The J domain of Tpr2 regulates its interaction with the proapoptotic and cell-cycle checkpoint protein, Rad9

Hsp70 Inhibits the Replication of Fowl Adenovirus Serotype 4 by Suppressing Viral Hexon with the Assistance of DnaJC7

Fowl adenovirus serotype 4 (FAdV-4) infection results in serious hepatitis-hydropericardium syndrome (HHS) in broilers, which has caused great economic losses to the poultry industry; however, the specific host responses to FAdV-4 remain unknown. In this study, we identified 141 high-confidence protein-protein interactions (PPIs) between the main viral proteins (Hexon, Fiber 1, Fiber 2, and Penton bases) and host proteins via a liquid chromatography-tandem mass spectrometry (LC-MS/MS) assay. We found that heat shock protein 70 (Hsp70), the protein with the highest score, and its cofactor DnaJ heat shock protein 40 family member C7 (DnaJC7) could negatively regulate the replication of FAdV-4. Furthermore, the nucleotide binding domain (NBD) of Hsp70 and the J domain of DnaJC7 were necessary for inhibiting FAdV-4 replication. We verified that DnaJC7 as a bridge could bind to Hsp70 and Hexon, assisting the indirect interaction between Hsp70 and Hexon. In addition, we found that FAdV-4 infection strongly induced the expression of autophagy proteins and cellular Hsp70 in a dose-dependent manner. Blockage of Hexon by Hsp70 overexpression was significantly reduced when the autophagy pathway was blocked by the specific inhibitor chloroquine (CQ). Our results showed that Hsp70 was co-opted by DnaJC7 to interact with viral Hexon and inhibited Hexon through the autophagy pathway, leading to a considerable restriction of FAdV-4 replication. IMPORTANCE FAdV-4, as the main cause of HHS, has quickly spread all over the world in recent years, seriously threatening the poultry industry. The aim of this study was to identify the important host proteins that have the potential to regulate the life cycle of FAdV-4. We found that Hsp70 and DnaJC7 played crucial roles in regulating the amount of viral Hexon and extracellular viral titers. Moreover, we demonstrated that Hsp70 interacted with viral Hexon with the assistance of DnaJC7, followed by suppressing Hexon protein through the autophagy pathway. These results provide new insight into the role of the molecular chaperone complex Hsp70-DnaJC7 in FAdV-4 infection and suggest a novel strategy for anti-FAdV-4 drug development by targeting the specific interactions among Hsp70, DnaJC7 and Hexon.

DnaJC7 in Amyotrophic Lateral Sclerosis

Protein misfolding is a common basis of many neurodegenerative diseases including amyotrophic lateral sclerosis (ALS). Misfolded proteins, such as TDP-43, FUS, Matrin3, and SOD1, mislocalize and form the hallmark cytoplasmic and nuclear inclusions in neurons of ALS patients. Cellular protein quality control prevents protein misfolding under normal conditions and, particularly, when cells experience protein folding stress due to the fact of increased levels of reactive oxygen species, genetic mutations, or aging. Molecular chaperones can prevent protein misfolding, refold misfolded proteins, or triage misfolded proteins for degradation by the ubiquitin–proteasome system or autophagy. DnaJC7 is an evolutionarily conserved molecular chaperone that contains both a J-domain for the interaction with Hsp70s and tetratricopeptide domains for interaction with Hsp90, thus joining these two major chaperones’ machines. Genetic analyses reveal that pathogenic variants in the gene encoding DnaJC7 cause familial and sporadic ALS. Yet, the underlying ALS-associated molecular pathophysiology and many basic features of DnaJC7 function remain largely unexplored. Here, we review aspects of DnaJC7 expression, interaction, and function to propose a loss-of-function mechanism by which pathogenic variants in DNAJC7 contribute to defects in DnaJC7-mediated chaperoning that might ultimately contribute to neurodegeneration in ALS.

Regulation of p53 and Cancer Signaling by Heat Shock Protein 40/J-Domain Protein Family Members

Heat shock proteins (HSPs) are molecular chaperones that assist diverse cellular activities including protein folding, intracellular transportation, assembly or disassembly of protein complexes, and stabilization or degradation of misfolded or aggregated proteins. HSP40, also known as J-domain proteins (JDPs), is the largest family with over fifty members and contains highly conserved J domains responsible for binding to HSP70 and stimulation of the ATPase activity as a co-chaperone. Tumor suppressor p53 (p53), the most frequently mutated gene in human cancers, is one of the proteins that functionally interact with HSP40/JDPs. The majority of p53 mutations are missense mutations, resulting in acquirement of unexpected oncogenic activities, referred to as gain of function (GOF), in addition to loss of the tumor suppressive function. Moreover, stability and levels of wild-type p53 (wtp53) and mutant p53 (mutp53) are crucial for their tumor suppressive and oncogenic activities, respectively. However, the regulatory mechanisms of wtp53 and mutp53 are not fully understood. Accumulating reports demonstrate regulation of wtp53 and mutp53 levels and/or activities by HSP40/JDPs. Here, we summarize updated knowledge related to the link of HSP40/JDPs with p53 and cancer signaling to improve our understanding of the regulation of tumor suppressive wtp53 and oncogenic mutp53 GOF activities.

Validation of the pathogenic role of rare DNAJC7 variants in Chinese patients with amyotrophic lateral sclerosis

DNAJC7 has recently been recognized as a novel amyotrophic lateral sclerosis (ALS) risk gene. To date, few studies have screened DNAJC7 mutations in Chinese population. Further studies are needed to clarify the clinical and genetic features of DNAJC7-related ALS. Sporadic ALS (sALS) patients and controls were enrolled in this study. Variants were detected by whole-exome sequencing and validated via Sanger sequencing. Gene-based burden analysis was conducted. Potentially damaging variants in DNAJC7 were identified in 3 sALS patients. The frequency of bulbar onset was significantly higher in DNAJC7-related ALS patients than in the whole group. However, burden analysis showed no enrichment of rare DNAJC7 variants in sALS patients. Reported variant N369T showed no significant difference in distribution among different groups. In conclusion, DNAJC7 variants may be associated with ALS but not play a main role in Chinese patients. DNAJC7-related ALS patients tended to have a bulbar onset. Our study supported the pathogenic role of DNAJC7 in ALS and expanded the phenotypic and genetic spectrum of DNAJC7-related ALS.

Expression of SGTA correlates with prognosis and tumor cell proliferation in human hepatocellular carcinoma

To investigate the potential role of small glutamine-rich TPR-containing protein A (SGTA) in hepatocarcinogenesis, immunohistochemistry and Western blot were performed to detect the expression of SGTA in clinical Hepatocellular carcinoma (HCC) samples, adjacent nontumorous liver tissues and HCC cell lines. In addition, expression of SGTA was correlated with clinicopathological variables and univariate and multivariate survival analyses were performed to determine the prognostic significance. Moreover, the biological significance of the aberrant expression of SGTA was investigated in vitro. Both immunohistochemistry evaluation and Western blot analyses demonstrated that SGTA was overexpressed in HCC tissues compared with adjacent nontumorous liver tissues. Expression of SGTA directly correlated with the histological grades of HCC and high expression of SGTA was associated with a poor prognosis. SGTA depletion by siRNA inhibited cell proliferation, blocked S-phase and mitotic entry in Huh7 cells. Western blot analyses showed that SGTA depletion decreased cyclin A and cyclin B levels. Taken together, owing to overexpression of SGTA in HCC and its important role in predicting poor prognosis and the development of HCC, SGTA could be a potential prognostic marker and therapeutic target of HCC.

Co-chaperon DnaJC7/TPR2 enhances p53 stability and activity through blocking the complex formation between p53 and MDM2

Tumor suppressor p53 plays a critical role in the regulation of DNA damage response. Upon severe DNA damage, p53 promotes apoptosis to eliminate cells with seriously damaged DNA to maintain genomic integrity. Pro-apoptotic function of p53 is tightly linked to its sequence-specific transactivation ability. In the present study, we have identified co-chaperon DnaJC7/TPR2 as a novel binding partner of p53 by yeast-based two-hybrid screening. In the two-hybrid screening, we used the central DNA-binding domain of p53 as a bait. Co-immunoprecipitation experiments demonstrated that DnaJC7 is associated with p53 in mammalian cells. Luciferase reporter and colony formation assays revealed that DnaJC7 enhances p53-dependent transcriptional as well as growth-suppressive activity. Forced expression of DnaJC7 induced to extend a half-life of p53, indicating that DnaJC7-mediated activation of p53 might be at least in part due to its prolonged half-life. Consistent with these observations, the amount of p53/MDM2 complex was markedly reduced in the presence of DnaJC7, suggesting that DnaJC7 dissociates MDM2 from p53. Taken together, our present findings strongly suggest that DnaJC7 participates in p53/MDM2 negative feedback regulatory pathway, and thereby enhancing the stability and activity of p53.

The role of RAD9 in tumorigenesis

RAD9 regulates multiple cellular processes that influence genomic integrity, and for at least some of its functions the protein acts as part of a heterotrimeric complex bound to HUS1 and RAD1 proteins. RAD9 participates in DNA repair, including base excision repair, homologous recombination repair and mismatch repair, multiple cell cycle phase checkpoints and apoptosis. In addition, functions including the transactivation of downstream target genes, immunoglobulin class switch recombination, as well as 3'-5' exonuclease activity have been reported. Aberrant RAD9 expression has been linked to breast, lung, thyroid, skin and prostate tumorigenesis, and a cause-effect relationship has been demonstrated for the latter two. Interestingly, human RAD9 overproduction correlates with prostate cancer whereas deletion of Mrad9, the corresponding mouse gene, in keratinocytes leads to skin cancer. These results reveal that RAD9 protein can function as an oncogene or tumor suppressor, and aberrantly high or low levels can have deleterious health consequences. It is not clear which of the many functions of RAD9 is critical for carcinogenesis, but several alternatives are considered herein and implications for the development of novel cancer therapies based on these findings are examined.

Role of the cochaperone Tpr2 in Hsp90 chaperoning

The molecular chaperones Hsp90 and Hsp70 are highly regulated by various cochaperones that participate in the activation of steroid receptors. Here we study Tpr2 (also called DjC7), a TPR domain-containing type III J protein implicated in steroid receptor chaperoning. We propose that Tpr2 plays a role in the Hsp90-dependent chaperoning of the progesterone receptor (PR). Tpr2 overexpression or knockdown resulted in slight reductions in PR transcriptional activity in HeLa cells. Immunoprecipitation and pulldown experiments indicated that Tpr2 associates with Hsp90 and Hsp70 complexes, some of which also contain the PR. Tpr2 can bind Hsp90 and Hsp70 simultaneously, which is also a property of the cochaperone Hop. However, unlike Hop, Tpr2 binding to Hsp70 in the presence of Hsp90 is ATP-dependent, and Tpr2 cannot replace Hop in Hsp90 chaperoning in vitro or in vivo. While Tpr2 was not detected as a component of PR heterocomplexes in cell lysates, purified Tpr2 bound the PR readily. Surprisingly, Tpr2 replaced type I and II J proteins in the Hsp90-dependent chaperoning of the PR and the protein kinase, Chk1. Unlike other J proteins, Tpr2 promoted the accumulation of Hsp70 in PR heterocomplexes in the presence of Hsp90. Thus, Tpr2 has the potential to regulate PR chaperoning.

Telomere and telomerase modulation by the mammalian Rad9/Rad1/Hus1 DNA-damage-checkpoint complex

Telomeres, the termini of linear chromosomes, are exceptional in that they are DNA ends that do not normally trigger a DNA-damage response (DDR) and are compatible with normal cellular proliferation. Mammalian telomeres are nevertheless a physiological substrate of the DDR apparatus, as shown by the fact that the inactivation of genes encoding certain DDR factors results in telomere dysfunction. However, how DDR factors are integrated with telomere physiology, including telomere length regulation by the specialized reverse transcriptase telomerase, is still largely unclear. Here we report that the mammalian Rad9/Rad1/Hus1 (911) checkpoint complex, which localizes to sites of genome damage and promotes DDR signaling, is an integral component of the telomere in human and mouse cells. By the use of quantitative telomere-length measurements, we demonstrate severe telomeric shortening in both Hus1-deficient mouse embryonic fibroblasts and thymocytes from conditional Hus1-knockout mice. We also show that 911 is found in association with catalytically competent telomerase in cell lysates and is a positive regulator of its DNA polymerase activity. These findings identify an unanticipated function for the 911 checkpoint complex at telomeres in mammals and provide a mechanistic link between the activity of DNA-damage-checkpoint proteins and the telomere-maintenance machinery.

Progression of secondary hyperparathyroidism involves deregulation of genes related to DNA and RNA stability

BACKGROUND

Renal secondary hyperparathyroidism in its late stages becomes autonomous, so excessive parathyroid hormone (PTH) secretion no longer responds to physiologic stimuli or to aggressive medical treatment.

METHODS

To gain molecular understanding of progression of renal secondary hyperparathyroidism, normal and hyperplastic parathyroid tissue with diffuse and nodular growth were analyzed. The results were also compared to parathyroid adenomas. The analysis was performed by high-density oligonucleotide microarray and bidirectional subtraction library.

RESULTS

Analysis of the DNA arrays found 16 overexpressed and 132 repressed genes in the nodules while the subtraction library produced 34 overexpressed and 40 repressed genes. The differentially expressed genes between diffuse and nodular samples included some related to DNA stability and repair (TALDO1, PRDX2, DDB1, XRCC1, and POLB), RNA stability and degradation (OASL and AUF1), protein synthesis and processing (PFDN5, HSPD1, and NACA), cell growth (CDC25C and GRPR), and tumorigenesis and cell cycle (VIL2 and TPD52).

CONCLUSION

According to the function described for the deregulated genes, when secondary hyperparathyroidism becomes autonomous and refractory to treatment, RNA degradation may be increased while DNA integrity may be compromised. These two mechanisms, combined with deregulation of genes related to growth and differentiation show the complex pathway of parathyroid glands' evolution in renal hyperparathyroidism and may explain the large amount of molecular cytogenetic aberrations found in refractory hyperparathyroidism. Considering that some of the genes with altered expression in nodular hyperplasia lead to irreversible consequences in the genomic integrity of the cells, an adequate and early management of the secondary hyperparathyroidism of chronic kidney disease becomes mandatory.

Overexpression of small glutamine-rich TPR-containing protein promotes apoptosis in 7721 cells

It is known that small glutamine-rich TPR-containing protein (SGT) is the member of TPR motif family. However, the biological functions of SGT remain unclear. In this paper, we report that SGT plays a role in apoptotic signaling. Ectopic expression of SGT enhances DNA fragment and nucleus breakage after the induction of apoptosis. Increasing mRNA level of SGT is also observed in 7721 cells undergoing apoptosis, knockdown the expression of endogenous SGT contributes to the decrease of apoptosis of 7721 cells. Deletion analysis reveals that TPR domain is critical to pro-apoptotic function of SGT. Furthermore, we demonstrated that the PARP cleavage and cytochrome c release are enhanced when SGT is overexpressed in 7721 cells during apoptosis. Collectively, our results indicate that SGT is a new pro-apoptotic factor.

Heat-shock proteins as regulators of apoptosis

Heat-shock proteins are produced in response to different types of stress conditions making cells resistant to stress-induced cell damage. Under normal conditions, heat-shock proteins play numerous roles in cell function, including modulating protein activity by changing protein conformation, promoting multiprotein complex assembly/disassembly, regulating protein degradation within the proteasome pathway, facilitating protein translocation across organellar membranes, and ensuring proper folding of nascent polypeptide chains during protein translation. When cells are stressed, a common response is to undergo cell death by one of two pathways, either 'necrosis' or 'apoptosis'. Recently, both routes to cell death have been revealed to share similar mechanisms, with heat-shock proteins and their cofactors responsible for inhibiting both apoptotic and necrotic pathways. We therefore briefly summarize recent reports showing molecular evidence of cell death regulation by heat-shock proteins and their cochaperones.