cDNA cloning and functional analysis of p28 (Nas6p) and p40.5 (Nas7p), two novel regulatory subunits of the 26S proteasome

Identification of molecular signatures defines the differential proteostasis response in induced spinal and cranial motor neurons

Amyotrophic lateral sclerosis damages proteostasis, affecting spinal and upper motor neurons earlier than a subset of cranial motor neurons. To aid disease understanding, we exposed induced cranial and spinal motor neurons (iCrMNs and iSpMNs) to proteotoxic stress, under which iCrMNs showed superior survival, quantifying the transcriptome and proteome for >8,200 genes at 0, 12, and 36 h. Two-thirds of the proteome showed cell-type differences. iSpMN-enriched proteins related to DNA/RNA metabolism, and iCrMN-enriched proteins acted in the endoplasmic reticulum (ER)/ER chaperone complex, tRNA aminoacylation, mitochondria, and the plasma/synaptic membrane, suggesting that iCrMNs expressed higher levels of proteins supporting proteostasis and neuronal function. When investigating the increased proteasome levels in iCrMNs, we showed that the activity of the 26S proteasome, but not of the 20S proteasome, was higher in iCrMNs than in iSpMNs, even after a stress-induced decrease. We identified Ublcp1 as an iCrMN-specific regulator of the nuclear 26S activity.

Small-Molecule Gankyrin Inhibition as a Therapeutic Strategy for Breast and Lung Cancer

Gankyrin is an oncoprotein responsible for the development of numerous cancer types. It regulates the expression levels of multiple tumor suppressor proteins (TSPs) in liver cancer; however, gankyrin's regulation of these TSPs in breast and lung cancers has not been thoroughly investigated. Additionally, no small-molecule gankyrin inhibitor has been developed which demonstrates potent anti-proliferative activity against gankyrin overexpressing breast and lung cancers. Herein, we are reporting the structure-based design of gankyrin-binding small molecules which potently inhibited the proliferation of gankyrin overexpressing A549 and MDA-MB-231 cancer cells, reduced colony formation, and inhibited the growth of 3D spheroids in an in vitro tumor simulation model. Investigations demonstrated that gankyrin inhibition occurs through either stabilization or destabilization of its 3D structure. These studies shed light on the mechanism of small-molecule inhibition of gankyrin and demonstrate that gankyrin is a viable therapeutic target for the treatment of breast and lung cancer.

Identification of Tumor-Suppressive miR-30e-3p Targets: Involvement of SERPINE1 in the Molecular Pathogenesis of Head and Neck Squamous Cell Carcinoma

Recently, our studies revealed that some passenger strands of microRNAs (miRNAs) were closely involved in cancer pathogenesis. Analysis of miRNA expression signatures showed that the expression of miR-30e-3p (the passenger strand of pre-miR-30e) was significantly downregulated in cancer tissues. In this study, we focused on miR-30e-3p (the passenger strand of pre-miR-30e). We addressed target genes controlled by miR-30e-3p that were closely associated with the molecular pathogenesis of head and neck squamous cell carcinoma (HNSCC). Ectopic expression assays demonstrated that the expression of miR-30e-3p attenuated cancer cell malignant phenotypes (e.g., cell proliferation, migration, and invasive abilities). Our analysis of miR-30e-3p targets revealed that 11 genes (ADA, CPNE8, C14orf126, ERGIC2, HMGA2, PLS3, PSMD10, RALB, SERPINE1, SFXN1, and TMEM87B) were expressed at high levels in HNSCC patients. Moreover, they significantly predicted the short survival of HNSCC patients based on 5-year overall survival rates (p < 0.05) in The Cancer Genome Atlas (TCGA). Among these targets, SERPINE1 was found to be an independent prognostic factor for patient survival (multivariate Cox regression; hazard ratio = 1.6078, p < 0.05). Aberrant expression of SERPINE1 was observed in HNSCC clinical samples by immunohistochemical analysis. Functional assays by targeting SERPINE1 expression revealed that the malignant phenotypes (e.g., proliferation, migration, and invasion abilities) of HNSCC cells were suppressed by the silencing of SERPINE1 expression. Our miRNA-based approach will accelerate our understanding of the molecular pathogenesis of HNSCC.

A druggable pocket on PSMD10Gankyrin that can accommodate an interface peptide and doxorubicin

BACKGROUND

PSMD10Gankyrin, a proteasomal chaperone is also an oncoprotein. Overexpression of PSMD10Gankyrin is associated with poor prognosis and survival in many cancers. Therefore, PSMD10Gankyrin is a sought-after drug target in many hard-to-treat cancers. However, its surface appears flat and undruggable. Here, we build on our earlier discovery of a common hot spot region that defined the interface of multiple interacting partners of PSMD10Gankyrin to expose vulnerable spots for a peptide and a small molecule inhibitor.

METHODS

High throughput virtual screening was used to screen compounds against PSMD10Gankyrin. Interaction of PSMD10Gankyrin with the drug or protein (CLIC1) or peptide was studied using any one or more of these techniques; Microscale Thermophoresis, limited trypsinolysis, SPR and ITC. Cytotoxic effect of doxorubicin was evaluated using MTT assay.

RESULTS

We identified doxorubicin as the first-generation small molecule inhibitor of PSMD10Gankyrin. K116 and to a lesser extent R41 on PSMD10Gankyrin contribute to the bulk of binding energy for the peptide EEVD, CLIC1 and doxorubicin. We further demonstrate that PSMD10Gankyrin is an intended target for doxorubicin in cells.

GENERAL SIGNIFICANCE

Drug design against protein interactions in general and PSMD10Gankyrin in particular, remains a challenge. We provide consolidated biophysical evidence for the use of a shared interface motif EEVD as a possible inhibitor of interaction network in cancers driven by PSMD10Gankyrin. We identify a chemical scaffold for designing novel inhibitors of PSMD10Gankyrin. These findings will impact the field of protein interactions in the context of disease biology/drug discovery.

Case Report: Contiguous Xq22.3 Deletion Associated with ATS-ID Syndrome: From Genotype to Further Delineation of the Phenotype

Alport syndrome with intellectual disability (ATS-ID, AMME complex; OMIM #300194) is an X-linked contiguous gene deletion syndrome associated with an Xq22.3 locus mainly characterized by hematuria, renal failure, hearing loss/deafness, neurodevelopmental disorder (NDD), midface retrusion, and elliptocytosis. It is thought that ATS-ID is caused by the loss of function of COL4A5 (ATS) and FACL4 (ACSL4) genes through the interstitial (micro)deletion of chromosomal band Xq22.3. We report detailed phenotypic description and results from genome-wide screening of a Czech family with diagnosis ATS-ID (proband, maternal uncle, and two female carriers). Female carriers showed mild clinical features of microscopic hematuria only, while affected males displayed several novel clinical features associated with ATS-ID. Utilization of whole-exome sequencing discovered the presence of approximately 3 Mb of deletion in the Xq23 area, which affected 19 genes from TSC22D3 to CHRDL1. We compared the clinical phenotype with previously reported three ATS-ID families worldwide and correlated their clinical manifestations with the incidence of genes in both telomeric and centromeric regions of the deleted chromosomal area. In addition to previously described phenotypes associated with aberrations in AMMECR1 and FACL4, we identified two genes, members of tripartite motif family MID2 and subunit of the proteasome PA700/19S complex (PSMD10), respectively, as prime candidate genes responsible for additional clinical features observed in our patients with ATS-ID. Overall, our findings further improve the knowledge about the clinical impact of Xq23 deletions and bring novel information about phenotype/genotype association of this chromosomal aberration.

Genetically incorporated crosslinkers reveal NleE attenuates host autophagy dependent on PSMD10

Autophagy acts as a pivotal innate immune response against infection. Some virulence effectors subvert the host autophagic machinery to escape the surveillance of autophagy. The mechanism by which pathogens interact with host autophagy remains mostly unclear. However, traditional strategies often have difficulty identifying host proteins that interact with effectors due to the weak, dynamic, and transient nature of these interactions. Here, we found that Enteropathogenic Escherichia coli (EPEC) regulates autophagosome formation in host cells dependent on effector NleE. The 26S Proteasome Regulatory Subunit 10 (PSMD10) was identified as a direct interaction partner of NleE in living cells by employing genetically incorporated crosslinkers. Pairwise chemical crosslinking revealed that NleE interacts with the N-terminus of PSMD10. We demonstrated that PSMD10 homodimerization is necessary for its interaction with ATG7 and promotion of autophagy, but not necessary for PSMD10 interaction with ATG12. Therefore, NleE-mediated PSMD10 in monomeric state attenuates host autophagosome formation. Our study reveals the mechanism through which EPEC attenuates host autophagy activity.

Role of a 19S Proteasome Subunit- PSMD10Gankyrin in Neurogenesis of Human Neural Progenitor Cells

PSMD10^Gankyrin, a proteasome assembly chaperone, is a widely known oncoprotein which aspects many hall mark properties of cancer. However, except proteasome assembly chaperon function its role in normal cell function remains unknown. To address this issue, we induced PSMD10^Gankyrin overexpression in HEK293 cells and the resultant large-scale changes in gene expression profile were analyzed. We constituted networks from microarray data of these differentially expressed genes and carried out extensive topological analyses. The overrecurring yet consistent theme that appeared throughout analysis using varied network metrics is that all genes and interactions identified as important would be involved in neurogenesis and neuronal development. Intrigued we tested the possibility that PSMD10^Gankyrin may be strongly associated with cell fate decisions that commit neural stem cells to differentiate into neurons. Overexpression of PSMD10^Gankyrin in human neural progenitor cells facilitated neuronal differentiation via β-catenin Ngn1 pathway. Here for the first time we provide preliminary and yet compelling experimental evidence for the involvement of a potential oncoprotein – PSMD10^Gankyrin, in neuronal differentiation.

The Oncoprotein Gankyrin/PSMD10 as a Target of Cancer Therapy

Gankyrin (also called PSMD10, p28, or p28^GANK) is a crucial oncoprotein that is upregulated in various cancers and assumed to play pivotal roles in the initiation and progression of tumors. Although the in vitro function of gankyrin is relatively well characterized, its role in vivo remains to be elucidated. We have investigated the function of gankyrin in vivo by producing mice with liver parenchymal cell-specific gankyrin ablation (Alb-Cre;gankyrin^f/f) and gankyrin deletion both in liver parenchymal and in non-parenchymal cells (Mx1-Cre;gankyrin^f/f). Gankyrin deficiency both in non-parenchymal cells and parenchymal cells, but not in parenchymal cells alone, reduced STAT3 activity, interleukin-6 production, and cancer stem cell marker expression, leading to attenuated tumorigenic potential in the diethylnitrosamine hepatocarcinogenesis model. Essentially similar results were obtained by analyzing mice with intestinal epithelial cell-specific gankyrin ablation (Villin-Cre;Gankyrin^f/f) and gankyrin deletion both in myeloid and epithelial cells (Mx1-Cre;Gankyrin^f/f) in the colitis-associated cancer model. Clinically, gankyrin expression in the tumor microenvironment was negatively correlated with progression-free survival in patients undergoing treatment with Sorafenib for hepatocellular carcinomas. These findings indicate important roles played by gankyrin in non-parenchymal cells as well as parenchymal cells in the pathogenesis of liver cancers and colorectal cancers, and suggest that by acting both on cancer cells and on the tumor microenvironment, anti-gankyrin agents would be promising as therapeutic and preventive strategies against various cancers, and that an in vitro cell culture models that incorporate the effects of non-parenchymal cells and gankyrin would be useful for the study of human cell transformation.

Dysregulation of Nrf2 in Hepatocellular Carcinoma: Role in Cancer Progression and Chemoresistance

The liver executes versatile functions and is the chief organ for metabolism of toxicants/xenobiotics. Hepatocellular carcinoma (HCC) is the most common primary liver malignancy and the third foremost cause of cancer death worldwide. Oxidative stress is a key factor related with the development and progression of HCC. Nuclear factor erythroid 2 [NF-E2]-related factor 2 (Nrf2) is a cytosolic transcription factor, which regulates redox homeostasis by activating the expression of an array of antioxidant response element-dependent genes. Nrf2 displays conflicting roles in normal, healthy liver and HCC; in the former, Nrf2 offers beneficial effects, whereas in the latter it causes detrimental effects favouring the proliferation and survival of HCC. Sustained Nrf2 activation has been observed in HCC and facilitates its progression and aggressiveness. This review summarizes the role and mechanism(s) of action of Nrf2 dysregulation in HCC and therapeutic options that can be employed to modulate this transcription factor.

miR-214 regulates papillary thyroid carcinoma cell proliferation and metastasis by targeting PSMD10

MicroRNAs (miRNAs) have important effects on cancer occurrence and development by adjusting gene expression. The aim of the present study was to examine the role of miR-214 in papillary thyroid carcinoma cell proliferation and metastasis, and its molecular mechanisms. miR-214 was demonstrated to be markedly downregulated in papillary thyroid carcinoma tissues and cells compared with normal, and this was significantly associated with lymph node metastasis, tumor size and TNM stage. Upregulation of miR-214 significantly decreased cell proliferation, and promoted cell apoptosis and cell cycle arrest in papillary thyroid carcinoma cell lines in vitro. By contrast, downregulation of miR-214 resulted in the opposite effects. In addition, miR-214 mimics significantly decreased papillary thyroid carcinoma cell migration and invasion, which was correlated with decreased expression levels of matrix metallopeptidase (MMP)-2 and MMP-9. Restoration of miR-214 expression in papillary thyroid carcinoma cells decreased the activities associated with epithelial-mesenchymal transition (EMT). Furthermore, proteasome 26S subunit non-ATPase 10 (PSMD10) was predicted to be a target of miR-214. Experimental results demonstrated that miR-214 negatively regulated PSMD10 expression by targeting its 3′ untranslated region directly. Knockdown of PSMD10 reduced papillary thyroid carcinoma cell clone formation, migration and invasion, most likely by repressing glycogen synthase kinase (GSK)-3β/β-catenin and AKT signaling. Finally, a negative correlation was observed between the expression levels of miR-214 and PSMD10 in papillary thyroid carcinoma tissues. Taken together, these data suggested that miR-214 might be a candidate target for the treatment of papillary thyroid carcinoma.

Gankyrin: a novel promising therapeutic target for hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is known as fifth common malignancies and third common cause of cancer-related death worldwide. The identification of various mechanisms which are involved in hepatocarcinogenesis contributes in finding a variety of cellular and molecular targets for HCC diagnosis, prevention and therapy. Among various identified targets in HCC pathogenesis, Gankyrin is a crucial oncoprotein that is up-regulated in HCC and plays a pivotal role in the initiation and progression of the HCC. Oncogenic role of Gankyrin has been found to stem from inhibition of two ubiquitous tumour suppressor proteins, retinoblastoma protein (pRb) and P53, and also modulation of several vital cellular signalling pathways including Wnt/β-Catenin, NF-κB, STAT3/Akt, IL-1β/IRAK-1 and RhoA/ROCK. As a result, Gankyrin can be considered as a potential candidate for diagnosis and treatment of HCC. In this review, we summarized the physiological function and the significant role of Gankyrin as an important therapeutic target in HCC.

Inducible liver-specific overexpression of gankyrin in zebrafish results in spontaneous intrahepatic cholangiocarcinoma and hepatocellular carcinoma formation

Liver cancer is the second leading cause of death worldwide. As such, establishing animal models of the disease is important for both basic and translational studies that move toward developing new therapies. Gankyrin is a critical oncoprotein in the genetic control of liver pathology. In order to evaluate the oncogenic role of gankyrin without cancer cell inoculation and drug treatment, we overexpressed gankyrin under the control of the fabp10a promoter. A Tet-Off system was used to drive expression in hepatocytes. At seven to twelve months of age, gankyrin transgenic fish spontaneously incurred persistent hepatocyte damage, steatosis, cholestasis, cholangitis, fibrosis and hepatic tumors. The tumors were both hepatocellular carcinoma (HCC) and intrahepatic cholangiocarcinoma (ICC). ICC is the second most frequent primary liver cancer in human patients and the first to develop in this tumor model. We further investigated the role of complement C3, a central molecule of the complement system, and found the expression levels of both in mRNA and protein are decreased during tumorigenesis. Together, these findings suggest that gankyrin can promote malignant transformation of liver cells in the context of persistent liver injury. This transformation may be related to compensatory proliferation and the inflammatory microenvironment. The observed decrease in complement C3 may allow transforming cells to escape coordinated induction of the immune response. Herein, we demonstrate an excellent zebrafish model for liver cancers that will be useful for studying the molecular mechanisms of tumorgenesis.

Gankyrin has an antioxidative role through the feedback regulation of Nrf2 in hepatocellular carcinoma

Yang et al. identify a feedback loop between gankyrin, an oncoprotein overexpressed in human hepatocellular carcinoma (HCC), and Nrf2. The positive feedback modulates a series of antioxidant enzymes that lower intracellular reactive oxygen species to confer protection from mitochondrial damage and cell death.

Oxidative stress status has a key role in hepatocellular carcinoma (HCC) development and progression. Normally, reactive oxygen species (ROS) levels are tightly controlled by an inducible antioxidant program that responds to cellular stressors. How HCC cells respond to excessive oxidative stress remains elusive. Here, we identified a feedback loop between gankyrin, an oncoprotein overexpressed in human HCC, and Nrf2 maintaining the homeostasis in HCC cells. Mechanistically, gankyrin was found to interact with the Kelch domain of Keap1 and effectively competed with Nrf2 for Keap1 binding. Increased expression of gankyrin in HCC cells blocked the binding between Nrf2 and Keap1, inhibiting the degradation of Nrf2 by proteasome. Interestingly, accumulation and translocation of Nrf2 increased the transcription of gankyrin through binding to the ARE elements in the promoter of gankyrin. The positive feedback regulation involving gankyrin and Nrf2 modulates a series of antioxidant enzymes, thereby lowering intracellular ROS and conferring a steadier intracellular environment, which prevents mitochondrial damage and cell death induced by excessive oxidative stress. Our results indicate that gankyrin is a regulator of cellular redox homeostasis and provide a link between oxidative stress and the development of HCC.

Prognostic and clinicopathological significance of Gankyrin overexpression in cancers: evidence from a meta-analysis

Many studies have indicated that Gankyrin is a promising and novel prognostic tumor biomarker. However, the results of different studies remained controversial. Hence, a meta-analysis was undertaken to investigate the association between Gankyrin expression and cancer prognosis. Eligible studies were identified by searching the electronic databases PubMed, Embase, and Cochrane Library up to November 2015. Prognostic value of Gankyrin expression was evaluated by hazard ratio with 95% confidence interval (CI). Meanwhile, relative risk (RR) with 95% CI was used to assess the effects of Gankyrin expression on clinicopathological parameters. In total, ten studies with 1,326 patients were included for final analysis. A significant association was found between Gankyrin overexpression and poorer overall survival in patients with cancer (hazard ratio =1.73, 95% CI: 1.29–2.31, P=0.000). In the subgroup analysis, the association was also detected in Chinese patients and patients with cancers of the digestive system. The pooled RR indicated that Gankyrin overexpression was related to advanced tumor–node–metastasis stage (RR =0.72, 95% CI: 0.60–0.86, P=0.000), positive lymph node metastasis (RR =1.66, 95% CI: 1.41–1.94, P=0.000), and distant metastasis (RR =1.43, 95% CI: 1.20–1.70, P<0.000). The meta-analysis demonstrated that Gankyrin is a novel biomarker for predicting cancers, especially digestive system cancers, and is more suitable for predicting cancer prognoses in Asians.

The ubiquitin-proteasome system and its potential application in hepatocellular carcinoma therapy

The ubiquitin-proteasome system (UPS) is a complicated tightly controlled system in charge of degrading 80-90% of proteins, and is central to regulating cellular function and keeping protein homeostasis. Therefore, the components of UPS attract considerable attention as potential targets for hepatocellular carcinoma (HCC) therapy. The clinical success of bortezomib in multiple myeloma and mantle cell lymphoma patients has set the precedent for therapeutically targeting this pathway. This review will provide an overview of the UPS in HCC and the current status of therapeutic strategies.

p28(GANK) associates with p300 to attenuate the acetylation of RelA

Oncoprotein p28(GANK), overexpressed in hepatocellular carcinomas (HCC), binds to RelA and retains NF-κB in the cytoplasm to suppress NF-κB transactivation. However, the mechanism has not yet been elucidated. In this study, we clarified the mechanism of NF-κB regulated by p28(GANK). p28(GANK) reduced TNF-α-induced nuclear translocation of RelA/NF-κB independent of HDAC3. p28(GANK) interacted with p300 to attenuate assembly of RelA with p300, which lessened acetylation of RelA on the lysine 310 sites. Moreover, overexpression of p28(GANK) attenuated the capability of NF-κB binding to the target gene IκBα promoter, but also weakened adriamycin-induced NF-κB pro-apoptotic gene Fas and FasL expression, which subsequently made p53-deficient tumor cells resistance to adriamycin. These results present mechanistic insight into the key role of p28(GANK) in post-translational regulation of RelA/NF-κB.

Uncovering buffered pleiotropy: a genome-scale screen for mel-28 genetic interactors in Caenorhabditis elegans

mel-28 (maternal-effect-lethal-28) encodes a conserved protein required for nuclear envelope function and chromosome segregation in Caenorhabditis elegans. Because mel-28 is a strict maternal-effect lethal gene, its function is required in the early embryo but appears to be dispensable for larval development. We wanted to test the idea that mel-28 has postembryonic roles that are buffered by the contributions of other genes. To find genes that act coordinately with mel-28, we did an RNA interference−based genetic interaction screen using mel-28 and wild-type larvae. We screened 18,364 clones and identified 65 genes that cause sterility in mel-28 but not wild-type worms. Some of these genes encode components of the nuclear pore. In addition we identified genes involved in dynein and dynactin function, vesicle transport, and cell-matrix attachments. By screening mel-28 larvae we have bypassed the requirement for mel-28 in the embryo, uncovering pleiotropic functions for mel-28 later in development that are normally provided by other genes. This work contributes toward revealing the gene networks that underlie cellular processes and reveals roles for a maternal-effect lethal gene later in development.

Up-regulated oncoprotein P28GANK correlates with proliferation and poor prognosis of human glioma

Background

The significance of p28GANK in gliomas remains unknown. This study aims to clarify the clinical significance of p28GANK in human gliomas.

Methods

The expression of p28GANK in 138 gliomas and 50 matched para-cancerous tissues was detected by immunohistochemical staining, and statistical analyses were performed to test the correlation of p28GANK with clinical parameters. To investigate the effects of p28GANK down-regulation on the growth of cells both in vitro and in vivo, an siRNA targeting p28GANK was transfected into U251 cells.

Results

P28GANK expression was significantly higher in tumor specimens than in matched para-cancerous tissues. Over-expressed p28GANK significantly correlated with high karnofsky performance score (KPS), advanced WHO grade and poor overall survival of the patients. Univariate analysis showed that WHO grade and KPS also correlated with the survival of patients, and multivariate analysis suggested that KPS and p28GANK expression were two independent prognostic factors. Moreover, p28GANK gene silencing decreased the malignant growth of U251 cells both in vitro and in vivo.

Conclusions

Increased expression of p28GANK is correlated with poor clinical outcomes in glioma patients. The down-regulation of p28GANK significantly inhibited cell proliferation, indicating that p28GANK might be a potential therapeutic target for glioma treatment.

AMP-activated protein kinase phosphorylates cardiac troponin I and alters contractility of murine ventricular myocytes

RATIONALE

AMP-activated protein kinase (AMPK) is an important regulator of energy balance and signaling in the heart. Mutations affecting the regulatory γ2 subunit have been shown to cause an essentially cardiac-restricted phenotype of hypertrophy and conduction disease, suggesting a specific role for this subunit in the heart.

OBJECTIVE

The γ isoforms are highly conserved at their C-termini but have unique N-terminal sequences, and we hypothesized that the N-terminus of γ2 may be involved in conferring substrate specificity or in determining intracellular localization.

METHODS AND RESULTS

A yeast 2-hybrid screen of a human heart cDNA library using the N-terminal 273 residues of γ2 as bait identified cardiac troponin I (cTnI) as a putative interactor. In vitro studies showed that cTnI is a good AMPK substrate and that Ser150 is the principal residue phosphorylated. Furthermore, on AMPK activation during ischemia, Ser150 is phosphorylated in whole hearts. Using phosphomimics, measurements of actomyosin ATPase in vitro and force generation in demembraneated trabeculae showed that modification at Ser150 resulted in increased Ca(2+) sensitivity of contractile regulation. Treatment of cardiomyocytes with the AMPK activator 5-aminoimidazole-4-carboxamide ribonucleotide (AICAR) resulted in increased myocyte contractility without changing the amplitude of Ca(2+) transient and prolonged relaxation despite shortening the time constant of Ca(2+) transient decay (tau). Compound C prevented the effect of AICAR on myocyte function. These results suggest that AMPK activation increases myocyte contraction and prolongs relaxation by increasing myofilament Ca(2+) sensitivity.

CONCLUSIONS

We conclude that cTnI phosphorylation by AMPK may represent a novel mechanism of regulation of cardiac function.

The oncoprotein p28GANK establishes a positive feedback loop in β-catenin signaling

p28(GANK) (also known as PSMD10 or gankyrin) is a novel oncoprotein that is highly expressed in hepatocellular carcinoma (HCC). Through its interaction with various proteins, p28(GANK) mediates the degradation of the tumor suppressor proteins Rb and p53. Although p53 was reported to downregulate β-catenin, whether p28(GANK) is involved in the regulation of β-catenin remains uncertain. Here we report that both growth factors and Ras upregulate p28(GANK) expression through the activation of the phosphoinositide 3-kinase-AKT pathway. Upregulation of p28(GANK) expression subsequently enhanced the transcription activity of β-catenin. This effect was observed in p53-deficient cells, suggesting a p53-independent mechanism for the p28(GANK)-mediated activation of β-catenin. p28(GANK) overexpression also reduced E-cadherin protein levels, leading to increased release of free β-catenin into the cytoplasm from the cadherin-bound pool. Interestingly, exogenous expression of p28(GANK) resulted in elevated expression of the endogenous protein. We also observed that both β-catenin and c-Myc were transcriptional activators of p28(GANK), and a correlation between p28(GANK) overexpression and c-Myc, cyclin D1 and β-catenin activation in primary human HCC. Together, these results suggest that p28(GANK) expression is regulated by a positive feedback loop involving β-catenin, which may play a critical role in tumorigenesis and the progression of HCC.

Intracellular signaling and hepatocellular carcinoma

Liver cancer is the fifth most common cancer and the third most common cause of cancer related death in the world. The recent development of new techniques for the investigations of global change in the gene expression, signaling pathways and wide genome binding has provided novel information for the mechanisms underlying liver cancer progression. Although these studies identified gene expression signatures in hepatocellular carcinoma, the early steps of the development of hepatocellular carcinomas (HCC) are not well understood. The development of HCC is a multistep process which includes the progressive alterations of gene expression leading to the increased proliferation and to liver cancer. This review summarizes recent progress in the identification of the key steps of the development of HCC with the focus on early events of carcinogenesis and on the role of translational and epigenetic alterations in the development of HCC. Quiescent stage of the liver is supported by several tumor suppressor proteins including p53, Rb and C/EBPα. Studies with chemical models of liver carcinogenesis and with human HCC have shown that the elevation of gankyrin is responsible for the elimination of these three proteins at early steps of carcinogenesis. Later stages of progression of the liver cancer are associated with alterations in many signaling pathways including translation which leads to epigenetic silencing/activation of many genes. Particularly, recent reports suggest a critical role of histone deacetylase 1, HDAC1, in the development of HCC through the interactions with transcription factors such as C/EBP family proteins.

Proteasome system of protein degradation and processing

In eukaryotic cells, degradation of most intracellular proteins is realized by proteasomes. The substrates for proteolysis are selected by the fact that the gate to the proteolytic chamber of the proteasome is usually closed, and only proteins carrying a special "label" can get into it. A polyubiquitin chain plays the role of the "label": degradation affects proteins conjugated with a ubiquitin (Ub) chain that consists at minimum of four molecules. Upon entering the proteasome channel, the polypeptide chain of the protein unfolds and stretches along it, being hydrolyzed to short peptides. Ubiquitin per se does not get into the proteasome, but, after destruction of the "labeled" molecule, it is released and labels another molecule. This process has been named "Ub-dependent protein degradation". In this review we systematize current data on the Ub-proteasome system, describe in detail proteasome structure, the ubiquitination system, and the classical ATP/Ub-dependent mechanism of protein degradation, as well as try to focus readers' attention on the existence of alternative mechanisms of proteasomal degradation and processing of proteins. Data on damages of the proteasome system that lead to the development of different diseases are given separately.

Gankyrin promotes the proliferation of human pancreatic cancer

Previous studies in our laboratory have suggested that gankyrin expression is correlated with a malignant phenotype in colorectal cancer. Here, we investigated the possible role of gankyrin in pancreatic carcinogenesis. Gankyrin expression was significantly increased in pancreatic cancer compared to non-cancerous tissues. This expression significantly enhanced cancer cell proliferation and growth in vitro and in vivo. Suppression of gankyrin downregulated cyclin A, cyclin D1, cyclin E, CDK2, CDK4, PCNA and p-Rb but upregulated p27, Rb and p53. However, gankyrin overexpression led to opposite results. Thus, gankyrin could enhance pancreatic cancer cell proliferation by promoting cell cycle progression and p53 degradation.

Assembly, structure, and function of the 26S proteasome

The 26S proteasome is a large multiprotein complex involved in the regulated degradation of ubiquitinated proteins in the cell. The 26S proteasome has been shown to control an increasing number of essential biochemical mechanisms of the cellular lifecycle including DNA synthesis, repair, transcription, translation, and cell signal transduction. Concurrently, it is increasingly seen that malfunction of the ubiquitin proteasome system contributes to the pathogenesis of disease. The recent identification of four molecular chaperones, in addition to five previously identified chaperones, have provided mechanistic insight into how this cellular megastructure is assembled in the cell. These data, together with new insights into the structure and function of the proteasome, provide a much better understanding of this complex protease.

Isolation of mammalian 26S proteasomes and p97/VCP complexes using the ubiquitin-like domain from HHR23B reveals novel proteasome-associated proteins

Recent studies, mainly in yeast, have identified various cofactors that associate with the 26S proteasome and appear to influence its function. To identify these proteins in different cells and physiological states, we developed a method to gently and rapidly isolate 26S proteasomes and associated proteins without the need for genetic modifications of the proteasome. This method is based on the affinity of this complex for the ubiquitin-like (UBL) domain of hHR23B and elution with a competing polypeptide containing a ubiquitin-interacting motif. Associated with 26S proteasomes from rat muscle were a variety of known proteasome-interacting proteins, activators, and ubiquitin conjugates. In addition, we identified over 40 proteins not previously known to associate with the 26S proteasome, some of which were tightly associated with the proteasome in a substoichiometric fashion, e.g., the deubiquitinating enzymes USP5/isopeptidase T and USP7/HAUSP and the ubiquitin ligases ARF-BP1/HUWE1 and p600/UBR4. By altering buffer conditions, we also purified by this approach complexes of the ATPase p97/VCP associated with its adaptor proteins Ufd1-Npl4, p47, SAKS1, and FAF1, all of which contain ubiquitin-binding motifs. These complexes were isolated with ubiquitin conjugates bound and were not previously known to bind to the UBL domain of hHR23B. These various UBL-interacting proteins, dubbed the UBL interactome, represent a network of proteins that function together in ubiquitin-dependent proteolysis, and the UBL method offers many advantages for studies of the diversity, functions, and regulation of 26S proteasomes and p97 complexes under different conditions.

Gankyrin Oncoprotein: Structure, Function, and Involvement in Cancer

Gankyrin, a newly defined oncoprotein also known as PSMD10 and P28, functions as a dual-negative regulator of the two most prominent tumor suppressor pathways, the CDK/pRb and HDM2/P53 pathways. Its aberrant expression has been prevalently found in human hepatocellular carcinomas (HCC) and esophagus squamous cell carcinomas (ESCC), indicative of the potential of gankyrin as a rational diagnostic and therapeutic target in cancers. Here, we review the unique structural features and functional diversity of gankyrin, and discuss its implication in cancer diagnostics and therapeutics from the perspective of chemical biology.

p28GANK inhibits endoplasmic reticulum stress-induced cell death via enhancement of the endoplasmic reticulum adaptive capacity

It has been shown that oncoprotein p28(GANK), which is consistently overexpressed in human hepatocellular carcinoma (HCC), plays a critical role in tumorigenesis of HCC. However, the underlying mechanism remains unclear. Here, we demonstrated that p28(GANK) inhibits apoptosis in HCC cells induced by the endoplasmic reticulum (ER) stress. During ER stress, p28(GANK) enhances the unfolded protein response, promotes ER recovery from translational repression, and thereby facilitates cell's ability to cope with the stress conditions. Furthermore, p28(GANK) upregulates glucose-regulated protein 78 (GRP78), a key ER chaperone protein, which subsequently enhances the ER folding capacity and promotes recovery from ER stress. We also demonstrated that p28(GANK) increases p38 mitogen-activated protein kinase and Akt phosphorylation, and inhibits nuclear factor kappa B (NF-kappaB) activation under ER stress, which in turn contributes to GRP78 upregulation. Taken together, our results indicate that p28(GANK) inhibits ER stress-induced apoptosis in HCC cells, at least in part, by enhancing the adaptive response and GRP78 expression. We propose that p28(GANK) has potential implications for HCC progression under the ER stress conditions.

Functional characterization of human oncoprotein gankyrin in Zebrafish

Gankyrin is an oncoprotein containing seven ankyrin repeats that is overexpressed in hepatocellular carcinoma (HCC). Gankyrin binds to Mdm2, which results in accelerated ubiquitylation via degradation of p53, and it also plays an important role in cell proliferation. However, little is known about the relationships between p53 levels, cell proliferation, and gankyrin over-expression. In order to investigate the influence of gankyrin protein on p53 and Mdm2 in a zebrafish model, we injected human gankyrin (hgankyrin) containing expression vectors (pCS2-hgankyrin, pCS2- hgankyrin-EGFP) into zebrafish embryos. To measure p53 and Mdm2 expression in hgankyrin-injected embryos, RT-PCR, Northern blot and in-situ hybridization and BrdU immunostaining were used. In addition, to know the effect of hgankyrin on cell proliferation in vitro, cell viability assays such as MTT, trypan blue staining and RT-PCR following transfection of hgankyrin-containing vector into HEK 293 cell line were performed. In vivo results indicated that p53 mRNA levels decreased but those of Mdm2 were not decreased in the presence of hgankyrin. These results suggest that gankyrin downregulates p53 expression and not Mdm2 expression. In the study of cell proliferation, BrdU-positive cells were predominantly increased in the head and tail regions in hgankyrin-injected zebrafish. Additional in vitro studies using trypan blue staining and MTT assay showed that gankyrin-expressing HEK 293 cells proliferated at a faster rate, indicating that gankyrin promotes cell proliferation. Our results demonstrate that hgankyrin overexpression downregulates p53 expression and promotes cell proliferation in zebrafish. Gankyrin may play an important role in tumorigenesis via its effects on p53 and cell proliferation.

Overexpression of a new gene P28GANK confers multidrug resistance of gastric cancer cells

Here we investigated the roles of P28GANK in multidrug resistance of gastric cancer cells and the possible mechanisms. We constructed the siRNA vector of P28GANK and transfected it into human vincristine-resistant gastric adenocarcinoma cell line SGC7901/VCR. Down-regulation of P28GANK could enhance the sensitivity of SGC7901/VCR cells towards anticancer drugs and could decrease the capacity of cells to efflux adriamycin. P28GANK could down-regulate the expression of P-gp, but not affect MRP or GST. In vivo experiment also confirmed our above results. Further study of the biological functions of P28GANK might be helpful for understanding the mechanisms of MDR in gastric cancer.

Hepatocellular carcinoma and the ubiquitin-proteasome system

Hepatocellular carcinoma is one of the largest causes of cancer-related deaths worldwide for which there are very limited treatment options that are currently effective. The ubiquitin-proteasome system has rapidly become acknowledged as both critical for normal cellular function and a frequent target of de-regulation leading to disease. This review appraises the evidence linking the ubiquitin-proteasome system with this devastatingly intractable cancer and asks whether it may prove to be fertile ground for the development of novel therapeutic interventions against hepatocellular carcinoma.

Oncoprotein p28 GANK binds to RelA and retains NF-kappaB in the cytoplasm through nuclear export

p28(GANK) (also known as PSMD10, p28 and gankyrin) is an ankyrin repeat anti-apoptotic oncoprotein that is commonly overexpressed in hepatocellular carcinomas and increases the degradation of p53 and Rb. NF-kappaB (nuclear factor-kappaB) is known to be sequestered in the cytoplasm by I kappaB (inhibitor of NF-kappaB) proteins, but much less is known about the cytoplasmic retention of NF-kappaB by other cellular proteins. Here we show that p28(GANK) inhibits NF-kappaB activity. As a nuclear-cytoplasmic shuttling protein, p28(GANK) directly binds to NF-kappaB/RelA and exports RelA from nucleus through a chromosomal region maintenance-1 (CRM-1) dependent pathway, which results in the cytoplasmic retention of NF-kappaB/RelA. We demonstrate that all the ankyrin repeats of p28(GANK) are required for the interaction with RelA and that the N terminus of p28(GANK), which contains the nuclear export sequence (NES), is responsible for suppressing NF-kappaB/RelA nuclear translocation. These results suggest that overexpression of p28(GANK) prevents the nuclear localization and inhibits the activity of NF-kappaB/RelA.

Association of gankyrin protein expression with early clinical stages and insulin-like growth factor-binding protein 5 expression in human hepatocellular carcinoma

Gankyrin (also known as PSMD10) is a liver oncoprotein that interacts with multiple proteins including MDM2 and accelerates degradation of the tumor suppressors p53 and Rb. We produced a monoclonal anti-gankyrin antibody and immunohistochemically assessed the clinicopathological significance of gankyrin overexpression in 43 specimens of human hepatocellular carcinoma (HCC). Specific cytoplasmic staining for gankyrin was observed in 62.8% (27/43) of HCCs, which was significantly associated with low TNM stage (P = 0.004), no capsular invasion (P = 0.018), no portal venous invasion (P = 0.008), and no intrahepatic metastasis (P = 0.012). The cumulative survival rate of patients with gankyrin-positive HCC was significantly higher than that with gankyrin-negative HCC (P = 0.037). p53 and MDM2 were positively stained by antibodies in 30.2% and 23.3%, respectively, of HCCs, but neither was inversely associated with gankyrin expression. In the Huh-7 human HCC cell line, overexpression of gankyrin up-regulated expression of insulin-like growth factor binding protein 5 (IGFBP-5), whereas suppression of gankyrin expression by siRNA down-regulated it. Supression of IGFBP-5 expression inhibited proliferation of Huh-7 cells as well as U-2 OS osteosarcoma cells. In HCC specimens, positive staining for IGFBP-5 was observed by immunohistochemistry in 41.9% (18/43), and the level of expression was significantly correlated with that of gankyrin (rho = 0.629, P < 0.001).

CONCLUSION

These results suggest that gankyrin plays an oncogenic role(s) mainly at the early stages of human hepatocarcinogenesis, and that IGFBP-5 inducible by gankyrin overexpression may be involved in it.

Gankyrin oncoprotein overexpression as a critical factor for tumor growth in human esophageal squamous cell carcinoma and its clinical significance

To elucidate the possible involvement of gankyrin in ESCC progression and the effect of its down-regulation in ESCC, we investigated the expression of gankyrin in ESCC tissues comparing it with the corresponding normal esophageal epithelia and tested a short-hairpin RNA (shRNA) expression vector for gankyrin in ESCC cell lines. Gankyrin protein expression in 11 ESCC cell lines (KYSE series) was examined by RT-PCR and western blot. The expression of gankyrin mRNA in 30 ESCC tissues was compared with the corresponding normal epithelia by Real-time PCR. Expression of gankyrin protein was immunohistochemically analyzed in the ESCC of 103 patients. A gankyrin-shRNA vector was stably transfected into KYSE 170 cells to assess the role of gankyrin in cell motility, invasion and proliferation in vitro and tumor formation in vivo. Gankyrin expression increased in all 11 ESCC cell lines. Real-time PCR revealed that gankyrin expression was higher in the cancerous tissue for all 30 patients. In immunohistochemistry, gankyrin overexpression was correlated with lower survival rate (p = 0.0001), extent of the primary tumor, lymph node metastasis, distant lymph node metastasis and stage (p = 0.0072, p = 0.0004, p = 0.0172 and p = 0.0002, respectively). A shRNA vector against gankyrin repressed growth, cell motility, invasiveness in vitro and tumor formation in vivo. Gankyrin overexpression is associated with poor prognosis. It may play an important role in ESCC tumor progression and could be a potentially important therapeutic gene target in ESCC.

Evidence that proteasome-dependent degradation of the retinoblastoma protein in cells lacking A-type lamins occurs independently of gankyrin and MDM2

Background

A-type lamins, predominantly lamins A and C, are nuclear intermediate filaments believed to act as scaffolds for assembly of transcription factors. Lamin A/C is necessary for the retinoblastoma protein (pRB) stabilization through unknown mechanism(s). Two oncoproteins, gankyrin and MDM2, are known to promote pRB degradation in other contexts. Consequently, we tested the hypothesis that gankyrin and/or MDM2 are required for enhanced pRB degradation in Lmna^−/− fibroblasts. Principal Findings. To determine if gankyrin promotes pRB destabilization in the absence of lamin A/C, we first analyzed its protein levels in Lmna^−/− fibroblasts. Both gankyrin mRNA levels and protein levels are increased in these cells, leading us to further investigate its role in pRB degradation. Consistent with prior reports, overexpression of gankyrin in Lmna^+/+ cells destabilizes pRB. This decrease is functionally significant, since gankyrin overexpressing cells are resistant to p16^ink4a-mediated cell cycle arrest. These findings suggest that lamin A-mediated degradation of pRB would be gankyrin-dependent. However, effective RNAi-enforced reduction of gankyrin expression in Lmna^−/− cells was insufficient to restore pRB stability. To test the importance of MDM2, we disrupted the MDM2-pRB interaction by transfecting Lmna^−/− cells with p14^arf. p14^arf expression was also insufficient to stabilize pRB or confer cell cycle arrest, suggesting that MDM2 also does not mediate pRB degradation in Lmna^−/− cells.

Conclusions/Significance

Our findings suggest that pRB degradation in Lmna^−/− cells occurs by gankyrin and MDM2-independent mechanisms, leading us to propose the existence of a third proteasome-dependent pathway for pRB degradation. Two findings from this study also increase the likelihood that lamin A/C functions as a tumor suppressor. First, protein levels of the oncoprotein gankyrin are elevated in Lmna^−/− fibroblasts. Second, Lmna^−/− cells are refractory to p14^arf-mediated cell cycle arrest, as was previously shown with p16^ink4a. Potential roles of lamin A/C in the suppression of tumorigenesis are discussed.

Structural basis for the recognition between the regulatory particles Nas6 and Rpt3 of the yeast 26S proteasome

The 26S proteasome-dependent protein degradation is an evolutionarily conserved process. The mammalian oncoprotein gankyrin, which associates with S6 of the proteasome, facilitates the degradation of pRb, and thus possibly acts as a bridging factor between the proteasome and its substrates. However, the mechanism of the proteasome-dependent protein degradation in yeast is poorly understood. Here, we report the tertiary structure of the complex between Nas6 and a C-terminal domain of Rpt3, which are the yeast orthologues of gankyrin and S6, respectively. The concave region of Nas6 bound to the alpha-helical domain of Rpt3. The stable interaction between Nas6 and Rpt3 was mediated by intermolecular interactions composed of complementary charged patches. The recognition of Rpt3 by Nas6 in the crystal suggests that Nas6 is indeed a subunit of the 26S proteasome. These results provide a structural basis for the association between Nas6 and the heterohexameric ATPase ring of the proteasome through Rpt3.

Purification, crystallization and preliminary X-ray diffraction analysis of the non-ATPase subunit Nas6 in complex with the ATPase subunit Rpt3 of the 26S proteasome from Saccharomyces cerevisiae

The non-ATPase subunit Nas6, which is the human orthologue of gankyrin, was co-expressed with the C-terminal domain of the ATPase subunit Rpt3 of the yeast 26S proteasome in Escherichia coli, purified to near-homogeneity and crystallized using the hanging-drop vapour-diffusion method. The protein crystallized in space group P2(1), with unit-cell parameters a = 60.38, b = 100.22, c = 72.20 A, beta = 94.70 degrees and with three Nas6-Rpt3C molecules per asymmetric unit. The crystal diffracted to beyond 2.2 A resolution using synchrotron radiation.

Structure of the Oncoprotein Gankyrin in Complex with S6 ATPase of the 26S Proteasome

Gankyrin is an oncoprotein commonly overexpressed in most hepatocellular carcinomas. Gankyrin interacts with S6 ATPase of the 19S regulatory particle of the 26S proteasome and enhances the degradation of the tumor suppressors pRb and p53. Here, we report the structure of gankyrin in complex with the C-terminal domain of S6 ATPase. Almost all of the seven ankyrin repeats of gankyrin interact, through its concave region, with the C-terminal domain of S6 ATPase. The intermolecular interactions occur through the complementary charged residues between gankyrin and S6 ATPase. Biochemical studies based on the structure of the complex revealed that gankyrin interacts with pRb in both the presence and absence of S6 ATPase; however, the E182 residue in gankyrin is essential for the pRb interaction. These results provide a structural basis for the involvement of gankyrin in the pRb degradation pathway, through its association with S6 ATPase of the 26S proteasome.

Effects of Body Weight and Nutrition on Mammary Protein Expression Profiles in Holstein Heifers

A proteomics approach was used to characterize biochemical and cellular mechanisms governing effects of peripubertal feeding on heifer mammary development. Mammary parenchymal tissue from 24 Holstein heifers randomly assigned to treatments arranged in a 2 x 2 factorial design was used to generate 2-dimensional protein maps of mammary tissue extracts. Heifers were reared on 1 of 2 dietary treatments, restricted (650 g/ d of daily gain) or elevated (950 g/d of daily gain) and killed at 1 of 2 body weights (BW, 200 or 350 kg). Cytosolic mammary gland extracts were prepared from frozen mammary parenchyma. Proteome maps of extracts were constructed using PDQuest software. Densities of 820 protein spots were analyzed using the MIXED procedure of SAS. Protein spots were characterized by changes in profiles of expression in response to increased BW, dietary treatment, or both. Dietary treatment influenced the expression of 131 protein spots, whereas heifer BW influenced the expression of 108 spots. The 22 most highly influenced (statistically) spots were excised and submitted for mass spectrometric analyses. Returned protein names and accession numbers were used in National Center for Biotechnology Information database searches to obtain information on the identified proteins. For example, one of the proteins that differed by dietary treatment, transferrin, a binding protein of insulin-like growth factor binding protein-3, was identified via these methods. Possible roles of this and other proteins in mammary development are described. We concluded that a proteomic approach is an effective tool for identifying the proteins involved in bovine mammary development.

Gene therapy strategies for hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is one of the most frequent cancers worldwide. Effective therapy to this cancer is currently lacking, creating an urgent need for new therapeutic strategies for HCC. Gene therapy approach that relies on the transduction of cells with genetic materials, such as apoptotic genes, suicide genes, genes coding for antiangiogenic factors or immunomodulatory molecules, small interfering RNA (siRNA), or oncolytic viral vectors, may provide a promising strategy. The aforementioned strategies have been largely evaluated in the animal models with HCC or liver metastasis. Due to the diversity of vectors and therapeutic genes, being used alone or in combination, gene therapy approach may generate great beneficial effects to control the growth of tumors within the liver.