Insulin-like growth factor-I protects cells from ER stress-induced apoptosis via enhancement of the adaptive capacity of endoplasmic reticulum

Cardiovascular protection of YiyiFuzi powder and the potential mechanisms through modulating mitochondria-endoplasmic reticulum interactions

Cardiovascular diseases (CVD) remain the leading cause of death worldwide and represent a major public health challenge. YiyiFuzi Powder (YYFZ), composed of Coicis semen and Fuzi, is a classical traditional Chinese medicine prescription from the Synopsis of Golden Chamber dating back to the Han Dynasty. Historically, YYFZ has been used to treat various CVD, rooted in Chinese therapeutic principles. Network pharmacology analysis indicated that YYFZ may exhibit direct or indirect effects on mitochondria-endoplasmic reticulum (ER) interactions. This review, focusing on the cardiovascular protective effects of Coicis semen and Fuzi, summarizes the potential mechanisms by which YYFZ acts on mitochondria and the ER. The underlying mechanisms are associated with regulating cardiovascular risk factors (such as blood lipids and glucose), impacting mitochondrial structure and function, modulating ER stress, inhibiting oxidative stress, suppressing inflammatory responses, regulating cellular apoptosis, and maintaining calcium ion balance. The involved pathways include, but were not limited to, upregulating the IGF-1/PI3K/AKT, cAMP/PKA, eNOS/NO/cGMP/SIRT1, SIRT1/PGC-1α, Klotho/SIRT1, OXPHOS/ATP, PPARα/PGC-1α/SIRT3, AMPK/JNK, PTEN/PI3K/AKT, β2-AR/PI3K/AKT, and modified Q cycle signaling pathways. Meanwhile, the MCU, NF-κB, and JAK/STAT signaling pathways were downregulated. The PERK/eIF2α/ATF4/CHOP, PERK/SREBP-1c/FAS, IRE1, PINK1-dependent mitophagy, and AMPK/mTOR signaling pathways were bidirectionally regulated. High-quality experimental studies are needed to further elucidate the underlying mechanisms of YYFZ in CVD treatment.

Insulin reduces endoplasmic reticulum stress-induced apoptosis by decreasing mitochondrial hyperpolarization and caspase-12 in INS-1 pancreatic β-cells

Pancreatic β-cell mass is a critical determinant of insulin secretion. Severe endoplasmic reticulum (ER) stress causes β-cell apoptosis; however, the mechanisms of progression and suppression are not yet fully understood. Here, we report that the autocrine/paracrine function of insulin reduces ER stress-induced β-cell apoptosis. Insulin reduced the ER-stress inducer tunicamycin- and thapsigargin-induced cell viability loss due to apoptosis in INS-1 β-cells. Moreover, the effect of insulin was greater than that of insulin-like growth factor-1 at physiologically relevant concentrations. Insulin did not attenuate the ER stress-induced increase in unfolded protein response genes. ER stress did not induce cytochrome c release from mitochondria. Mitochondrial hyperpolarization was induced by ER stress and prevented by insulin. The protonophore/mitochondrial oxidative phosphorylation uncoupler, but not the antioxidants N-acetylcysteine and α-tocopherol, exhibited potential cytoprotection during ER stress. Both procaspase-12 and cleaved caspase-12 levels increased under ER stress. The caspase-12 inhibitor Z-ATAD-FMK decreased ER stress-induced apoptosis. Caspase-12 overexpression reduced cell viability, which was diminished in the presence of insulin. Insulin decreased caspase-12 levels at the post-translational stages. These results demonstrate that insulin protects against ER stress-induced β-cell apoptosis in this cell line. Furthermore, mitochondrial hyperpolarization and increased caspase-12 levels are involved in ER stress-induced and insulin-suppressed β-cell apoptosis.

Insulin-like growth factor family and prostate cancer: new insights and emerging opportunities

Prostate cancer is the second most commonly diagnosed cancer in men. The mammalian insulin-like growth factor (IGF) family is made up of three ligands (IGF-I, IGF-II, and insulin), three receptors (IGF-I receptor (IGF-1R), insulin receptor (IR), and IGF-II receptor (IGF-2R)), and six IGF-binding proteins (IGFBPs). IGF-I and IGF-II were identified as potent mitogens and were previously associated with an increased risk of cancer development including prostate cancer. Several reports showed controversy about the expression of the IGF family and their connection to prostate cancer risk due to the high degree of heterogeneity among prostate tumors, sampling bias, and evaluation techniques. Despite that, it is clear that several IGF family members play a role in prostate cancer development, metastasis, and androgen-independent progression. In this review, we aim to expand our understanding of prostate tumorigenesis and regulation through the IGF system. Further understanding of the role of IGF signaling in PCa shows promise and needs to be considered in the context of a comprehensive treatment strategy.

Endoplasmic reticulum stress PERK-ATF4-CHOP pathway is involved in non-alcoholic fatty liver disease in type 1 diabetic rats: The rescue effect of treatment exercise and insulin-like growth factor I

Endoplasmic Reticulum Stress (ERS) is a key factor in the development of Non-Alcoholic Fatty Liver Disease (NAFLD) in diabetes. The current study aimed to examine the effects of exercise and IGF-I on ERS markers in liver tissue. Rats were divided into five groups (n = 8 per group), including control (CON), diabetes (DIA), diabetes + exercise (DIA + EX), diabetes + IGF-I (DIA + IGF-I), and diabetes + exercise + IGF-I (DIA + EX + IGF-I). Type 1 diabetes was induced by an I.P. injection of streptozotocin (60 mg/kg). After 30 days of treatment with exercise or IGF-I alone or in combination, liver tissue was assessed for caspase 12, 8, and CHOP protein levels, and expression of ERS markers (ATF-6, PERK, IRE-1A) and lipid metabolism-involved genes (FAS, FXR, SREBP-1c) by western immunoblotting. In addition, for the evaluation of histopathological changes in the liver, Hematoxylin - Eosin and Masson's Trichrome staining were done. Compared to the control group, diabetes significantly caused liver fibrosis, induced ERS, increased caspase 12 and 8 levels in the liver, and changed expression levels of genes associated with lipid metabolism, including FAS, FXR, and SREBP-1c. Treatment with either exercise or IGF-I reduced fibrosis levels suppressed ER stress markers and apoptosis, and improved expression of genes associated with lipid metabolism. In addition, simultaneous treatment with exercise and IGF-I showed a synergistic effect compared to DIA + E and DIA + IGF-I. The results suggest that IGF-1 and exercise reduced liver fibrosis possibly by reducing ERS, creating adaptive ER stress status, and improving protein folding.

Involvement of IGF1 in endoplasmic reticulum stress contributes to cataract formation through regulating Nrf2/NF-κB signaling

Endoplasmic reticulum (ER) stress is reportedly involved in the development of ophthalmic diseases. This study aimed to investigate the role and potential mechanism of insulin-like growth factor 1 (IGF1) in ER stress. A mouse cataract model was constructed by subcutaneous injection of sodium selenite, and sh-IGF1 was used to evaluate the effect of silencing IGF1 on cataract progression. Slit-lamp and histological examination of the lens were performed to examine lens damage. The regulatory effects of IGF1 on inflammatory responses, oxidative stress, and ER stress were evaluated using ELISA, reverse transcription-quantitative PCR (RT-qPCR), and immunoblotting analysis. Tunicamycin was used to induce ER stress in the lens of epithelial cells. The NF-E2 related factor-2 (Nrf2) inhibitor ML385 and nuclear factor-κB (NF-κB) agonist diprovocim were used to confirm whether IGF1 regulates inflammation and ER stress through Nrf2/NF-κB signaling. Silencing IGF1 alleviated lens damage and reduced lens turbidity in the cataract mice. Silencing IGF1 inhibited inflammatory response, oxidative stress and ER stress response. Meanwhile, IGF1 was highly expressed in sodium selenite-treated lens epithelial cells. The ER stress agonist tunicamycin suppressed cell viability as well as induced ER stress, oxidative stress and inflammation. Silencing IGF1 increased cell viability, EdU-positive rate and migration. Also, silencing of IGF1 reduced inflammation and ER stress via regulating Nrf2/NF-κB pathway. This study reveals silencing IGF1 attenuated cataract through regulating Nrf2/NF-κB signaling, which shares novel insights into the underlying mechanism of cataract and provides potential therapeutic target for cataract.

Aberrant Splicing of INS Impairs Beta-Cell Differentiation and Proliferation by ER Stress in the Isogenic iPSC Model of Neonatal Diabetes

One of the causes of diabetes in infants is the defect of the insulin gene (INS). Gene mutations can lead to proinsulin misfolding, an increased endoplasmic reticulum (ER) stress and possible beta-cell apoptosis. In humans, the mechanisms underlying beta-cell failure remain unclear. We generated induced pluripotent stem cells (iPSCs) from a patient diagnosed with neonatal diabetes mellitus carrying the INS mutation in the 2nd intron (c.188-31G>A) and engineered isogenic CRISPR/Cas9 mutation-corrected cell lines. Differentiation into beta-like cells demonstrated that mutation led to the emergence of an ectopic splice site within the INS and appearance of the abnormal RNA transcript. Isogenic iPSC lines differentiated into beta-like cells showed a clear difference in formation of organoids at pancreatic progenitor stage of differentiation. Moreover, MIN6 insulinoma cell line expressing mutated cDNA demonstrated significant decrease in proliferation capacity and activation of ER stress and unfolded protein response (UPR)-associated genes. These findings shed light on the mechanism underlying the pathogenesis of monogenic diabetes.

Elucidation of ER stress and UPR pathway in sialic acid-deficient cells: Pathological relevance to GNEM

Accumulation of misfolded proteins in endoplasmic reticulum (ER) generates a stress condition in the cell. The cell combats ER stress by activating unfolded protein response (UPR) and ERAD (ER stress-associated degradation) pathway. Failure to restore favorable folding environment results in cell dysfunction and apoptosis. Various neurodegenerative disorders are characterized by the accumulation of misfolded protein, protein aggregates, and ER stress. GNE myopathy (GNEM) is a neuromuscular disorder pathologically characterized by rimmed vacuole formation due to the accumulation of protein aggregates. More than 200 mutations in key sialic acid biosynthetic enzyme UDP-N-acetylglucosamine 2-epimerase/N-acetylmannosamine kinase (GNE) have been identified worldwide in the muscle biopsies of GNE myopathy patients. However, the cellular and molecular pathomechanism leading to the disease ar poorly understood. In the present study, the phenomenon of ER stress has been elucidated in GNE mutant cells overexpressing GNE mutations of Indian origin. The effect of GNE mutations on activation of UPR signaling via inositol-requiring transmembrane kinase/endoribonuclease 1 (IRE-1), protein kinase RNA-like endoplasmic reticulum kinase (PERK), and activating transcription factor-6 (ATF6) were deciphered to understand the effect of GNE mutations on these proteins. GRP78 was upregulated with increased X-box-binding protein-1 (XBP-1) splicing and CCAAT/enhancer-binding protein (C/EBP) homologous protein (CHOP) upregulation leading to increased apoptosis of GNE mutant cells. Insulin-like growth factor 1 (IGF-1) ligand rescued the cells from apoptotic phenotype by supporting cell survival mechanism. Our study indicates a balance of cell death and survival that decides cell fate and offers potential therapeutic targets to combat ER stress in diseases associated with dysfunctional UPR pathway.

The special unfolded protein response in plasma cells

The high rate of antibody production places considerable metabolic and folding stress on plasma cells (PC). Not surprisingly, they rely on the unfolded protein response (UPR), a universal signaling, and transcriptional network that monitors the health of the secretory pathway and mounts cellular responses to stress. Typically, the UPR utilizes three distinct stress sensors in the ER membrane, each regulating a subset of targets to re-establish homeostasis. PC use a specialized UPR scheme-they preemptively trigger the UPR via developmental signals and suppress two of the sensors, PERK and ATF6, relying on IRE1 alone. The specialized PC UPR program is tuned to the specific needs at every stage of development-from early biogenesis of secretory apparatus, to massive immunoglobulin expression later. Furthermore, the UPR in PC integrates with other pathways essential in a highly secretory cell-mTOR pathway that ensures efficient synthesis, autophagosomes that recycle components of the synthetic machinery, and apoptotic signaling that controls cell fate in the face of excessive folding stress. This specialized PC program is not shared with other secretory cells, for reasons yet to be defined. In this review, we give a perspective into how and why PC need such a unique UPR program.

The Effects of Insulin-Like Growth Factor I and BTP-2 on Acute Lung Injury

Acute lung injury (ALI) afflicts approximately 200,000 patients annually and has a 40% mortality rate. The COVID-19 pandemic has massively increased the rate of ALI incidence. The pathogenesis of ALI involves tissue damage from invading microbes and, in severe cases, the overexpression of inflammatory cytokines such as tumor necrosis factor-α (TNF-α) and interleukin-1β (IL-1β). This study aimed to develop a therapy to normalize the excess production of inflammatory cytokines and promote tissue repair in the lipopolysaccharide (LPS)-induced ALI. Based on our previous studies, we tested the insulin-like growth factor I (IGF-I) and BTP-2 therapies. IGF-I was selected, because we and others have shown that elevated inflammatory cytokines suppress the expression of growth hormone receptors in the liver, leading to a decrease in the circulating IGF-I. IGF-I is a growth factor that increases vascular protection, enhances tissue repair, and decreases pro-inflammatory cytokines. It is also required to produce anti-inflammatory 1,25-dihydroxyvitamin D. BTP-2, an inhibitor of cytosolic calcium, was used to suppress the LPS-induced increase in cytosolic calcium, which otherwise leads to an increase in proinflammatory cytokines. We showed that LPS increased the expression of the primary inflammatory mediators such as toll like receptor-4 (TLR-4), IL-1β, interleukin-17 (IL-17), TNF-α, and interferon-γ (IFN-γ), which were normalized by the IGF-I + BTP-2 dual therapy in the lungs, along with improved vascular gene expression markers. The histologic lung injury score was markedly elevated by LPS and reduced to normal by the combination therapy. In conclusion, the LPS-induced increases in inflammatory cytokines, vascular injuries, and lung injuries were all improved by IGF-I + BTP-2 combination therapy.

Pregnancy-associated plasma protein-aa regulates endoplasmic reticulum-mitochondria associations

Endoplasmic reticulum (ER) and mitochondria form close physical associations to facilitate calcium transfer, thereby regulating mitochondrial function. Neurons with high metabolic demands, such as sensory hair cells, are especially dependent on precisely regulated ER-mitochondria associations. We previously showed that the secreted metalloprotease pregnancy-associated plasma protein-aa (Pappaa) regulates mitochondrial function in zebrafish lateral line hair cells (Alassaf et al., 2019). Here, we show that pappaa mutant hair cells exhibit excessive and abnormally close ER-mitochondria associations, suggesting increased ER-mitochondria calcium transfer. pappaa mutant hair cells are more vulnerable to pharmacological induction of ER-calcium transfer. Additionally, pappaa mutant hair cells display ER stress and dysfunctional downstream processes of the ER-mitochondria axis including altered mitochondrial morphology and reduced autophagy. We further show that Pappaa influences ER-calcium transfer and autophagy via its ability to stimulate insulin-like growth factor-1 bioavailability. Together our results identify Pappaa as a novel regulator of the ER-mitochondria axis.

Insulin-like growth factor 1-receptor signaling stimulates GRP78 expression through the PI3K/AKT/mTOR/ATF4 axis

GRP78, a major molecular chaperone, is critical for the folding and maturation of membrane and secretory proteins and serves as the master regulator of the unfolded protein response. Thus, GRP78 is frequently upregulated in highly proliferative cells to cope with elevated protein synthesis and metabolic stress. IGF-1 is a potent regulator of cell growth, metabolism and survival. Previously we discovered that GRP78 is a novel downstream target of IGF-1 signaling by utilizing mouse embryonic fibroblast model systems where the IGF-1 receptor (IGF-1R) was either overexpressed (R+) or knockout (R-). Here we investigated the mechanisms whereby GRP78 is upregulated in the R+ cells. Our studies revealed that suppression of PI3K/AKT/mTOR downstream of IGF-1R signaling resulted in concurrent decrease in GRP78 and the transcription factor ATF4. Through knock-down and overexpression studies, we established ATF4 as the essential downstream nodal of the PI3K/AKT/mTOR signaling pathway critical for GRP78 transcriptional upregulation mediated by IGF-1R.

P-STAT3 Inhibition Activates Endoplasmic Reticulum Stress-Induced Splenocyte Apoptosis in Chronic Stress

Chronic stress leads to immunosuppression and induces splenocyte apoptosis. STAT3 is a transcription factor that regulates immunity and apoptosis; however, it is unclear whether the increased expression of phosphorylated STAT3 (p-STAT3) observed in chronic stress is related to splenocyte apoptosis. To explore the relationship between splenocyte apoptosis and STAT3 in chronic stress, we treated rats undergoing a 21-day chronic restraint stress program with the STAT3 inhibitor S3I-201. This chronic stress model was verified by observing rats’ behavior and measuring their serum corticosterone levels. Chronic stress led to increased expression of anti-inflammatory cytokines, and p-STAT3 inhibition enhanced splenocyte apoptosis in chronic stress. We detected key proteins in three apoptotic pathways to determine which pathway mediated increasing splenocyte apoptosis and found that the death receptor pathway was the main apoptotic pathway that occurred in the spleen during chronic stress. The unfolded protein response (UPR) was also activated, but the Bcl-2 family was not involved in chronic stress. P-STAT3 inhibition had no influence on the Bcl-2 family and the death receptor pathway; however, p-STAT3 inhibition disrupted the pro-survival function of the UPR by decreasing the expression of ATF6α and p-IRE1α. Furthermore, p-STAT3 inhibition activated endoplasmic reticulum stress by promoting the expression of CHOP, p-JNK, and procaspase-12. Collectively, these findings indicate that the increased p-STAT3 expression during chronic stress may promote splenocyte survival by activating the UPR. Consequently, STAT3 and the UPR may be considered as potential therapeutic targets for chronic stress in the future.

Insulin-like growth factor receptor signaling in breast tumor epithelium protects cells from endoplasmic reticulum stress and regulates the tumor microenvironment

BACKGROUND

Early analyses of human breast cancer identified high expression of the insulin-like growth factor type 1 receptor (IGF-1R) correlated with hormone receptor positive breast cancer and associated with a favorable prognosis, whereas low expression of IGF-1R correlated with triple negative breast cancer (TNBC). We previously demonstrated that the IGF-1R acts as a tumor and metastasis suppressor in the Wnt1 mouse model of TNBC. The mechanisms for how reduced IGF-1R contributes to TNBC phenotypes is unknown.

METHODS

We analyzed the METABRIC dataset to further stratify IGF-1R expression with patient survival and specific parameters of TNBC. To investigate molecular events associated with the loss of IGF-1R function in breast tumor cells, we inhibited IGF-1R in human cell lines using an IGF-1R blocking antibody and analyzed MMTV-Wnt1-mediated mouse tumors with reduced IGF-1R function through expression of a dominant-negative transgene.

RESULTS

Our analysis of the Molecular Taxonomy of Breast Cancer International Consortium (METABRIC) dataset revealed association between low IGF-1R and reduced overall patient survival. IGF-1R expression was inversely correlated with patient survival even within hormone receptor-positive breast cancers, indicating reduced overall patient survival with low IGF-1R was not due simply to low IGF-1R expression within TNBCs. Inhibiting IGF-1R in either mouse or human tumor epithelial cells increased reactive oxygen species (ROS) production and activation of the endoplasmic reticulum stress response. IGF-1R inhibition in tumor epithelial cells elevated interleukin (IL)-6 and C-C motif chemokine ligand 2 (CCL2) expression, which was reversed by ROS scavenging. Moreover, the Wnt1/dnIGF-1R primary tumors displayed a tumor-promoting immune phenotype. The increased CCL2 promoted an influx of CD11b⁺ monocytes into the primary tumor that also had increased matrix metalloproteinase (MMP)-2, MMP-3, and MMP-9 expression. Increased MMP activity in the tumor stroma was associated with enhanced matrix remodeling and collagen deposition. Further analysis of the METABRIC dataset revealed an increase in IL-6, CCL2, and MMP-9 expression in patients with low IGF-1R, consistent with our mouse tumor model and data in human breast cancer cell lines.

CONCLUSIONS

Our data support the hypothesis that reduction of IGF-1R function increases cellular stress and cytokine production to promote an aggressive tumor microenvironment through infiltration of immune cells and matrix remodeling.

The Role of the Anti-Aging Protein Klotho in IGF-1 Signaling and Reticular Calcium Leak: Impact on the Chemosensitivity of Dedifferentiated Liposarcomas

By inhibiting Insulin-Like Growth Factor-1-Receptor (IGF-1R) signaling, Klotho (KL) acts like an aging- and tumor-suppressor. We investigated whether KL impacts the aggressiveness of liposarcomas, in which IGF-1R signaling is frequently upregulated. Indeed, we observed that a higher KL expression in liposarcomas is associated with a better outcome for patients. Moreover, KL is downregulated in dedifferentiated liposarcomas (DDLPS) compared to well-differentiated tumors and adipose tissue. Because DDLPS are high-grade tumors associated with poor prognosis, we examined the potential of KL as a tool for overcoming therapy resistance. First, we confirmed the attenuation of IGF-1-induced calcium (Ca²⁺)-response and Extracellular signal-Regulated Kinase 1/2 (ERK1/2) phosphorylation in KL-overexpressing human DDLPS cells. KL overexpression also reduced cell proliferation, clonogenicity, and increased apoptosis induced by gemcitabine, thapsigargin, and ABT-737, all of which are counteracted by IGF-1R-dependent signaling and activate Ca²⁺-dependent endoplasmic reticulum (ER) stress. Then, we monitored cell death and cytosolic Ca²⁺-responses and demonstrated that KL increases the reticular Ca²⁺-leakage by maintaining TRPC6 at the ER and opening the translocon. Only the latter is necessary for sensitizing DDLPS cells to reticular stressors. This was associated with ERK1/2 inhibition and could be mimicked with IGF-1R or MEK inhibitors. These observations provide a new therapeutic strategy in the management of DDLPS.

A Human Genome-Wide RNAi Screen Reveals Diverse Modulators that Mediate IRE1α-XBP1 Activation

Activation of the unfolded protein response (UPR) signaling pathways is linked to multiple human diseases, including cancer. The inositol-requiring kinase 1α (IRE1α)-X-box binding protein 1 (XBP1) pathway is the most evolutionarily conserved of the three major signaling branches of the UPR. Here, we performed a genome-wide siRNA screen to obtain a systematic assessment of genes integrated in the IRE1α-XBP1 axis. We monitored the expression of an XBP1-luciferase chimeric protein in which luciferase was fused in-frame with the spliced (active) form of XBP1. Using cells expressing this reporter construct, we identified 162 genes for which siRNA inhibition resulted in alteration in XBP1 splicing. These genes express diverse types of proteins modulating a wide range of cellular processes. Pathway analysis identified a set of genes implicated in the pathogenesis of breast cancer. Several genes, including BCL10, GCLM, and IGF1R, correlated with worse relapse-free survival (RFS) in an analysis of patients with triple-negative breast cancer (TNBC). However, in this cohort of 1,908 patients, only high GCLM expression correlated with worse RFS in both TNBC and non-TNBC patients. Altogether, our study revealed unidentified roles of novel pathways regulating the UPR, and these findings may serve as a paradigm for exploring novel therapeutic opportunities based on modulating the UPR.Implications: Genome-wide RNAi screen identifies novel genes/pathways that modulate IRE1α-XBP1 signaling in human tumor cells and leads to the development of improved therapeutic approaches targeting the UPR.Visual Overview: http://mcr.aacrjournals.org/content/molcanres/16/5/745/F1.large.jpg Mol Cancer Res; 16(5); 745-53. ©2018 AACR.

The role of declining adaptive homeostasis in ageing

Adaptive homeostasis is "the transient expansion or contraction of the homeostatic range for any given physiological parameter in response to exposure to sub-toxic, non-damaging, signalling molecules or events, or the removal or cessation of such molecules or events" (Davies, 2016). Adaptive homeostasis enables biological systems to make continuous short-term adjustments for optimal functioning despite ever-changing internal and external environments. Initiation of adaptation in response to an appropriate signal allows organisms to successfully cope with much greater, normally toxic, stresses. These short-term responses are initiated following effective signals, including hypoxia, cold shock, heat shock, oxidative stress, exercise-induced adaptation, caloric restriction, osmotic stress, mechanical stress, immune response, and even emotional stress. There is now substantial literature detailing a decline in adaptive homeostasis that, unfortunately, appears to manifest with ageing, especially in the last third of the lifespan. In this review, we present the hypothesis that one hallmark of the ageing process is a significant decline in adaptive homeostasis capacity. We discuss the mechanistic importance of diminished capacity for short-term (reversible) adaptive responses (both biochemical and signal transduction/gene expression-based) to changing internal and external conditions, for short-term survival and for lifespan and healthspan. Studies of cultured mammalian cells, worms, flies, rodents, simians, apes, and even humans, all indicate declining adaptive homeostasis as a potential contributor to age-dependent senescence, increased risk of disease, and even mortality. Emerging work points to Nrf2-Keap1 signal transduction pathway inhibitors, including Bach1 and c-Myc, both of whose tissue concentrations increase with age, as possible major causes for age-dependent loss of adaptive homeostasis.

Anti-pancreatic cancer activity of ONC212 involves the unfolded protein response (UPR) and is reduced by IGF1-R and GRP78/BIP

Pancreatic cancer is chemo-resistant and metastasizes early with an overall five-year survival of ∼8.2%. First-in-class imipridone ONC201 is a small molecule in clinical trials with anti-cancer activity. ONC212, a fluorinated-ONC201 analogue, shows preclinical efficacy in melanoma and hepatocellular-cancer models. We investigated efficacy of ONC201 and ONC212 against pancreatic cancer cell lines (N=16 including 9 PDX-cell lines). We demonstrate ONC212 efficacy in 4 in-vivo models including ONC201-resistant tumors. ONC212 is active in pancreatic cancer as single agent or in combination with 5-fluorouracil, irinotecan, oxaliplatin or RTK inhibitor crizotinib. Based on upregulation of pro-survival IGF1-R in some tumors, we found an active combination of ONC212 with inhibitor AG1024, including in vivo. We show a rationale for targeting pancreatic cancer using ONC212 combined with targeting the unfolded-protein response and ER chaperones such as GRP78/BIP. Our results lay the foundation to test imipridones, anti-cancer agents, in pancreatic cancer, that is refractory to most drugs.

The Unfolded Protein Response in Amelogenesis and Enamel Pathologies

During the secretory phase of their life-cycle, ameloblasts are highly specialized secretory cells whose role is to elaborate an extracellular matrix that ultimately confers both form and function to dental enamel, the most highly mineralized of all mammalian tissues. In common with many other “professional” secretory cells, ameloblasts employ the unfolded protein response (UPR) to help them cope with the large secretory cargo of extracellular matrix proteins transiting their ER (endoplasmic reticulum)/Golgi complex and so minimize ER stress. However, the UPR is a double-edged sword, and, in cases where ER stress is severe and prolonged, the UPR switches from pro-survival to pro-apoptotic mode. The purpose of this review is to consider the role of the ameloblast UPR in the biology and pathology of amelogenesis; specifically in respect of amelogenesis imperfecta (AI) and fluorosis. Some forms of AI appear to correspond to classic proteopathies, where pathological intra-cellular accumulations of protein tip the UPR toward apoptosis. Fluorosis also involves the UPR and, while not of itself a classic proteopathic disease, shares some common elements through the involvement of the UPR. The possibility of therapeutic intervention by pharmacological modulation of the UPR in AI and fluorosis is also discussed.

Proteostasis and ageing: insights from long-lived mutant mice

The global increase in life expectancy is creating significant medical, social and economic challenges to current and future generations. Consequently, there is a need to identify the fundamental mechanisms underlying the ageing process. This knowledge should help develop realistic interventions capable of combatting age‐related disease, and thus improving late‐life health and vitality. While several mechanisms have been proposed as conserved lifespan determinants, the loss of proteostasis – where proteostasis is defined here as the maintenance of the proteome – appears highly relevant to both ageing and disease. Several studies have shown that multiple proteostatic mechanisms, including the endoplasmic reticulum (ER)‐induced unfolded protein response (UPR), the ubiquitin–proteasome system (UPS) and autophagy, appear indispensable for longevity in many long‐lived invertebrate mutants. Similarly, interspecific comparisons suggest that proteostasis may be an important lifespan determinant in vertebrates. Over the last 20 years a number of long‐lived mouse mutants have been described, many of which carry single‐gene mutations within the growth‐hormone, insulin/IGF‐1 or mTOR signalling pathways. However, we still do not know how these mutations act mechanistically to increase lifespan and healthspan, and accordingly whether mechanistic commonality occurs between different mutants. Recent evidence supports the premise that the successful maintenance of the proteome during ageing may be linked to the increased lifespan and healthspan of long‐lived mouse mutants.

Hyperactivation of the Insulin Signaling Pathway Improves Intracellular Proteostasis by Coordinately Up-regulating the Proteostatic Machinery in Adipocytes

Hyperinsulinemia, which is associated with aging and metabolic disease, may lead to defective protein homeostasis (proteostasis) due to hyperactivation of insulin-sensitive pathways such as protein synthesis. We investigated the effect of chronic hyperinsulinemia on proteostasis by generating a time-resolved map of insulin-regulated protein turnover in adipocytes using metabolic pulse-chase labeling and high resolution mass spectrometry. Hyperinsulinemia increased the synthesis of nearly half of all detected proteins and did not affect protein degradation despite suppressing autophagy. Unexpectedly, this marked elevation in protein synthesis was accompanied by enhanced protein stability and folding and not by markers of proteostasis stress such as protein carbonylation and aggregation. The improvement in proteostasis was attributed to a coordinate up-regulation of proteins in the global proteostasis network, including ribosomal, proteasomal, chaperone, and endoplasmic reticulum/mitochondrial unfolded protein response proteins. We conclude that defects associated with hyperactivation of the insulin signaling pathway are unlikely attributed to defective proteostasis because up-regulation of protein synthesis by insulin is accompanied by up-regulation of proteostatic machinery.

Repression of Mcl-1 and disruption of the Mcl-1/Bak interaction in myeloma cells couple ER stress to mitochondrial apoptosis

As myeloma cells actively produce and secrete immunoglobulins, they are prone to ER stress, which if unresolved leads to apoptosis. We found that myeloma cell death induced by the ER stressor Thapsigargin was highly variable, ranging from 2 to 89%. Induction of ATF4 and CHOP was observed in myeloma cells under Thapsigargin independently of cell death. The decrease in Mcl-1 was associated with protein translation inhibition and identified as a crucial factor in Thapsigargin sensitivity, since it was the only Bcl-2 family protein differentially modified between sensitive and resistant myeloma cells. Bak but not Bax was found to contribute to Thapsigargin-induced apoptosis. Appropriately, a basal Mcl-1/Bak interaction was demonstrated in Thapsigargin-sensitive cells. Of note, the only pro-apoptotic protein freed from Mcl-1 under Thapsigargin was Bak, whereas Mcl-1/Noxa or Mcl-1/Bim complexes were simultaneously increased. Thus, the disruption of the basal Mcl-1/Bak complex in Thapsigargin-sensitive cells seemed to be an essential event in cell death induction, probably favored by the induced Noxa and Bim BH3-only proteins. These findings underscore the implication of the Mcl-1/Bak axis in myeloma cell death triggered by Thapsigargin.

IRS1 deficiency protects β-cells against ER stress-induced apoptosis by modulating sXBP-1 stability and protein translation

Endoplasmic reticulum (ER) stress is among several pathological features that underlie β-cell failure in the development of type 1 and type 2 diabetes. Adaptor proteins in the insulin/insulin-like-growth factor-1 signaling pathways, such as insulin receptor substrate-1 (IRS1) and IRS2, differentially impact β-cell survival but the underlying mechanisms remain unclear. Here we report that β-cells deficient in IRS1 (IRS1KO) are resistant, while IRS2 deficiency (IRS2KO) makes them susceptible to ER stress-mediated apoptosis. IRS1KOs exhibited low nuclear accumulation of spliced XBP-1 due to its poor stability, in contrast to elevated accumulation in IRS2KO. The reduced nuclear accumulation in IRS1KO was due to protein instability of Xbp1 secondary to proteasomal degradation. IRS1KO also demonstrated an attenuation in their general translation status in response to ER stress revealed by polyribosomal profiling. Phosphorylation of eEF2 was dramatically increased in IRS1KO enabling the β-cells to adapt to ER stress by blocking translation. Furthermore, significantly high ER calcium (Ca²⁺) was detected in IRS1KO β-cells even upon induction of ER stress. These observations suggest that IRS1 could be a therapeutic target for β-cell protection against ER stress-mediated cell death by modulating XBP-1 stability, protein synthesis, and Ca²⁺ storage in the ER.

Obesity and Diabetes: The Increased Risk of Cancer and Cancer-Related Mortality

Obesity and type 2 diabetes are becoming increasingly prevalent worldwide, and both are associated with an increased incidence and mortality from many cancers. The metabolic abnormalities associated with type 2 diabetes develop many years before the onset of diabetes and, therefore, may be contributing to cancer risk before individuals are aware that they are at risk. Multiple factors potentially contribute to the progression of cancer in obesity and type 2 diabetes, including hyperinsulinemia and insulin-like growth factor I, hyperglycemia, dyslipidemia, adipokines and cytokines, and the gut microbiome. These metabolic changes may contribute directly or indirectly to cancer progression. Intentional weight loss may protect against cancer development, and therapies for diabetes may prove to be effective adjuvant agents in reducing cancer progression. In this review we discuss the current epidemiology, basic science, and clinical data that link obesity, diabetes, and cancer and how treating obesity and type 2 diabetes could also reduce cancer risk and improve outcomes.

Endoplasmic reticulum stress is involved in the neuroprotective effect of propofol

Propofol is a common clinically used intravenous anaesthetic agent with antioxidative property. It has been thought to have neuroprotection in vitro and in vivo. However, the underlying mechanisms remain unclear. Endoplasmic reticulum (ER) stress plays an important role in regulating the signaling pathways concerning cell death and survival. Therefore, we wondered whether the neuroprotective effects of propofol are associated with its regulation on ER stress. In this study, we found that propofol up-regulated BiP and attenuated tunicamycin-induced neural cell death. Propofol pretreatment also inhibited tunicamycin-induced up-regulation of C/EBP homologous protein (CHOP). We also found that propofol or tunicamycin alone increased the levels of spliced XBP1 (XBP1s) and cleaved activating transcription factor 6 (ATF6), an active form of ATF6. However, pretreatment with propofol attenuated the levels of phosphorylated protein kinase receptor-like ER kinase, phosphorylated elF2α, ATF4, and caspase-3, but failed to affect the increase of cleaved ATF6 and XBP1s, induced by tunicamycin. Knockdown endogenous BiP with siRNA abolished the suppression of propofol on tunicamycin-mediated activation of CHOP and caspase-3. Meanwhile, knockdown BiP attenuated the protective effects of propofol on the neural cells exposed to tunicamycin. These data suggest that ER stress is involved in the neuroprotection of propofol via differentially regulating the unfolded protein response pathway, in which BiP plays an important role in initiating the adaptive ER stress and inhibiting the apoptotic ER stress.

Discovery of a novel target for the dysglycemic chromogranin A fragment pancreastatin: interaction with the chaperone GRP78 to influence metabolism

RATIONALE

The chromogranin A-derived peptide pancreastatin (PST) is a dysglycemic, counter-regulatory peptide for insulin action, especially in liver. Although previous evidence for a PST binding protein has been reported, such a receptor has not been identified or sequenced.

METHODS AND RESULTS

We used ligand affinity to purify the PST target, with biotinylated human PST (hCHGA273-301-amide) as "bait" and mouse liver homogenate as "prey", and identified GRP78 (a.k.a. "78 kDa Glucose Regulated Protein", HSPA5, BIP) as a major interacting partner of PST. GRP78 belongs to the family of heat shock proteins (chaperones), involved in several cellular processes including protein folding and glucose metabolism. We analyzed expression of GRP78 in the absence of PST in a mouse knockout model lacking its precursor CHGA: hepatic transcriptome data revealed global over-expression of not only GRP78 but also other heat shock transcripts (of the "adaptive UPR") in CHGA(-/-) mice compared to wild-type (+/+). By contrast, we found a global decline in expression of hepatic pro-apoptotic transcripts in CHGA(-/-) mice. GRP78's ATPase enzymatic activity was dose-dependently inhibited by PST (IC50∼5.2 µM). PST also inhibited the up-regulation of GRP78 expression during UPR activation (by tunicamycin) in hepatocytes. PST inhibited insulin-stimulated glucose uptake in adipocytes, and increased hepatic expression of G6Pase (the final step in gluconeogenesis/glycogenolysis). In hepatocytes not only PST but also other GRP78-ATPase inhibitors (VER-155008 or ADP) increased G6Pase expression. GRP78 over-expression inhibited G6Pase expression in hepatocytes, with partial restoration by GRP78-ATPase inhibitors PST, VER-155008, or ADP.

CONCLUSIONS

Our results indicate that an unexpected major hepatic target of PST is the adaptive UPR chaperone GRP78. PST not only binds to GRP78 (in pH-dependent fashion), but also inhibits GRP78's ATPase enzymatic activity, and impairs its biosynthetic response to UPR activation. PST decreases insulin-stimulated cellular glucose uptake, and PST as well as other chaperone ATPase activity inhibitors augment expression of G6Pase; GRP78 over-expression antagonizes this PST action. Analysis of the novel PST/GRP78 interaction may provide a new avenue of investigation into cellular glycemic control as well as dysglycemia.

Triethylene Glycol Dimethacrylate Induction of Apoptotic Proteins in Pulp Fibroblasts

Objective

Monomers such as triethylene glycol dimethacrylate (TEGDMA) can leach from dental composites. TEGDMA-induced apoptosis in human pulp has been reported. However, the apoptotic (pro or anti) proteins involved in this process remain unclear. Therefore, the purpose of this study was to determine which apoptotic proteins are enhanced or suppressed during TEGDMA-induced apoptosis.

Materials and Methods

Human pulp fibroblasts (HPFs) were incubated with different TEGDMA concentrations (0.125-1.0 mM) and cytotoxicity was determined. TEGDMA was shown to be cell cytotoxic at concentrations of 0.50 mM and higher. The highest concentration with no significant cytotoxicity was then incubated (0.25 mM TEGDMA) with the HPFs. Cell lysates were then prepared and the protein concentrations determined. Human Apoptosis Array kits were utilized to detect the relative levels of 43 apoptotic proteins.

Results

HPFs exposed to TEGDMA showed significant increases in multiple pro-apoptotic proteins such as Bid, Bim, Caspase 3, Caspase 8, and Cytochrome c at 24 hours. Some anti-apoptotic proteins were also altered.

Conclusions

The results indicated that TEGDMA activates both the extrinsic and intrinsic apoptotic pathways.

FGF-2 prevents cancer cells from ER stress-mediated apoptosis via enhancing proteasome-mediated Nck degradation

Induction of ER (endoplasmic reticulum) stress-mediated apoptosis in cancer cells represents an alternative approach for cancer therapy. Whether FGF-2 (fibroblast growth factor 2)-induced survival signals may interact with ER stress signalling in cancer cells remains elusive. In the present study, we showed that pretreatment with FGF-2 decreased the inhibition of DNA synthesis and induction of apoptosis by two different ER stress inducers, TM (tunicamycin) and TG (thapsigargin), in both human hepatoblastoma HepG2 cells and breast cancer MCF-7 cells. Pretreatment with FGF-2 prevented ER stress-mediated apoptosis by decreasing ER stress-induced CHOP [C/EBP (CCAAT/enhancer-binding protein)-homologous protein] expression. We further demonstrated that pretreatment with FGF-2 mediated the decrease in TM-induced CHOP expression and apoptosis through ERK1/2 (extracellular-signal-regulated kinases 1 and 2) pathway. Finally, we demonstrated that FGF-2 promoted proteasome-mediated degradation of Nck (non-catalytic region of tyrosine kinase adaptor protein), an SH (Src homology) 2/SH3-containing adaptor protein. Whereas overexpression of Nck1 decreased FGF-2-induced ERK1/2 phosphorylation to inhibit the effect of FGF-2 on TM-induced CHOP expression and apoptosis, a decrease in Nck expression prevented TM-induced CHOP expression and apoptosis. Taken together, the findings of the present study provide the first evidence that Nck plays a pivotal role in integrating FGF-2 and ER stress signals to counteract the ER stress deleterious effect on cancer cell survival.

Inositol-requiring enzyme 1α is required for gut development in Xenopus lavies embryos

AIM: To investigate the role of inositol-requiring enzyme 1α (IRE1α) in gut development of Xenopus lavies embryos.

METHODS: Xenopus embryos were obtained with in vitro fertilization and cultured in 0.1 × MBSH. One and half nanogram of IRE1α, 1 ng of IRE1α-GR mRNA, 1 ng of IRE1αΔC-GR mRNA, and 50 ng of IRE1α morpholino oligonucleotide (MO) or XBP1(C)MO were injected into four blastomeres at 4-cell stage for scoring the phenotype and marker gene analysis. To rescue the effect of IRE1α MO, 1 ng of IRE1α-GR mRNA was co-injected with 50 ng of MO. For the activation of the GR-fusion proteins, dexamethasone was prepared as 5 mmol/L stock solutions in 100% ethanol and applied to the mRNA injected embryos at desired stages in a concentration of 10 μmol/L in 0.1 × MBSH. Embryos were kept in dexamethasone up to stage 41. Whole-mount in situ hybridization was used to determine specific gene expression, such as IRE1α, IRE1β, Xbra and Xsox17α. IRE1α protein expression during Xenopus embryogenesis was detected by Western blotting.

RESULTS: In the whole-mount in situ hybridization analysis, xenopus IRE1α and IRE1β showed quite different expression pattern during tadpole stage. The relatively higher expression of IRE1α was observed in the pancreas, and significant transcription of IRE1β was found in the liver. IRE1α protein could be detected at all developmental stages analyzed, from stage 1 to stage 42. Gain-of-function assay showed that IRE1α mRNA injected embryos at tailbud stage were nearly normal and the expression of the pan-mesodermal marker gene Xbra and the endodermal gene Xsox17α at stage 10.5 was not significantly changed in embryos injected with IRE1α mRNA as compared to uninjected control embryos. And at tadpole stage, the embryos injected with IRE1α-GR mRNA did not display overt phenotype, such as gut-coiling defect. Loss-of-function assay demonstrated that the IRE1α MO injected embryos were morphologically normal before the tailbud stages. We did not observe a significant change of mesodermal and endodermal marker gene expression, while after stage 40, about 80% of the MO injected embryos exhibited dramatic gut defects in which the guts did not coil, but other structures outside the gastrointestinal tract were relatively normal. To test if the phenotypes were specifically caused by the knockdown of IRE1α, a rescue experiment was performed by co-injection of IRE1α-GR mRMA with IRE1α MO. The data obtained demonstrated that the gut coiling defect was rescued. The deletion mutant of IRE1α was constructed, consisting of the N-terminal part without the C-terminal kinase and RNase domains named IRE1αΔC, to investigate the functional domain of IRE1α. Injection of IRE1αΔC-GR mRNA caused similar morphological alterations with gut malformation by interfering with the function of endogenous xIRE1α. In order to investigate if IRE1α/XBP1 pathway was involved in gut development, 50 ng of XBP1 MO was injected and the results showed that knockdown of XBP1 resulted in similar morphological alterations with gut-coiling defect at tadpole stage.

CONCLUSION: IRE1α is not required for germ layer formation but for gut development in Xenopus lavies and it may function via XBP1-dependent pathway.

GRP78/BiP is a novel downstream target of IGF-1 receptor mediated signaling

Glucose regulated protein 78/immunoglobulin binding protein (GRP78/BiP) is an endoplasmic reticulum (ER) chaperone protein and master regulator of the unfolded protein response (UPR). The response of GRP78 to overt pharmacologically induced ER stress is well established, whereas the modulation of GRP78 to physiologic changes is less characterized. In this study, we examined the regulation of GRP78 in response to reduced IGF-1 growth factor signaling, a common consequence of calorie restriction (CR). ER chaperone protein expression was quantified in cell lysates prepared from the livers of calorie restricted (CR) and ad libitum fed mice, as well as MEFs grown in normal medium or serum starved. The requirement of IGF-1 signaling on GRP78 expression was studied using MEFs with IGF-1 receptor overexpression (R+) or deletion (R-), and the regulatory mechanism was examined using mTORC1 and PI3K inhibitors, as well as R- cells with knockdown of transcription factor FOXO1 compared to shRNA control. We observed a 40% reduction in GRP78 protein expression in CR mice and in serum-starved MEF cells. R- cells had drastically reduced AKT phosphorylation and exhibited lower levels of ER chaperones, in particular 80% less GRP78. Despite an 80% reduction in GRP78 expression, R- cells were not under chronic ER stress, but were fully capable of activating the UPR. Neither forced expression of FOXO1-AAA nor knockdown of FOXO1 in R- cells affected GRP78 expression. In conclusion, we report that IGF-1 receptor signaling regulates GRP78 expression via the PI3K/AKT/mTORC1 axis independent of the canonical UPR and FOXO1.

Insulin-like growth factor-1 inhibits 6-hydroxydopamine-mediated endoplasmic reticulum stress-induced apoptosis via regulation of heme oxygenase-1 and Nrf2 expression in PC12 cells

Endoplasmic reticulum (ER) stress and oxidative stress appear to play a critical role in the progression of Parkinson's disease (PD). Insulin-like growth factor (IGF)-1, a 70-amino acid polypeptide trophic factor, acts as a potent neurotrophic, neurogenic, and neuroprotective/anti-apoptotic factor. In this study, we investigated the protective mechanisms of IGF-1 in rat pheochromocytoma PC12 cells exposed to the PD-related neurotoxin 6-hydroxydopamine (6-OHDA). The transcription factor nuclear factor erythroid 2-related factor 2 (Nrf2) coordinates expression of genes required for free radical scavenging, detoxification of xenobiotics, and maintenance of redox potential. Exposure of cells to 6-OHDA resulted in an increase in ER-stress-induced apoptotic cell death, which was significantly reduced by treatment of cells with IGF-1. IGF-1 treatment significantly increased BiP and C/EBP homologous protein expression in 6-OHDA-treated cultures. IGF-1 protected cells from 6-OHDA-induced insult by inhibiting intracellular reactive oxygen species generation. Compared with vehicle-treated controls, the expression of Nrf2 and heme oxygenase-1 (HO-1) was increased in 6-OHDA-treated cells. IGF-1 significantly up-regulated HO-1 in cells exposed to 6-OHDA. These results suggest that IGF-1 augment cellular anti-oxidant defense mechanism, at least in part, through the up-regulation of HO-1 expression.

PERK is required at the ER-mitochondrial contact sites to convey apoptosis after ROS-based ER stress

Endoplasmic reticulum stress is emerging as an important modulator of different pathologies and as a mechanism contributing to cancer cell death in response to therapeutic agents. In several instances, oxidative stress and the onset of endoplasmic reticulum (ER) stress occur together; yet, the molecular events linking reactive oxygen species (ROS) to ER stress-mediated apoptosis are currently unknown. Here, we show that PERK (RNA-dependent protein kinase (PKR)-like ER kinase), a key ER stress sensor of the unfolded protein response, is uniquely enriched at the mitochondria-associated ER membranes (MAMs). PERK(-/-) cells display disturbed ER morphology and Ca(2+) signaling as well as significantly weaker ER-mitochondria contact sites. Re-expression of a kinase-dead PERK mutant but not the cytoplasmic deletion mutant of PERK in PERK(-/-) cells re-establishes ER-mitochondria juxtapositions and mitochondrial sensitization to ROS-mediated stress. In contrast to the canonical ER stressor thapsigargin, during ROS-mediated ER stress, PERK contributes to apoptosis twofold by sustaining the levels of pro-apoptotic C/EBP homologous protein (CHOP) and by facilitating the propagation of ROS signals between the ER and mitochondria through its tethering function. Hence, this study reveals an unprecedented role of PERK as a MAMs component required to maintain the ER-mitochondria juxtapositions and propel ROS-mediated mitochondrial apoptosis. Furthermore, it suggests that loss of PERK may cause defects in cell death sensitivity in pathological conditions linked to ROS-mediated ER stress.

Insulin-like growth factor-1 and central neurodegenerative diseases

The previously undisputed neuroprotective role of insulin-like growth factor 1 (IGF-1) has been challenged by recent observations in IGF-1 receptor (IGF-1R) defective mutants. As new ligand-dependent and ligand-independent roles for IGF-1R are now emerging, new insights into the biologic role of brain IGF-1R and its connection with serum and brain IGF-1 function are urgently required. In the meantime, treatment of specific neurodegenerative diseases with IGF-1 may still be explored using adequate preclinical procedures.

Deletion of muscle GRP94 impairs both muscle and body growth by inhibiting local IGF production

Insulin-like growth factors (IGFs) are critical for development and growth of skeletal muscles, but because several tissues produce IGFs, it is not clear which source is necessary or sufficient for muscle growth. Because it is critical for production of both IGF-I and IGF-II, we ablated glucose-regulated protein 94 (GRP94) in murine striated muscle to test the necessity of local IGFs for normal muscle growth. These mice exhibited smaller skeletal muscles with diminished IGF contents but with normal contractile function and no apparent endoplasmic reticulum stress response. This result shows that muscles rely on GRP94 primarily to support local production of IGFs, a pool that is necessary for normal muscle growth. In addition, body weights were ∼30% smaller than those of littermate controls, and circulating IGF-I also decreased significantly, yet glucose homeostasis was maintained with little disruption to the growth hormone pathway. The growth defect was complemented on administration of recombinant IGF-I. Thus, unlike liver production of IGF-I, muscle IGF-I is necessary not only locally but also globally for whole-body growth.

The IGF1 pathway genes and their association with age of puberty in cattle

Insulin-like growth factor I (somatomedin C) (IGF1) influences gonadotrophin-releasing hormone (GnRH) neurons during puberty, and GnRH release guides pubertal development. Therefore, genes of the IGF1 pathway are biological candidates for the identification of single-nucleotide polymorphisms (SNPs) affecting age of puberty. In a genome-wide association study, genotyped heifers were Tropical Composite (TCOMP, n = 866) or Brahman (BRAH, n = 843), with observation of age at first corpus luteum defining puberty. We examined SNPs in or near genes of the IGF1 pathway and report seven genes associated with age at puberty in cattle: IGF1R, IGFBP2, IGFBP4, PERK (HUGO symbol EIF2AK3), PIK3R1, GSK3B and IRS1. SNPs in the IGF1 receptor (IGF1R) showed the most promising associations: two SNPs were associated with puberty in TCOMP (P < 0.05) and one in BRAH (P = 0.00009). This last SNP explained 2% of the genetic variation (R(2) = 2.04%) for age of puberty in BRAH. Hence, IGF1R was examined further. Additional SNPs were genotyped, and haplotypes were analysed. To test more SNPs in this gene, four new SNPs from dbSNP were selected and genotyped. Single SNP and haploytpe analysis revealed associations with age of puberty in both breeds. There were two haplotypes of 12 IGF1R SNPs associated with puberty in BRAH (P < 0.05) and one in TCOMP (P < 0.05). One haplotype of two SNPs was associated (P < 0.01) with puberty in BRAH, but not in TCOMP. In conclusion, the IGF1 pathway appeared more relevant for age of puberty in Brahman cattle, and IGF1R showed higher significance when compared with other genes from the pathway.

Disturbance of Ca2+ homeostasis converts pro-Met into non-canonical tyrosine kinase p190MetNC in response to endoplasmic reticulum stress in MHCC97 cells

c-Met, the tyrosine-kinase receptor for hepatocyte growth factor, plays a critical role in the tumorigenesis of hepatocellular carcinoma (HCC). However, the underlying mechanism remains incompletely understood. The mature c-Met protein p190Met(αβ) (consists of a α subunit and a β subunit) is processed from pro-Met. Here we show that pro-Met is processed into p190Met(NC) by sarco/endoplasmic reticulum calcium-ATPase (SERCA) inhibitor thapsigargin. p190Met(NC) compensates for the degradation of p190Met(αβ) and protects human HCC cells from apoptosis mediated by endoplasmic reticulum (ER) stress. In comparison with p190Met(αβ), p190Met(NC) is not cleaved and is expressed as a single-chain polypeptide. Thapsigargin-initiated p190Met(NC) expression depends on the disturbance of ER calcium homeostasis. Once induced, p190Met(NC) is activated independent of hepatocyte growth factor engagement. p190Met(NC) contributes to sustained high basal activation of c-Met downstream pathways during ER calcium disturbance-mediated ER stress. Both p38 MAPK-promoted glucose-regulated protein 78 (GRP78) expression and sustained high basal activation of PI3K/Akt and MEK/ERK are involved in the cytoprotective function of p190Met(NC). Importantly, the expression of p190Met(NC) is detected in some HCC cases. Taken together, these data provide a potential mechanism to explain how c-Met promotes HCC cells survival in response to ER stress. We propose that context-specific processing of c-Met protein is implicated in HCC progression in stressful microenvironments.

GRP94: An HSP90-like protein specialized for protein folding and quality control in the endoplasmic reticulum

Glucose-regulated protein 94 is the HSP90-like protein in the lumen of the endoplasmic reticulum and therefore it chaperones secreted and membrane proteins. It has essential functions in development and physiology of multicellular organisms, at least in part because of this unique clientele. GRP94 shares many biochemical features with other HSP90 proteins, in particular its domain structure and ATPase activity, but also displays distinct activities, such as calcium binding, necessitated by the conditions in the endoplasmic reticulum. GRP94's mode of action varies from the general HSP90 theme in the conformational changes induced by nucleotide binding, and in its interactions with co-chaperones, which are very different from known cytosolic co-chaperones. GRP94 is more selective than many of the ER chaperones and the basis for this selectivity remains obscure. Recent development of molecular tools and functional assays has expanded the spectrum of clients that rely on GRP94 activity, but it is still not clear how the chaperone binds them, or what aspect of folding it impacts. These mechanistic questions and the regulation of GRP94 activity by other proteins and by post-translational modification differences pose new questions and present future research avenues. This article is part of a Special Issue entitled: Heat Shock Protein 90 (HSP90).

Pro-osteogenic trophic effects by PKA activation in human mesenchymal stromal cells

Human mesenchymal stromal cells (hMSCs) are able to differentiate into a wide variety of cell types, which makes them an interesting source for tissue engineering applications. On the other hand, these cells also secrete a broad panel of growth factors and cytokines that can exert trophic effects on surrounding tissues. In bone tissue engineering applications, the general assumption is that direct differentiation of hMSCs into osteoblasts accounts for newly observed bone formation in vivo. However, the secretion of bone-specific growth factors, but also pro-angiogenic factors, could also contribute to this process. We recently demonstrated that secretion of bone specific growth factors can be enhanced by treatment of hMSCs with the small molecule db-cAMP (cAMP) and here we investigate the biological activity of these secreted factors. We demonstrate that conditioned medium contains a variety of secreted growth factors, with differences between medium from basic-treated and cAMP-treated hMSCs. We show that conditioned medium from cAMP-treated hMSCs increases proliferation of various cell types and also induces osteogenic differentiation, whereas it has differential effects on migration. Microarray analysis on hMSCs exposed to conditioned medium confirmed upregulation of pathways involved in proliferation as well as osteogenic differentiation. Our data suggests that trophic factors secreted by hMSCs can be tuned for specific applications and that a good balance between differentiation on the one hand and secretion of bone trophic factors on the other, could potentially enhance bone formation for bone tissue engineering applications.

Critical role of the STAT3 pathway in the cardioprotective efficacy of zoniporide in a model of myocardial preservation - the rat isolated working heart

BACKGROUND AND PURPOSE

Ischemia-reperfusion injury plays an important role in the development of primary allograft failure after heart transplantation. Inhibition of the Na+/H+ exchanger is one of the most promising therapeutic strategies for treating ischemia-reperfusion injury. Here we have characterized the cardioprotective efficacy of zoniporide and the underlying mechanisms in a model of myocardial preservation using rat isolated working hearts.

EXPERIMENTAL APPROACH

Rat isolated hearts subjected to 6 h hypothermic (1-4°C) storage followed by 45 min reperfusion at 37°C were treated with zoniporide at different concentrations and timing. Recovery of cardiac function, levels of total and phosphorylated protein kinase B, extracellular signal-regulated kinase 1/2, glycogen synthase kinase-3β and STAT3 as well as cleaved caspase 3 were measured at the end of reperfusion. Lactate dehydrogenase release into coronary effluent before and post-storage was also measured.

KEY RESULTS

Zoniporide concentration-dependently improved recovery of cardiac function after reperfusion. The functional recovery induced by zoniporide was accompanied by up-regulation of p-extracellular signal-regulated kinase 1/2 and p-STAT3, and by reduction in lactate dehydrogenase release and cleaved caspase 3. There were no significant differences in any of the above indices when zoniporide was administered before, during or after ischemia. The STAT3 inhibitor, stattic, abolished zoniporide-induced improvements in functional recovery and up-regulation of p-STAT3 after reperfusion.

CONCLUSIONS AND IMPLICATIONS

Zoniporide is a potent cardioprotective agent and activation of STAT3 plays a critical role in the cardioprotective action of zoniporide. This agent shows promise as a supplement to storage solutions to improve preservation of donor hearts.

The impact of diabetes on survival in women with ovarian cancer

OBJECTIVE

Diabetes is increasingly common among cancer patients and plausible biologic mechanisms exist by which diabetes may influence cancer prognosis. We aimed to investigate the impact of diabetes on ovarian cancer outcomes.

METHODS

We assessed the outcomes of 570 non-diabetic and 72 diabetic patients with epithelial ovarian, fallopian tube, and primary peritoneal cancer over a ten-year period. All inpatient and outpatient records were reviewed. The primary end points were overall and disease-free survival.

RESULTS

Of the 642 cases, 11.2% had type II diabetes. Diabetics were more likely to be older, had a higher BMI (33.4 vs. 27.8), and had more comorbid conditions. Diabetics were less likely to have been surgically staged as compared to non-diabetics (p=0.04) although stage, grade, and likelihood of optimal cytoreduction were similar between groups. Over a period of 10 years, with an average of 44 months of follow-up, the median overall survival for diabetics was 1503 days. The median overall survival for non-diabetics was 2464 days (log rank test, p=0.02). In a Cox proportional hazards multivariable model, diabetes remained a significant predictor of overall survival (HR=2.04, p<0.01).

CONCLUSIONS

Diabetics with ovarian cancer demonstrate strikingly poorer survival. The underlying reason for this is yet unknown and deserves further attention. Differences in care, competing risks of death, and changes within the tumor biology are plausible mechanisms for the observed difference in survival.

Ghrelin suppresses tunicamycin- or thapsigargin-triggered endoplasmic reticulum stress-mediated apoptosis in primary cultured rat cortical neuronal cells

Ghrelin functions as a neuroprotective agent and rescues neurons from various insults. However, the molecular mechanisms underlying ghrelin neuroprotection remains to be elucidated. An accumulation of unfolded proteins in the endoplasmic reticulum (ER) leads to ER stress and then induces ER stress-mediated cell death. Here, we report that acylated ghrelin inhibited tunicamycin- or thapsigargin-triggered ER stress-induced apoptotic cell death in primary rat cortical neurons. An analysis using a specific inhibitor of phosphatidylinositol-3-kinase (PI3K), LY294002, showed that ghrelin prevented apoptosis via the activation of PI3K signaling pathway. Ghrelin suppressed tunicamycin- or thapsigargin-induced upregulation and nuclear translocation of C/EBP homologous protein (CHOP). Ghrelin also inhibited tunicamycin or thapsigargin induction of PRK-like ER kinase (PERK), eukaryotic translation initiation factor-2α (eIF2α) and activating transcription factor (ATF) 4. Exposure of cells to tunicamycin or thapsigargin resulted in nuclear translocation of forkhead box protein O1 (Foxo1), which was reduced by pretreatment with ghrelin. The protective effect of ghrelin was accompanied by an increased phosphorylation of Akt and glycogen synthase kinase (GSK)-3β. Furthermore, ghrelin phosphorylated and inactivated pro-apoptotic BAD and Foxo1. In addition, phospho-Akt was translocated to the nucleus in response to ghrelin and PI3K inhibition by LY294002 prevented ghrelin-induced effect on phospho-Akt localization. Our study suggests that suppression of CHOP activation via the inhibition of PERK/eIF2α/ATF4 pathway and prevention of Foxo1 activation and nuclear translocation may contribute to ghrelin-mediated neuroprotection during ER stress responses. Our data also suggest that PI3K/Akt-mediated inactivation of GSK-3β, BAD and Foxo1 may be associated with the anti-apoptotic effect of ghrelin.

A protective role for CD154 in hepatic steatosis in mice

Inflammation and lipid metabolism pathways are linked, and deregulation of this interface may be critical in hepatic steatosis. The importance of the dialog between inflammatory signaling pathways and the unfolded protein response (UPR) in metabolism has been underlined. Herein, we studied the role of CD154, a key mediator of inflammation, in hepatic steatosis. To this end, Balb/c mice, wild-type or deficient in CD154 (CD154KO), were fed a diet rich in olive oil. In vitro, the effect of CD154 was studied on primary hepatocyte cultures and hepatocyte-derived cell lines. Results showed that CD154KO mice fed a diet rich in olive oil developed hepatic steatosis associated with reduced apolipoprotein B100 (apoB100) expression and decreased secretion of very low-density lipoproteins. This phenotype correlated with an altered UPR as assessed by reduced X-Box binding protein-1 (XBP1) messenger RNA (mRNA) splicing and reduced phosphorylation of eukaryotic initiation factor 2α. Altered UPR signaling in livers of CD154KO mice was confirmed in tunicamycin (TM) challenge experiments. Treatment of primary hepatocyte cultures and hepatocyte-derived cell lines with soluble CD154 increased XBP1 mRNA splicing in cells subjected to either oleic acid (OA) or TM treatment. Moreover, CD154 reduced the inhibition of apoB100 secretion by HepG2 cells grown in the presence of high concentrations of OA, an effect suppressed by XBP1 mRNA silencing and in HepG2 cells expressing a dominant negative form of inositol requiring ER-to-nucleus signaling protein-1. The control of the UPR by CD154 may represent one of the mechanisms involved in the pathophysiology of hepatic steatosis.

CONCLUSION

Our study identifies CD154 as a new mediator of hepatic steatosis.

The critical role of GRP78 in physiologic and pathologic stress

GRP78 is a major endoplasmic reticulum chaperone as well as a master regulator of the unfolded protein response. In addition to playing an essential role in early embryonic development, recent studies have emerged specifically implicating GRP78 and chaperone integrity in the aging process and age-related diseases. Another exciting discovery is the regulation of GRP78 by insulin/IGF-1 signaling pathways impacting cell proliferation and survival. Mouse models of cancer, in combination with cell culture studies, validate the critical role of GRP78 in tumorigenesis and tumor angiogenesis. Further, these studies demonstrate the ability of GRP78 to suppress oncogenic PI3K/AKT signaling. The discovery of cell surface GRP78, in cancer cells and cells undergoing ER stress, presents a novel therapeutic strategy.

Insulin modulates induction of glucose-regulated protein 78 during endoplasmic reticulum stress via augmentation of ATF4 expression in human neuroblastoma cells

The effect of insulin on endoplasmic reticulum (ER) stress was investigated. Insulin protected cell death induced by ER stress and increased glucose-regulated protein 78 (GRP78) mRNA and protein levels. Insulin also significantly increased activating transcription factor-4 (ATF4) protein in the nucleus, which was inhibited by LY294002, a phosphatidylinositol 3-kinase (PI-3 kinase) inhibitor. The increase of ATF4 protein by insulin was not due to transcriptional or translational up-regulation but to a post-translational mechanism. Knockdown of ATF4 by siRNA significantly inhibited GRP78 induction by insulin. These results indicate that insulin modulated ER stress-induced GRP78 expression occurs via ATF4 up-regulation.

GRP94 in ER quality control and stress responses

A system of endoplasmic reticulum (ER) chaperones has evolved to optimize the output of properly folded secretory and membrane proteins. An important player in this network is Glucose Regulated Protein 94 (GRP94). Over the last decade, new structural and functional data have begun to delineate the unique characteristics of GRP94 and have solidified its importance in ER quality control pathways. This review describes our current understanding of GRP94 and the four ways in which it contributes to the ER quality control: (1) chaperoning the folding of proteins; (2) interacting with other components of the ER protein folding machinery; (3) storing calcium; and (4) assisting in the targeting of malfolded proteins to ER-associated degradation (ERAD).