Diverse effects of mutations in exon II of the von Hippel-Lindau (VHL) tumor suppressor gene on the interaction of pVHL with the cytosolic chaperonin and pVHL-dependent ubiquitin ligase activity

Osteocytic oxygen sensing: Distinct impacts of VHL and HIF-2alpha on bone integrity

Skeletal fracture resistance emerges from multiple components of bone structure like microarchitecture, matrix mineralization, and organization. These characteristics are engendered via mechanisms like the hypoxia-inducible factors (HIF) pathway, involving two paralogs, HIF-1α and HIF-2α. Under normoxia, HIF-α is targeted for degradation via von-Hippel Lindau (VHL); hypoxia enables HIF-α stabilization and induction of target genes. We previously showed that osteocytic Vhl deletion or expression of degradation-resistant HIF-2α cDR female mice each produced high bone mass, whereas degradation-resistant osteocytic HIF-1α produced no overt phenotype. We report within that Vhl cKO increased bone strength, while HIF-2α cDR displayed markedly reduced bone strength below Cre-negative controls. This suggests that VHL and HIF-2α drive distinct responses that promote disparate effects on bone strength. Both Vhl deletion or HIF-2α accumulation generated two discrete bone morphologies: an outer lamellar cortex and a woven, poorly mineralized endocortex that imparted dramatically different functional outcomes. Our studies reveal novel influence of osteocytic HIF-2α signaling on collagen matrix organization, mineralization, and bone strength.

Molecular chaperones: Guardians of tumor suppressor stability and function

The term 'tumor suppressor' describes a widely diverse set of genes that are generally involved in the suppression of metastasis, but lead to tumorigenesis upon loss-of-function mutations. Despite the protein products of tumor suppressors exhibiting drastically different structures and functions, many share a common regulatory mechanism-they are molecular chaperone 'clients'. Clients of molecular chaperones depend on an intracellular network of chaperones and co-chaperones to maintain stability. Mutations of tumor suppressors that disrupt proper chaperoning prevent the cell from maintaining sufficient protein levels for physiological function. This review discusses the role of the molecular chaperones Hsp70 and Hsp90 in maintaining the stability and functional integrity of tumor suppressors. The contribution of cochaperones prefoldin, HOP, Aha1, p23, FNIP1/2 and Tsc1 as well as the chaperonin TRiC to tumor suppressor stability is also discussed. Genes implicated in renal cell carcinoma development-VHL, TSC1/2, and FLCN-will be used as examples to explore this concept, as well as how pathogenic mutations of tumor suppressors cause disease by disrupting protein chaperoning, maturation, and function.

The von Hippel-Lindau protein forms fibrillar amyloid assemblies that are mitigated by the anti-amyloid molecule Purpurin

The von Hippel-Lindau protein (pVHL) is a tumor suppressor involved in oxygen regulation via dynamic nucleocytoplasmic shuttling. It plays a crucial role in cell survival by degrading hypoxia-inducible factors (HIFs). Mutations in the VHL gene cause angiogenic tumors, characterized as VHL syndrome. However, aggressive tumors involving wild-type pVHL have also been described but the underlying mechanism remains to be revealed. We have previously shown that pVHL possesses several short amyloid-forming motifs, making it aggregation-prone. In this study, using a series of biophysical assays, we demonstrated that a pVHL-derived fragment (pVHL104-140) that harbors the nuclear export motif and HIF binding site, forms amyloid-like fibrillar structures in vitro by following secondary-nucleation-based kinetics. The peptide also formed amyloids at acidic pH that mimics the tumor microenvironment. We, subsequently, validated the amyloid formation by pVHL in vitro. Using the Curli-dependent amyloid generator (C-DAG) expression system, we confirmed the amyloidogenesis of pVHL in bacterial cells. The pVHL amyloids are an attractive target for therapeutics of the VHL syndrome. Accordingly, we demonstrated in vitro that Purpurin is a potent inhibitor of pVHL fibrillation. The amyloidogenic behavior of wild-type pVHL and its inhibition provide novel insights into the molecular underpinning of the VHL syndrome and its possible treatment.

CCT3 as a Diagnostic and Prognostic Biomarker in Cervical Cancer

The chaperonin-containing TCP1 complex subunit 3 (CCT3) has been reported to be involved in the development and prognosis of many tumors, including cervical cancer (CC). This study aimed to analyze the expression and prognostic value of CCT3 in CC by bioinformatics and retrospective study. CCT3 gene expression profiles and clinical information in CC were downloaded from the cancer genome atlas (TCGA) and gene expression omnibus (GEO) databases. CCT3 expression was verified by quantitative real-time polymerase chain reaction (RT-qPCR), Western blot, and immunohistochemistry (IHC). Logistic regression and chi-square testing were used to analyze the relationship between CCT3 expression and the clinical characteristics of CC. Kaplan-Meier and Cox analyses were used to evaluate whether CCT3 affects the prognosis of CC. Nomogram and calibration curves were used to test the predictive value of CCT3. The expression of CCT3 in CC tissues was significantly upregulated compared with that in adjacent benign tissues, and was related to HPV16/18 infection, grade, and positive lymph nodes. High expression of CCT3 is associated with poor prognosis of CC and can be used as an independent risk factor for CC. The prognostic model based on CCT3 and CC clinical features has good predictive ability. CCT3 is overexpressed in CC, which is related to poor prognosis and expected to become a biomarker for CC.

Current understanding on the role of CCT3 in cancer research

Chaperonin containing TCP1 Subunit 3 (CCT3) is an important member of the chaperone protein family, providing a favorable environment for the correct folding of proteins in cell division, proliferation, and apoptosis pathways, which is involved in a variety of biological processes as well as the development and invasion of many malignant tumors. Many malignancies have been extensively examined with CCT3. It is presently used as a possible target for the treatment of many malignancies since it is not only a novel biomarker for the screening and diagnosis of different tumors, but it is also closely associated with tumor progression, prognosis, and survival. Recent studies have shown that the expression of CCT3 is up-regulated in some tumors, such as liver cancer, breast cancer, colon cancer, acute myeloid leukemia, etc. In this paper, we review the role of CCT3 in various tumors.

The Role of VHL in the Development of von Hippel-Lindau Disease and Erythrocytosis

Von Hippel-Lindau disease (VHL disease or VHL syndrome) is a familial multisystem neoplastic syndrome stemming from germline disease-associated variants of the VHL tumor suppressor gene on chromosome 3. VHL is involved, through the EPO-VHL-HIF signaling axis, in oxygen sensing and adaptive response to hypoxia, as well as in numerous HIF-independent pathways. The diverse roles of VHL confirm its implication in several crucial cellular processes. VHL variations have been associated with the development of VHL disease and erythrocytosis. The association between genotypes and phenotypes still remains ambiguous for the majority of mutations. It appears that there is a distinction between erythrocytosis-causing VHL variations and VHL variations causing VHL disease with tumor development. Understanding the pathogenic effects of VHL variants might better predict the prognosis and optimize management of the patient.

MicroRNA-148a/152 cluster restrains tumor stem cell phenotype of colon cancer via modulating CCT6A

Accumulating evidence has presented that microRNA-148a/152 (miR-148a/152) acts as the tumor inhibitor in various cancers. In this article, we aimed to probe the inhibition of colon cancer stem cells by miR-148a/152 cluster via regulation of CCT6A. miR-148a/152 and CCT6A expression in colon cancer tissues and cells was detected. The relationship between miR-148a/152 expression and the clinicopathological features of patients with colon cancer was analyzed. Colon cancer stem cells (CD44+/CD133+) were selected and high/low expression of miR-148a/152 plasmids were synthesized to intervene CD44+/CD133+ colon cancer stem cells to investigate the function of miR-148a/152 in invasion, migration, proliferation, colony formation and apoptosis of cells. The growth status of nude mice was observed to verify the in-vitro results. The relationship between miR-148a/152 and CCT6A was analyzed. CCT6A upregulated and miR-148a/152 downregulated in colon cancer tissues. MiR-148a/152 expression was correlated with tumor node metastasis stage, lymph node metastasis and differentiation degree. Upregulated miR-148a/152 depressed CCT6A expression and restrained invasion and migration ability, colony formation and proliferation, induced cell apoptosis, depressed OCT4, Nanog and SOX2 mRNA expression of colon cancer stem cells, and descended tumor weight and volume in nude mice. CCT6A was a target gene of miR-148a/152. Overexpression of CCT6A protected colon cancer stem cells. Functional studies showed that upregulation of miR-148a/152 can suppress the migration, invasion and proliferation of CD44+/CD133+ colon cancer stem cells, advance its apoptosis via inhibition of CCT6A expression.

VHL-P138R and VHL-L163R Novel Variants: Mechanisms of VHL Pathogenicity Involving HIF-Dependent and HIF-Independent Actions

The von Hippel-Lindau (VHL) disease is an autosomal dominant cancer syndrome caused by mutations in the VHL tumor suppressor gene. VHL protein (pVHL) forms a complex (VBC) with Elongins B-C, Cullin2, and Rbx1. Although other functions have been discovered, the most described function of pVHL is to recognize and target hypoxia-inducible factor (HIF) for degradation. This work comprises the functional characterization of two novel variants of the VHL gene (P138R and L163R) that have been described in our center in patients with VHL disease by in vitro, in vivo, and in silico approaches. In vitro, we found that these variants have a significantly shorter half-life compared to wild-type VHL but still form a functional VBC complex. Altered fibronectin deposition was evidenced for both variants using immunofluorescence. In vivo studies revealed that both variants failed to suppress tumor growth. By means of molecular dynamics simulations, we inspected in silico the nature of the changes introduced by each variant in the VBC complex. We have demonstrated the pathogenicity of P138R and L163R novel variants, involving HIF-dependent and HIF-independent mechanisms. These results provide the basis for future studies regarding the impact of structural alterations on posttranslational modifications that drive pVHL's fate and functions.

Defining candidate mRNA and protein EV biomarkers to discriminate ccRCC and pRCC from non-malignant renal cells in vitro

Renal cell carcinoma (RCC) accounts for over 400,000 new cases and 175,000 deaths annually. Diagnostic RCC biomarkers may prevent overtreatment in patients with early disease. Extracellular vesicles (EVs) are a promising source of RCC biomarkers because EVs carry proteins and messenger RNA (mRNA) among other biomolecules. We aimed to identify biomarkers and assess biological functions of EV cargo from clear cell RCC (ccRCC), papillary RCC (pRCC), and benign kidney cell lines. EVs were enriched from conditioned cell media by size exclusion chromatography. The EV proteome was assessed using Tandem Mass Tag mass spectrometry (TMT-MS) and NanoString nCounter technology was used to profile 770 cancer-related mRNA present in EVs. The heterogeneity of protein and mRNA abundance and identification highlighted the heterogeneity of EV cargo, even between cell lines of a similar pathological group (e.g., ccRCC or pRCC). Overall, 1726 proteins were quantified across all EV samples, including 181 proteins that were detected in all samples. In the targeted profiling of mRNA by NanoString, 461 mRNAs were detected in EVs from at least one cell line, including 159 that were present in EVs from all cell lines. In addition to a shared EV cargo signature, pRCC, ccRCC, and/or benign renal cell lines also showed unique signatures. Using this multi-omics approach, we identified 34 protein candidate pRCC EV biomarkers and 20 protein and 8 mRNA candidate ccRCC EV biomarkers for clinical validation.

Histone deacetylase inhibitor induced pVHL-independent degradation of HIF-1α and hierarchical quality control of pVHL via chaperone system

The mortality rate of ovarian cancer is increasing and the role of hypoxia inducible factor-1α (HIF-1α) in tumor progression has been confirmed. von Hippel-Lindau tumor suppressor protein (pVHL) binds HIF-1α and mediates proteasome degradation of HIF-1α. Besides, histone deacetylase inhibitor (HDACi) mitigates tumor growth via targeting HIF-1α, whereas underlying mechanism still requires investigation. In this research, we exposed ovarian cancer cell lines OV-90 and SKOV-3 to escalating concentrations of HDACi LBH589. As a result, cell viability was significantly suppressed and expression of HIF-1α was remarkably reduced along with decreased levels of signal molecules, including phosphoinositide 3-kinase (PI3K) and glycogen synthase kinase 3β (GSK3β) (P = 0.000). Interestingly, pVHL was expressed in a notably declining tendency (P = 0.000). Chaperone heat shock protein-70 (HSP70) was expressed in an ascending manner, whereas expression of chaperonin TCP-1α was reduced clearly (P = 0.000). Besides, co-inhibition of pVHL plus HDAC did not contribute to a remarkable difference in HIF-1α expression as compared with single HDAC inhibition. Furthermore, both cell lines were transfected with plasmids of VHL plus VHL binding protein-1 (VBP-1). Consequently, the expression of HIF-1α as well as lactate dehydrogenase-A (LDHA) was remarkably decreased (P = 0.000). These findings indicate HDACi may repress expression of HIF-1α via inhibiting PI3K and GSK3β and promote degradation of HIF-1α via HSP70, independent of pVHL. Additionally, a sophisticated network of HDAC and chaperones may involve in pVHL quality control.

CCT5 interacts with cyclin D1 promoting lung adenocarcinoma cell migration and invasion

Cyclin D1 (CCND1) has been identified as a metastatic promoter in various tumors including lung adenocarcinoma (LUAD), a subtype of non small cell lung cancer (NSCLC). The previous observation revealed that CCND1 was upregulated in NSCLC and predicted poor prognosis of LUAD patients. In this study, we examined a chaperonin containing TCP1 subunit 5 (CCT5) protein interacts with CCND1 in LUAD. Immunofluorescence demonstrated the co-localization of CCT5 and CCND1 protein in LUAD cells. CCT5 expression was detected with both immunohistochemistry (IHC) and bioinformatics analyses. Similar with the expression pattern of CCND1, CCT5 displayed a high level in LUAD tissues compared to non cancerous lung specimens. Patients with high CCT5 expression showed a significant shorter overall survival relative to those with low expression level. Furthermore, upregulated CCT5 exhibited significant positive correlation with TNM stage of LUAD patients in both IHC analyses and bioinformatics. Knocking down CCT5 remarkably inhibited LUAD cell migration and invasion in vitro by inactivating PI3K/AKT and its downstream EMT signals, which could abrogated the accelerated migration and invasion caused by CCND1 overexpression. In summary, our study discovered a highly expressed protein CCT5 in LUAD which interacted with CCND1 and promoted migration and invasion of LUAD cells by positively moderating PI3K/AKT-induced EMT pathway.

TCP1 regulates PI3K/AKT/mTOR signaling pathway to promote proliferation of ovarian cancer cells

OBJECTIVE

TCP1 is one of the eight subunits of the TCP1 ring complex (TRiC) or the multi-protein mammalian cytosolic chaperone complex. TRiC participates in protein folding and regulates the expression of multiple signaling proteins and cytoskeletal components in cells. Although the clinical importance of its subunits has been clarified in various carcinomas, the function of TCP1 in ovarian cancer (OC) remains unclear. We aimed to identify the association between the expression of TCP1 and the development of epithelial OC (EOC) and patient prognosis, and explore the underlying mechanisms of TCP1 on the tumor progression of OC cells.

METHODS

TCP1 protein expression was tested in various ovarian tissues by immunohistochemistry, and the correlation between TCP1 expression and clinical physiologic or pathologic parameters of patients with EOC was analyzed. The relationship between TCP1 expression and the prognosis of patients with OC was investigated and analyzed using the Kaplan-Meier (KM) plotter online database. The expression level of TCP1 was then tested in different OC cell lines by Western blotting. Further, a model using OC cell line A2780 was constructed to study the functions of TCP1 in growth, migration, and invasion of human EOC cells. Finally, the possible regulating signaling pathways were discussed.

RESULTS

TCP1 protein expression in OC or borderline tissues was significantly higher than that in benign ovarian tumors and normal ovarian tissue. The upregulated expression of TCP1 in OC was positively associated with the differentiation grade and FIGO stage of tumors and predicted poor clinical outcomes. Compared with IOSE-80 cells, TCP1 protein was overexpressed in A2780 cells. TCP1 knockdown using shRNA lentivirus inhibited the viability of A2780 cells. Western blotting showed that the phosphatidylinositol-3 kinase (PI3K) signaling pathway was activated in the tumor invasion in EOC driven by TCP1.

CONCLUSION

Upregulated TCP1 is correlated with the poor prognosis of patients with OC. The mechanism of cancer progression promoted by TCP1 upregulation may be linked to the activation of the PI3K signaling pathway, and TCP1 may serve as a novel target for the treatment of OC.

Chaperonin-Containing TCP-1 Promotes Cancer Chemoresistance and Metastasis through the AKT-GSK3β-β-Catenin and XIAP-Survivin Pathways

Simple Summary

CCT is a chaperonin that participates in folding intracellular proteins. We found that endogenously high expression of the subunit CCT-β is associated with a poorer chemotherapy response in clinical cancer patients. Using two cancer cell lines with higher CCT-β levels, a triple-negative breast cancer cell line MDA-MB-231 and a highly metastatic non-small-cell lung cancer cell line CL1-5, we demonstrated that upregulation of CCT-β expression correlated with chemoresistance and metastasis of these cancer cells in vitro and in vivo. Mechanistic studies allowed us to identify the AKT-GSK3β-β-catenin and XIAP-Survivin pathways promoted by CCT-β to account for the observations. The results provided by our studies are important for developing diagnostic and therapeutic strategies for combating CCT-β-overexpressed cancers.

Abstract

Chaperonin-containing TCP-1 (CCT) is a chaperonin composed of eight subunits that participates in intracellular protein folding. Here, we showed that increased levels of subunits of CCT, particularly CCT-β, were significantly correlated with lower survival rates for cancer patients. Endogenously high expression of CCT-β was found in cancer cell lines, such as the triple-negative breast cancer cell line MDA-MB-231 and the highly metastatic non-small-cell lung cancer cell line CL1-5. Knocking down CCT-β in these cancer cells led to decreased levels of anti-apoptotic proteins, such as XIAP, as well as inhibited phosphorylation of Ser473-AKT and GSK3, resulting in decrease of the nucleus-entering form of β-catenin; these changes reduced the chemoresistance and migration/invasion of the cells. Conversely, overexpression of CCT-β recovered the chemoresistance and cell migration/invasion by promoting the AKT-GSK3β-β-catenin and XIAP-Survivin pathways. Coimmunoprecipitation data revealed that the CCT complex might directly bind and stabilize XIAP and β-catenin. This study not only elucidates the roles of CCT in chemoresistance and metastasis, which are two major obstacles for current cancer therapy, but also provides a possible therapeutic strategy against cancers with overexpressed CCT-β.

The Genotype-Phenotype Association of Von Hipple Lindau Disease Based on Mutation Locations: A Retrospective Study of 577 Cases in a Chinese Population

Purpose

Von Hippel-Lindau (VHL) disease is a hereditary kidney cancer syndrome, with which patients are more likely to get affected by renal cell carcinoma (RCC), pancreatic cyst or tumor (PCT), central nervous system hemangioblastoma (CHB), retinal angiomas (RA), and pheochromocytoma (PHEO). Mutations of VHL gene located in 3p25 may impair the function of the VHL protein and lead to the disease. It's unclear why obvious phenotype varieties exist among VHL patients. Here we aimed to ascertain whether the mutation types and locations affect the phenotype.

Methods

We enrolled 577 Chinese VHL patients from 211 families and divided them into three groups and six subgroups according to their mutation types and locations. Cox survival analysis and Kaplan-Meier analysis were used to compare intergroup age-related tumor risks.

Results

Patients with nonsense or frameshift mutations that were located before residues 117 of VHL protein (NoF1 subgroup) hold lower age-related risks of VHL associated tumors (HR = 0.638, 95%CI 0.461-0.883, p = 0.007), CHB (HR = 0.596, 95%CI 0.409-0.868, p = 0.007) or PCT (HR = 0.595, 95%CI 0.368-0.961, p = 0.034) than patients whose mutations were located after residues 117 (NoF2 subgroup). Patients in NoF1 subgroup still had lower age-related risks of CHB (HR = 0.652, 95%CI 0.476-0.893, p = 0.008) and PCT (HR = 0.605, 95%CI 0.398-0.918, p = 0.018) compared with those in combined NoF2 subgroup and other truncating mutation patients. NoF1 subgroup correspondingly had a longer estimated median lifespan (64 vs. 55 year, p = 0.037) than NoF2 subgroup. Among patients with missense mutations of VHL, only a small minority (23 of 286 missense mutations carriers) carried mutations involving neither HIF-α binding region nor elongin C binding region, who were grouped in MO subgroup. MO subgroup seemed to have a higher age-related risk of PHEO. In the whole cohort (n = 577), PHEO was an independent protective factor for CHB (p = 0.001) and survival (p = 0.005). RA and CHB failed to predict the age-related risk of each other.

Conclusion

The mutation types and locations of VHL gene are associated with phenotypes. Genetic counselors could predict phenotypes more accurately based on more detailed genotype-phenotype correlations. Further genotype-phenotype studies should focus on the prediction of tumor recurrence, progression, and metastasis. The deep molecular mechanism of genotype-phenotype correlation is worth further exploring.

Interaction with p53 explains a pro-proliferative function for VHL in cancer

The von Hippel-Lindau (VHL) protein binds and degrades hypoxia-inducible factors (HIF) hydroxylated by prolyl-hydroxylases under normoxia. Although originally described as a tumor suppressor, there is growing evidence that VHL may paradoxically promote tumor growth. The significance of its described interactions with many other proteins remains unclear. We found that VHL interacts with p53, preventing its tetramerization, promoter binding and expression of its target genes p21, PUMA, and Bax. VHL limited the decrease in proliferation and increase in apoptosis caused by p53 activation, independent of prolyl-hydroxylation and HIF activity, and its presence in tumors caused a resistance to p53-inducing chemotherapy in vivo. We propose that VHL has both anti-tumor function, via HIF degradation, and a new pro-tumor function via p53 target (p21, PUMA, Bax) inhibition. Because p53 plays a critical role in tumor biology, is activated by many chemotherapies, and because VHL levels vary among different tumors and its function can even be lost by mutations in some tumors, our results have important clinical applications. KEY MESSAGES: VHL and p53 physically interact and VHL inhibits p53 activity by limiting the formation of p53 tetramers. VHL attenuates the expression of p53 target genes in response to p53 stimuli. The inhibition of p53 by VHL is independent of HIF and prolyl-hydroxylation.

TCP1γ Subunit Is Indispensable for Growth and Infectivity of Leishmania donovani

T-complex protein-1 (TCP1) is a ubiquitous group II chaperonin and is known to fold various proteins, such as actin and tubulin. In Leishmania donovani, the γ subunit of TCP1 (LdTCP1γ) has been cloned and characterized. It forms a high-molecular-weight homo-oligomeric complex that performs ATP-dependent protein folding. In the present study, we evaluated the essentiality of the LdTCP1γ gene. Gene replacement studies indicated that LdTCP1γ is essential for parasite survival. The LdTCP1γ single-allele-replacement mutants exhibited slowed growth and decreased infectivity in mouse macrophages compared to the growth and infectivity of the wild-type parasites. Modulation of LdTCP1γ expression in promastigotes also modulated cell cycle progression. Suramin, an antitrypanosomal drug, not only inhibited the luciferase refolding activity of the recombinant LdTCP1γ (rLdTCP1γ) homo-oligomeric complex but also exhibited potential antileishmanial efficacy both in vitro and in vivo The interaction of suramin and LdTCP1γ was further validated by isothermal titration calorimetry. The study suggests LdTCP1γ as a potential drug target and also provides a framework for the development of a new class of drugs.

Extracellular Vesicles from Neurosurgical Aspirates Identifies Chaperonin Containing TCP1 Subunit 6A as a Potential Glioblastoma Biomarker with Prognostic Significance

Glioblastoma, WHO-grade IV glioma, carries a dismal prognosis owing to its infiltrative growth and limited treatment options. Glioblastoma-derived extracellular vesicles (EVs; 30-1000 nm membranous particles) influence the microenvironment to mediate tumor aggressiveness and carry oncogenic cargo across the blood-brain barrier into the circulation. As such, EVs are biomarker reservoirs with enormous potential for assessing glioblastoma tumors in situ. Neurosurgical aspirates are rich sources of EVs, isolated directly from glioma microenvironments. EV proteomes enriched from glioblastoma (n = 15) and glioma grade II-III (n = 7) aspirates are compared and 298 differentially-abundant proteins (p-value < 0.00496) are identified using quantitative LC-MS/MS. Along with previously reported glioblastoma-associated biomarkers, levels of all eight subunits of the key molecular chaperone, T-complex protein 1 Ring complex (TRiC), are higher in glioblastoma-EVs, including CCT2, CCT3, CCT5, CCT6A, CCT7, and TCP1 (p < 0.00496). Analogous increases in TRiC transcript levels and DNA copy numbers are detected in silico; CCT6A has the greatest induction of expression and amplification in glioblastoma and shows a negative association with survival (p = 0.006). CCT6A is co-localized with EGFR at 7p11.2, with a strong tendency for co-amplification (p < 0.001). Immunohistochemistry corroborates the CCT6A proteomics measurements and indicated a potential link between EGFR and CCT6A tissue expression. Putative EV-biomarkers described here should be further assessed in peripheral blood.

The TCP1 ring complex is associated with malignancy and poor prognosis in hepatocellular carcinoma

TCP1 ring complex (TRiC) participates in protein folding in cells, regulating the expression of many tumor-related proteins and the cell cycle. Although the clinical significance of its subunits has been widely discussed in various malignancies, limited studies have explored its function in hepatocellular carcinoma (HCC) in the perspective of a complex. This study discusses the clinical significance of the TRiC subunits in HCC patients in terms of expression level, prognostic value, and potential mechanism. We used HCC samples from Nanfang hospital, data from The Cancer Genome Atlas (TCGA) database and information from the Gene Expression Omnibus (GEO) database with statistical methods and Gene Set Enrichment Analysis (GSEA) to analyze the gene expression levels of TRiC subunits along with survival data. We found altered expressions of the TRiC subunits in HCC, including significantly increased TCP1/CCT2/CCT3/CCT4/CCT5/CCT6A/CCT7/CCT8 expressions as well as decreased CCT6B expression, which predict poor prognosis and are associated with tumor progression. Moreover, the expression levels of these genes were pairwise correlated in HCC, indicating that the function of the entire complex should be explored as a functional macrocosm. Finally, we identified that the overexpressions of TCP1/CCT2/CCT3/CCT4/CCT5/CCT6A are involved in the dysregulation of Myc target genes, hypoxia-inducible factor (HIF) target genes and cell cycle especially the G1/S transition. Our study found that all TRiC subunits are aberrantly co-expressed in HCC, and these components have potential as therapeutic targets.

Assessment of Stabilization and Activity of the HIFs Important for Hypoxia-Induced Signalling in Cancer Cells

Blood vessels in tumors contain chaotic branching structures and leaky vessel lumens, resulting in uneven supply of oxygen in the tumor microenvironment. High metabolic and proliferation rate of tumor cells further depletes the local oxygen supply. Therefore, hypoxia is a common phenomenon in multiple solid malignancies. Hypoxia-inducible factors (HIFs) regulate the transcription of a spectrum of genes, which are vitally important for tumor cell adaption under hypoxia, and shape the tumor microenvironment to become more favorable for progression. HIFs are involved in almost every step of cancer development through inducing angiogenesis, metabolic reprogramming, metastasis, cancer stemness maintenance, chemoresistance, and immune evasion. Here, we describe methods for the assessment of HIF activity, as well as identification of novel transcriptional targets of HIFs in vitro and in vivo.

Suppression of CCT3 inhibits malignant proliferation of human papillary thyroid carcinoma cell

Papillary thyroid carcinoma (PTC) is the most frequently occurring subtype of thyroid cancer. A certain portion of PTCs can progress to recurrent metastatic cancer. Currently, there remains no effective molecular target therapy for PTCs. As a subunit of the chaperonin containing TCP1 (CCT) complex, CCT3 is involved in various biological processes. CCT3 has been reported to drive the proliferation of hepatocellular carcinoma cells. Nevertheless, it remains unknown whether CCT3 regulates the development of PTC. The present study examined CCT3 protein expression in 30 PTC samples from patients undergoing thyroidectomy. A significant increase was observed in CCT3 expression in the PTC samples compared with the matched adjacent normal thyroid tissues. Lentiviral-mediated small interfering RNAs were used to knock down CCT3 in K1 cells. It was observed that the expression of CCT3 was significantly suppressed in K1 cells infected with lentivirus containing a CCT3-targeting short hairpin RNA. Our results showed that CCT3 knockdown markedly decreased the proliferation and cell cycle progression of K1 cells. In addition, the knockdown of CCT3 induced apoptosis of K1 cell. Taken together, the findings of the present study indicated that CCT3 presents as a potential molecular marker of PTC and regulates the development of PTC in humans.

Silencing P2X7 receptor downregulates the expression of TCP-1 involved in lymphoma lymphatic metastasis

P2X₇R is an ATP-gated cation channel that participates in cell proliferation and apoptosis. TCP-1 assists with the protein folding. According to our previous research, the P2X₇R has a potential role in P388D1 lymphoid neoplasm cells dissemination to peripheral lymph nodes. In order to make a further exploration about the probable mechanism, the lymph nodes which metastasized by P2X₇R-silenced P388D1 cells or non-silenced cells were analyzed by 2DE and a MALDI-TOF-based proteomics approach. In the 64 proteins which were differentially expressed between two groups, TCP-1 was found to be significantly decreased in P2X₇R shRNA group compared to controls. This correlation was also found in subsequent experiments in vivo and in vitro. The positive correlation between P2X₇R and TCP-1 was also proved in both lymphoma and benign lymphadenopathy tissues from patients. It indicates that TCP-1 may be a crucial downstream molecular of P2X₇R and plays a novel role in lymphoid neoplasm metastasis.

Mining for genes related to choroidal neovascularization based on the shortest path algorithm and protein interaction information

BACKGROUND

Choroidal neovascularization (CNV) is a serious eye disease that may cause visual loss, especially for older people. Many factors have been proven to induce this disease including age, gender, obesity, and so on. However, until now, we have had limited knowledge on CNV's pathogenic mechanism. Discovering the genes that underlie this disease and performing extensive studies on them can help us to understand how CNV occurs and design effective treatments.

METHODS

In this study, we designed a computational method to identify novel CNV-related genes in a large protein network constructed using the protein-protein interaction information in STRING. The candidate genes were first extracted from the shortest paths connecting any two known CNV-related genes and then filtered by a permutation test and using knowledge of their linkages to known CNV-related genes.

RESULTS

A list of putative CNV-related candidate genes was accessed by our method. These genes are deemed to have strong relationships with CNV.

CONCLUSIONS

Extensive analyses of several of the putative genes such as ANK1, ITGA4, CD44 and others indicate that they are related to specific biological processes involved in CNV, implying they may be novel CNV-related genes.

GENERAL SIGNIFICANCE

The newfound putative CNV-related genes may provide new insights into CNV and help design more effective treatments. This article is part of a Special Issue entitled "System Genetics" Guest Editor: Dr. Yudong Cai and Dr. Tao Huang.

Molecular chaperone CCT3 supports proper mitotic progression and cell proliferation in hepatocellular carcinoma cells

CCT3 was one of the subunits of molecular chaperone CCT/TRiC complex, which plays a central role in maintaining cellular proteostasis. We demonstrated that expressions of CCT3 mRNA and protein are highly up-regulated in hepatocellular carcinoma (HCC) tissues, and high level of CCT3 is correlated with poor survival in cancer patients. In HCC cell lines, CCT3 depletion suppresses cell proliferation by inducing mitotic arrest at prometaphase and apoptosis eventually. We also identified CCT3 as a novel regulator of spindle integrity and as a requirement for proper kinetochore-microtubule attachment during mitosis. Moreover, we found that CCT3 depletion sensitizes HCC cells to microtubule destabilizing drug Vincristine. Collectively, our study suggests that CCT3 is indispensible for HCC cell proliferation, and provides a potential drug target for treatment of HCC.

Structural Basis for Modulation of Quality Control Fate in a Marginally Stable Protein

The human von Hippel-Lindau (VHL) tumor suppressor is a marginally stable protein previously used as a model substrate of eukaryotic refolding and degradation pathways. When expressed in the absence of its cofactors, VHL cannot fold and is quickly degraded by the quality control machinery of the cell. We combined computational methods with in vivo experiments to examine the basis of the misfolding propensity of VHL. By expressing a set of randomly mutated VHL sequences in yeast, we discovered a more stable mutant form. Subsequent modeling suggested the mutation had caused a conformational change affecting cofactor and chaperone interaction, and this hypothesis was then confirmed by additional knockout and overexpression experiments targeting a yeast cofactor homolog. These findings offer a detailed structural basis for the modulation of quality control fate in a model misfolded protein and highlight burial mode modeling as a rapid means to detect functionally important conformational changes in marginally stable globular domains.

Integrated proteomic and metabolic analysis of breast cancer progression

One of the most persistent hallmarks of cancer biology is the preference of tumor cells to derive energy through glycolysis as opposed to the more efficient process of oxidative phosphorylation (OXPHOS). However, little is known about the molecular cascades by which oncogenic pathways bring about this metabolic switch. We carried out a quantitative proteomic and metabolic analysis of the MCF10A derived cell line model of breast cancer progression that includes parental cells and derivatives representing three different tumor grades of Ras-driven cancer with a common genetic background. A SILAC (Stable Isotope Labeling by Amino acids in Cell culture) labeling strategy was used to quantify protein expression in conjunction with subcellular fractionation to measure dynamic subcellular localization in the nucleus, cytosol and mitochondria. Protein expression and localization across cell lines were compared to cellular metabolic rates as a measure of oxidative phosphorylation (OXPHOS), glycolysis and cellular ATP. Investigation of the metabolic capacity of the four cell lines revealed that cellular OXPHOS decreased with breast cancer progression independently of mitochondrial copy number or electron transport chain protein expression. Furthermore, glycolytic lactate secretion did not increase in accordance with cancer progression and decreasing OXPHOS capacity. However, the relative expression and subcellular enrichment of enzymes critical to lactate and pyruvate metabolism supported the observed extracellular acidification profiles. This analysis of metabolic dysfunction in cancer progression integrated with global protein expression and subcellular localization is a novel and useful technique for determining organelle-specific roles of proteins in disease.

The cytosolic chaperonin CCT/TRiC and cancer cell proliferation

The molecular chaperone CCT/TRiC plays a central role in maintaining cellular proteostasis as it mediates the folding of the major cytoskeletal proteins tubulins and actins. CCT/TRiC is also involved in the oncoprotein cyclin E, the Von Hippel-Lindau tumour suppressor protein, cyclin B and p21(ras) folding which strongly suggests that it is involved in cell proliferation and tumor genesis. To assess the involvement of CCT/TRiC in tumor genesis, we quantified its expression levels and activity in 18 cancer, one non-cancer human cell lines and a non-cancer human liver. We show that the expression levels of CCT/TRiC in cancer cell lines are higher than that in normal cells. However, CCT/TRiC activity does not always correlate with its expression levels. We therefore documented the expression levels of CCT/TRiC modulators and partners PhLP3, Hop/P60, prefoldin and Hsc/Hsp70. Our analysis reveals a functional interplay between molecular chaperones that might account for a precise modulation of CCT/TRiC activity in cell proliferation through changes in the cellular levels of prefoldin and/or Hsc/p70 and CCT/TRiC client protein availability. Our observation and approaches bring novel insights in the role of CCT/TRiC-mediated protein folding machinery in cancer cell development.

Proteostasis modulators prolong missense VHL protein activity and halt tumor progression

Although missense mutations of the von Hippel-Lindau disease (VHL) gene are the most common germline mutation underlying this heritable cancer syndrome, the mechanism of tumorigenesis is unknown. We found a quantitative reduction of missense mutant VHL protein (pVHL) in tumors associated with physiologic mRNA expression. Although mutant pVHL is unstable and degraded contemporarily with translation, it retains its E3 ligase function, including hypoxia-inducible factor degradation. The premature pVHL degradation is due to misfolding and imbalance of chaperonin binding. Histone deacetylase inhibitors (HDACIs) can modulate this pathway by inhibiting the HDAC-Hsp90 chaperone axis, stabilizing pVHL, and restoring activity comparable to wild-type protein, both in vitro and in animal models. Furthermore, HDACI-mediated stabilization of missense pVHL significantly attenuates the growth of 786-O rodent tumor model. These findings provide direct biological insight into VHL-associated tumors and elucidate a treatment paradigm for VHL.

State of the science: an update on renal cell carcinoma

Renal cell carcinomas (RCC) are emerging as a complex set of diseases that are having a major socioeconomic impact and showing a continued rise in incidence throughout the world. As the field of urologic oncology faces these trends, several major genomic and mechanistic discoveries are altering our core understanding of this multitude of cancers, including several new rare subtypes of renal cancers. In this review, these new findings are examined and placed in the context of the well-established association of clear cell RCC (ccRCC) with mutations in the von Hippel-Lindau (VHL) gene and resultant aberrant hypoxia inducible factor (HIF) signaling. The impact of novel ccRCC-associated genetic lesions on chromatin remodeling and epigenetic regulation is explored. The effects of VHL mutation on primary ciliary function, extracellular matrix homeostasis, and tumor metabolism are discussed. Studies of VHL proteostasis, with the goal of harnessing the proteostatic machinery to refunctionalize mutant VHL, are reviewed. Translational efforts using molecular tools to elucidate discriminating features of ccRCC tumors and develop improved prognostic and predictive algorithms are presented, and new therapeutics arising from the earliest molecular discoveries in ccRCC are summarized. By creating an integrated review of the key genomic and molecular biological disease characteristics of ccRCC and placing these data in the context of the evolving therapeutic landscape, we intend to facilitate interaction among basic, translational, and clinical researchers involved in the treatment of this devastating disease, and accelerate progress toward its ultimate eradication.

Drosophila Mgr, a Prefoldin subunit cooperating with von Hippel Lindau to regulate tubulin stability

Mutations in Drosophila merry-go-round (mgr) have been known for over two decades to lead to circular mitotic figures and loss of meiotic spindle integrity. However, the identity of its gene product has remained undiscovered. We now show that mgr encodes the Prefoldin subunit counterpart of human von Hippel Lindau binding-protein 1. Depletion of Mgr from cultured cells also leads to formation of monopolar and abnormal spindles and centrosome loss. These phenotypes are associated with reductions of tubulin levels in both mgr flies and mgr RNAi-treated cultured cells. Moreover, mgr spindle defects can be phenocopied by depleting β-tubulin, suggesting Mgr function is required for tubulin stability. Instability of β-tubulin in the mgr larval brain is less pronounced than in either mgr testes or in cultured cells. However, expression of transgenic β-tubulin in the larval brain leads to increased tubulin instability, indicating that Prefoldin might only be required when tubulins are synthesized at high levels. Mgr interacts with Drosophila von Hippel Lindau protein (Vhl). Both proteins interact with unpolymerized tubulins, suggesting they cooperate in regulating tubulin functions. Accordingly, codepletion of Vhl with Mgr gives partial rescue of tubulin instability, monopolar spindle formation, and loss of centrosomes, leading us to propose a requirement for Vhl to promote degradation of incorrectly folded tubulin in the absence of functional Prefoldin. Thus, Vhl may play a pivotal role: promoting microtubule stabilization when tubulins are correctly folded by Prefoldin and tubulin destruction when they are not.

Targeted therapy in renal cancer

Renal cell cancer (RCC) has an increasing incidence internationally and is a disease for which there have been limited therapeutic options until recently. The last decade has seen a vastly improved understanding of the biological and clinical factors that predict the outcome of this disease. We now understand some of the different molecular underpinnings of renal clear cell carcinoma by mutation or silencing of the von Hippel Lindau (VHL) gene and subsequent deregulated proliferation and angiogenesis. Survival in advanced disease is predicted by factors (performance status, anemia, hypercalcemia, and serum lactate dehydrogenase, time from diagnosis to recurrence) incorporated into the Memorial Sloan Kettering Cancer Center (MSKCC) criteria (also referred to as 'Motzer' criteria). These criteria allow classification of patients with RCC into good, intermediate and poor risk categories with median overall survivals of 22 months, 12 months and 5.4 months, respectively. Predicated upon these advances, six new targeted drugs (sorafenib, sunitinib, temsirolimus, everolimus, bevacizumab and pazopanib) have been tested in well-designed phase III trials, selected or stratified for MSKCC risk criteria, with positive results. All of these new drugs act at least in part through vascular endothelial growth factor (VEGF) mediated pathways with other potential therapeutic impact on platelet-derived growth factor (PDGF), raf kinase and mammalian target of rapamycin (mTOR) pathways. Importantly, data from each of these trials show a consistent doubling of progression-free survival (PFS) over prior standard of care treatments. In addition, sorafenib, sunitinib and temsirolimus, have demonstrated significant overall survival (OS) benefits as well; further follow-up is required to determine whether the disease control exhibited by everolimus and pazopanib will translate into a survival advantage. These drugs are generally well tolerated, as demonstrated by quality-of-life improvement in clinical trials, and result in clinical benefit for in excess of 70% of patients treated. They have challenged the traditional outcomes of clinical trial design by achieving their benefits with relatively few radiographic responses, but high rates of disease stability. The unique side-effect profile coupled with the chronicity of therapy requires increased vigilance to maximize exposure to the drugs while maintaining quality of life and minimizing toxicity. This review focuses on the background, clinical development and practical use of these new drugs in RCC.

VHL mutations and dysregulation of pVHL- and PTEN-controlled pathways in multilocular cystic renal cell carcinoma

Multilocular cystic renal cell carcinoma is a rare renal cell carcinoma with an excellent prognosis. To clarify the relationship with typical clear cell renal cell carcinoma, we evaluated 15 cases of multilocular cystic renal cell carcinomas diagnosed according to the 2004 WHO classification. Von Hippel Lindau (VHL) gene mutations were determined by whole genome amplification and direct sequencing. Carbonic anhydrase 9 (CAIX), a hypoxia-inducible factor (HIF) target, paired box gene 2 (PAX2), cyclin-dependent kinase inhibitor p27 and glycogen synthase kinase 3-β (GSK3β) were immunohistochemically evaluated as members of the VHL protein (pVHL)- and phosphatase and tensin homolog (PTEN)-controlled pathways. VHL mutations were identified in 3 of 12 (25%) tumors. Inactivated GSK3β, decreased PTEN expression and PAX2 positivity were observed in the vast majority of the multilocular cystic renal cell carcinomas. Strong nuclear staining of p27 was seen in 14 of 15 cases. Compared with multilocular cystic renal cell carcinomas, expression frequencies of PAX2, p-GSK3β, PTEN and CAIX were similar in a set of low-grade, early-stage clear cell renal cell carcinomas, whereas only 30% had strong p27 positivity. These results are consistent with the hypothesis that multilocular cystic renal cell carcinomas are related at the molecular level with clear cell renal cell carcinomas. Maintenance of a strong subcellular p27 expression in all multilocular cystic renal cell carcinomas analyzed may in part explain the excellent prognosis of these tumor patients.

Small molecule regulators of Rb-E2F pathway as modulators of transcription

The retinoblastoma tumor suppressor protein, Rb, plays a major role in the regulation of mammalian cell cycle progression. It has been shown that Rb function is essential for the proper modulation of G1/S transition and inactivation of Rb contributes to deregulated cell proliferation. Rb exerts its cell cycle regulatory functions mainly by targeting the E2F family of transcription factors and Rb has been shown to physically interact with E2Fs 1, 2 and 3, repressing their transcriptional activity. Multiple genes involved in DNA synthesis and cell cycle progression are regulated by E2Fs, and Rb prevents their expression by inhibiting E2F activity, inducing growth arrest. It has been established that inactivation of Rb by phosphorylation, mutation, or by the interaction of viral oncoproteins leads to a release of the repression of E2F activity, facilitating cell cycle progression. Rb-mediated repression of E2F activity involves the recruitment of a variety of transcriptional co-repressors and chromatin remodeling proteins, including histone deacetylases, DNA methyltransferases and Brg1/Brm chromatin remodeling proteins. Inactivation of Rb by sequential phosphorylation events during cell cycle progression leads to a dissociation of these co-repressors from Rb, facilitating transcription. It has been found that small molecules that prevent the phosphorylation of Rb prevent the dissociation of certain co-repressors from Rb, especially Brg1, leading to the maintenance of Rb-mediated transcriptional repression and cell cycle arrest. Such small molecules have anti-cancer activities and will also act as valuable probes to study chromatin remodeling and transcriptional regulation.

Regulation of receptor for activated C kinase 1 protein by the von Hippel-Lindau tumor suppressor in IGF-I-induced renal carcinoma cell invasiveness

von Hippel-Lindau (VHL) tumor suppressor loss is associated with renal cell carcinoma (RCC) pathogenesis. Meanwhile, aberrant activation of the insulin-like growth factor-I (IGF-I) signaling has been implicated in the development of highly invasive metastatic RCC. However, the link between VHL inactivation and RCC invasiveness is still unexplored. Here, we show that the receptor for activated C kinase 1 (RACK1) is a novel pVHL-interacting protein. pVHL competes with IGF-I receptor (IGF-IR) for binding to RACK1 thus potentially modulating the downstream IGF-I signal pathway. Upon IGF-I stimulation, pVHL-deficient RCC cells exhibit increased RACK1/IGF-IR binding and increased IGF-IR tyrosine kinase activity. pVHL-deficient RCC cells also demonstrate elevated PI3K/Akt signaling and matrix metalloproteinase-2 activity that culminates in enhanced cellular invasiveness, which can be partially suppressed by RACK1 small interfering RNA. Domain mapping analysis showed that the pVHL α-domain and the RACK1 WD 6-7 domains are critical for the interaction. Additionally, the RACK1 expression level is not regulated by pVHL expression status, suggesting that pVHL modifies RACK1 functions independent of the VHL/elongin E3 ubiquitin ligase complex. Our data indicate that RACK1 serves as a direct mediator between loss of pVHL function and enhanced IGF-IR signaling pathway in RCC.

VHL mutations linked to type 2C von Hippel-Lindau disease cause extensive structural perturbations in pVHL

pVHL (von Hippel-Lindau tumor suppressor protein) is the substrate recognition subunit of the CBC(VHL) ubiquitin ligase complex promoting the degradation of hypoxia-inducible factor subunits, HIF-1/2alpha. Mutational inactivation of pVHL causes the hereditary von Hippel-Lindau tumor syndrome, which predisposes affected individuals to hemangioblastomas, renal cell carcinomas, and pheochromocytomas. Whereas the development of hemangioblastomas and renal cell carcinomas has been attributed to impaired HIF-1/2alpha down-regulation by pVHL mutant proteins, the molecular defects underlying the development of pheochromocytomas are still unknown. Here, we present a detailed biochemical analysis of pVHL mutant proteins linked to type 2C (pheochromocytoma only) von Hippel-Lindau disease. Type 2C-associated mutations caused extensive structural perturbations of pVHL, as revealed by the reduced stability, increased proteolytic susceptibility, and dramatically altered NMR spectrum of recombinant, mutant pVHL-ElonginC-ElonginB complexes in vitro. In human cell lines, type 2C-linked mutations destabilized the CBC(VHL) ubiquitin ligase complex and resulted in reduced cellular pVHL levels. Together, our data reveal unexpectedly strong structural defects of type 2C-associated pVHL mutant proteins that are likely to affect both HIF-1/2alpha-related and -unrelated pVHL functions in the pathogenesis of pheochromocytomas.

Subcellular dynamics of the VHL tumor suppressor: on the move for HIF degradation

The von Hippel–Lindau (VHL) tumor suppressor protein, the recognition component of an E3 ubiquitin ligase complex, recruits the α-subunit of the hypoxia-inducible factor (HIFα) for oxygen-dependent degradation. The ability of VHL to mediate efficient degradation of HIFα is also dependent on its oxygen/pH-regulated subcellular trafficking. Under aerobic conditions, VHL engages in nuclear–cytoplasmic trafficking that requires ongoing transcription and is mediated by a novel nuclear export motif, the transcription-dependent nuclear export motif (TD-NEM). Disease-causing mutations targeting TD-NEM restrain VHL from mediating efficient oxygen-dependent degradation of HIFα by altering its subcellular dynamics. In addition, decreasing the extracellular pH, during anaerobic metabolism, stabilizes HIFα by triggering the relocalization and static detention of VHL to nucleoli. Together, these recent findings support the critical role of subcellular trafficking and dynamic properties for the function of VHL in promoting HIF regulation and tumor suppression.

von Hippel-Lindau tumor suppressor gene-dependent mRNA stabilization of the survival factor parathyroid hormone-related protein in human renal cell carcinoma by the RNA-binding protein HuR

We have shown that parathyroid hormone-related protein (PTHrP) is a survival factor for human renal cell carcinoma (RCC) and that its expression is negatively regulated by the von Hippel-Lindau (VHL) tumor suppressor gene at the level of messenger RNA (mRNA) stability, as observed for tumor growth factors (TGFs). Our goals were to analyze the alternative splicing of PTHrP mRNA in human RCC and from these results to identify VHL/hypoxia-induced factor (HIF) system-regulated mRNA-binding proteins involved in PTHrP mRNA stability. We used: (i) a panel of human RCC cells expressing or not VHL; (ii) VHL-deficient 786-0 cells transfected with active or inactive VHL and (iii) human RCC samples and corresponding normal tissues. By quantitative real-time reverse transcription-polymerase chain reaction analysis, the 141 PTHrP mRNA isoform was found to be predominant in all cells and tumors (80%). In cells transfected with VHL, the expressions of all isoforms were decreased by 50%. Eight proteins with molecular weights ranging from 20 to 75 kDa were found to bind to biotinylated transcripts spanning the 141 PTHrP mRNA AU-rich 3'-untranslated region whose abundancy was dependent on VHL expression. The protein having an apparent molecular weight of 30 kDa was identified by western blot as HuR, a RNA-binding protein with stabilizing functions on various mRNA coding for proteins important in malignant transformation including vascular endothelial growth factor and TGF-beta. PTHrP expression studies confirmed the involvement of HuR in PTHrP upregulation in this disease. Common mRNA-binding proteins regulated by the VHL/HIF system may constitute new therapeutic opportunities against human RCC that remains refractory to therapies.

VHL type 2B mutations retain VBC complex form and function

BACKGROUND

von Hippel-Lindau disease is characterized by a spectrum of hypervascular tumors, including renal cell carcinoma, hemangioblastoma, and pheochromocytoma, which occur with VHL genotype-specific differences in penetrance. VHL loss causes a failure to regulate the hypoxia inducible factors (HIF-1alpha and HIF-2alpha), resulting in accumulation of both factors to high levels. Although HIF dysregulation is critical to VHL disease-associated renal tumorigenesis, increasing evidence points toward gradations of HIF dysregulation contributing to the degree of predisposition to renal cell carcinoma and other manifestations of the disease.

METHODOLOGY/PRINCIPAL FINDINGS

This investigation examined the ability of disease-specific VHL missense mutations to support the assembly of the VBC complex and to promote the ubiquitylation of HIF. Our interaction analysis supported previous observations that VHL Type 2B mutations disrupt the interaction between pVHL and Elongin C but maintain partial regulation of HIF. We additionally demonstrated that Type 2B mutant pVHL forms a remnant VBC complex containing the active members ROC1 and Cullin-2 which retains the ability to ubiquitylate HIF-1alpha.

CONCLUSIONS

Our results suggest that subtypes of VHL mutations support an intermediate level of HIF regulation via a remnant VBC complex. These findings provide a mechanism for the graded HIF dysregulation and genetic predisposition for cancer development in VHL disease.

Nuclear E-cadherin and VHL immunoreactivity are prognostic indicators of clear-cell renal cell carcinoma

The loss of functional von Hippel-Lindau (VHL) tumor suppressor gene is associated with the development of clear-cell renal cell carcinoma (CC-RCC). Recently, VHL was shown to promote the transcription of E-cadherin, an adhesion molecule whose expression is inversely correlated with the aggressive phenotype of numerous epithelial cancers. Here, we performed immunohistochemistry on CC-RCC tissue microarrays to determine the prognostic value of E-cadherin and VHL with respect to Fuhrman grade and clinical prognosis. Low Fuhrman grade and good prognosis associated with positive VHL and E-cadherin immunoreactivity, whereas poor prognosis and high-grade tumors associated with a lack of E-cadherin and lower frequency of VHL staining. A significant portion of CC-RCC with positive VHL immunostaining correlated with nuclear localization of C-terminally cleaved E-cadherin. DNA sequencing revealed in a majority of nuclear E-cadherin-positive CC-RCC, subtle point mutations, deletions and insertions in VHL. Furthermore, nuclear E-cadherin was not observed in chromophobe or papillary RCC, as well as matched normal kidney tissue. In addition, nuclear E-cadherin localization was recapitulated in CC-RCC xenografts devoid of functional VHL or reconstituted with synthetic mutant VHL grown in SCID mice. These findings provide the first evidence of aberrant nuclear localization of E-cadherin in CC-RCC harboring VHL mutations, and suggest potential prognostic value of VHL and E-cadherin in CC-RCC.

Cancer-causing mutations in a novel transcription-dependent nuclear export motif of VHL abrogate oxygen-dependent degradation of hypoxia-inducible factor

It is thought that degradation of nuclear proteins by the ubiquitylation system requires nuclear-cytoplasmic trafficking of E3 ubiquitin ligases. The von Hippel-Lindau (VHL) tumor suppressor protein is the substrate recognition component of a Cullin-2-containing E3 ubiquitin ligase that recruits hypoxia-inducible factor (HIF) for oxygen-dependent degradation. We demonstrated that VHL engages in nuclear-cytoplasmic trafficking that requires ongoing transcription to promote efficient HIF degradation. Here, we report the identification of a discreet motif, DXGX(2)DX(2)L, that directs transcription-dependent nuclear export of VHL and which is targeted by naturally occurring mutations associated with renal carcinoma and polycythemia in humans. The DXGX(2)DX(2)L motif is also found in other proteins, including poly(A)-binding protein 1, to direct its transcription-dependent nuclear export. We define DXGX(2)DX(2)L as TD-NEM (transcription-dependent nuclear export motif), since inhibition of transcription by actinomycin D or 5,6-dichlorobenzimidazole abrogates its nuclear export activity. Disease-causing mutations of key residues of TD-NEM restrain the ability of VHL to efficiently mediate oxygen-dependent degradation of HIF by altering its nuclear export dynamics without affecting interaction with its substrate. These results identify a novel nuclear export motif, further highlight the role of nuclear-cytoplasmic shuttling of E3 ligases in degradation of nuclear substrates, and provide evidence that disease-causing mutations can target subcellular trafficking.

Sorafenib

Sorafenib is a small molecule inhibitor of several kinases involved in tumour proliferation and tumour angiogenesis including Raf, VEGFR and platelet derived growth factor receptor. In vivo Raf kinase inhibition has been observed in pharmacodynamic studies. Sorafenib is one of several VEGF-targeting compounds with recently demonstrated substantial anti-tumour effects in metastatic renal cell carcinoma. Delay in time to disease progression has been demonstrated in cytokine-refractory metastatic renal cell carcinoma, and further investigation is ongoing in a wide variety of tumour types. Sorafenib is well tolerated, with common toxicities including rash, diarrhoea, hand-foot skin reaction, fatigue and hypertension, when administered as the standard dose of 400 mg b.i.d.

The evolving role of surgery for advanced renal cell carcinoma in the era of molecular targeted therapy

PURPOSE

Thoughtful integration of surgical and medical approaches to metastatic renal cell carcinoma is paramount for maximizing disease control. Accomplishing this in the current era of targeted molecular therapies presents unique challenges and opportunities.

MATERIALS AND METHODS

A systematic review of the MEDLINE and PubMed databases, and relevant urological and oncological journals was performed pertaining to cytoreductive nephrectomy, metastasectomy, targeted molecular therapies for renal cell carcinoma, and neoadjuvant and adjuvant approaches to the management of advanced renal cell carcinoma.

RESULTS

Cytoreductive nephrectomy provides an overall survival advantage in select patients with metastatic renal cell carcinoma who receive subsequent interferon-alpha. However, cytokine therapies are now being supplanted by targeted molecular approaches that block the effects of vascular endothelial growth factor and other molecular events. Although cytoreductive nephrectomy remains a standard of care, limited insight into the biological effects of nephrectomy on mechanisms such as immunoregulation and angiogenesis precludes definitive statements about how to integrate surgery and targeted agents. Ongoing investigation involving basic science and translational research is required to optimize the integration of these approaches. Adjuvant and neoadjuvant vascular endothelial growth factor targeted approaches to renal cell carcinoma are now also being explored and the unique side effects of these agents, including potential effects on wound healing and vascular integrity, require careful consideration.

CONCLUSIONS

Integrated approaches involving surgery and vascular endothelial growth factor targeted therapies hold much promise for the management of advanced renal cell carcinoma. Prospective clinical testing with vigilant attention to the risk-benefit ratio and thoughtful evaluation of biological correlates are required to optimize these approaches.

Characterization and over-expression of chaperonin t-complex proteins in colorectal cancer

The chaperonins are key molecular complexes, which are essential in the folding of proteins to produce stable and functionally competent protein conformations. One member of the chaperonin group of proteins is TCP1 (chaperonin containing t-complex polypeptide 1, or CCT), but little is known about this protein in tumours. In this study, we used comparative proteomic analysis to show that t-complex protein subunits TCP1 beta and TCP1 epsilon are over-expressed in colorectal adenocarcinomas. Monoclonal antibodies to these proteins were developed and the expression and cellular localization of these two proteins in colorectal cancer were analysed by immunohistochemistry on a colorectal cancer tissue microarray. In colorectal cancer, TCP1 beta cellular localization was exclusively cytoplasmic, whereas TCP1 epsilon staining was seen in both the nucleus and the cytoplasm. Both cytoplasmic TCP1 beta and cytoplasmic TCP1 epsilon were significantly over-expressed (p < 0.001 for each protein) in primary colorectal cancer and also showed increased expression with advancing Dukes' stage (p = 0.018 for TCP1 beta and p = 0.045 for TCP1 epsilon). A trend was also identified between over-expression of cytoplasmic TCP1 beta and reduced patient survival (p = 0.05). These results show that both TCP1 beta and TCP1 epsilon are over-expressed in colorectal cancer and indicate a role for TCP1 beta and TCP1 epsilon in colorectal cancer progression.

On the brotherhood of the mitochondrial chaperones mortalin and heat shock protein 60

The heat shock chaperones mortalin/mitochondrial heat shock protein 70 (mtHsp70) and Hsp60 are found in multiple subcellular sites and function in the folding and intracellular trafficking of many proteins. The chaperoning activity of these 2 proteins involves different structural and functional mechanisms. In spite of providing an excellent model for an evolutionarily conserved molecular "brotherhood", their individual functions, although overlapping, are nonredundant. As they travel to various locations, both chaperones acquire different binding partners and exert a more divergent involvement in tumorigenesis, cellular senescence, and immunology. An understanding of their functional biology may lead to novel designing and development of therapeutic strategies for cancer and aging.

Regulation of angiogenesis by hypoxia-inducible factor 1

Hypoxia is an imbalance between oxygen supply and demand that occurs in cancer and in ischemic cardiovascular disease. Hypoxia-inducible factor 1 (HIF-1) was originally identified as the transcription factor that mediates hypoxia-induced erythropoietin expression. More recently, the delineation of molecular mechanisms of angiogenesis has revealed a critical role for HIF-1 in the regulation of angiogenic growth factors. In this review, we discuss the role of HIF-1 in developmental, adaptive and pathological angiogenesis. In addition, potential therapeutic interventions involving modulation of HIF-1 activity in ischemic cardiovascular disease and cancer will be discussed.

Role of the chaperonin CCT/TRiC complex in G protein betagamma-dimer assembly

Gbetagamma dimer formation occurs early in the assembly of heterotrimeric G proteins. On nondenaturing (native) gels, in vitro translated, (35)S-labeled Ggamma subunits traveled primarily according to their pI and apparently were not associated with other proteins. In contrast, in vitro translated, (35)S-labeled Gbeta subunits traveled at a high apparent molecular mass (approximately 700 kDa) and co-migrated with the chaperonin CCT complex (also called TRiC). Different FLAG-Gbeta isoforms coprecipitated CCT/TRiC to a variable extent, and this correlated with the ability of the different Gbeta subunits to efficiently form dimers with Ggamma. When translated Ggamma was added to translated Gbeta, a new band of low apparent molecular mass (approximately 50 kDa) was observed, which was labeled by either (35)S-labeled Gbeta or Ggamma, indicating that it is a dimer. Formation of the Gbetagamma dimer was ATP-dependent and inhibited by either adenosine 5'-O-(thiotriphosphate) or aluminum fluoride in the presence of Mg(2+). This inhibition led to increased association of Gbeta with CCT/TRiC. Although Ggamma did not bind CCT/TRiC, addition of Ggamma to previously synthesized Gbeta caused its release from the CCT/TRiC complex. We conclude that the chaperonin CCT/TRiC complex binds to and folds Gbeta subunits and that CCT/TRiC mediates Gbetagamma dimer formation by an ATP-dependent reaction.

VEGF-targeted therapy in renal cell carcinoma: Active drugs and active choices

Several molecular pathways are implicated in renal cell carcinoma (RCC) pathogenesis, including von Hippel--Lindau (VHL) gene inactivation leading to vascular endothelial growth factor (VEGF) expression. Therapeutic targeting of VEGF and related pathways has been undertaken in metastatic RCC. Substantial clinical activity has been reported for multiple agents, leading to several clinical questions regarding the optimal use of these agents. The biology, clinical results, and future considerations regarding VEGF-targeted agents in RCC are presented in this article.

Renal cell carcinoma risk in type 2 von Hippel-Lindau disease correlates with defects in pVHL stability and HIF-1alpha interactions

The von Hippel-Lindau (VHL) tumor suppressor protein is the substrate binding subunit of the CBC(VHL) E3 ubiquitin ligase complex. Mutations in the VHL gene cause a variety of tumors with complex genotype/phenotype correlations. Type 2A and type 2B VHL disease are characterized by a low or high risk of renal cell carcinoma, respectively. To investigate the molecular basis underlying the difference between disease types 2A and 2B, we performed a detailed biochemical analysis of the two most frequent type 2A mutations, Y98 H and Y112 H, in comparison to type 2B mutations in the same residues, Y98N and Y112N. While none of these mutations affected the assembly of CBC(VHL) complexes, the type 2A mutant proteins exhibited higher stabilities at physiological temperature. Moreover, the type 2A mutant proteins possessed higher binding affinities for the key cellular substrate, hypoxia-inducible transcription factor 1 (HIF-1alpha). Consistent with these results, type 2A but not type 2B mutant VHL proteins retained significant ubiquitin ligase activity towards HIF-1alpha in vitro. We propose that this residual ubiquitin ligase activity is sufficient to suppress renal cell carcinogenesis in vivo.

SU11248 and AG013736: Current Data and Future Trials in Renal Cell Carcinoma

Several molecular pathways are implicated in renal cell carcinoma (RCC) pathogenesis, including the von Hippel-Lindau gene inactivation leading to vascular endothelial growth factor (VEGF) and platelet derived growth factor (PDGF) expression. SU11248 and AG013736 are small-molecule inhibitors of the tyrosine kinase portion of the VEGF and PDGF receptors. Substantial clinical activity has been reported for these agents in metastatic RCC trials, leading to additional investigations in a variety of settings.