosis. By contrast, antibodies directed against the COOH-terminal domain of GPR78 (anti-CTD antibody), are antagonists which down regulate pro-proliferative signaling and upregulate p53. Unfolded protein response (UPR) signaling plays an important role in cell survival and proliferation as well as apoptosis. We, therefore, studied the effect of anti-CTD antibody on UPR signaling in 1-LN and DU-145 prostate cancer cells. Treatment of these cells, which express GRP78 on their cell surface, with this antibody significantly downregulated IRE1-alpha, PERK, and ATF6alpha-dependent UPR signaling. By contrast, the pro-apoptotic protein GADD153 was elevated. Anti-CTD antibody treatment also elevated apoptotic components, cleaved PARP-1, and Erdj5. In general, a two to threefold effect was observed for the parameters which were studied. These studies suggest that anti-CTD antibody induces growth inhibitory and pro-apoptotic effects by modulating UPR signaling in human prostate cancer cells.