Identification of novel VHL target genes and relationship to hypoxic response pathways

Genotype-phenotype correlation of ocular von Hippel-Lindau disease in Koreans

This scientific report aims to investigate the genotype-phenotype correlations of retinal hemangioblastoma (RH) in von Hippel-Lindau (VHL) disease. The study included 77 patients with genetically confirmed VHL disease who visited an ophthalmology clinic for the evaluation of RH. The presence, location, and size of RH were evaluated, Patients were categorized into three groups based on variants: HIF-1α binding site missense (HM), non-HIF-1α binding site missense (nHM), and truncating (TR) mutations. Fifty-six patients (72.7%) had RH in either eye, and 24 had bilateral RH. Sixteen patients (20.8%) had juxtapapillary RH in either eye. Nine patients had RH ≥ 2.0 disc diameters in size. VHL c.208G>A variant was the most frequent single mutation. Compared with patients having nHM mutations (15 patients) in VHL gene, patients with HM mutations (33 patients) or TR mutations (26 patients) presented a greater number of eyes affected (p = 0.007 and 0.004, respectively), a greater number of RH (p = 0.012 and 0.003, respectively), and more frequent presentation of large RH ≥ 2.0 disc diameters (p = 0.012, and 0.013, respectively). In conclusion, this study provides a deeper understanding of the genetic spectrum of VHL disease in Korean VHL disease and highlights the importance of the location of missense mutations regarding the risk of RH.

GPR56 signaling pathway network and its dynamics in the mesenchymal transition of glioblastoma

G protein-coupled receptor 56 (GPR56/ADGRG1) is a multifunctional adhesion GPCR involved in diverse biological processes ranging from development to cancer. In our earlier study, we reported that GPR56 is expressed heterogeneously in glioblastoma (GBM) and is involved in the mesenchymal transition, making it a promising therapeutic target (Ganesh et al., 2022). Despite its important role in cancer, its mechanism of action or signaling is not completely understood. Thus, based on transcriptomic, proteomic, and phosphoproteomic differential expression data of GPR56 knockdown U373-GBM cells included in our above study along with detailed literature mining of the molecular events plausibly associated with GPR56 activity, we have constructed a signaling pathway map of GPR56 as may be applicable in mesenchymal transition in GBM. The map incorporates more than 100 molecular entities including kinases, receptors, ion channels, and others associated with Wnt, integrin, calcium signaling, growth factors, and inflammation signaling pathways. We also considered intracellular and extracellular factors that may influence the activity of the pathway entities. Here we present a curated signaling map of GPR56 in the context of GBM and discuss the relevance and plausible cross-connectivity across different axes attributable to GPR56 function. GPR56 signaling and mesenchymal transition.

GATA3 induces the pathogenicity of Th17 cells via regulating GM-CSF expression

T-bet-expressing Th17 (T-bet+RORγt+) cells are associated with the induction of pathology during experimental autoimmune encephalomyelitis (EAE) and the encephalitic nature of these Th17 cells can be explained by their ability to produce GM-CSF. However, the upstream regulatory mechanisms that control Csf2 (gene encoding GM-CSF) expression are still unclear. In this study, we found that Th17 cells dynamically expressed GATA3, the master transcription factor for Th2 cell differentiation, during their differentiation both in vitro and in vivo. Early deletion of Gata3 in three complimentary conditional knockout models by Cre-ERT2, hCd2 Cre and Tbx21 Cre, respectively, limited the pathogenicity of Th17 cells during EAE, which was correlated with a defect in generating pathogenic T-bet-expressing Th17 cells. These results indicate that early GATA3-dependent gene regulation is critically required to generate a de novo encephalitogenic Th17 response. Furthermore, a late deletion of Gata3 via Cre-ERT2 in the adoptive transfer EAE model resulted in a cell intrinsic failure to induce EAE symptoms which was correlated with a substantial reduction in GM-CSF production without affecting the generation and/or maintenance of T-bet-expressing Th17 cells. RNA-Seq analysis of Gata3-sufficient and Gata3-deficient CNS-infiltrating CD4+ effector T cells from mixed congenic co-transfer recipient mice revealed an important, cell-intrinsic, function of GATA3 in regulating the expression of Egr2, Bhlhe40, and Csf2. Thus, our data highlights a novel role for GATA3 in promoting and maintaining the pathogenicity of T-bet-expressing Th17 cells in EAE, via putative regulation of Egr2, Bhlhe40, and GM-CSF expression.

G protein gamma subunit, a hidden master regulator of GPCR signaling

Heterotrimeric G proteins (αβγ subunits) that are activated by G protein-coupled receptors (GPCRs) mediate the biological responses of eukaryotic cells to extracellular signals. The α subunits and the tightly bound βγ subunit complex of G proteins have been extensively studied and shown to control the activity of effector molecules. In contrast, the potential roles of the large family of γ subunits have been less studied. In this review, we focus on present knowledge about these proteins. Induced loss of individual γ subunit types in animal and plant models result in strikingly distinct phenotypes indicating that γ subtypes play important and specific roles. Consistent with these findings, downregulation or upregulation of particular γ subunit types result in various types of cancers. Clues about the mechanistic basis of γ subunit function have emerged from imaging the dynamic behavior of G protein subunits in living cells. This shows that in the basal state, G proteins are not constrained to the plasma membrane but shuttle between membranes and on receptor activation βγ complexes translocate reversibly to internal membranes. The translocation kinetics of βγ complexes varies widely and is determined by the membrane affinity of the associated γ subtype. On translocating, some βγ complexes act on effectors in internal membranes. The variation in translocation kinetics determines differential sensitivity and adaptation of cells to external signals. Membrane affinity of γ subunits is thus a parsimonious and elegant mechanism that controls information flow to internal cell membranes while modulating signaling responses.

Epigenetic analysis in placentas from sickle cell disease patients reveals a hypermethylation profile

Pregnancy in Sickle Cell Disease (SCD) women is associated to increased risk of clinical and obstetrical complications. Placentas from SCD pregnancies can present increased abnormal findings, which may lead to placental insufficiency, favoring adverse perinatal outcome. These placental abnormalities are well known and reported, however little is known about the molecular mechanisms, such as epigenetics. Thus, our aim was to evaluate the DNA methylation profile in placentas from women with SCD (HbSS and HbSC genotypes), compared to uncomplicated controls (HbAA). We included in this study 11 pregnant women with HbSS, 11 with HbSC and 21 with HbAA genotypes. Illumina Methylation EPIC BeadChip was used to assess the whole placental DNA methylation. Pyrosequencing was used for array data validation and qRT-PCR was applied for gene expression analysis. Our results showed high frequency of hypermethylated CpGs sites in HbSS and HbSC groups with 73.5% and 76.2% respectively, when compared with the control group. Differentially methylated regions (DMRs) also showed an increased hypermethylation status for the HbSS (89%) and HbSC (86%) groups, when compared with the control group methylation data. DMRs were selected for methylation validation (4 DMRs-HbSS and 3 DMRs the HbSC groups) and after analyses three were validated in the HbSS group, and none in the HbSC group. The gene expression analysis showed differential expression for the PTGFR (-2.97-fold) and GPR56 (3.0-fold) genes in the HbSS group, and for the SPOCK1 (-2.40-fold) and ADCY4 (1.80-fold) genes in the HbSC group. Taken together, these data strongly suggest that SCD (HbSS and HbSC genotypes) can alter placental DNA methylation and lead to gene expression changes. These changes possibly contribute to abnormal placental development and could impact in the clinical course, especially for the fetus, possibly leading to increased risk of abortion, fetal growth restriction (FGR), stillbirth, small for gestational age newborns and prematurity.

Multi-Omics Analysis of Glioblastoma and Glioblastoma Cell Line: Molecular Insights Into the Functional Role of GPR56 and TG2 in Mesenchymal Transition

G protein-coupled receptor 56 (GPR56/ADGRG1) is an adhesion GPCR with an essential role in brain development and cancer. Elevated expression of GPR56 was observed in the clinical specimens of Glioblastoma (GBM), a highly invasive primary brain tumor. However, we found the expression to be variable across the specimens, presumably due to the intratumor heterogeneity of GBM. Therefore, we re-examined GPR56 expression in public domain spatial gene expression data and single-cell expression data for GBM, which revealed that GPR56 expression was high in cellular tumors, infiltrating tumor cells, and proliferating cells, low in microvascular proliferation and peri-necrotic areas of the tumor, especially in hypoxic mesenchymal-like cells. To gain a better understanding of the consequences of GPR56 downregulation in tumor cells and other molecular changes associated with it, we generated a sh-RNA-mediated GPR56 knockdown in the GBM cell line U373 and performed transcriptomics, proteomics, and phospho-proteomics analysis. Our analysis revealed enrichment of gene signatures, pathways, and phosphorylation of proteins potentially associated with mesenchymal (MES) transition in the tumor and concurrent increase in cell invasion and migration behavior of the GPR56 knockdown GBM cells. Interestingly, our analysis also showed elevated expression of Transglutaminase 2 (TG2) - a known interactor of GPR56, in the knockdown cells. The inverse expression of GPR56 and TG2 was also observed in intratumoral, spatial gene expression data for GBM and in GBM cell lines cultured in vitro under hypoxic conditions. Integrating all these observations, we propose a putative functional link between the inverse expression of the two proteins, the hypoxic niche and the mesenchymal status in the tumor. Hypoxia-induced downregulation of GPR56 and activation of TG2 may result in a network of molecular events that contribute to the mesenchymal transition of GBM cells, and we propose a putative model to explain this functional and regulatory relationship of the two proteins.

Subtype-dependent regulation of Gβγ signalling

G protein-coupled receptors (GPCRs) transmit information to the cell interior by transducing external signals to heterotrimeric G protein subunits, Gα and Gβγ subunits, localized on the inner leaflet of the plasma membrane. Though the initial focus was mainly on Gα-mediated events, Gβγ subunits were later identified as major contributors to GPCR-G protein signalling. A broad functional array of Gβγ signalling has recently been attributed to Gβ and Gγ subtype diversity, comprising 5 Gβ and 12 Gγ subtypes, respectively. In addition to displaying selectivity towards each other to form the Gβγ dimer, numerous studies have identified preferences of distinct Gβγ combinations for specific GPCRs, Gα subtypes and effector molecules. Importantly, Gβ and Gγ subtype-dependent regulation of downstream effectors, representing a diverse range of signalling pathways and physiological functions have been found. Here, we review the literature on the repercussions of Gβ and Gγ subtype diversity on direct and indirect regulation of GPCR/G protein signalling events and their physiological outcomes. Our discussion additionally provides perspective in understanding the intricacies underlying molecular regulation of subtype-specific roles of Gβγ signalling and associated diseases.

Annona muricata silver nanoparticles exhibit strong anticancer activities against cervical and prostate adenocarcinomas through regulation of CASP9 and the CXCL1/CXCR2 genes axis

BACKGROUND

Green synthesized nanoparticles have been earmarked for use in nanomedicine including for the development of better anticancer drugs.

OBJECTIVE

The aim of this study was to undertake biochemical evaluation of anticancer activities of green synthesized silver nanoparticles (AgNPs) from ethanolic extracts of fruits (AgNPs-F) and leaves (AgNPs-L) of Annona muricata.

METHODS

Previously synthesized silver nanoparticles were used for the study. The effects of the AgNPs and 5-Fluorouracil were studied on PC3, HeLa and PNT1A cells. The resazurin, migration and colonogenic assays as well as qRT-PCR were employed.

RESULTS

The AgNPs-F displayed significant antiproliferative effects against HeLa cells with an IC50 of 38.58μg/ml and PC3 cells with an IC50 of 48.17μg/ml but selectively spared normal PNT1A cells (selectivity index of 7.8), in comparison with first line drug 5FU and AgNPs-L whose selectivity index were 3.56 and 2.26 respectively. The migration assay revealed potential inhibition of the metastatic activity of the cells by the AgNPs-F while the colonogenic assay indicated the permanent effect of the AgNPs-F on the cancer cells yet being reversible on the normal cells in contrast with 5FU and AgNPs-L. CASP9 was significantly over expressed in all HeLa cells treated with the AgNPs-F (1.53-fold), AgNPs-L (1.52-fold) and 5FU (4.30-fold). CXCL1 was under expressed in HeLa cells treated with AgNPs-F (0.69-fold) and AgNPs-L (0.58-fold) and over expressed in cells treated with 5FU (4.95-fold), but the difference was not statistically significant. CXCR2 was significantly over expressed in HeLa cells treated with 5FU (8.66-fold) and AgNPs-F (1.12-fold) but under expressed in cells treated with AgNPs-L (0.76-fold).

CONCLUSIONS

Here we show that biosynthesized AgNPs especially AgNPs-F can be used in the development of novel and better anticancer drugs. The mechanism of action of the AgNPs involves activation of the intrinsic apoptosis pathway through upregulation of CASP9 and concerted down regulation of the CXCL1/ CXCR2 gene axis.

Molecular heterogeneity of guanine nucleotide binding-protein γ subunit 4 in left- and right-sided colon cancer

Molecular heterogeneity determines the differences in the pathological features, prognosis and survival after relapse when comparing left-sided colon cancer (LCC) and right-sided colon cancer (RCC). At present, the discrepancy in the underlying molecular events between the two types of colon cancer has not been thoroughly investigated. The present study aimed to explore novel targets to predict the disease stage and prognosis of LCC and RCC. Expression analysis of guanine nucleotide binding-protein γ subunit 4 (GNG4) was performed using the Gene Expression Profiling Interactive Analysis (GEPIA) and Oncomine databases. Survival and association analyses were performed using GEPIA and the colon adenocarcinoma dataset from The Cancer Genome Atlas database. GNG4-positive cells in a tissue microarray were examined using immunohistochemistry. According to the GNG4 expression data from Caucasian patients included in the TCGA dataset, GNG4 was highly expressed and positively associated with pathological stage and overall survival (OS) rates in colon cancer. GNG4 expression was higher in LCC than in RCC. Patients with LCC with high GNG4 expression exhibited higher pathological stage and lower survival rates, whereas this was not observed in patients with RCC. In addition, the clinical tissues used in the microarray showed that GNG4 expression was increased in Chinese patients with LCC compared with that in patients with RCC. Consistently, GNG4 expression was negatively associated with OS in patients with LCC, but not in patients with RCC. However, no association was observed between GNG4 expression and the disease stage of colon cancer in both patients with LCC and RCC. Overall, the molecular heterogeneity of GNG4 in LCC and RCC suggests that GNG4 may be used as a diagnostic and prognostic biomarker in patients with LCC.

Metabolic Regulation of the Epigenome Drives Lethal Infantile Ependymoma

Posterior fossa A (PFA) ependymomas are lethal malignancies of the hindbrain in infants and toddlers. Lacking highly recurrent somatic mutations, PFA ependymomas are proposed to be epigenetically driven tumors for which model systems are lacking. Here we demonstrate that PFA ependymomas are maintained under hypoxia, associated with restricted availability of specific metabolites to diminish histone methylation, and increase histone demethylation and acetylation at histone 3 lysine 27 (H3K27). PFA ependymomas initiate from a cell lineage in the first trimester of human development that resides in restricted oxygen. Unlike other ependymomas, transient exposure of PFA cells to ambient oxygen induces irreversible cellular toxicity. PFA tumors exhibit a low basal level of H3K27me3, and, paradoxically, inhibition of H3K27 methylation specifically disrupts PFA tumor growth. Targeting metabolism and/or the epigenome presents a unique opportunity for rational therapy for infants with PFA ependymoma.

The IGF-II-Insulin Receptor Isoform-A Autocrine Signal in Cancer: Actionable Perspectives

Insulin receptor overexpression is a common event in human cancer. Its overexpression is associated with a relative increase in the expression of its isoform A (IR^A), a shorter variant lacking 11 aa in the extracellular domain, conferring high affinity for the binding of IGF-II along with added intracellular signaling specificity for this ligand. Since IGF-II is secreted by the vast majority of malignant solid cancers, where it establishes autocrine stimuli, the co-expression of IGF-II and IR^A in cancer provides specific advantages such as apoptosis escape, growth, and proliferation to those cancers bearing such a co-expression pattern. However, little is known about the exact role of this autocrine ligand–receptor system in sustaining cancer malignant features such as angiogenesis, invasion, and metastasis. The recent finding that the overexpression of angiogenic receptor kinase EphB4 along with VEGF-A is tightly dependent on the IGF-II/IR^A autocrine system independently of IGFIR provided new perspectives for all malignant IGF2omas (those aggressive solid cancers secreting IGF-II). The present review provides an updated view of the IGF system in cancer, focusing on the biology of the autocrine IGF-II/IR^A ligand–receptor axis and supporting its underscored role as a malignant-switch checkpoint target.

DNA methylation of GHSR, GNG4, HOXD9 and SALL3 is a common epigenetic alteration in thymic carcinoma

Thymic epithelial tumors comprise thymoma, thymic carcinoma and neuroendocrine tumors of the thymus. Recent studies have revealed that the incidence of somatic non‑synonymous mutations is significantly higher in thymic carcinoma than in thymoma. However, limited information is currently available on epigenetic alterations in these types of cancer. In this study, we thus performed genome‑wide screening of aberrantly methylated CpG islands in thymoma and thymic carcinoma using Illumina HumanMethylation450 K BeadChip. We identified 92 CpG islands significantly hypermethylated in thymic carcinoma in relation to thymoma and selected G protein subunit gamma 4 (GNG4), growth hormone secretagogue receptor (GHSR), homeobox D9 (HOXD9) and spalt like transcription factor 3 (SALL3), which are related to cancer. We examined the promoter methylation of 4 genes in 46 thymic epithelial tumors and 20 paired thymus tissues using bisulfite pyrosequencing. Promoter methylation was significantly higher in thymic carcinoma than in thymoma and revealed a high discrimination between thymic carcinoma and thymoma in all 4 genes. Promoter methylation was higher in thymic carcinoma than in the thymus. No significant differences were observed in the promoter methylation of GNG4, HOXD9, or SALL3 between thymoma and the thymus. The promoter methylation of the 4 genes was not significantly higher in advanced‑stage tumors than in early‑stage tumors in all thymic epithelial tumors. Among the 4 genes, relapse‑free survival was significantly worse in tumors with a higher DNA methylation than in those with a lower DNA methylation in all thymic epithelial tumors. Moreover, relapse‑free survival was significantly worse in thymomas with a higher DNA methylation of HOXD9 and SALL3 than in those with a lower DNA methylation. On the whole, the findings of this study indicated that the promoter methylation of cancer‑related genes was significantly higher in thymic carcinoma than in thymoma and the thymus. This is a common epigenetic alteration of high diagnostic value in thymic carcinoma and may be involved in the carcinogenesis of thymic carcinoma. However, epigenetic alterations in the 3 genes, apart from GHSR, are not involved in the tumorigenesis of thymoma.

Predictors of disease aggressiveness influence outcome from immunotherapy treatment in renal clear cell carcinoma

Renal clear cell carcinoma (RCC) is the most common type of kidney cancer and has a high propensity for metastasis. While treatment with immune checkpoint inhibitors, such as anti-PD-1, have shown modest improvements in survival for RCC, it is difficult to identify responders from non-responders. Attempts to elucidate the mechanisms associated with differential response to checkpoint inhibitors have been limited by small sample size making it difficult to detect meaningful associations. We utilized existing large datasets from The Cancer Genome Atlas (TCGA) to first find predictors of disease aggressiveness in the tumor microenvironment (TME) and hypothesized that these same predictors may influence response to immunotherapy. We found primary metastatic (M1-stage IV) tumors exhibit high immune infiltration, and high TP53-inactivation induced senescence activity compared to non-metastatic (M0-Stage I/II) tumors. Moreover, some TME features inferred from deconvolution algorithms, which differ between M0 and M1 tumors, also influence overall survival. A focused analysis identified interactions between tumor TP53-inactivation induced senescence activity and expression of inflammatory molecules in pre-treatment RCC tumors, which predict both change in tumor size and response to checkpoint blockade therapy. We also noted frequency of inactivating mutations in the protein polybromo-1 (PBRM1) gene was found to be negatively associated with TP53-inactivation induced senescence enrichment. Our findings suggest a mechanism by which tumor TP53-inactivation induced senescence can modulate the TME and thereby influence outcome from checkpoint blockade therapy.

Cancer-Associated IDH1 Promotes Growth and Resistance to Targeted Therapies in the Absence of Mutation

Oncogenic mutations in two isocitrate dehydrogenase (IDH)-encoding genes (IDH1 and IDH2) have been identified in acute myelogenous leukemia, low-grade glioma, and secondary glioblastoma (GBM). Our in silico and wet-bench analyses indicate that non-mutated IDH1 mRNA and protein are commonly overexpressed in primary GBMs. We show that genetic and pharmacologic inactivation of IDH1 decreases GBM cell growth, promotes a more differentiated tumor cell state, increases apoptosis in response to targeted therapies, and prolongs the survival of animal subjects bearing patient-derived xenografts (PDXs). On a molecular level, diminished IDH1 activity results in reduced α-ketoglutarate (αKG) and NADPH production, paralleled by deficient carbon flux from glucose or acetate into lipids, exhaustion of reduced glutathione, increased levels of reactive oxygen species (ROS), and enhanced histone methylation and differentiation marker expression. These findings suggest that IDH1 upregulation represents a common metabolic adaptation by GBMs to support macromolecular synthesis, aggressive growth, and therapy resistance.

Epigenetically silenced GNG4 inhibits SDF1α/CXCR4 signaling in mesenchymal glioblastoma

The most common and aggressive form of primary brain tumor in adults is glioblastoma (GBM). From the global DNA methylation profiling study, previously published from our laboratory, we identified Guanine Nucleotide binding-protein Gamma subunit 4 (GNG4) to be one of the most hyper methylated and down regulated genes in GBM. GBM derived cell lines showed reduced GNG4 transcript levels, which could be reversed by methylation inhibitor treatment. Bisulphite sequencing confirmed the methylation status in glioblastoma tumor tissue and GBM derived cell lines. Overexpression of GNG4 was found to inhibit proliferation and colony formation of GBM cell lines and in vitro transformation of immortalized human astrocytes, thus suggesting a potential tumor suppressor role of GNG4 in GBM. Correlation of GNG4 transcript levels with that of all GPCRs from TCGA data revealed chemokine receptors as the potential target of GNG4. Furthermore, exogenous over expression of GNG4 inhibited SDF1α/CXCR4-dependent chemokine signaling as seen by reduced pERK and pJNK and GBM cell migration. The inhibitory association between GNG4 and SDF1α/CXCR4 was more evident in mesenchymal subtype of GBM. Thus, this study identifies GNG4 as an inhibitor of SDF1α/CXCR4-dependent signaling and emphasizes the significance of epigenetic inactivation of GNG4 in glioblastoma, especially in mesenchymal subtype.

(1)H NMR metabolomics analysis of renal cell carcinoma cells: Effect of VHL inactivation on metabolism

Von Hippel-Lindau (VHL) is an onco-suppressor involved in oxygen and energy-dependent promotion of protein ubiquitination and proteosomal degradation. Loss of function mutations of VHL (VHL-cells) result in organ specific cancers with the best studied example in renal cell carcinomas. VHL has a well-established role in deactivation of hypoxia-inducible factor (HIF-1) and in regulation of PI3K/AKT/mTOR activity. Cell culture metabolomics analysis was utilized to determined effect of VHL and HIF-1α or HIF-2α on metabolism of renal cell carcinomas (RCC). RCC cells were stably transfected with VHL or shRNA designed to silence HIF-1α or HIF-2α genes. Obtained metabolic data was analysed qualitatively, searching for overall effects on metabolism as well as quantitatively, using methods developed in our group in order to determine specific metabolic changes. Analysis of the effect of VHL and HIF silencing on cellular metabolic footprints and fingerprints provided information about the metabolic pathways affected by VHL through HIF function as well as independently of HIF. Through correlation network analysis as well as statistical analysis of significant metabolic changes we have determined effects of VHL and HIF on energy production, amino acid metabolism, choline metabolism as well as cell regulation and signaling. VHL was shown to influence cellular metabolism through its effect on HIF proteins as well as by affecting activity of other factors.

Adhesion GPCRs in Tumorigenesis

Alterations in the homeostasis of several adhesion GPCRs (aGPCRs) have been observed in cancer. The main cellular functions regulated by aGPCRs are cell adhesion, migration, polarity, and guidance, which are all highly relevant to tumor cell biology. Expression of aGPCRs can be induced, increased, decreased, or silenced in the tumor or in stromal cells of the tumor microenvironment, including fibroblasts and endothelial and/or immune cells. For example, ADGRE5 (CD97) and ADGRG1 (GPR56) show increased expression in many cancers, and initial functional studies suggest that both are relevant for tumor cell migration and invasion. aGPCRs can also impact the regulation of angiogenesis by releasing soluble fragments following the cleavage of their extracellular domain (ECD) at the conserved GPCR-proteolytic site (GPS) or other more distal cleavage sites as typical for the ADGRB (BAI) family. Interrogation of in silico cancer databases suggests alterations in other aGPCR members and provides the impetus for further exploration of their potential role in cancer. Integration of knowledge on the expression, regulation, and function of aGPCRs in tumorigenesis is currently spurring the first preclinical studies to examine the potential of aGPCR or the related pathways as therapeutic targets.

Novel Homozygous Mutation of the Internal Translation Initiation Start Site of VHL is Exclusively Associated with Erythrocytosis: Indications for Distinct Functional Roles of von Hippel-Lindau Tumor Suppressor Isoforms

Congenital secondary erythrocytosis is a rare disorder characterized by increased red blood cell production. An important cause involves defects in the oxygen sensing pathway, in particular the PHD2-VHL-HIF axis. Mutations in VHL are also associated with the von Hippel-Lindau tumor predisposition syndrome. The differences in phenotypic expression of VHL mutations are poorly understood. We report on three patients with erythrocytosis, from two unrelated families. All patients show exceptionally high erythropoietin (EPO) levels, and are homozygous for a novel missense mutation in VHL: c.162G>C p.(Met54Ile). The c.162G>C mutation is the most upstream homozygous VHL mutation described so far in patients with erythrocytosis. It abolishes the internal translational start codon, which directs expression of VHLp19, resulting in the production of only VHLp30. The exceptionally high EPO levels and the absence of VHL-associated tumors in the patients suggest that VHLp19 has a role for regulating EPO levels that VHLp30 does not have, whereas VHLp30 is really the tumor suppressor isoform.

Metabolic regulation of T cell differentiation and function

Upon encountering pathogens, T cells mount immune responses by proliferating, increasing cellular mass and differentiating. These cellular changes impose significant energetic challenges on T cells. It was believed that TCR and cytokine-mediated signaling are dominant dictators of T cell-mediated immune responses. Recently, it was recognized that T cells utilize metabolic transporters and metabolic sensors that allow them to rapidly respond to nutrient-limiting inflammatory environments. Metabolic sensors allow T cells to find a balance between energy consumption (anabolic metabolism) and production (catabolic metabolism) in order to mount effective immune responses. Also, metabolic regulators interact with cytokine-dependent transcriptional regulators, suggesting a more integrative and advanced model of T cell activation and differentiation. In this review, we will discuss recent discoveries regarding the roles of metabolic regulators in effector and memory T cell development and their interaction with canonical transcription factors.

The HILDA complex coordinates a conditional switch in the 3'-untranslated region of the VEGFA mRNA

Cell regulatory circuits integrate diverse, and sometimes conflicting, environmental cues to generate appropriate, condition-dependent responses. Here, we elucidate the components and mechanisms driving a protein-directed RNA switch in the 3'UTR of vascular endothelial growth factor (VEGF)-A. We describe a novel HILDA (hypoxia-inducible hnRNP L-DRBP76-hnRNP A2/B1) complex that coordinates a three-element RNA switch, enabling VEGFA mRNA translation during combined hypoxia and inflammation. In addition to binding the CA-rich element (CARE), heterogeneous nuclear ribonucleoprotein (hnRNP) L regulates switch assembly and function. hnRNP L undergoes two previously unrecognized, condition-dependent posttranslational modifications: IFN-γ induces prolyl hydroxylation and von Hippel-Lindau (VHL)-mediated proteasomal degradation, whereas hypoxia stimulates hnRNP L phosphorylation at Tyr(359), inducing binding to hnRNP A2/B1, which stabilizes the protein. Also, phospho-hnRNP L recruits DRBP76 (double-stranded RNA binding protein 76) to the 3'UTR, where it binds an adjacent AU-rich stem-loop (AUSL) element, "flipping" the RNA switch by disrupting the GAIT (interferon-gamma-activated inhibitor of translation) element, preventing GAIT complex binding, and driving robust VEGFA mRNA translation. The signal-dependent, HILDA complex coordinates the function of a trio of neighboring RNA elements, thereby regulating translation of VEGFA and potentially other mRNA targets. The VEGFA RNA switch might function to ensure appropriate angiogenesis and tissue oxygenation during conflicting signals from combined inflammation and hypoxia. We propose the VEGFA RNA switch as an archetype for signal-activated, protein-directed, multi-element RNA switches that regulate posttranscriptional gene expression in complex environments.

HIF-1α deletion partially rescues defects of hematopoietic stem cell quiescence caused by Cited2 deficiency

Cited2 is a transcriptional modulator involved in various biologic processes including fetal liver hematopoiesis. In the present study, the function of Cited2 in adult hematopoiesis was investigated in conditional knockout mice. Deletion of Cited2 using Mx1-Cre resulted in increased hematopoietic stem cell (HSC) apoptosis, loss of quiescence, and increased cycling, leading to a severely impaired reconstitution capacity as assessed by 5-fluorouracil treatment and long-term transplantation. Transcriptional profiling revealed that multiple HSC quiescence- and hypoxia-related genes such as Egr1, p57, and Hes1 were affected in Cited2-deficient HSCs. Because Cited2 is a negative regulator of HIF-1, which is essential for maintaining HSC quiescence, and because we demonstrated previously that decreased HIF-1α gene dosage partially rescues both cardiac and lens defects caused by Cited2 deficiency, we generated Cited2 and HIF-1α double-knockout mice. Additional deletion of HIF-1α in Cited2-knockout BM partially rescued impaired HSC quiescence and reconstitution capacity. At the transcriptional level, deletion of HIF-1α restored expression of p57 and Hes1 but not Egr1 to normal levels. Our results suggest that Cited2 regulates HSC quiescence through both HIF-1-dependent and HIF-1-independent pathways.

Suppression of breast tumor growth and metastasis by an engineered transcription factor

Maspin is a tumor and metastasis suppressor playing an essential role as gatekeeper of tumor progression. It is highly expressed in epithelial cells but is silenced in the onset of metastatic disease by epigenetic mechanisms. Reprogramming of Maspin epigenetic silencing offers a therapeutic potential to lock metastatic progression. Herein we have investigated the ability of the Artificial Transcription Factor 126 (ATF-126) designed to upregulate the Maspin promoter to inhibit tumor progression in pre-established breast tumors in immunodeficient mice. ATF-126 was transduced in the aggressive, mesenchymal-like and triple negative breast cancer line, MDA-MB-231. Induction of ATF expression in vivo by Doxycycline resulted in 50% reduction in tumor growth and totally abolished tumor cell colonization. Genome-wide transcriptional profiles of ATF-induced cells revealed a gene signature that was found over-represented in estrogen receptor positive (ER+) "Normal-like" intrinsic subtype of breast cancer and in poorly aggressive, ER+ luminal A breast cancer cell lines. The comparison transcriptional profiles of ATF-126 and Maspin cDNA defined an overlapping 19-gene signature, comprising novel targets downstream the Maspin signaling cascade. Our data suggest that Maspin up-regulates downstream tumor and metastasis suppressor genes that are silenced in breast cancers, and are normally expressed in the neural system, including CARNS1, SLC8A2 and DACT3. In addition, ATF-126 and Maspin cDNA induction led to the re-activation of tumor suppressive miRNAs also expressed in neural cells, such as miR-1 and miR-34, and to the down-regulation of potential oncogenic miRNAs, such as miR-10b, miR-124, and miR-363. As expected from its over-representation in ER+ tumors, the ATF-126-gene signature predicted favorable prognosis for breast cancer patients. Our results describe for the first time an ATF able to reduce tumor growth and metastatic colonization by epigenetic reactivation of a dormant, normal-like, and more differentiated gene program.

The expression pattern of Von Hippel-Lindau tumor suppressor protein, MET proto-oncogene, and TFE3 transcription factor oncoprotein in renal cell carcinoma in Upper Egypt

BACKGROUND

Genetic alterations in renal cell carcinoma (RCC) involve tumor suppressor genes such as Von Hippel-Lindau (VHL); proto-oncogenes such as MET and transcription factors such as TFE3 oncoprotein.

AIM

To examine the clinicopathologic features and the expression of some oncogenic molecules in various RCCs in patients from Upper Egypt.

MATERIALS AND METHODS

The authors examined the expression pattern of pVHL; MET; and TFE3 proteins in 59 RCC using immunoperoxidase staining methods. The study group consisted of clear cell RCCs (CRCC); papillary RCCs type 1 (PRCC1); papillary RCCs type 2 (PRCC2); Xp11-2 translocation RCCs (XP11.2RCC); chromophobe RCCs (ChRCC); and sarcomatoid RCCs (SRCC).

RESULTS

Variations were found in the expression of these molecules in the different types of RCCs. The mean age of RCCs among Egyptians was 52.70 ± 1.73 years; with male sex predominance. Mass lesion; pain; and hematuria were the main presenting features. Metastatic disease was more frequent with CRCC variant. pVHL expression was strong in PCRCC2; Xp11.2RCC; and ChRCC; moderate in CRCC; and weak in both PRCC1 and sarcomatoid RCC. MET protein expression was moderate in Xp11.2RCC; PRCC1; PRCC2; and sarcomatoid RCC. TFE3 protein expression was strong in Xp11.2RCC and PRCC2 variants. The expression was moderate in PRCC1; CRCC; ChRCC; and sarcomatoid RCC. Positive correlation was found in the expression of the different proteins (pVHL; MET; and TFE3) and some histological features (tumor grade; inflammation; necrosis and metastasis) and the presence of metastasis and some histological features (inflammation and/or necrosis).

CONCLUSIONS

This study provides the first indication about the clinicopathologic features of RCCs in Upper Egypt. The variable expression of these molecules in the different variants of RCC suggests that several oncogenic pathways are operational in their development.

Renal cell carcinoma

Renal Cell Carcinoma (RCC) has the highest mortality rate of the genitourinary cancers and the incidence of RCC has risen steadily. If detected early, RCC is curable by surgery although a minority are at risk of recurrence. Increasing incidental detection and an ageing population has led to active surveillance as an option for patients with small renal masses. RCC is heterogeneous and comprises several histological cell types with different genetics, biology and behavior. The identification of the genes predisposing to inherited syndromes with RCC has provided much of our knowledge of the molecular basis of early sporadic RCC. Many of the oncogenes and tumor suppressor genes that are mutated leading to pathway dysregulation in RCC remain to be elucidated. Global studies of copy number, gene sequencing, gene expression, miRNA expression and gene methylation in primary RCC will lead towards this goal. The natural history of RCC indicated by candidate precursor lesions, multifocal or bilateral disease, growth rate of small renal masses under surveillance, and high risk populations provide insight into the behavior of this disease. The use of molecular markers for early detection and prognosis merits more attention with ongoing advances in omics technologies. This review focuses on early RCC, that is disease confined within the renal capsule.

Hypoxia interferes with connective tissue growth factor (CTGF) gene expression in human proximal tubular cell lines

BACKGROUND

Hypoxia plays an important role in kidney injury. By the stabilization of the transcription factor HIF-1, hypoxia affects gene expression also in tubular epithelial cells. Increased expression of connective tissue growth factor (CTGF) is observed in different kidney diseases and is associated with deteriorating renal function. Therefore, we hypothesized that the expression of CTGF might be modulated under hypoxic conditions.

METHODS

The human proximal tubular epithelial cell lines HK-2 and HKC-8 were treated with reduced oxygen tension (1% O(2)) or the hypoxia mimetic dimethyloxalyl glycine (DMOG). CTGF was analysed by Western blotting, real-time RT-PCR and luciferase gene expression assays.

RESULTS

Exposure of HK-2 or HKC-8 cells to hypoxia or treatment with DMOG for up to 24 h reduced cellular as well as secreted CTGF protein synthesis. Downregulation was also detectable at the mRNA level and was confirmed by reporter gene assays. Hypoxic repression of CTGF synthesis was dependent on HIF-1, as shown by HIF-1alpha knockdown by siRNA. Furthermore, exposure to hypoxia reduced CTGF synthesis in response to TGF-beta. A negative correlation between HIF-1alpha accumulation and CTGF synthesis was also observed in renal cell carcinoma cells (RCC4 and RCC10). Reexpression of von Hippel-Lindau protein reduced HIF-1alpha and increased CTGF synthesis.

CONCLUSIONS

We provide evidence that hypoxia inhibits CTGF synthesis in human proximal tubular epithelial cells, involving HIF-1alpha. Under hypoxic conditions, induction of CTGF by TGF-beta was repressed. The reduced synthesis of the profibrotic factor CTGF may contribute to a potential protective effect of hypoxic preconditioning in acute renal injury.

Molecular investigations to improve diagnostic accuracy in patients with ARC syndrome

Arthrogryposis, Renal dysfunction and Cholestasis (ARC) syndrome is a multi-system autosomal recessive disorder caused by germline mutations in VPS33B. The detection of germline VPS33B mutations removes the need for diagnostic organ biopsies (these carry a>50% risk of life-threatening haemorrhage due to platelet dysfunction); however, VPS33B mutations are not detectable in approximately 25% of patients. In order further to define the molecular basis of ARC we performed mutation analysis and mRNA and protein studies in patients with a clinical diagnosis of ARC. Here we report novel mutations in VPS33B in patients from Eastern Europe and South East Asia. One of the mutations was present in 7 unrelated Korean patients. Reduced expression of VPS33B and cellular phenotype was detected in fibroblasts from patients clinically diagnosed with ARC with and without known VPS33B mutations. One mutation-negative patient was found to have normal mRNA and protein levels. This patient's clinical condition improved and he is alive at the age of 2.5 years. Thus we show that all patients with a classical clinical course of ARC had decreased expression of VPS33B whereas normal VPS33B expression was associated with good prognosis despite initial diagnosis of ARC.

The histone demethylases JMJD1A and JMJD2B are transcriptional targets of hypoxia-inducible factor HIF

Posttranslational histone modifications serve to store epigenetic information and control both nucleosome assembly and recruitment of non-histone proteins. Histone methylation occurs on arginine and lysine residues and is involved in the regulation of gene transcription. A dynamic control of these modifications is exerted by histone methyltransferases and the recently discovered histone demethylases. Here we show that the hypoxia-inducible factor HIF-1alpha binds to specific recognition sites in the genes encoding the jumonji family histone demethylases JMJD1A and JMJD2B and induces their expression. Accordingly, hypoxic cells express elevated levels of JMJD1A and JMJD2B mRNA and protein. Furthermore, we find increased expression of JMJD1A and JMJD2B in renal cancer cells that have lost the von Hippel Lindau tumor suppressor protein VHL and therefore display a deregulated expression of hypoxia-inducible factor. Studies on ectopically expressed JMJD1A and JMJD2B indicate that both proteins retain their histone lysine demethylase activity in hypoxia and thereby might impact the hypoxic gene expression program.

Nutrition-induced catch-up growth increases hypoxia inducible factor 1alpha RNA levels in the growth plate

Although catch-up growth is a well-known phenomenon, the local pathways at the epiphyseal growth plate that govern this process remain poorly understood. To study the mechanisms governing catch-up growth in the growth plate, we subjected prepubertal rats to 10 days of 40% food restriction, followed by a renewal of the regular food supply to induce catch-up growth. The animals were weighed daily, and their humeral length was measured at sacrifice. The proximal tibial epiphyseal growth plates (EGPs) were studied, and findings were compared with EGPs from animals fed ad libitum and animals under food restriction. The gene expression profile in the growth plates was examined using DNA microarrays, and the expression levels of selected genes were validated by real-time polymerase chain reaction. To localize gene expression in different growth plate zones, microdissection was used. Protein levels and localization were examined using immunohistochemistry. We showed that the expression level of 550 genes decreased during food restriction and increased during catch-up growth, starting already one day after refeeding. HIF-1alpha, as well as several of its downstream targets, was found among these genes. Immunohistochemistry showed a similar pattern for HIF-1alpha protein abundance. Additionally, HIF-1alpha mRNA and protein levels were higher in the proliferating than in the hypertrophic zone, and this distribution was unaffected by nutritional status. These findings indicate that nutrition has a profound effect on gene expression level during growth plate growth, and suggest an important role for HIF-1alpha in the growth plate and its response to nutritional manipulation.

MUC4 Mucin Potentiates Pancreatic Tumor Cell Proliferation, Survival, and Invasive Properties and Interferes with Its Interaction to Extracellular Matrix Proteins

MUC4, a transmembrane mucin, is aberrantly expressed in pancreatic adenocarcinomas while remaining undetectable in the normal pancreas. Recent studies have shown that the expression of MUC4 is associated with the progression of pancreatic cancer and is inversely correlated with the prognosis of pancreatic cancer patients. In the present study, we have examined the phenotypic and molecular consequences of MUC4 silencing with an aim of establishing the mechanistic basis for its observed role in the pathogenesis of pancreatic cancer. The silencing of MUC4 expression was achieved by stable expression of a MUC4-specific short hairpin RNA in CD18/HPAF, a highly metastatic pancreatic adenocarcinoma cell line. A significant decrease in MUC4 expression was detected in MUC4-knockdown (CD18/HPAF-siMUC4) cells compared with the parental and scrambled short interfering RNA-transfected (CD18/HPAF-Scr) control cells by immunoblot analysis and immunofluorescence confocal microscopy. Consistent with our previous observation, inhibition of MUC4 expression restrained the pancreatic tumor cell growth and metastasis as shown in an orthotopic mouse model. Our in vitro studies revealed that MUC4-associated increase in tumor cell growth resulted from both the enhanced proliferation and reduced cell death. Furthermore, MUC4 expression was also associated with significantly increased invasiveness (P < or = 0.05) and changes in actin organization. The presence of MUC4 on the cell surface was shown to interfere with the tumor cell-extracellular matrix interactions, in part, by inhibiting the integrin-mediated cell adhesion. An altered expression of growth- and metastasis-associated genes (LI-cadherin, CEACAM6, RAC1, AnnexinA1, thrombomodulin, epiregulin, S100A4, TP53, TP53BP, caspase-2, caspase-3, caspase-7, plakoglobin, and neuregulin-2) was also observed as a consequence of the silencing of MUC4. In conclusion, our study provides experimental evidence that supports the functional significance of MUC4 in pancreatic cancer progression and indicates a novel role for MUC4 in cancer cell signaling.

Interferon-α Resistance Associated Genes in Renal Cell Carcinoma Identified by Expression Profiling

PURPOSE

We identified differentially expressed genes associated with response to pegylated interferon-alpha treatment in patients with renal cell carcinoma.

MATERIALS AND METHODS

We performed expression profiling on renal cell carcinoma specimens isolated from 23 patients with metastatic disease who were subsequently treated with interferon. Significance Analysis for Microarrays software was used to identify genes that were differentially expressed between patients with partial response compared to those with disease progression.

RESULTS

A candidate gene approach looking at VHL and known target genes did not identify any genes whose expression correlated with patient response. A global analysis of approximately 54,000 probe sets identified 4 genes that had expression correlated with response. Reverse transcriptase-polymerase chain reaction analysis of 2 of these genes confirmed that they were more highly expressed in tumors from patients who responded to interferon-alpha. Interestingly, both of these genes mapped to 4q31-32, a region that has been implicated as the site of a potential tumor suppressor gene in renal cell carcinoma.

CONCLUSIONS

We have identified 4 genes (3 uncharacterized and 1 known) that may prove useful in predicting response to interferon-alpha treatment in patients with renal cell carcinoma.

Mammalian Tumor Suppressor Int6 Specifically Targets Hypoxia Inducible Factor 2α for Degradation by Hypoxia- and pVHL-independent Regulation

The hypoxia-inducible factors HIF-1 alpha and HIF-2 alpha are structurally similar as regards their DNA-binding and dimerization domains, but differ in their transactivation domains and, as is shown by experiments using hif-1 alpha(-/-) and hif-2 alpha(-/-) mice, in their functions. This implies that HIF-1 alpha and HIF-2 alpha may have unique target genes. To address this discrepancy and identify HIF-2 alpha-specific target genes, we performed yeast two-hybrid analysis and identified the tumor suppressor Int6/eIF3e/p48 as a novel target gene product involved in HIF-2 alpha regulation. The int6 gene was first identified from a screen in which the mouse mammary tumor virus was employed as an insertional mutagen to identify genes whose functions are critical for breast tumor formation. Here, by using two-hybrid analysis, immunoprecipitation in mammalian cells, and HRE-reporter assays, we report the specific interaction of HIF-2 alpha (but not HIF-1 alpha or HIF-3 alpha) with Int6. The results indicate that the direct interaction of Int6 induces proteasome inhibitor-sensitive HIF-2 alpha degradation. This degradation was clearly observed in renal cell carcinoma 786-O cells, and was found to be both hypoxia- and pVHL-independent. Furthermore, Int6 protein knockdown by int6-siRNA vectors or the dominant-negative mutant Int6-Delta C increased endogenous HIF-2 alpha expression, even under normoxia, and induced sets of critical angiogenic factors comprising vascular endoplasmic growth factor, angiopoietin, and basic fibroblast growth factor mRNA. These results indicate that Int6 is a novel and critical determinant of HIF-2 alpha-dependent angiogenesis as well as cancer formation, and that int6-siRNA transfer may be an effective therapeutic strategy in pathological conditions such as heart and brain ischemia, hepatic cirrhosis, and obstructive vessel diseases.

VHL mutation analysis in patients with isolated central nervous system haemangioblastoma

Haemangioblastomas of the CNS are a cardinal feature of von Hippel-Lindau (VHL) disease, a dominantly inherited multisystem familial cancer syndrome caused by germline mutation of the VHL tumour suppressor gene. We investigated the frequency of VHL mutations in 188 patients presenting with a single haemangioblastoma, no family history of VHL disease and no evidence of retinal or abdominal manifestations of the disease at the time of diagnosis. We found that approximately 4% of patients had a detectable VHL mutation and all of these cases presented age 40 years or less. Although the identification of a germline VHL mutation has important consequences for the patient (e.g. risk of further CNS and extra-CNS tumours) and their relatives, four patients had germline VHL missense mutations [C162Y, D179N and R200W (two patients)] that may represent haemangioblastoma-only and/or low penetrance mutations. Approximately 5% of patients without a detectable VHL mutation subsequently developed a further 'VHL type tumour' (in most cases a further CNS haemangioblastoma). These findings suggest that a subset of patients with apparently sporadic CNS haemangioblastoma will have a germline VHL mutation but may not be at risk for developing classical VHL disease and a further group may be mosaic for a germline VHL mutation that cannot be detected in blood cells.

Hypoxia-inducible factors: central regulators of the tumor phenotype

Low oxygen levels are a defining characteristic of solid tumors, and responses to hypoxia contribute substantially to the malignant phenotype. Hypoxia-induced gene transcription promotes characteristic tumor behaviors, including angiogenesis, invasion, metastasis, de-differentiation and enhanced glycolytic metabolism. These effects are mediated, at least in part, by targets of the hypoxia-inducible factors (HIFs). The HIFs function as heterodimers comprising an oxygen-labile alpha-subunit and a stable beta-subunit also referred to as ARNT. HIF-1alpha and HIF-2alpha stimulate the expression of overlapping as well as unique transcriptional targets, and their induction can have distinct biological effects. New targets and novel mechanisms of dysregulation place the HIFs in an ever more central role in tumor biology and have led to development of pharmacological inhibitors of their activity.

Identification of novel VHL targets that are associated with the development of renal cell carcinoma

von Hippel-Lindau (VHL) disease is a dominantly inherited family cancer syndrome characterized by the development of retinal and central nervous system haemangioblastomas, renal cell carcinoma (RCC) and phaeochromocytoma. Specific germline VHL mutations may predispose to haemangioblastomas, RCC and phaeochromocytoma to a varying extent. Although dysregulation of the hypoxia-inducible transcription factor-2 and JunB have been linked to the development of RCC and phaeochromocytoma, respectively, the precise basis for genotype-phenotype correlations in VHL disease have not been defined. To gain insights into the pathogenesis of RCC in VHL disease we compared gene expression microarray profiles in a RCC cell line expressing a Type 1 or Type 2B mutant pVHL (RCC-associated) to those of a Type 2A or 2C mutant (not associated with RCC). We identified 19 differentially expressed novel VHL target genes linked to RCC development. Eight targets were studied in detail by quantitative real-time polymerase chain reaction (three downregulated and five upregulated by wild-type VHL) and for six genes the effect of VHL inactivation was mimicked by hypoxia (but hypoxic-induction of smooth muscle alpha-actin 2 was specific for a RCC cell line). The potential role of four RCC-associated VHL target genes was assessed in vitro. NB thymosin beta (TMSNB) and proteinase-activated receptor 2 (PAR2) (both downregulated by wt pVHL) increased cell growth and motility in a RCC cell line, but aldehyde dehydrogenase (ALDH)1 and ALDH7 had no effect. These findings implicate TMSNB and PAR2 candidate oncogenes in the pathogenesis of VHL-associated RCC.

Evolving concepts in pheochromocytoma and paraganglioma

PURPOSE OF REVIEW

The pheochromocytoma field has recently undergone a paradigm shift. This review will highlight some of these novel findings, including their impact on our understanding of the disease biology and influence on clinical management.

RECENT FINDINGS

Identification of novel susceptibility loci and recognition of a high rate of germline mutations in pheochromocytomas indicate that their genetic diversity is broader and more complex than previously estimated. Further, increased risk of tumor malignancy and aggressiveness in certain patients with succinate dehydrogenase subunit B(SDHB) mutations suggest that they may have prognostic value as predictors of pheochromocytoma behavior. Finally, discovery of a shared activation of the hypoxic response in pheochromocytomas with mutations in VHL and SDH genes and uncovering of a common JunB-mediated apoptosis defect in the major hereditary groups of pheochromocytoma have provided a mechanistic basis for the clinical similarities between these distinct syndromes.

SUMMARY

The notion that 'sporadic'-appearing tumors may in fact be components of one of multiple hereditary syndromes has a major impact on surveillance and follow-up of patients and their at-risk family members. Likewise, the ability to predict tumor malignancy has the potential to improve the prognosis of these patients. Importantly, insights into the biology of pheochromocytomas have provided clues on pathway interactions in cancers and have laid the ground for generation of new hypotheses on the cell-of-origin of these tumors. Pheochromocytomas have therefore emerged as key models for understanding cancer biology and for paving the way for future designer treatment in this and other cancers.

GPR56, an atypical G protein-coupled receptor, binds tissue transglutaminase, TG2, and inhibits melanoma tumor growth and metastasis

The survival and growth of tumor cells in a foreign environment is considered a rate-limiting step during metastasis. To identify genes that may be essential for this process, we isolated highly metastatic variants from a poorly metastatic human melanoma cell line and performed expression analyses of metastases and primary tumors from these cells. GPR56 is among the genes markedly down-regulated in the metastatic variants. We show that overexpression of GPR56 suppresses tumor growth and metastasis, whereas reduced expression of GPR56 enhances tumor progression. Levels of GPR56 do not correlate with growth rate in vitro, suggesting that GPR56 may mediate growth suppression by interaction with a component in the tumor microenvironment in vivo. We show that GPR56 binds specifically to tissue transglutaminase, TG2, a widespread component of tissue and tumor stroma previously implicated as an inhibitor of tumor progression. We discuss the mechanisms whereby GPR56-TG2 interactions may suppress tumor growth and metastasis.

Molecular pathogenetics of renal cancer

Recent developments in genetics and molecular biology have led to an increased understanding of the pathobiology of renal cancer. Thorough knowledge of the molecular pathways associated with renal cancer is a prerequisite for novel potential therapeutic interventions. Studies are ongoing to evaluate novel anticancer agents that target specific molecular entities. This article reviews current knowledge on the genetics and molecular pathogenesis of sporadic and inherited forms of renal cancer.

The transmembrane protein meckelin (MKS3) is mutated in Meckel-Gruber syndrome and the wpk rat

Meckel-Gruber syndrome is a severe autosomal, recessively inherited disorder characterized by bilateral renal cystic dysplasia, developmental defects of the central nervous system (most commonly occipital encephalocele), hepatic ductal dysplasia and cysts and polydactyly. MKS is genetically heterogeneous, with three loci mapped: MKS1, 17q21-24 (ref. 4); MKS2, 11q13 (ref. 5) and MKS3 (ref. 6). We have refined MKS3 mapping to a 12.67-Mb interval (8q21.13-q22.1) that is syntenic to the Wpk locus in rat, which is a model with polycystic kidney disease, agenesis of the corpus callosum and hydrocephalus. Positional cloning of the Wpk gene suggested a MKS3 candidate gene, TMEM67, for which we identified pathogenic mutations for five MKS3-linked consanguineous families. MKS3 is a previously uncharacterized, evolutionarily conserved gene that is expressed at moderate levels in fetal brain, liver and kidney but has widespread, low levels of expression. It encodes a 995-amino acid seven-transmembrane receptor protein of unknown function that we have called meckelin.

Mitochondrial succinate is instrumental for HIF1alpha nuclear translocation in SDHA-mutant fibroblasts under normoxic conditions

The genes encoding succinate dehydrogenase (SDH) subunits B, C and D, act as tumour suppressors in neuro-endocrine tissues. Tumour formation has been associated with succinate accumulation. In paraganglioma cells, two forms of SDHA (type I, II) were found which might preclude significant succinate accumulation in the case of a mutation in either form. In fibroblasts only SDHA type I is found. In these cells, SDHA type I mutation leads to SDH deficiency, succinate accumulation and hypoxia-inducible factor 1alpha(HIF1alpha) nuclear translocation. HIF1alpha nuclear translocation was not observed in ATPase-deficient fibroblasts with increased superoxide production and was found to be independent of cellular iron availability in SDHA-mutant cells. This suggests that neither superoxides nor iron were causative of HIF1alpha nuclear translocation. Conversely, alpha-ketoglutarate (alpha-KG) inhibits this nuclear translocation. Therefore, the pseudo-hypoxia pathway in SDH-deficient cells depends on the HIF1alphaprolyl hydroxylase product/substrate (succinate/alpha-KG) equilibrium. In SDH deficiency, organic acids thus appear instrumental in the HIF1alpha-dependent cascade suggesting a direct link between SDH and tumourigenesis.

Autocrine signaling of platelet-derived growth factor regulates disabled-2 expression during megakaryocytic differentiation of K562 cells

Platelet-derived growth factor (PDGF) is involved in megakaryocytopoiesis and is secreted into the culture medium during megakaryocytic differentiation of human leukemic cells. We investigate whether PDGF plays a role in the regulation of the adapter protein Disabled-2 (DAB2) that expresses abundantly in platelets and megakaryocytes. Western blot analysis revealed that conditioned medium from 12-O-tetradecanoylphorbol-13-acetate (TPA)-treated, megakaryocytic differentiating K562 cells upregulated DAB2 expression. DAB2 induction and megakaryocytic differentiation was abrogated when cells were co-treated with the PDGF receptor inhibitor STI571 or when the conditioned medium was derived from TPA-plus STI571-treated cells. Although the level of PDGF mRNA was not altered by STI571, an approximate 44% decrease in PDGF in the conditioned medium was observed. Consistent with these findings, interfering PDGF signaling by PDGF neutralization antibody or dominant negative PDGF receptors attenuated DAB2 expression. Accordingly, transfection of an expression plasmid encoding secreted PDGF upregulated DAB2. This study shows for the first time that PDGF autocrine signaling regulates DAB2 expression during megakaryocytic differentiation.