Stress-dependent Daxx-CHIP interaction suppresses the p53 apoptotic program

The chaperone-assisted selective autophagy complex dynamics and dysfunctions

Each protein must be synthesized with the correct amino acid sequence, folded into its native structure, and transported to a relevant subcellular location and protein complex. If any of these steps fail, the cell has the capacity to break down aberrant proteins to maintain protein homeostasis (also called proteostasis). All cells possess a set of well-characterized protein quality control systems to minimize protein misfolding and the damage it might cause. Autophagy, a conserved pathway for the degradation of long-lived proteins, aggregates, and damaged organelles, was initially characterized as a bulk degradation pathway. However, it is now clear that autophagy also contributes to intracellular homeostasis by selectively degrading cargo material. One of the pathways involved in the selective removal of damaged and misfolded proteins is chaperone-assisted selective autophagy (CASA). The CASA complex is composed of three main proteins (HSPA, HSPB8 and BAG3), essential to maintain protein homeostasis in muscle and neuronal cells. A failure in the CASA complex, caused by mutations in the respective coding genes, can lead to (cardio)myopathies and neurodegenerative diseases. Here, we summarize our current understanding of the CASA complex and its dynamics. We also briefly discuss how CASA complex proteins are involved in disease and may represent an interesting therapeutic target.Abbreviation ALP: autophagy lysosomal pathway; ALS: amyotrophic lateral sclerosis; AMOTL1: angiomotin like 1; ARP2/3: actin related protein 2/3; BAG: BAG cochaperone; BAG3: BAG cochaperone 3; CASA: chaperone-assisted selective autophagy; CMA: chaperone-mediated autophagy; DNAJ/HSP40: DnaJ heat shock protein family (Hsp40); DRiPs: defective ribosomal products; EIF2A/eIF2α: eukaryotic translation initiation factor 2A; EIF2AK1/HRI: eukaryotic translation initiation factor 2 alpha kinase 1; GABARAP: GABA type A receptor-associated protein; HDAC6: histone deacetylase 6; HSP: heat shock protein; HSPA/HSP70: heat shock protein family A (Hsp70); HSP90: heat shock protein 90; HSPB8: heat shock protein family B (small) member 8; IPV: isoleucine-proline-valine; ISR: integrated stress response; KEAP1: kelch like ECH associated protein 1; LAMP2A: lysosomal associated membrane protein 2A; LATS1: large tumor suppressor kinase 1; LIR: LC3-interacting region; MAP1LC3/LC3: microtubule associated protein 1 light chain 3; MTOC: microtubule organizing center; MTOR: mechanistic target of rapamycin kinase; NFKB/NF-κB: nuclear factor kappa B; NFE2L2: NFE2 like bZIP transcription factor 2; PLCG/PLCγ: phospholipase C gamma; polyQ: polyglutamine; PQC: protein quality control; PxxP: proline-rich; RAN translation: repeat-associated non-AUG translation; SG: stress granule; SOD1: superoxide dismutase 1; SQSTM1/p62: sequestosome 1; STUB1/CHIP: STIP1 homology and U-box containing protein 1; STK: serine/threonine kinase; SYNPO: synaptopodin; TBP: TATA-box binding protein; TARDBP/TDP-43: TAR DNA binding protein; TFEB: transcription factor EB; TPR: tetratricopeptide repeats; TSC1: TSC complex subunit 1; UBA: ubiquitin associated; UPS: ubiquitin-proteasome system; WW: tryptophan-tryptophan; WWTR1: WW domain containing transcription regulator 1; YAP1: Yes1 associated transcriptional regulator.

Multiomics analysis reveals the mechanical stress-dependent changes in trabecular meshwork cytoskeletal-extracellular matrix interactions

Trabecular meshwork (TM) tissue is subjected to constant mechanical stress due to the ocular pulse created by the cardiac cycle. This brings about alterations in the membrane lipids and associated cell-cell adhesion and cell-extracellular matrix (ECM) interactions, triggering intracellular signaling responses to counter mechanical insults. A loss of such response can lead to elevated intraocular pressure (IOP), a major risk factor for primary open-angle glaucoma. This study is aimed to understand the changes in signaling responses by TM subjected to mechanical stretch. We utilized multiomics to perform an unbiased mRNA sequencing to identify changes in transcripts, mass spectrometry- (MS-) based quantitative proteomics for protein changes, and multiple reaction monitoring (MRM) profiling-based MS and high-performance liquid chromatography (HPLC-) based MS to characterize the lipid changes. We performed pathway analysis to obtain an integrated map of TM response to mechanical stretch. The human TM cells subjected to mechanical stretch demonstrated an upregulation of protein quality control, oxidative damage response, pro-autophagic signal, induction of anti-apoptotic, and survival signaling. We propose that mechanical stretch-induced lipid signaling via increased ceramide and sphingomyelin potentially contributes to increased TM stiffness through actin-cytoskeleton reorganization and profibrotic response. Interestingly, increased phospholipids and diacylglycerol due to mechanical stretch potentially enable cell membrane remodeling and changes in signaling pathways to alter cellular contractility. Overall, we propose the mechanistic interplay of macromolecules to bring about a concerted cellular response in TM cells to achieve mechanotransduction and IOP regulation when TM cells undergo mechanical stretch.

Generation of a CHIP isogenic human iPSC-derived cortical neuron model for functional proteomics

The neuroprotective E3-ubiquitin ligase CHIP is linked to healthy aging. Here, we present a protocol using a patient-derived iPSC line with a triplication of the α-synuclein gene to produce gene-edited cells isogenic for CHIP. We describe iPSC differentiation into cortical neurons and their identity validation. We then detail mass spectrometry-based approaches (SWATH-MS) to identify dominant changes in the steady state proteome generated by loss of CHIP function. This protocol can be adapted to other proteins that impact proteostasis in neurons.

For complete details on the use and execution of this protocol, please refer to Dias et al. (2021).

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Generation of human iPSCs that are isogenic for the E3-ligase CHIP

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Differentiation of iPSCs into cortical neurons and validation over 80-days

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Preparation of cortical neurons samples suitable for label free proteomic analysis

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SWATH-MS measurement of steady state protein levels to facilitate pathway analysis

Anticancer effects of acteoside: Mechanistic insights and therapeutic status

Cancer, the uncontrolled proliferation and metastasis of abnormal cells, is a major public health issue worldwide. To date, several natural compounds have been reported with their efficacy in the treatment of different types of cancer. Chemotherapeutic agents are used in cancer treatment and prevention, among other aspects. Acteoside is a phenylethanoid glycoside, first isolated from Verbascum sinuatum, which has demonstrated multiple effects, including antioxidant, anti-epileptic, neuroprotective, anti-inflammatory, antifungal, antihypertensive, and anti-leishmanial properties. This review gathered, analyzed, and summarized the literature on acteoside and its anticancer properties. All the available information about this compound and its role in different types of cancer was collected using different scientific search engines, including PubMed, Scopus, Springer Link, Wiley Online, Web of Science, Scifinder, ScienceDirect, and Google Scholar. Acteoside is found in a variety of plants and has been shown to have anticancer activity in many experimental models through oxidative stress, apoptosis, anti-angiogenesis, anti-invasion, anti-metastasis, synergism with other agents, and anti-proliferative effects through modulation of several pathways. In conclusion, acteoside exhibited potent anticancer activity against different cancer cell lines through modulating several cancer signaling pathways in different non- and pre-clinical experimental models and thus could be a strong candidate for further clinical studies.

Carboxy terminus of HSP70-interacting protein (CHIP) attenuates the stemness of thyroid cancer cells through decreasing OCT4 protein stability

Cancer cell stemness results in the occurrence and progression of tumors and Oct4 (octamer-binding transcription factor) has been confirmed to be a critical contributor and marker of cancer cell stemness. Here, we aimed to explore the underlying mechanisms contributing to Oct4 protein stability, which is necessary for thyroid cancer (TC) cell stemness. We indicated that carboxy terminus of HSP70-interacting protein (CHIP) protein was lowly expressed in TC tissues and cells, and positively correlated with the overall survival of TC patients. By analyzing the co-expression network in TC tissues, we found that CHIP and Oct4 expression exhibited a negative correlation. Functional experiments showed that CHIP knockdown promoted the stemness of TC cells, while CHIP overexpression reduced the stemness of TC spheroids formed by TC cells, in which CHIP expression was significantly decreased. Furthermore, CHIP had no effect on TC cell viability. Mechanistic studies revealed that CHIP directly interacted with Oct4 protein and induced Oct4 ubiquitination, whereas a catalytic CHIP mutant (H260Q) did not. And CHIP regulated the stemness of TC cells in an Oct4-dependent manner. Overall, this work indicates that the CHIP/Oct4 axis is essential for TC cell stemness.

CHIP and BAP1 Act in Concert to Regulate INO80 Ubiquitination and Stability for DNA Replication

The INO80 chromatin remodeling complex has roles in many essential cellular processes, including DNA replication. However, the mechanisms that regulate INO80 in these processes remain largely unknown. We previously reported that the stability of Ino80, the catalytic ATPase subunit of INO80, is regulated by the ubiquitin proteasome system and that BRCA1-associated protein-1 (BAP1), a nuclear deubiquitinase with tumor suppressor activity, stabilizes Ino80 via deubiquitination and promotes replication fork progression. However, the E3 ubiquitin ligase that targets Ino80 for proteasomal degradation was unknown. Here, we identified the C-terminus of Hsp70-interacting protein (CHIP), the E3 ubiquitin ligase that functions in cooperation with Hsp70, as an Ino80-interacting protein. CHIP polyubiquitinates Ino80 in a manner dependent on Hsp70. Contrary to our expectation that CHIP degrades Ino80, CHIP instead stabilizes Ino80 by extending its halflife. The data suggest that CHIP stabilizes Ino80 by inhibiting degradative ubiquitination. We also show that CHIP works together with BAP1 to enhance the stabilization of Ino80, leading to its chromatin binding. Interestingly, both depletion and overexpression of CHIP compromise replication fork progression with little effect on fork stalling, as similarly observed for BAP1 and Ino80, indicating that an optimal cellular level of Ino80 is important for replication fork speed but not for replication stress suppression. This work therefore idenitifes CHIP as an E3 ubiquitin ligase that stabilizes Ino80 via nondegradative ubiquitination and suggests that CHIP and BAP1 act in concert to regulate Ino80 ubiquitination to fine-tune its stability for efficient DNA replication.

DAXX in cancer: phenomena, processes, mechanisms and regulation

DAXX displays complex biological functions. Remarkably, DAXX overexpression is a common feature in diverse cancers, which correlates with tumorigenesis, disease progression and treatment resistance. Structurally, DAXX is modular with an N-terminal helical bundle, a docking site for many DAXX interactors (e.g. p53 and ATRX). DAXX's central region folds with the H3.3/H4 dimer, providing a H3.3-specific chaperoning function. DAXX has two functionally critical SUMO-interacting motifs. These modules are connected by disordered regions. DAXX's structural features provide a framework for deciphering how DAXX mechanistically imparts its functions and how its activity is regulated. DAXX modulates transcription through binding to transcription factors, epigenetic modifiers, and chromatin remodelers. DAXX's localization in the PML nuclear bodies also plays roles in transcriptional regulation. DAXX-regulated genes are likely important effectors of its biological functions. Deposition of H3.3 and its interactions with epigenetic modifiers are likely key events for DAXX to regulate transcription, DNA repair, and viral infection. Interactions between DAXX and its partners directly impact apoptosis and cell signaling. DAXX's activity is regulated by posttranslational modifications and ubiquitin-dependent degradation. Notably, the tumor suppressor SPOP promotes DAXX degradation in phase-separated droplets. We summarize here our current understanding of DAXX's complex functions with a focus on how it promotes oncogenesis.

Inhibition of apoptosis via CHIP-mediated proteasomal degradation of TAp73α

TAp73, a homologous of tumor suppressor p53, regulates apoptosis in a p53-independent manner and its suppressive as well as stimulatory role in promoting angiogenesis has been reported. It exists in multiple isoforms which varies structurally in their N-terminus and C-terminus region and crucial interplay among them guides the decision of cell survival and death. As molecular chaperones control both stability and degradation of TAp73, selective regulation of p73 isoforms has implication upon developing new therapeutic for hypoxic tumor. We have discovered that under DNA damage carboxy terminus Hsp70 interacting protein (CHIP's) antiapoptotic function is displayed via its E3 ligase activity that inhibits exclusively TAp73α-mediated apoptosis in cancer cell. The decrease in TAp73α level by CHIP as it is supported by increased ubiquitination pattern is reverted back by sh-CHIP. Further, the transactivation of p53-downstream apoptotic genes BAX, PUMA and PIG3 by TAp73α is also shown to be subsequently inhibited by CHIP. The tetratricopeptide TPR-domain of CHIP in its amino-terminus interacts with the carboxy-terminus of TAp73α and ΔNp73α and as a result, U-BOX domain of CHIP in the carboxy-terminus is able to ubiquitinate TAp73α for proteasomal degradation. Due to lack of C-terminus in TAp73β, CHIP fails to interact with and degrade it. In conclusion, we have thus uncovered for the first time a novel mechanism of chaperone-assisted regulation of p73 stability as well as its apoptotic functions by CHIP that might be utilized to develop new anticancer strategies.

Syntaphilin Ubiquitination Regulates Mitochondrial Dynamics and Tumor Cell Movements

Syntaphilin (SNPH) inhibits the movement of mitochondria in tumor cells, preventing their accumulation at the cortical cytoskeleton and limiting the bioenergetics of cell motility and invasion. Although this may suppress metastasis, the regulation of the SNPH pathway is not well understood. Using a global proteomics screen, we show that SNPH associates with multiple regulators of ubiquitin-dependent responses and is ubiquitinated by the E3 ligase CHIP (or STUB1) on Lys111 and Lys153 in the microtubule-binding domain. SNPH ubiquitination did not result in protein degradation, but instead anchored SNPH on tubulin to inhibit mitochondrial motility and cycles of organelle fusion and fission, that is dynamics. Expression of ubiquitination-defective SNPH mutant Lys111→Arg or Lys153→Arg increased the speed and distance traveled by mitochondria, repositioned mitochondria to the cortical cytoskeleton, and supported heightened tumor chemotaxis, invasion, and metastasis in vivo Interference with SNPH ubiquitination activated mitochondrial dynamics, resulting in increased recruitment of the fission regulator dynamin-related protein-1 (Drp1) to mitochondria and Drp1-dependent tumor cell motility. These data uncover nondegradative ubiquitination of SNPH as a key regulator of mitochondrial trafficking and tumor cell motility and invasion. In this way, SNPH may function as a unique, ubiquitination-regulated suppressor of metastasis.Significance: These findings reveal a new mechanism of metastasis suppression by establishing the role of SNPH ubiquitination in inhibiting mitochondrial dynamics, chemotaxis, and metastasis. Cancer Res; 78(15); 4215-28. ©2018 AACR.

Metformin pharmacogenomics: a genome-wide association study to identify genetic and epigenetic biomarkers involved in metformin anticancer response using human lymphoblastoid cell lines

Metformin is currently considered as a promising anticancer agent in addition to its anti-diabetic effect. To better individualize metformin therapy and explore novel molecular mechanisms in cancer treatment, we conducted a pharmacogenomic study using 266 lymphoblastoid cell lines (LCLs). Metformin cytotoxicity assay was performed using the MTS assay. Genome-wide association (GWA) analyses were performed in LCLs using 1.3 million SNPs, 485k DNA methylation probes, 54k mRNA expression probe sets, and metformin cytotoxicity (IC50s). Top candidate genes were functionally validated using siRNA screening, followed by MTS assay in breast cancer cell lines. Further study of one top candidate, STUB1, was performed to elucidate the mechanisms by which STUB1 might contribute to metformin action. GWA analyses in LCLs identified 198 mRNA expression probe sets, 12 SNP loci, and 5 DNA methylation loci associated with metformin IC50 with P-values <10−4 or <10−5. Integrated SNP/methylation loci-expression-IC50 analyses found 3 SNP loci or 5 DNA methylation loci associated with metformin IC50 through trans-regulation of expression of 11 or 26 genes with P-value <10−4. Functional validation of top 61 candidate genes in 4 IPA networks indicated down regulation of 14 genes significantly altered metformin sensitivity in two breast cancer cell lines. Mechanistic studies revealed that the E3 ubiquitin ligase, STUB1, could influence metformin response by facilitating proteasome-mediated degradation of cyclin A. GWAS using a genomic data-enriched LCL model system, together with functional and mechanistic studies using cancer cell lines, help us to identify novel genetic and epigenetic biomarkers involved in metformin anticancer response.

CHIP: A new modulator of human malignant disorders

Carboxyl terminus of Hsc70-interacting protein (CHIP) is known as a chaperone-associated E3 for a variety of protein substrates. It acts as a link between molecular chaperones and ubiquitin-proteasome system. Involved in the process of protein clearance, CHIP plays a critical role in maintaining protein homeostasis in diverse conditions. Here, we provide a comprehensive review of our current understanding of CHIP and summarize recent advances in CHIP biology, with a focus on CHIP in the setting of malignancies.

Essential Roles of E3 Ubiquitin Ligases in p53 Regulation

The ubiquitination pathway and proteasomal degradation machinery dominantly regulate p53 tumor suppressor protein stability, localization, and functions in both normal and cancerous cells. Selective E3 ubiquitin ligases dominantly regulate protein levels and activities of p53 in a large range of physiological conditions and in response to cellular changes induced by exogenous and endogenous stresses. The regulation of p53’s functions by E3 ubiquitin ligases is a complex process that can lead to positive or negative regulation of p53 protein in a context- and cell type-dependent manner. Accessory proteins bind and modulate E3 ubiquitin ligases, adding yet another layer of regulatory control for p53 and its downstream functions. This review provides a comprehensive understanding of p53 regulation by selective E3 ubiquitin ligases and their potential to be considered as a new class of biomarkers and therapeutic targets in diverse types of cancers.

Regulation of autophagic flux by CHIP

Autophagy is a major degradation system which processes substrates through the steps of autophagosome formation, autophagosome-lysosome fusion, and substrate degradation. Aberrant autophagic flux is present in many pathological conditions including neurodegeneration and tumors. CHIP/STUB1, an E3 ligase, plays an important role in neurodegeneration. In this study, we identified the regulation of autophagic flux by CHIP (carboxy-terminus of Hsc70-interacting protein). Knockdown of CHIP induced autophagosome formation through increasing the PTEN protein level and decreasing the AKT/mTOR activity as well as decreasing phosphorylation of ULK1 on Ser757. However, degradation of the autophagic substrate p62 was disturbed by knockdown of CHIP, suggesting an abnormality of autophagic flux. Furthermore, knockdown of CHIP increased the susceptibility of cells to autophagic cell death induced by bafilomycin A1. Thus, our data suggest that CHIP plays roles in the regulation of autophagic flux.

Lafora disease proteins laforin and malin negatively regulate the HIPK2-p53 cell death pathway

Lafora disease (LD) is an autosomal recessive, progressive, and fatal form of a neurodegenerative disorder characterized by the presence of Lafora polyglucosan bodies. LD is caused by defects in either the laforin protein phosphatase or the malin E3 ubiquitin ligase. Laforin and malin were shown play key roles in proteolytic processes, unfolded stress response, and glycogen metabolism. Therefore, the LD proteins laforin and malin are thought to function as pro-survival factors and their loss thus could result in neurodegeneration. To understand the molecular pathway leading to the cell death in LD, in the present study, we investigated the possible role of LD proteins in the p53-mediated cell death pathway. We show that loss of laforin or malin results in the increased level and activity of p53, both in cellular and animal models of LD, and that this is primarily due to the increased levels of Hipk2, a proapoptotic activator of p53. Overexpression of laforin or malin confers protection against Hipk2-mediated cell death by targeting the Hipk2 to the cytoplasmic compartment. Taken together, our study strengthens the notion that laforin and malin are pro-survival factors, and that the activation of Hipk2-p53 cell death pathway might underlie neurodegeneration in LD.

Emerging evidence of coding mutations in the ubiquitin-proteasome system associated with cerebellar ataxias

Cerebellar ataxia (CA) is a disorder associated with impairments in balance, coordination, and gait caused by degeneration of the cerebellum. The mutations associated with CA affect functionally diverse genes; furthermore, the underlying genetic basis of a given CA is unknown in many patients. Exome sequencing has emerged as a cost-effective technology to discover novel genetic mutations, including autosomal recessive CA (ARCA). Five recent studies that describe how exome sequencing performed on a diverse pool of ARCA patients revealed 14 unique mutations in STUB1, a gene that encodes carboxy terminus of Hsp70-interacting protein (CHIP). CHIP mediates protein quality control through chaperone and ubiquitin ligase activities and is implicated in alleviating proteotoxicity in several neurodegenerative diseases. However, these recent studies linking STUB1 mutations to various forms of ataxia are the first indications that CHIP is directly involved in the progression of a human disease. Similar exome-sequencing studies have revealed novel mutations in ubiquitin-related proteins associated with CA and other neurological disorders. This review provides an overview of CA, describes the benefits and limitations of exome sequencing, outlines newly discovered STUB1 mutations, and theorizes on how CHIP and other ubiquitin-related proteins function to prevent neurological deterioration.

Verbascoside promotes apoptosis by regulating HIPK2-p53 signaling in human colorectal cancer

Background

We investigated the role of the HIPK2–p53 signaling pathway in tumorigenesis and resistance to the drug Verbascoside (VB) in colorectal cancer (CRC), using in vivo and in vitro experiments.

Methods

Primary human CRC samples and normal intestinal tissues from patients were analyzed for HIPK2 expression by immunohistochemistry (IHC) and its expression was correlated against patients’ clinicopathological characteristics. Human CRC HCT-116 cells were implanted in BALB/c nude mice; mice with xenografted tumors were randomly administrated vehicle (control), 20, 40, or 80 mg/mL VB, or 1 mg/mL fluorouracil (5-FU). HIPK2, p53, Bax, and Bcl-2 expression in these tumors were determined by IHC. In vitro effects of VB on CRC cell proliferation and apoptosis were measured by CCK-8 assay and flow cytometry; HIPK2, p53, p-p53, Bax, and Bcl-2 were measured by western blot.

Results

IHC analysis for 100 human CRC tumor samples and 20 normal intestinal tissues, showed HIPK2 expression to inversely correlate with Dukes stage and depth of invasion in CRC (P < 0.05). In vivo, the inhibition rates of 20, 40, and 80 mg/mL VB on CRC xenograft tumor weight were 42.79%, 53.90%, and 60.99%, respectively, and were accompanied by increased expression of HIPK2, p53, and Bax, and decreased Bcl-2 expression in treated tumors. In vitro, VB significantly inhibited proliferation of CRC cell lines HCT-116, HT-29, LoVo, and SW620, in a time- and dose-dependent manner. The apoptosis rates of 25, 50, and 100 μM VB on HCT-116 cells were 10.83 ± 1.28, 11.25 ± 1.54, and 20.19 ± 2.87%, and on HT-29 cells were 18.92 ± 6.12, 21.57 ± 4.05, and 25.14 ± 6.73%, respectively. In summary, VB treatment significantly enhanced the protein expression of pro-apoptotic HIPK2, p53, p-p53, Bax, and decreased anti-apoptotic Bcl-2 expression in CRC cells.

Conclusions

HIPK2 protein modulates the phosphorylation status of p53, and levels of Bax and Bcl-2 in CRC. We also found that VB effectively activated the HIPK2–p53 signaling pathway, resulting in increased CRC cell apoptosis.

The ubiquitin ligase CHIP prevents SirT6 degradation through noncanonical ubiquitination

The ubiquitin ligase CHIP (carboxyl terminus of Hsp70-interacting protein) regulates protein quality control, and CHIP deletion accelerates aging and reduces the life span in mice. Here, we reveal a mechanism for CHIP's influence on longevity by demonstrating that CHIP stabilizes the sirtuin family member SirT6, a lysine deacetylase/ADP ribosylase involved in DNA repair, metabolism, and longevity. In CHIP-deficient cells, SirT6 protein half-life is substantially reduced due to increased proteasome-mediated degradation, but CHIP overexpression in these cells increases SirT6 protein expression without affecting SirT6 transcription. CHIP noncanonically ubiquitinates SirT6 at K170, which stabilizes SirT6 and prevents SirT6 canonical ubiquitination by other ubiquitin ligases. In CHIP-depleted cells, SirT6 K170 mutation increases SirT6 half-life and prevents proteasome-mediated degradation. The global decrease in SirT6 expression in the absence of CHIP is associated with decreased SirT6 promoter occupancy, which increases histone acetylation and promotes downstream gene transcription in CHIP-depleted cells. Cells lacking CHIP are hypersensitive to DNA-damaging agents, but DNA repair and cell viability are rescued by enforced expression of SirT6. The discovery of this CHIP-SirT6 interaction represents a novel protein-stabilizing mechanism and defines an intersection between protein quality control and epigenetic regulation to influence pathways that regulate the biology of aging.

Expression of carboxyl terminus of Hsp70-interacting protein (CHIP) indicates poor prognosis in human gallbladder carcinoma

Gallbladder carcinoma (GBC) is a lethal neoplasm, and new prognostic markers are required. Deregulation of E3 ligases contributes to cancer development and is associated with poor prognosis. Carboxyl terminus of heat shock protein 70-interacting protein (CHIP) is a U-box-type E3 ubiquitin ligase, the role of which has not been evaluated in GBC. Therefore, the present study investigated CHIP expression in GBC and its prognostic significance. In the present study, CHIP expression was measured in 78 tumor specimens of GBC by immunohistochemistry and the correlation between CHIP expression and clinicopathological factors was analyzed. Of the tumor specimens, 26.9% showed high staining intensity [the CHIP high expression group (HEG)]. The CHIP-HEG was not associated with other common clinicopathological parameters, including T stage, and lymph node and distant metastases. CHIP-HEG patients had a significantly worse prognosis than patients with low CHIP expression with median cancer-specific survival times of 8.0 months (range, 1-34 months) and 13.0 months (range, 1-110 months), respectively (P=0.023). Multivariate analyses showed that CHIP expression was close to being an independent risk factor for predicting patient survival. CHIP expression may be associated with a poor prognosis in GBC. Since CHIP is not associated with other clinicopathological prognostic factors, it may serve as an ideal molecular marker for predicting patient outcomes.

Decreased expression of the carboxyl terminus of heat shock cognate 70 interacting protein in human gastric cancer and its clinical significance

The carboxyl terminus of heat shock cognate 70 interacting protein (CHIP) is an E3 ubiquitin ligase, which can promote ubiquitylation and degradation of many tumor-related proteins. However, the expression of CHIP in human gastric cancer has not been investigated. In this study, the mRNA and protein levels of CHIP expression in 53 cases of gastric cancer and matched normal tissues were determined by quantitative real-time PCR, western blotting and immunohistochemistry. We showed that CHIP was registered from basal to middle portions of normal gastric mucosa. CHIP expression was notably decreased or lost in human gastric cancer samples compared with the matched normal non-cancer samples. The correlations between CHIP downregulation and the clinicopathological characteristics were also evaluated. The expression of CHIP was significantly lower in the gastric cancer samples compared to the matched normal samples at both mRNA and protein levels (P<0.05 and P<0.05, respectively). More importantly, the downregulation of CHIP was correlated with TNM stage (P=0.048) and lymph node metastasis (P=0.010) at the mRNA levels. In addition, the downregulation of CHIP was correlated with lymph node metastasis (P=0.021) and tumor differentiation (P=0.009) at the protein levels. Taken together, at both mRNA and protein levels, the decreased expression of CHIP was correlated with lymph node metastasis. Furthermore, our study suggests that a negative correlation exists between CHIP expression and tumor malignancy in human gastric cancer.

Haploinsufficiency of the E3 ubiquitin ligase C-terminus of heat shock cognate 70 interacting protein (CHIP) produces specific behavioral impairments

The multifunctional E3 ubiquitin ligase CHIP is an essential interacting partner of HSP70, which together promote the proteasomal degradation of client proteins. Acute CHIP overexpression provides neuroprotection against neurotoxic mitochondrial stress, glucocorticoids, and accumulation of toxic amyloid fragments, as well as genetic mutations in other E3 ligases, which have been shown to result in familial Parkinson's disease. These studies have created a great deal of interest in understanding CHIP activity, expression and modulation. While CHIP knockout mice have the potential to provide essential insights into the molecular control of cell fate and survival, the animals have been difficult to characterize in vivo due to severe phenotypic and behavioral dysfunction, which have thus far been poorly characterized. Therefore, in the present study we conducted a battery of neurobehavioral and physiological assays of adult CHIP heterozygotic (HET) mutant mice to provide a better understanding of the functional consequence of CHIP deficiency. We found that CHIP HET mice had normal body and brain weight, body temperature, muscle tone and breathing patterns, but do have a significant elevation in baseline heart rate. Meanwhile basic behavioral screens of sensory, motor, emotional and cognitive functions were normative. We observed no alterations in performance in the elevated plus maze, light-dark preference and tail suspension assays, or two simple cognitive tasks: novel object recognition and spontaneous alternation in a Y maze. Significant deficits were found, however, when CHIP HET mice performed wire hang, inverted screen, wire maneuver, and open field tasks. Taken together, our data indicate a clear subset of behaviors that are altered at baseline in CHIP deficient animals, which will further guide whole animal studies of the effects of CHIP dysregulation on cardiac function, brain circuitry and function, and responsiveness to environmental and cellular stress.

Ubc13 and COOH terminus of Hsp70-interacting protein (CHIP) are required for growth hormone receptor endocytosis

Growth hormone receptor (GHR) endocytosis is a highly regulated process that depends on the binding and activity of the multimeric ubiquitin ligase, SCF(βTrCP) (Skp Cullin F-box). Despite a specific interaction between β-transducin repeat-containing protein (βTrCP) and the GHR, and a strict requirement for ubiquitination activity, the receptor is not an obligatory target for SCF(βTrCP)-directed Lys(48) polyubiquitination. We now show that also Lys(63)-linked ubiquitin chain formation is required for GHR endocytosis. We identified both the ubiquitin-conjugating enzyme Ubc13 and the ubiquitin ligase COOH terminus of Hsp70 interacting protein (CHIP) as being connected to this process. Ubc13 activity and its interaction with CHIP precede endocytosis of GHR. In addition to βTrCP, CHIP interacts specifically with the cytosolic tails of the dimeric GHR, identifying both Ubc13 and CHIP as novel factors in the regulation of cell surface availability of GHR.

The chaperone-assisted E3 ligase C terminus of Hsc70-interacting protein (CHIP) targets PTEN for proteasomal degradation

The tumor suppressor, PTEN is key to the regulation of diverse cellular processes, making it a prime candidate to be tightly regulated. The PTEN level is controlled in a major way by E3 ligase-mediated degradation through the Ubiquitin-Proteasome System (UPS). Nedd 4-1, XIAP, and WWP2 have been shown to maintain PTEN turnover. Here, we report that CHIP, the chaperone-associated E3 ligase, induces ubiquitination and regulates the proteasomal turnover of PTEN. It was apparent from our findings that PTEN transiently associates with the molecular chaperones and thereby gets diverted to the degradation pathway through its interaction with CHIP. The TPR domain of CHIP and parts of the N-terminal domain of PTEN are required for their interaction. Overexpression of CHIP leads to elevated ubiquitination and a shortened half-life of endogenous PTEN. On the other hand, depletion of endogenous CHIP stabilizes PTEN. CHIP is also shown to regulate PTEN-dependent transcription presumably through its down-regulation. PTEN shared an inverse correlation with CHIP in human prostate cancer patient samples, thereby triggering the prospects of a more complex mode of PTEN regulation in cancer.

Death-associated protein 6 (Daxx) mediates cAMP-dependent stimulation of Cyp11a1 (P450scc) transcription

SF-1 is a key transcription factor for all steroidogenic genes. It up-regulates the expression of the steroidogenic Cyp11a1 gene in the adrenal in a pathway stimulated by cAMP through HIPK3-mediated JNK/c-Jun phosphorylation. In the present study, we have investigated the factors mediating cAMP-dependent HIPK3 action to potentiate the activity of SF-1 for Cyp11a1 transcription in mouse adrenocortical Y1 cells. We found Daxx, a HIPK kinase substrate in the apoptosis pathway, was phosphorylated by HIPK3 at Ser-669 in response to cAMP stimulation. Daxx participated in SF-1-dependent Cyp11a1 expression as shown by experiments involving both overexpression and down-regulation via a dominant negative Daxx mutant. The S669A mutant of Daxx, which could not be phosphorylated by HIPK3, lost the ability to potentiate SF-1 activity for Cyp11a1 expression. The enhancement of SF-1 activity by Daxx required JNK and c-Jun phosphorylation. Thus, Daxx functioned as a signal transducer linking cAMP-stimulated HIPK3 activity with JNK/c-Jun phosphorylation and SF-1-dependent Cyp11a1 transcription for steroid synthesis.

Carboxyl terminus of Hsp70-interacting protein (CHIP) contributes to human glioma oncogenesis

Malignant glioma is the most common adult primary brain tumor, and the mechanism of its oncogenesis is poorly understood. Growing evidence has shown that E3 ubiquitin ligases can promote tumorgenesis of glioma. CHIP is an E3 ubiquitin ligase that can induce ubiquitylation and degradation of many tumor-related proteins, and it has been reported to act as an upstream regulator in breast cancer; however, its role in human gliomas has not been evaluated yet. In this study, the expression of CHIP in glioma tissues was studied using immunohistochemistry. CHIP expression in glioma cells was studied by real-time RT-PCR, western blot and double immunofluorescence staining. The role of CHIP in glioma oncogenesis was investigated by lentivirus-mediated RNA interference (RNAi) and overexpression in vitro and in vivo. We showed CHIP expression in glioma samples was related to tumor grades, with stronger staining in high-grade gliomas than in low-grade gliomas. Knocking down of CHIP suppressed proliferation, colony formation of U251 and U87 glioma cells, while overexpression of CHIP resulted in enhanced proliferation and colony formation in vitro. In a nude mouse xenograft model, intratumoral injection of CHIP RNAi lentivirus significantly delayed tumor growth. In contrast, overexpression of CHIP resulted in enhanced tumor growth in vivo. After CHIP RNAi, both survivin mRNA and protein were decreased, while CHIP overexpression induced increased mRNA and protein levels of survivin. This is the first study demonstrating CHIP contributes to oncogenesis of glioma.

Docking-dependent ubiquitination of the interferon regulatory factor-1 tumor suppressor protein by the ubiquitin ligase CHIP

Characteristically for a regulatory protein, the IRF-1 tumor suppressor turns over rapidly with a half-life of between 20-40 min. This allows IRF-1 to reach new steady state protein levels swiftly in response to changing environmental conditions. Whereas CHIP (C terminus of Hsc70-interacting protein), appears to chaperone IRF-1 in unstressed cells, formation of a stable IRF-1·CHIP complex is seen under specific stress conditions. Complex formation, in heat- or heavy metal-treated cells, is accompanied by a decrease in IRF-1 steady state levels and an increase in IRF-1 ubiquitination. CHIP binds directly to an intrinsically disordered domain in the central region of IRF-1 (residues 106-140), and this site is sufficient to form a stable complex with CHIP in cells and to compete in trans with full-length IRF-1, leading to a reduction in its ubiquitination. The study reveals a complex relationship between CHIP and IRF-1 and highlights the role that direct binding or "docking" of CHIP to its substrate(s) can play in its mechanism of action as an E3 ligase.

Daxx is reciprocally regulated by Mdm2 and Hausp

Daxx is a multifunctional protein, regulating a wide range of important functions including apoptosis and transcription. However, the way Daxx is regulated is poorly understood. In our previous studies, we have found that Daxx forms a complex with the E3 ubiquitin ligase Mdm2 and the de-ubiquitinase Hausp. In the present work, we show that Daxx is ubiquitinated by Mdm2 in both in vitro and in vivo systems and Mdm2 reduces Daxx expression upon over-expression. We further demonstrate that Hausp critically controls the cellular level of Daxx most likely by inducing Daxx de-ubiquitination. These results reveal Mdm2 and Hausp as important regulators for Daxx functions by controlling Daxx ubiquitination and stability.

Correlations and co-localizations of Hsp70 with XPA, XPG in human bronchial epithelia cells exposed to benzo[a]pyrene

Benzo[a]pyrene (BaP) is a ubiquitously distributed environmental pollutant known to cause DNA damage, which may be repaired through nucleotide excision repair (NER). The significantly negative correlation between Hsp70 levels and the level of DNA damage in workers exposed to coke oven emission had been found. However, little is known about how Hsp70 modulate the DNA repair process. In a series of experiments using the human bronchial epithelia cells (16HBE) exposed to different concentrations of BaP for 24h, we measured expression of NER subunit xeroderma pigmentosum (XP) group A, C, F, G (XPA, XPC, XPF, XPG), excision repair cross-complementing 1 (ERCC1) and Hsp70, and analyzed their possible correlations. Co-localizations of Hsp70 with NER subunit were detected by confocal microscope. We found that in vitro exposure to BaP reduced cell viability in a dose-dependent manner ranging from 2 to 64 microM. Our results showed that levels of XPA, XPG and Hsp70 significantly increased at cells exposed to 1 or 2muM BaP. In addition, curve estimation showed there was a significant correlation between relative ratios of Hsp70 and XPA, XPG in cells exposed to different concentrations of BaP. Moreover, confocal microscopy demonstrated increased co-localization of Hsp70 with XPA, XPG in nuclei of cells exposed to BaP. These results suggested that Hsp70 might play a role in nucleotide excision repair. However, the mechanisms underlying this observation need further investigation.