Hsc70 regulates accumulation of cyclin D1 and cyclin D1-dependent protein kinase

Hsp70: A Multifunctional Chaperone in Maintaining Proteostasis and Its Implications in Human Disease

Hsp70, a 70 kDa molecular chaperone, plays a crucial role in maintaining protein homeostasis. It interacts with the DnaJ family of co-chaperones to modulate the functions of client proteins involved in various cellular processes, including transmembrane transport, extracellular vesicle trafficking, complex formation, and proteasomal degradation. Its presence in multiple cellular organelles enables it to mediate stress responses, apoptosis, and inflammation, highlighting its significance in disease progression. Initially recognized for its essential roles in protein folding, disaggregation, and degradation, later studies have demonstrated its involvement in several human diseases. Notably, Hsp70 is upregulated in multiple cancers, where it promotes tumor proliferation and serves as a tumor immunogen. Additionally, epichaperome networks stabilize protein-protein interactions in large and long-lived assemblies, contributing to both cancer progression and neurodegeneration. However, extracellular Hsp70 (eHsp70) in the tumor microenvironment can activate immune cells, such as natural killer (NK) cells, suggesting its potential in immunotherapeutic interventions, including CAR T-cell therapy. Given its multifaceted roles in cellular physiology and pathology, Hsp70 holds immense potential as both a biomarker and a therapeutic target across multiple human diseases. This review highlights the structural and functional importance of Hsp70, explores its role in disease pathogenesis, and discusses its potential in diagnostic and therapeutic applications.

HSPA8 dampens SCAP/INSIG split and SREBP activation by reducing PKR-mediated INSIG phosphorylation

Lipid accumulation in renal tubules is a major determinant of diabetic kidney disease (DKD), and activation of SREBPs plays a central role in this process. Our study aims to explore whether HSPA8, a molecular chaperone, is the master regulator of INSIG/SREBPs function in DKD. Here, we show that tubular epithelial cell (TEC)-specific knockout of HSPA8 upregulates the phosphorylation of INSIG1 and INSIG2, which disrupts the interaction between INSIG proteins and SCAP, leading to SREBP activation. TEC-specific overexpression of HSPA8 restrains these changes. INSIG1/2 can be phosphorylated by protein kinase R (PKR), while HSPA8 recognizes PKR and recruits the E3 ubiquitin ligase to promote PKR ubiquitination and degradation. Under temporary hyperglycemic stimulation, SREBP1 transcriptionally activates HSPA8 expression. Conversely, persistent hyperglycemia reduces HSPA8 levels via promoting NF-κB-mediated transcriptional inhibition of HSPA8. Collectively, these findings indicate that the molecular chaperone HSPA8 serves as a negative feedback regulator of SREBPs, lipogenesis, and DKD development.

Heat shock protein family A member 8 is a prognostic marker for bladder cancer: Evidences based on experiments and machine learning

Heat shock protein member 8 (HSPA8) is one of the most abundant chaperones in eukaryotic cells, but its biological roles in bladder cancer (BC) are largely unclear. First, we observed that HSPA8 was abundant in both cell lines and tissues of BC, and the HSPA8-high group had poorer T stages and overall survival (OS) than the HSPA8-low group in the TCGA patients. Next, when we knocked down HSPA8 in BC cells, the growth and migration abilities were significantly decreased, the apoptosis rates were significantly increased, and the Ki67 fluorescence intensity was decreased in BC cells. Moreover, caspase 3 was significantly decreased with overexpression of HSPA8 in BC cells. After that, a machine learning prognostic model was created based on the expression of HSPA8 by applying LASSO Cox regression in TCGA and GEO patients. The model indicated that the low-risk (LR) group with BC had better tumour stages, lymphovascular invasion, and OS than the high-risk (HR) group. Additionally, the risk score was demonstrated to be an independent risk factor for the prognosis of BC by univariate and multivariate Cox analyses. Moreover, the HR group showed a greater rate of TP53 mutations and was mostly enriched in the ECM-receptor interaction pathway than the LR group. Importantly, lower CD8+ T-cell and NK cell infiltration, higher immune exclusion scores, higher expression of PD-L1 and CTLA4 and poorer immune checkpoint therapy effects were found in the HR group. These findings demonstrated how crucial HSPA8 plays a role in determining the prognosis of bladder cancer.

Immunoexpression Pattern of Autophagy Markers in Developing and Postnatal Kidneys of Dab1−/−(yotari) Mice

The purpose of this study was to compare the immunofluorescence patterns of autophagic markers: Light chain 3 beta (LC3B), Glucose regulating protein 78 (GRP78), Heat shock cognate 71 (HSC70) and Lysosomal-associated membrane protein 2A (LAMP2A) in the developing and postnatal kidneys of Dab1−/− (yotari) mice to those of wild-type samples. Embryos were obtained on gestation days 13.5 and 15.5 (E13.5 and E15.5), and adult animals were sacrificed at postnatal days 4, 11 and 14 (P4, P11, and P14). After fixation and dehydration, paraffin-embedded kidney tissues were sectioned and incubated with specific antibodies. Using an immunofluorescence microscope, sections were analyzed. For statistical analysis, a two-way ANOVA test and a Tukey’s multiple comparison test were performed with a probability level of p < 0.05. A significant increase in GRP78 and LAMP2A expression was observed in the renal vesicles and convoluted tubules of yotari in embryonic stages. In postnatal kidneys, all observed proteins showed higher signal intensities in proximal and distal convoluted tubules of yotari, while a higher percentage of LC3B-positive cells was also observed in glomeruli. Our findings suggest that all of the examined autophagic markers play an important role in normal kidney development, as well as the potential importance of these proteins in renal pathology, where they primarily serve a protective function and thus may be used as diagnostic and therapeutic targets.

KBTBD11, encoding a novel PPARγ target gene, is involved in NFATc1 proteolysis by interacting with HSC70 and HSP60

We previously revealed that Kbtbd11 mRNA levels increase during 3T3-L1 differentiation and Kbtbd11 knockdown suppresses whereas its overexpression promotes adipogenesis. However, how Kbtbd11 mRNA is regulated during adipocyte differentiation and how the KBTBD11 protein functions in adipocytes remain elusive. This study aimed to examine the transcriptional regulatory mechanism of Kbtbd11 during adipocyte differentiation, KBTBD11-interacting protein functions, and elucidate the role of KBTBD11 in adipocytes. First, we identified the PPRE consensus sequences in the Kbtbd11 exon 1- and intron 1-containing region and demonstrated that PPARγ acts on this region to regulate Kbtbd11 expression. Next, we purified the KBTBD11 protein complex from 3T3-L1 adipocytes and identified heat shock proteins HSC70 and HSP60 as novel KBTBD11-interacting proteins. HSC70 and HSP60 inhibition increased KBTBD11 protein levels that promoted NFATc1 ubiquitination. These data suggest that HSC70 and HSP60 are involved in KBTBD11 stabilization and are responsible for NFATc1 regulation on the protein level. In summary, this study describes first the protein regulatory mechanism of NFATc1 through the HSC70/HSP60-KBTBD11 interaction that could provide a potential new target for the differentiation and proliferation of various cells, including adipocytes and tumors.

SHetA2 Attack on Mortalin and Colleagues in Cancer Therapy and Prevention

Heat Shock Proteins of the 70-kDa family (HSP70s) do not cause cancer by themselves, but instead protect cells as they transform into cancer. These molecular chaperones bind numerous client proteins and utilize ATP hydrolysis to facilitate proper protein folding, formation of functional complexes and cellular localizations, or degradation of irreparably damaged proteins. Their transient upregulation by stressful situations avoids induction of programmed cell death. Continued upregulation of the mortalin, heat shock cognate (hsc70) and glucose regulated protein 78 (Grp78) support cancer development and progression by supporting pro-proliferative and metabolic functions and repressing pro-death functions of oncoproteins and tumor suppressor proteins. This review describes the discovery and development of a lead anti-cancer compound, sulfur heteroarotinoid A2 (SHetA2, NSC726189), which was originally developed to bind retinoic acid receptors, but was subsequently found to work independently of these receptors. The discovery and validation of mortalin, hsc70 and Grp78 as SHetA2 target proteins is summarized. The documented and hypothesized roles of these HSP70 proteins and their clients in the mechanism of SHetA2 inhibition of cancer without toxicity are discussed. Use of this mechanistic data to evaluate drug action in a cancer clinical trial and develop synergistic drug combinations is explained. Knowledge needed to optimize SHetA2 analogs for use in cancer therapy and prevention is proposed as future directions.

Zinc protoporphyrin binding to telomerase complexes and inhibition of telomerase activity

Zinc protoporphyrin (ZnPP), a naturally occurring metalloprotoporphyrin (MPP), is currently under development as a chemotherapeutic agent although its mechanism is unclear. When tested against other MPPs, ZnPP was the most effective DNA synthesis and cellular proliferation inhibitor while promoting apoptosis in telomerase positive but not telomerase negative cells. Concurrently, ZnPP down-regulated telomerase expression and was the best overall inhibitor of telomerase activity in intact cells and cellular extracts with IC50 and EC50  values of ca 2.5 and 6 µM, respectively. The natural fluorescence properties of ZnPP enabled direct imaging in cellular fractions using non-denaturing agarose gel electrophoresis, western blots, and confocal fluorescence microscopy. ZnPP localized to large cellular complexes (>600 kD) that contained telomerase and dysskerin as confirmed with immunocomplex mobility shift, immunoprecipitation, and immunoblot analyses. Confocal fluorescence studies showed that ZnPP co-localized with telomerase reverse transcriptase (TERT) and telomeres in the nucleus of synchronized S-phase cells. ZnPP also co-localized with TERT in the perinuclear regions of log phase cells but did not co-localize with telomeres on the ends of metaphase chromosomes, a site known to be devoid of telomerase complexes. Overall, these results suggest that ZnPP does not bind to telomeric sequences per se, but alternatively, interacts with other structural components of the telomerase complex to inhibit telomerase activity. In conclusion, ZnPP actively interferes with telomerase activity in neoplastic cells, thus promoting pro-apoptotic and anti-proliferative properties. These data support further development of natural or synthetic protoporphyrins for use as chemotherapeutic agents to augment current treatment protocols for neoplastic disease.

Similarities and Differences of Hsp70, hsc70, Grp78 and Mortalin as Cancer Biomarkers and Drug Targets

Background: Upregulation of Heath Shock Protein 70 (HSP70) chaperones supports cancer cell survival. Their high homology causes a challenge to differentiate them in experimental or prevention and treatment strategies. The objective of this investigation was to determine similarities and differences of Hsp70, hsc70, Grp78 and Mortalin members of the HSP70 family encoded by HSPA1, HSPA8, HSPA5 and HSPA9 genes, respectively. Methods: Literature reviews were conducted using HSPA1, HSPA5, HSPA8 and HSPA9 gene or protein names or synonyms combined with biological or cancer-relevant terms. Ingenuity Pathway Analysis was used to identify and compare profiles of proteins that directly bind individual chaperones and their associated pathways. TCGA data was probed to identify associations of hsc70 with cancer patient survival. ClinicalTrials.gov was used to identify HSP70 family studies. Results: The chaperones have similar protein folding functions. Their different cellular effects are determined by co-chaperones and client proteins combined with their intra- and extra-cellular localizations. Their upregulation is associated with worse patient prognosis in multiple cancers and can stimulate tumor immune responses or drug resistance. Their inhibition selectively kills cancer over healthy cells. Conclusions: Differences in Hsp70, hsc70, Grp78 and mortalin provide opportunities to calibrate HSP70 inhibitors for individual cancers and combination therapies.

Nematode CDC-37 and DNJ-13 form complexes and can interact with HSP-90

The molecular chaperones Hsc70 and Hsp90 are required for proteostasis control and specific folding of client proteins in eukaryotic and prokaryotic organisms. Especially in eukaryotes these ATP-driven molecular chaperones are interacting with cofactors that specify the client spectrum and coordinate the ATPase cycles. Here we find that a Hsc70-cofactor of the Hsp40 family from nematodes, DNJ-13, directly interacts with the kinase-specific Hsp90-cofactor CDC-37. The interaction is specific for DNJ-13, while DNJ-12 another DnaJ-like protein of C. elegans, does not bind to CDC-37 in a similar manner. Analytical ultracentrifugation is employed to show that one CDC-37 molecule binds to a dimeric DNJ-13 protein with low micromolar affinity. We perform cross-linking studies with mass spectrometry to identify the interaction site and obtain specific cross-links connecting the N-terminal J-domain of DNJ-13 with the N-terminal domain of CDC-37. Further AUC experiments reveal that both, the N-terminal part of CDC-37 and the C-terminal domain of CDC-37, are required for efficient interaction. Furthermore, the presence of DNJ-13 strengthens the complex formation between CDC-37 and HSP-90 and modulates the nucleotide-dependent effects. These findings on the interaction between Hsp40 proteins and Hsp90-cofactors provide evidence for a more intricate interaction between the two chaperone systems during client processing.

Proteostatic stress as a nodal hallmark of replicative aging

Aging is characterized by the progressive decline of physiology at the cell, tissue and organism level, leading to an increased risk of mortality. Proteotoxic stress, mitochondrial dysfunction and genomic instability are considered major universal drivers of cell aging, and accumulating evidence establishes clear biunivocal relationships among these key hallmarks. In this regard, the finite lifespan of the budding yeast, together with the extensive armamentarium of available analytical tools, has made this single cell eukaryote a key model to study aging at molecular and cellular levels. Here we review the current data that link proteostasis to cell cycle progression in the budding yeast, focusing on senescence as an inherent phenotype displayed by aged cells. Recent advances in high-throughput systems to study yeast mother cells while they replicate are providing crucial information on aging-related processes and their temporal interdependencies at a systems level. In our view, the available data point to the existence of multiple feedback mechanisms among the major causal factors of aging, which would converge into the loss of proteostasis as a nodal driver of cell senescence and death.

Assessing the oncolytic potential of rotavirus on mouse myeloma cell line Sp2/0-Ag14

INTRODUCTION

Cancer is the second leading cause of death in the United States, surpassed only by cardiovascular disease. However, cancer has now overtaken cardiovascular disease as the main cause of death in 12 countries in Western Europe. The burden of cancer is posing a major challenge to health care systems worldwide and demanding improvements in methods for cancer prevention, diagnosis, and treatment. Alternative and complementary strategies for orthodox surgery, radiotherapy, and chemotherapy need to be developed.

OBJECTIVE

To determine the oncolytic potential of tumor cell-adapted rotavirus in terms of their ability to infect and lysate murine myeloma Sp2/0-Ag14 cells.

MATERIALS AND METHODS

We inoculated rotaviruses Wt1-5, WWM, TRUYO, ECwt-O, and WTEW in Sp2/0-Ag14 cells and we examined their infectious effects by immunocytochemistry, immunofluorescence, flow cytometry, and DNA fragmentation assays.

RESULTS

Rotavirus infection involved the participation of some heat shock proteins, of protein disulfide isomerase (PDI), and integrin β3. We detected the accumulation of viral antigens within the virus-inoculated cells and in the culture medium in all the rotavirus isolates examined. The rotavirus-induced cell death mechanism in Sp2/0-Ag14 cells involved changes in cell membrane permeability, chromatin condensation, and DNA fragmentation, which were compatible with cytotoxicity and apoptosis.

CONCLUSIONS

The ability of the rotavirus isolates Wt1-5, WWM, TRUYO, ECwt-O, and WTEW to infect and cause cell death of Sp2/0-Ag14 cells through mechanisms that are compatible with virus-induced apoptosis makes them potential candidates as oncolytic agents.

Heat Shock Cognate 70 Functions as A Chaperone for the Stability of Kinetochore Protein CENP-N in Holocentric Insect Silkworms

The centromere, in which kinetochore proteins are assembled, plays an important role in the accurate congression and segregation of chromosomes during cell mitosis. Although the function of the centromere and kinetochore is conserved from monocentric to holocentric, the DNA sequences of the centromere and components of the kinetochore are varied among different species. Given the lack of core centromere protein A (CENP-A) and CENP-C in the lepidopteran silkworm Bombyx mori, which possesses holocentric chromosomes, here we investigated the role of CENP-N, another important member of the centromere protein family essential for kinetochore assembly. For the first time, cellular localization and RNA interference against CENP-N have confirmed its kinetochore function in silkworms. To gain further insights into the regulation of CENP-N in the centromere, we analyzed the affinity-purified complex of CENP-N by mass spectrometry and identified 142 interacting proteins. Among these factors, we found that the chaperone protein heat shock cognate 70 (HSC70) is able to regulate the stability of CENP-N by prohibiting ubiquitin-proteasome pathway, indicating that HSC70 could control cell cycle-regulated degradation of CENP-N at centromeres. Altogether, the present work will provide a novel clue to understand the regulatory mechanism for the kinetochore activity of CENP-N during the cell cycle.

Proteostasis collapse, a hallmark of aging, hinders the chaperone-Start network and arrests cells in G1

Loss of proteostasis and cellular senescence are key hallmarks of aging, but direct cause-effect relationships are not well understood. We show that most yeast cells arrest in G1 before death with low nuclear levels of Cln3, a key G1 cyclin extremely sensitive to chaperone status. Chaperone availability is seriously compromised in aged cells, and the G1 arrest coincides with massive aggregation of a metastable chaperone-activity reporter. Moreover, G1-cyclin overexpression increases lifespan in a chaperone-dependent manner. As a key prediction of a model integrating autocatalytic protein aggregation and a minimal Start network, enforced protein aggregation causes a severe reduction in lifespan, an effect that is greatly alleviated by increased expression of specific chaperones or cyclin Cln3. Overall, our data show that proteostasis breakdown, by compromising chaperone activity and G1-cyclin function, causes an irreversible arrest in G1, configuring a molecular pathway postulating proteostasis decay as a key contributing effector of cell senescence.

Molecular identification of HSPA8 as an accessory protein of a hyperpolarization-activated chloride channel from rat pulmonary vein cardiomyocytes

Pulmonary veins (PVs) are the major origin of atrial fibrillation. Recently, we recorded hyperpolarization-activated Cl^- current (I _{Cl, h}) in rat PV cardiomyocytes. Unlike the well-known chloride channel protein 2 (CLCN2) current, the activation curve of I _{Cl, h} was hyperpolarized as the Cl^- ion concentration ([Cl^-] _i ) increased. This current could account for spontaneous activity in PV cardiomyocytes linked to atrial fibrillation. In this study, we aimed to identify the channel underlying I _{Cl, h} Using RT-PCR amplification specific for Clcn2 or its homologs, a chloride channel was cloned from rat PV and detected in rat PV cardiomyocytes using immunocytochemistry. The gene sequence and electrophysiological functions of the protein were identical to those previously reported for Clcn2, with protein activity observed as a hyperpolarization-activated current by the patch-clamp method. However, the [Cl^-] _i dependence of activation was entirely different from the observed I _{Cl, h} of PV cardiomyocytes; the activation curve of the Clcn2-transfected cells shifted toward positive potential with increased [Cl^-] _i , whereas the I _{Cl, h} of PV and left ventricular cardiomyocytes showed a leftward shift. Therefore, we used MS to explore the possibility of additional proteins interacting with CLCN2 and identified an individual 71-kDa protein, HSPA8, that was strongly expressed in rat PV cardiomyocytes. With co-expression of HSPA8 in HEK293 and PC12 cells, the CLCN2 current showed voltage-dependent activation and shifted to negative potential with increasing [Cl^-] _i Molecular docking simulations further support an interaction between CLCN2 and HSPA8. These findings suggest that CLCN2 in rat heart contains HSPA8 as a unique accessory protein.

Death effector domain-containing protein induces vulnerability to cell cycle inhibition in triple-negative breast cancer

Lacking targetable molecular drivers, triple-negative breast cancer (TNBC) is the most clinically challenging subtype of breast cancer. In this study, we reveal that Death Effector Domain-containing DNA-binding protein (DEDD), which is overexpressed in > 60% of TNBCs, drives a mitogen-independent G1/S cell cycle transition through cytoplasm localization. The gain of cytosolic DEDD enhances cyclin D1 expression by interacting with heat shock 71 kDa protein 8 (HSC70). Concurrently, DEDD interacts with Rb family proteins and promotes their proteasome-mediated degradation. DEDD overexpression renders TNBCs vulnerable to cell cycle inhibition. Patients with TNBC have been excluded from CDK 4/6 inhibitor clinical trials due to the perceived high frequency of Rb-loss in TNBCs. Interestingly, our study demonstrated that, irrespective of Rb status, TNBCs with DEDD overexpression exhibit a DEDD-dependent vulnerability to combinatorial treatment with CDK4/6 inhibitor and EGFR inhibitor in vitro and in vivo. Thus, our study provided a rationale for the clinical application of CDK4/6 inhibitor combinatorial regimens for patients with TNBC.

Competition in the chaperone-client network subordinates cell-cycle entry to growth and stress

The precise coordination of growth and proliferation has a universal prevalence in cell homeostasis. As a prominent property, cell size is modulated by the coordination between these processes in bacterial, yeast, and mammalian cells, but the underlying molecular mechanisms are largely unknown. Here, we show that multifunctional chaperone systems play a concerted and limiting role in cell-cycle entry, specifically driving nuclear accumulation of the G1 Cdk-cyclin complex. Based on these findings, we establish and test a molecular competition model that recapitulates cell-cycle-entry dependence on growth rate. As key predictions at a single-cell level, we show that availability of the Ydj1 chaperone and nuclear accumulation of the G1 cyclin Cln3 are inversely dependent on growth rate and readily respond to changes in protein synthesis and stress conditions that alter protein folding requirements. Thus, chaperone workload would subordinate Start to the biosynthetic machinery and dynamically adjust proliferation to the growth potential of the cell.

Cyclin D1 Stability Is Partly Controlled by O-GlcNAcylation

Cyclin D1 is the regulatory partner of the cyclin-dependent kinases (CDKs) CDK4 or CDK6. Once associated and activated, the cyclin D1/CDK complexes drive the cell cycle entry and G1 phase progression in response to extracellular signals. To ensure their timely and accurate activation during cell cycle progression, cyclin D1 turnover is finely controlled by phosphorylation and ubiquitination. Here we show that the dynamic and reversible O-linked β-N-Acetyl-glucosaminylation (O-GlcNAcylation) regulates also cyclin D1 half-life. High O-GlcNAc levels increase the stability of cyclin D1, while reduction of O-GlcNAcylation strongly decreases it. Moreover, elevation of O-GlcNAc levels through O-GlcNAcase (OGA) inhibition significantly slows down the ubiquitination of cyclin D1. Finally, biochemical and cell imaging experiments in human cancer cells reveal that the O-GlcNAc transferase (OGT) binds to and glycosylates cyclin D1. We conclude that O-GlcNAcylation promotes the stability of cyclin D1 through modulating its ubiquitination.

Blocking nuclear export of HSPA8 after heat shock stress severely alters cell survival

The nuclear translocation of endogenous heat shock cognate protein HSPA8 is a requisite for cell survival during oxidative and heat shock stress. Upon these events, cytoplasmic HSPA8 is thought to concentrate within the nucleus and nucleolus. When the situation returns to normal, HSPA8 is released from its nuclear/nucleolar anchors and redistributes into the cytoplasm. By using different stress conditions and a 21-mer phosphopeptide tool called P140, which binds HSPA8 and hampers its chaperone properties, we deciphered the cellular and molecular effects arising during this vital cytoplasmic-nuclear-cytoplasmic shuttling process. Using the non-metastatic fibroblastoid cell line MRL/N-1 derived from a MRL/MpTn-gld/gld lupus-prone mouse, we discovered that P140 treatment neutralized the egress of HSPA8 from nucleus to cytoplasm in the cell recovery phase. This lack of relocation of HSPA8 into the cytoplasm of heat-shocked MRL/N-1 cells altered the ability of these cells to survive when a second mild oxidative stress mimicking inflammatory conditions was applied. Crosslinking experiments followed by proteomics studies showed that P140 binds regions close to nuclear import and export signal sequences encompassed within the HSPA8 structure. These data are consistent with HSPA8 having a crucial cell protective role against reactive oxygen species (ROS) production by mitochondria during inflammatory conditions.

Cdc48/p97 segregase is modulated by cyclin-dependent kinase to determine cyclin fate during G1 progression

Cells sense myriad signals during G1, and a rapid response to prevent cell cycle entry is of crucial importance for proper development and adaptation. Cln3, the most upstream G1 cyclin in budding yeast, is an extremely short-lived protein subject to ubiquitination and proteasomal degradation. On the other hand, nuclear accumulation of Cln3 depends on chaperones that are also important for its degradation. However, how these processes are intertwined to control G1-cyclin fate is not well understood. Here, we show that Cln3 undergoes a challenging ubiquitination step required for both degradation and full activation. Segregase Cdc48/p97 prevents degradation of ubiquitinated Cln3, and concurrently stimulates its ER release and nuclear accumulation to trigger Start. Cdc48/p97 phosphorylation at conserved Cdk-target sites is important for recruitment of specific cofactors and, in both yeast and mammalian cells, to attain proper G1-cyclin levels and activity. Cdk-dependent modulation of Cdc48 would subjugate G1 cyclins to fast and reversible state switching, thus arresting cells promptly in G1 at developmental or environmental checkpoints, but also resuming G1 progression immediately after proliferative signals reappear.

Therapeutic role of a synthesized calcium phosphate nanocomposite material on hepatocarcinogenesis in rats

Nanotechnology research is booming worldwide, and the general belief is that medical and biological applications will form the greatest sector of expansion over the next decade. With this in mind, this study was designed to evaluate the therapeutic effects of a synthesized tricalcium phosphate nanocomposite material (nano-TCP) on hepatocarcinoma in a rat model, as initiated with diethylnitrosamine (DEN) and promoted with phenobarbital (PB). Hepatocarcinoma was induced with intraperitoneal injections of DEN (50 mg·(kg body mass)(-1)) 3 times a week for 2 weeks. Three weeks after the last dose of DEN, the rats received PB (0.05 %, w/v) in their drinking water for a further 6 weeks. Nano-TCP (100 mg·(kg body mass)(-1)) was administered intraperitoneally 3 times per week to rats with HCC. At the end of the experimental period, liver samples were collected from all animals for biochemical and histopathological analysis. The degree of DNA fragmentation was analyzed, in addition to immune status, by measuring the levels of interferon-γ (IFN-γ), tumor necrosis factor-α (TNF-α), and interleukin-2 (IL-2). The activities of the most important free-radical scavengers of the antioxidant defense system as well as malondialdehyde (MDA) content and liver enzymes were measured. The levels of hepatic heat shock protein-70 (HSP-70), caspase-3, and metalloproteinase-9 were also measured as markers for inflammation and apoptosis. Histopathological examination of liver tissue was performed. The results revealed the potent efficacy of nano-TCP in repairing the fragmented DNA and ameliorating most of the investigated parameters by significant elevation in the levels of hepatic alanine aminotransferase (ALT), superoxide dismutase (SOD), and glutathione peroxidase (GPx) activities. On the other hand, there was a significant decrease in hepatic gamma-glutamyl transpeptidase (γ-GT), MDA, IL-2, IFN-γ, TNF-α, matrix metalloproteinase-9 (MMP-9), HSP-70, and caspase-3 levels upon treatment. The findings form histopathological examination of the liver tissues agreed with the biochemical results and confirmed the difference between the control and treatment groups. In conclusion, nano-TCP succeeded in treating hepatocarcinoma efficiently, and presents a new hope for patients to get safe, fast, and effective treatment.

The connexin 43 C-terminus: A tail of many tales

Connexins are chordate gap junction channel proteins that, by enabling direct communication between the cytosols of adjacent cells, create a unique cell signalling network. Gap junctional intercellular communication (GJIC) has important roles in controlling cell growth and differentiation and in tissue development and homeostasis. Moreover, several non-canonical connexin functions unrelated to GJIC have been discovered. Of the 21 members of the human connexin family, connexin 43 (Cx43) is the most widely expressed and studied. The long cytosolic C-terminus (CT) of Cx43 is subject to extensive post-translational modifications that modulate its intracellular trafficking and gap junction channel gating. Moreover, the Cx43 CT contains multiple domains involved in protein interactions that permit crosstalk between Cx43 and cytoskeletal and regulatory proteins. These domains endow Cx43 with the capacity to affect cell growth and differentiation independently of GJIC. Here, we review the current understanding of the regulation and unique functions of the Cx43 CT, both as an essential component of full-length Cx43 and as an independent signalling hub. We highlight the complex regulatory and signalling networks controlled by the Cx43 CT, including the extensive protein interactome that underlies both gap junction channel-dependent and -independent functions. We discuss these data in relation to the recent discovery of the direct translation of specific truncated forms of Cx43. This article is part of a Special Issue entitled: Gap Junction Proteins edited by Jean Claude Herve.

Targeting CDK4 and CDK6: From Discovery to Therapy

Biochemical and genetic characterization of D-type cyclins, their cyclin D-dependent kinases (CDK4 and CDK6), and the polypeptide CDK4/6 inhibitor p16(INK4)over two decades ago revealed how mammalian cells regulate entry into the DNA synthetic (S) phase of the cell-division cycle in a retinoblastoma protein-dependent manner. These investigations provided proof-of-principle that CDK4/6 inhibitors, particularly when combined with coinhibition of allied mitogen-dependent signal transduction pathways, might prove valuable in cancer therapy. FDA approval of the CDK4/6 inhibitor palbociclib used with the aromatase inhibitor letrozole for breast cancer treatment highlights long-sought success. The newest findings herald clinical trials targeting other cancers.

SIGNIFICANCE

Rapidly emerging data with selective inhibitors of CDK4/6 have validated these cell-cycle kinases as anticancer drug targets, corroborating longstanding preclinical predictions. This review addresses the discovery of these CDKs and their regulators, as well as translation of CDK4/6 biology to positive clinical outcomes and development of rational combinatorial therapies.

A novel heat shock protein alpha 8 (Hspa8) molecular network mediating responses to stress- and ethanol-related behaviors

Genetic differences mediate individual differences in susceptibility and responses to stress and ethanol, although, the specific molecular pathways that control these responses are not fully understood. Heat shock protein alpha 8 (Hspa8) is a molecular chaperone and member of the heat shock protein family that plays an integral role in the stress response and that has been implicated as an ethanol-responsive gene. Therefore, we assessed its role in mediating responses to stress and ethanol across varying genetic backgrounds. The hippocampus is an important mediator of these responses, and thus, was examined in the BXD family of mice in this study. We conducted bioinformatic analyses to dissect genetic factors modulating Hspa8 expression, identify downstream targets of Hspa8, and examined its role. Hspa8 is trans-regulated by a gene or genes on chromosome 14 and is part of a molecular network that regulates stress- and ethanol-related behaviors. To determine additional components of this network, we identified direct or indirect targets of Hspa8 and show that these genes, as predicted, participate in processes such as protein folding and organic substance metabolic processes. Two phenotypes that map to the Hspa8 locus are anxiety-related and numerous other anxiety- and/or ethanol-related behaviors significantly correlate with Hspa8 expression. To more directly assay this relationship, we examined differences in gene expression following exposure to stress or alcohol and showed treatment-related differential expression of Hspa8 and a subset of the members of its network. Our findings suggest that Hspa8 plays a vital role in genetic differences in responses to stress and ethanol and their interactions.

Interaction of Cx43 with Hsc70 regulates G1/S transition through CDK inhibitor p27

Connexin 43 (Cx43) functions as a cell growth suppressor. We have demonstrated that Cx43 interacts with heat shock cognate protein 70 (Hsc70) for regulating cell proliferation. Hsc70 interacts with CDK inhibitor p27, which regulates the assembly and subcellular localization of cyclin D1-CDK4-p27 complex. However, the involvement of p27 with Cx43-mediated cell cycle suppression is still poorly understood. Here, we report that nuclear accumulation of p27 is reduced by overexpression of Cx43, and that this reduction is restored by co-overexpression with Hsc70. We found that Cx43 competes with p27 for binding to Hsc70, and as a result, decreases the level of Hsc70 in cyclin D1-CDK4-p27 complex, leading to prevention of the nuclear translocation of the complex and the G1/S transition. Collectively, our findings suggest that, in Cx43 up-regulation, which is most likely an emergency measure, Cx43-Hsc70 interaction regulates cell cycle G1/S progression through a novel mechanism by which Cx43-Hsc70 interaction prevents the nuclear accumulation of p27 through controlling the nuclear translocation of cyclin D1-CDK4-p27 complex.

Oncogenic protein MTBP interacts with MYC to promote tumorigenesis

Despite its involvement in most human cancers, MYC continues to pose a challenge as a readily tractable therapeutic target. Here we identify the MYC transcriptional cofactors TIP48 and TIP49 and MYC as novel binding partners of Mdm2-binding protein (MTBP), a functionally undefined protein that we show is oncogenic and overexpressed in many human cancers. MTBP associated with MYC at promoters and increased MYC-mediated transcription, proliferation, neoplastic transformation, and tumor development. In breast cancer specimens, we determined overexpression of both MYC and MTBP was associated with a reduction in 10-year patient survival compared with MYC overexpression alone. MTBP was also frequently co-amplified with MYC in many human cancers. Mechanistic investigations implicated associations with TIP48/TIP49 as well as MYC in MTBP function in cellular transformation and the growth of human breast cancer cells. Taken together, our findings show MTBP functions with MYC to promote malignancy, identifying this protein as a novel general therapeutic target in human cancer.

Connexin43 functions as a novel interacting partner of heat shock cognate protein 70

Regulation of connexin43 (Cx43) expression affects cell proliferation, differentiation and apoptosis in a gap junctional intercellular communication (GJIC)-independent manner. However, the underlying mechanisms of Cx43-mediated cell cycle suppression are still poorly understood. To elucidate the molecular mechanism of Cx43-mediated cell cycle suppression, we searched for Cx43 interacting proteins by using a proteomics approach. Here, we have identified a Cx43-interacting protein, heat shock cognate protein 70 (Hsc70). We confirmed that Hsc70 directly binds to the C-terminus of Cx43, whereas Hsc54, a splice variant of Hsc70, does not, that Cx43 competes with cyclin D1 for binding to Hsc70, and that the nuclear accumulation of cyclin D1 is reduced by overexpression of Cx43 in a GJIC-independent manner, which is restored by co-overexpression with Hsc70. As a result, the cell proliferation is regulated by Cx43. Our results suggest that Cx43-Hsc70 interaction probably plays a critical role during G1/S progression.

Aberrant cell cycle reentry in human and experimental inclusion body myositis and polymyositis

Inclusion body myositis (IBM), a degenerative and inflammatory disorder of skeletal muscle, and Alzheimer's disease share protein derangements and attrition of postmitotic cells. Overexpression of cyclins and proliferating cell nuclear antigen (PCNA) and evidence for DNA replication is reported in Alzheimer's disease brain, possibly contributing to neuronal death. It is unknown whether aberrant cell cycle reentry also occurs in IBM. We examined cell cycle markers in IBM compared with normal control, polymyositis (PM) and non-inflammatory dystrophy sample sets. Next, we tested for evidence of reentry and DNA synthesis in C2C12 myotubes induced to express β-amyloid (Aβ42). We observed increased levels of Ki-67, PCNA and cyclins E/D1 in IBM compared with normals and non-inflammatory conditions. Interestingly, PM samples displayed similar increases. Satellite cell markers did not correlate with Ki-67-affected myofiber nuclei. DNA synthesis and cell cycle markers were induced in Aβ-bearing myotubes. Cell cycle marker and cyclin protein expressions were also induced in an experimental allergic myositis-like model of PM in mice. Levels of p21 (Cip1/WAF1), a cyclin-dependent kinase inhibitor, were decreased in affected myotubes. However, overexpression of p21 did not rescue cells from Aβ-induced toxicity. This is the first report of cell cycle reentry in human myositis. The absence of rescue and evidence for reentry in separate models of myodegeneration and inflammation suggest that new DNA synthesis may be a reactive response to either or both stressors.

Targeting the heat shock response in cancer: tipping the balance in transformed cells

The elucidation of the heat shock response (HSR) as a mediator of cellular stress has created a framework for understanding how these processes may promote tumorigenesis. Furthermore, the identification of specific components of the HSR and how they are co-opted by cancer cells has led to the discovery of new therapeutic targets. A wide range of small molecule inhibitors of the HSR are in various stages of development for clinical application in patients with cancer. The introduction of these novel small molecule inhibitors offers the opportunity for synergy with existing therapies and the potential for highly targeted treatments.

Tumor markers for hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is one of the most common malignant tumors with a high rate of morbidity and mortality. HCC affects approximately one million individuals annually worldwide, with the incidence equal to the mortality rate. In 2008, HCC was listed as the third most lethal cancer. Thus, early diagnosis is crucial for improving the survival rate for patients. α-fetoprotein (AFP) together with iconography and pathology detection are commonly used in the clinical early diagnosis of liver cancer. However, the specificity and sensitivity of AFP used in screening for liver cancer are not satisfactory. Athough the development of molecular biology has led to the identification of new tumor markers, including proteantigens, cytokines, enzymes and isoenzymes, as well as related genes that can be used in the treatment and prognosis of liver cancer, more tumor markers are required for effective early diagnosis of diseases and monitoring of the curative effect.

Molecular mechanisms of anti-tumor properties of P276-00 in head and neck squamous cell carcinoma

Background

Tumors of the head and neck present aggressive pathological behavior in patients due to high expression of CDK/CCND1 proteins. P276-00, a novel CDK inhibitor currently being tested in clinic, inhibits growth of several cancers in vitro and in vivo. The pre clinical activity of P276-00 in head and neck cancer and its potential mechanisms of action at molecular level are the focus of the current studies.

Method

We have investigated the anti-cancer activity of P276-00 in head and neck tumors in vitro and in vivo. Candidate gene expression profiling and cell based proteomic approaches were taken to understand the pathways affected by P276-00 treatment.

Results

It was observed that P276-00 is cytotoxic across various HNSCC cell lines with an IC₅₀ ranging from 1.0-1.5 μmoles/L and culminated in significant cell-cycle arrest in G1/S phase followed by apoptosis. P276-00 treatment suppressed cell proliferation through inhibition of CCND1 expression, reduced phosphorylation of retinoblastoma protein and abrogative transcription of E2F1 gene targets. Further, we observed that apoptosis was mediated through P53 activation leading to higher BAX/BCL-2 ratio and cleaved caspase-3 levels. It was also seen that P276-00 treatment reduced expression of tumor micro-environment proteins such as IL-6, secreted EGFR and HSPA8. Finally, P276-00 treatment resulted in significant tumor growth inhibition in xenograft tumor models via lowered proliferative activity of E2F1 and aggravated P53 mediated apoptosis.

Conclusion

In summary, we have observed that P276-00 inhibits cyclin-D/CDK4/P16/pRB/E2F axis and induces apoptosis by increased P53 phosphorylation in HNSCC cells. These results suggest a novel indication for P276-00 in head and neck cancer with a potential role for IL-6 and HSPA8 as candidate serum biomarkers.

CDK-dependent Hsp70 Phosphorylation controls G1 cyclin abundance and cell-cycle progression

In budding yeast, the essential functions of Hsp70 chaperones Ssa1–4 are regulated through expression level, isoform specificity, and cochaperone activity. Suggesting a novel regulatory paradigm, we find that phosphorylation of Ssa1 T36 within a cyclin-dependent kinase (CDK) consensus site conserved among Hsp70 proteins alters cochaperone and client interactions. T36 phosphorylation triggers displacement of Ydj1, allowing Ssa1 to bind the G1 cyclin Cln3 and promote its degradation. The stress CDK Pho85 phosphorylates T36 upon nitrogen starvation or pheromone stimulation, destabilizing Cln3 to delay onset of S phase. In turn, the mitotic CDK Cdk1 phosphorylates T36 to block Cln3 accumulation in G2/M. Suggesting broad conservation from yeast to human, CDK-dependent phosphorylation of Hsc70 T38 similarly regulates Cyclin D1 binding and stability. These results establish an active role for Hsp70 chaperones as signal transducers mediating growth control of G1 cyclin abundance and activity.

Sexual dimorphism of STGC3 tumor suppressor function in nasopharyngeal carcinoma CNE2 cells

STGC3 is a potential tumor suppressor in nasopharyngeal carcinoma. We previously found that CNE2 cells that re-expressed STGC3 formed smaller tumors in female mice than in male mice. Here, we investigated the sexual dimorphism of STGC3 as a tumor-suppressor in female and male nude mice injected subcutaneously with pcDNA3.1(+)-STGC3/CNE2 cells. ER-α was positively expressed in vitro in the CNE2 cells. The pcDNA3.1(+)-STGC3/CNE2 cell growth rate decreased after treatment with β-estradiol in vitro. There were significant differences in tumor size or mass between pcDNA3.1(+)-STGC3/CNE2 and control cases (P < 0.05), but there were significant differences in tumor size between female and male nude mice in the STGC3 transfection groups, and the pcDNA3.1(+)-STGC3/CNE2 tumor growth rate in the female nude mice was the lowest in all cases (P < 0.05). There were no significant differences between female and male nude mice in control groups. Furthermore, a greater number of cells were blocked in the G(0)/G(1) phase in pcDNA3.1(+)-STGC3/ CNE2 tumor xenografts in the female mice. Protemic analysis found 9 differentially expressed proteins in the pcDNA3.1-STGC3/CNE2 xenograft tissues in females and males. A heat shock 70 protein 8 isoform 2 variant was identified as a down-regulated protein associated with cell cycle control and its downstream factor cyclin D1 was also decreased in STGC3-repressed xenografts in female mice. The data above suggest that STGC3 and its associated proteins play an important role in nasopharyngeal carcinoma gender differences.

Comprehensive review on the HSC70 functions, interactions with related molecules and involvement in clinical diseases and therapeutic potential

Heat shock cognate protein 70 (HSC70) is a constitutively expressed molecular chaperone which belongs to the heat shock protein 70 (HSP70) family. HSC70 shares some of the structural and functional similarity with HSP70. HSC70 also has different properties compared with HSP70 and other heat shock family members. HSC70 performs its full functions by the cooperation of co-chaperones. It interacts with many other molecules as well and regulates various cellular functions. It is also involved in various diseases and may become a biomarker for diagnosis and potential therapeutic targets for design, discovery, and development of novel drugs to treat various diseases. In this article, we provide a comprehensive review on HSC70 from the literatures including the basic general information such as classification, structure and cellular location, genetics and function, as well as its protein association and interaction with other proteins. In addition, we also discussed the relationship of HSC70 and related clinical diseases such as cancer, cardiovascular, neurological, hepatic and many other diseases and possible therapeutic potential and highlight the progress and prospects of research in this field. Understanding the functions of HSC70 and its interaction with other molecules will help us to reveal other novel properties of this protein. Scientists may be able to utilize this protein as a biomarker and therapeutic target to make significant advancement in scientific research and clinical setting in the future.

Prenatal arsenic exposure alters gene expression in the adult liver to a proinflammatory state contributing to accelerated atherosclerosis

The mechanisms by which environmental toxicants alter developmental processes predisposing individuals to adult onset chronic disease are not well-understood. Transplacental arsenic exposure promotes atherogenesis in apolipoprotein E-knockout (ApoE^−/−) mice. Because the liver plays a central role in atherosclerosis, diabetes and metabolic syndrome, we hypothesized that accelerated atherosclerosis may be linked to altered hepatic development. This hypothesis was tested in ApoE^−/− mice exposed to 49 ppm arsenic in utero from gestational day (GD) 8 to term. GD18 hepatic arsenic was 1.2 µg/g in dams and 350 ng/g in fetuses. The hepatic transcriptome was evaluated by microarray analysis to assess mRNA and microRNA abundance in control and exposed pups at postnatal day (PND) 1 and PND70. Arsenic exposure altered postnatal developmental trajectory of mRNA and microRNA profiles. We identified an arsenic exposure related 51-gene signature at PND1 and PND70 with several hubs of interaction (Hspa8, IgM and Hnf4a). Gene ontology (GO) annotation analyses indicated that pathways for gluconeogenesis and glycolysis were suppressed in exposed pups at PND1, and pathways for protein export, ribosome, antigen processing and presentation, and complement and coagulation cascades were induced by PND70. Promoter analysis of differentially-expressed transcripts identified enriched transcription factor binding sites and clustering to common regulatory sites. SREBP1 binding sites were identified in about 16% of PND70 differentially-expressed genes. Western blot analysis confirmed changes in the liver at PND70 that included increases of heat shock protein 70 (Hspa8) and active SREBP1. Plasma AST and ALT levels were increased at PND70. These results suggest that transplacental arsenic exposure alters developmental programming in fetal liver, leading to an enduring stress and proinflammatory response postnatally that may contribute to early onset of atherosclerosis. Genes containing SREBP1 binding sites also suggest pathways for diabetes mellitus and rheumatoid arthritis, both diseases that contribute to increased cardiovascular disease in humans.

Staying alive: PI3K pathway promotes primordial follicle activation and survival in response to 3MC-induced ovotoxicity

3-Methylcholanthrene (3MC) is a potent ovotoxicant capable of causing premature ovarian failure through primordial follicle depletion. Despite 3MCs ovotoxicity having been established for 30 years, relatively little information exists on the mechanisms. In this study, we examined the effects of 3MC exposure on the immature ovarian follicle population. Microarray analysis revealed a complex mechanism of 3MC-induced ovotoxicity involving a number of cellular processes associated with xenobiotic metabolism, ovarian cancer, cell cycle progression, and cell death. 3MC exposure was also found to induce developing follicle atresia and aberrant primordial follicle activation via the stimulation of PI3K/Akt and mammalian target of rapamycin (mTOR) signaling pathways. Inhibition of PI3K/Akt signaling resulted in the severe depletion of the primordial follicle pool, with further analysis identifying increased Akt1-stimulated Bad phosphoinhibition in 3MC-treated primordial follicles. Our results suggest that the primordial follicle pool enters a "prosurvival" state upon 3MC exposure and that its depletion is due to a vicious cycle of primordial follicle activation in an attempt to replace developing follicles undergoing follicular atresia.

Identification of kinase substrates by bimolecular complementation assays

As a consequence of the transient nature of kinase-substrate interactions, the detection of kinase targets, although central for understanding many biological processes, has remained challenging. Here we present a straightforward procedure that relies on the comparison of wild type with activation-loop mutants in the kinase of interest by bimolecular complementation assays. As a proof of functionality, we present the identification and in vivo confirmation of substrates of the major cell-cycle kinase in Arabidopsis, revealing a direct link between cell proliferation and the control of the redox state.

p57(Kip2) and p27(Kip1) cooperate to maintain hematopoietic stem cell quiescence through interactions with Hsc70

Cell cycle regulators play critical roles in the balance between hematopoietic stem cell (HSC) dormancy and proliferation. In this study, we report that cell cycle entry proceeded normally in HSCs null for cyclin-dependent kinase (CDK) inhibitor p57 due to compensatory upregulation of p27. HSCs null for both p57 and p27, however, were more proliferative and had reduced capacity to engraft in transplantation. We found that heat shock cognate protein 70 (Hsc70) interacts with both p57 and p27 and that the subcellular localization of Hsc70 was critical to maintain HSC cell cycle kinetics. Combined deficiency of p57 and p27 in HSCs resulted in nuclear import of an Hsc70/cyclin D1 complex, concomitant with Rb phosphorylation, and elicited severe defects in maintaining HSC quiescence. Taken together, these data suggest that regulation of cytoplasmic localization of Hsc70/cyclin D1 complex by p57 and p27 is a key intracellular mechanism in controlling HSC dormancy.

Proteomic analysis of advanced colorectal cancer by laser capture microdissection and two-dimensional difference gel electrophoresis

The emergence of laser capture microdissection (LCM) and two-dimensional difference gel electrophoresis (2D-DIGE) has been shown to greatly improve the accuracy and sensitivity of global protein expression analysis. However, their combined use in profiling tumour proteome has rarely been reported. In this study, we applied these techniques to profile the protein expression changes of the late stage colorectal cancer (CRC) and its liver metastases. The study revealed that both the primary and secondary tumours showed a distinct protein expression profile compared to normal tissues, but were indistinguishable from each other. Differential analysis between the primary tumour and patient-matched normal colon mucosa identified a total of 71 proteins to be altered in CRC. Over 40% of these proteins have been previously reported as CRC-related proteins, validating the accuracy of the current analysis. We have also identified many previously unknown changes including overexpression of ACY1, HSC70, HnRNP I, HnRNP A3, SET, ANP32A and TUFM in CRC, which have been further verified by western blotting and immunohistochemistry. This study demonstrated that LCM in combination with 2D-DIGE is a powerful tool to analyse the proteome of tumour tissues and may lead to the identification of potential novel protein markers and therapeutic targets for cancer.

Heat shock proteins in oncology: diagnostic biomarkers or therapeutic targets?

Heat shock proteins (HSP) are a family of proteins induced in cells exposed to different insults. This induction of HSPs allows cells to survive stress conditions. Mammalian HSPs have been classified into six families according to their molecular size: HSP100, HSP90, HSP70, HSP60, HSP40 and small HSPs (15 to 30kDa) including HSP27. These proteins act as molecular chaperones either helping in the refolding of misfolded proteins or assisting in their elimination if they become irreversibly damaged. In recent years, proteomic studies have characterized several different HSPs in various tumor types which may be putative clinical biomarkers or molecular targets for cancer therapy. This has led to the development of a series of molecules capable of inhibiting HSPs. Numerous studies speculated that over-expression of HSP is in part responsible for resistance to many anti-tumor agents and chemotherapeutics. Hence, from a pharmacological point of view, the co-administration of HSP inhibitors together with other anti-tumor agents is of major importance in overcoming therapeutic resistance. In this review, we provide an overview of the current status of HSPs in autoimmune, cardiovascular, and neurodegenerative diseases with special emphasis on cancer.

PACSIN 2 represses cellular migration through direct association with cyclin D1 but not its alternate splice form cyclin D1b

Cyclin D1 overexpression is a common feature of many human malignancies. Genomic deletion analysis has demonstrated a key role for cyclin D1 in cellular proliferation, angiogenesis, and cellular migration. To investigate the mechanisms contributing to cyclin D1 functions, we purified cyclin D1a-associated complexes by affinity chromatography and identified the PACSIN 2 (protein kinase C and casein kinase substrate in neurons 2) protein by mass spectrometry. The PACSIN 2, but not the related PACSIN 1 and 3, directly bound wild-type cyclin D1 (cyclin D1a) at the carboxyl terminus, and failed to bind cyclin D1b, the alternative splicing variant of cyclin D1. PACSIN 2 knockdown induced cellular migration and reduced cell spreading in LNCaP cells expressing cyclin D1a. In cyclin D1(-/-) mouse embryonic fibroblasts (MEFs), cyclin D1a, but not cyclin D1b, reduced the cell spreading to a polarized morphology. siPACSIN 2 had no effect on cellular migration of cyclin D1(-/-) MEFs. Cyclin D1a restored the migratory ability of cyclin D1(-/-) MEFs, which was further enhanced by knocking down PACSIN 2 with siRNA. The cyclin D1-associated protein, PACSIN 2, regulates cell spreading and migration, which are dependent on cyclin D1 expression.

Cancer inhibition through circadian reprogramming of tumor transcriptome with meal timing

Circadian disruption accelerates cancer progression, whereas circadian reinforcement could halt it. Mice with P03 pancreatic adenocarcinoma (n = 77) were synchronized and fed ad libitum (AL) or with meal timing (MT) from Zeitgeber time (ZT) 2 to ZT6 with normal or fat diet. Tumor gene expression profiling was determined with DNA microarrays at endogenous circadian time (CT) 4 and CT16. Circadian mRNA expression patterns were determined for clock genes Rev-erbalpha, Per2, and Bmal1, cellular stress genes Hspa8 and Cirbp, and cyclin A2 gene Ccna2 in liver and tumor. The 24-hour patterns in telemetered rest-activity and body temperature and plasma corticosterone and insulin-like growth factor-I (IGF-I) were assessed. We showed that MT inhibited cancer growth by approximately 40% as compared with AL (P = 0.011) irrespective of calorie intake. Clock gene transcription remained arrhythmic in tumors irrespective of feeding schedule or diet. Yet, MT upregulated or downregulated the expression of 423 tumor genes, according to CT. Moreover, 36 genes involved in cellular stress, cell cycle, and metabolism were upregulated at one CT and downregulated 12 h apart. MT induced >10-fold circadian expression of Hspa8, Cirbp, and Ccna2 in tumors. Corticosterone or IGF-I patterns played no role in tumor growth inhibition. In contrast, MT consistently doubled the circadian amplitude of body temperature. Peak and trough respectively corresponded to peak expressions of Hspa8 and Cirbp in tumors. The reinforcement of the host circadian timing system with MT induced 24-hour rhythmic expression of critical genes in clock-deficient tumors, which translated into cancer growth inhibition. Targeting circadian clocks represents a novel potential challenge for cancer therapeutics.

Hsp72 chaperone function is dispensable for protection against stress-induced apoptosis

In addition to its role as a molecular chaperone, heat shock protein 72 (Hsp72) protects cells against a wide range of apoptosis inducing stresses. However, it is unclear if these two roles are functionally related or whether Hsp72 inhibits apoptosis by a mechanism independent of chaperone activity. The N-terminal adenosine triphosphatase domain, substrate-binding domain and the C-terminal EEVD regulatory motif of Hsp72 are all essential for chaperone activity. In this study, we show that Hsp72 mutants with a functional substrate-binding domain but lacking chaperone activity retain their ability to protect cells against apoptosis induced by heat and tumor necrosis factor alpha. In contrast, a deletion mutant lacking a functional substrate-binding domain has no protective capacity. The ability of the Hsp72 substrate-binding domain to inhibit apoptosis independent of the regulatory effects of the adenosine triphosphate-binding domain indicates that the inhibition of apoptosis may involve a stable binding interaction with a regulatory substrate rather than Hsp72 chaperone activity.

Phosphatidylinositol 3 kinase pathway and 4-hydroxy-2-nonenal-induced oxidative injury in the RPE

PURPOSE

4-Hydroxy-2-nonenal (4-HNE) is a major lipid peroxidation product in the retina and the retinal pigment epithelium. The purpose of the present study was to investigate how NF-E2-related factor-2 (Nrf2) and phosphatidylinositol 3 (PI3K) pathways affect the responses of cultured human retinal pigment epithelial (RPE) cells to 4-HNE.

METHODS

Cultured ARPE-19 cells were treated with different concentrations of 4-HNE and a PI3K inhibitor, LY294002. Intracellular glutathione (GSH) was measured by high-performance liquid chromatography (HPLC). The transcriptional activity of Nrf2 was measured by dual luciferase assay after transient transfection with reporter plasmids. The mRNA level of glutamate cysteine ligase (GCL) was quantified by real-time RT-PCR. Formation of HNE adduct on heat shock cognate protein 70 (Hsc70) was measured by immunoprecipitation and Western blot analyses.

RESULTS

Treatment with 4-HNE increased Nrf2 activity and GSH synthesis in a dose-dependent manner in cultured RPE cells. The modulatory subunit of GCL was upregulated by 4-HNE. Antioxidant responses were largely abolished by pretreatment with LY294002. The modification of Hsc70 by 4-HNE was increased when PI3K was inhibited.

CONCLUSIONS

The Nrf2-dependent antioxidant response protects against 4-HNE toxicity, and this protective mechanism is dependent on the functions of the PI3K pathway.