MIR-92 stimulates VEGF by inhibiting von Hippel-Lindau gene product in epithelial ovarian cancer

The molecular mechanisms underlying regulation of vascular endothelial growth factor (VEGF) in epithelial ovarian cancer (EOC) remain poorly defined. VEGF, a potent angiogenic factor, is up-regulated in a variety of cancers and contributes to angiogenesis in tumor tissues. The level of VEGF correlates with progression of malignancy. We previously reported that miR-92 is abnormally elevated in the plasma of EOC patients. Here, we tested the hypothesis that miR-92 inhibits von Hippel-Lindau gene product (VHL), a tumor suppressor gene, and in turn de-represses HIF-1α, a known key transcription factor for VEGF, to stimulate VEGF expression. Using a variety of biomedical methods including Western blot, RT-PCR, gene silencing, luciferase assay, and chromatin immunoprecipitation in both surgically-resected specimens and EOC cell culture, we established that EOC cells have elevated levels of HIF-1α and miR-92 expression, but the expression of VHL is reduced. We further demonstrated that miR-92 can target the VHL transcript to repress its expression. We also found that stabilized HIF-1α can form an active complex with transcriptional coactivator p300 and phosphorylated-STAT3 at the VEGF promoter to stimulate its expression. In addition, matrix metalloproteinases MMP-2 and MMP-9 are positively regulated by HIF-1α. These results suggest that miR-92 can potentially be considered as a novel therapeutical target in treatment of EOS.

[Hydroxysafflor yellow A up-regulates HIF-1alpha via inhibition of VHL and p53 in Eahy 926 cell line exposed to hypoxia]

In present study, we investigated the mechanism of regulating HIF-1alpha expression by hydroxysafflor yellow A (HSYA) in Eahy 926 cell line under 1% O2 hypoxia. Eahy 926 cells were incubated with HSYA (100, 10 and 1 micromol x L(-1)) under hypoxia for the indicated time after treatment. Cell proliferation rate was detected using MTT assays. VHL and p53 location and protein expression were analyzed by immunocytochemical stain. HIF-1alpha, VHL and p53 mRNA expression were detected by RT-PCR. Protein expression of HIF-1alpha, VHL and p53 were assayed by Western blotting method. HSYA at 100 micromol x L(-1) increased Eahy 926 cells proliferation rate under hypoxia. HIF-1alpha mRNA and protein expression were up-regulated in the presence of HSYA. VHL, p53 mRNA and protein expression decreased significantly after 8 hours of treatment under hypoxia. HSYA protected Eahy 926 cells from hypoxia, and up-regulated HIF-1alpha expression partially via its inhibition of VHL and p53 expression.

[Inactivation of the VHL gene in sporadic clear cell renal cancer]

Renal cell carcinoma is the most common variant of the kidney cancer, which accounts approximately 75% patients with this disease. The majority of those tumors are characterized by inactivation of the VHL gene suppressor as a result of mutations, allelic deletions and/or methylation. We have conducted the complex molecular-genetic analysis of 64 samples obtained from patients with the clear cell renal cancer. VHL mutations were detected by single strand conformation polymorphism and subsequent sequencing, loss of heterozygosity was analyzed using two STR-markers, methylation was tested by methylsensitive polymerase chain reaction. All revealed variations were statistically analyzed in respect to the parameters of primary tumors in various groups of patients. Seventeen VHL somatic mutations were detected, 12 from which were described for the first time. Allelic deletions of VHL were found in 31.6%, and methylation--in 7.8% samples of the renal cancer. As a whole, VHL inactivating events were presented in 46.9% cases of disease, in 51.7% -among renal cancer patients with first stage. We have not observed any association of mutations, loss of heterozygosity and methylation with clinical-pathological parameters of disease. Results of this investigation specify for expediency of further studies of molecular genetics aberrations in the VHL gene. Perhaps, it would promote renal cancer molecular markers evaluation, for example, a determination of suppressor genes methylated in renal cancer.

[Regulation of hypoxia inducible factor-1alpha on osteoblast function in osteogenesis]

OBJECTIVE

To explore the regulation of hypoxia inducible factor-1alpha (HIF-1alpha) on osteoblast function in osteogenesis.

METHODS

Skull-cap bone of HIF-1alpha Loxp/Loxp and VHL Loxp/Loxp C57/BL6 mice were taken out and cultured so as to obtain osteoblasts which were infected with the recombinant adenovirus Ad-Cre so as to conditionally knock out the HIF-1alpha gene and its up-stream gene for von Hippel-Lindau disease (VHL) using Cre-Loxp recombinase technique. Then the osteoblasts were cultured under 2% O2 for 48 hours. Real-time PCR and Western-blotting were used to detect the mRNA and protein expression of vascular endothelial growth factor (VEGF), core binding factor al (RunX2), alkaline phosphatase (ALP) and osteocalcin (OC). Transgenic FVB mice mated with C57/BL6 mice with both HIF-1alpha and VHL alleles to obtain the mice with the osteoblasts with the HIF-1alpha and VHL genes conditionally knocked-out. At the age of 3 months the distal femurs of HIF-1alpha/VHL conditionally knocked-out mice and wild type mice were obtained to undergo hematoxylin-eosin staining and micro-CT to evaluate the bone histomorphometry and bone mineral density (BMD).

RESULTS

The mRNA and protein expressions of VEGF, RunX2, ALP, and OC of the HIF-1alpha conditionally knocked-out osteoblasts were all decreased and the mRNA and protein expressions of VEGF, RunX2, ALP, and OC of the VHL conditionally knocked-out osteoblasts were all increased. The values of bone histomorphometry and bone mineral density (BMD) of the HIF-1alpha conditionally knocked-out mice were both significantly lower than those of the wild-type mice, whereas the values of bone histomorphometry and BMD of the VHL conditionally knocked-out mice were both significantly higher than those of the wild-type mice (all P < 0.01).

CONCLUSION

Under both the physiological and pathological hypoxia environment in bone tissues HIF-1alpha can promote the bone formation ability of osteoblast.

Over-expression of hypoxia-inducible factor 1 alpha in ovarian clear cell carcinoma

OBJECTIVE

Unlike other histological types of epithelial ovarian carcinoma, ovarian clear cell carcinoma is known to have very poor response to therapy even when discovered in its early stages. Since tumor hypoxia has been shown to be strongly associated with poor prognosis, deregulation of the representative factor of tissue hypoxia; hypoxia-inducible factor 1 alpha (HIF-1alpha) and related protein; Von Hippel-Lindau (VHL) may be associated with poor prognosis of ovarian clear cell carcinoma.

METHODS

Immunolocalization of both HIF-1alpha and VHL was performed on 56 cases of paraffin-embedded tissue sections of four different histological types of epithelial ovarian carcinoma and 5 cases of benign ovarian tumors as a control. Quantitative RT-PCR analysis of both HIF1A and VHL was performed on RNA isolated from 61 microdissected frozen tissues of four different histological types of epithelial ovarian carcinoma and 6 cases of normal ovarian epithelial cells. Expression levels of HIF-1alpha and VHL in different histological types and correlation between HIF-1alpha and VHL were determined by nonparametric analysis by Kruskal-Wallis and Spearman's test.

RESULTS

HIF-1alpha expression levels were significantly higher in ovarian clear cell carcinoma than in other histological types (P=0.001). We found no correlation between mRNA and protein expression level in any type of carcinoma specimens. Among endometrioid, serous, and mucinous carcinoma, there were no differences in HIF-1alpha expression (P=0.643). There was a negative correlation between HIF-1alpha and VHL in serous (r=-0.661, P=0.027) and in endometrioid carcinoma (r=-0.657 P=0.039), but no correlation was found between HIF-1alpha and VHL expression levels in ovarian clear cell carcinoma (P=0.60).

CONCLUSIONS

The results suggest that the role of hypoxia may change according to the histological type of ovarian carcinoma. High expression of HIF-1alpha and its independence from VHL in ovarian clear cell carcinoma may confer chemoresistance in this histological type.

Overexpression of von Hippel-Lindau tumor suppressor protein and antisense HIF-1alpha eradicates gliomas

The von Hippel-Lindau tumor suppressor protein (pVHL) suppresses tumor formation by binding the alpha subunits of hypoxia-inducible-factors responsible for stimulating tumor angiogenesis and glycolysis, and targeting them for ubiquitination and proteasomal destruction. Loss of pVHL leads to tumorigenesis and development of sporadic renal cell carcinomas and central nervous system hemangioblastomas. In the present study, we investigated whether engineered overexpression of pVHL in C6 glioma cells, which already express endogenous pVHL, would suppress the tumorigenicity of this particular tumor cell type. C6 cells overexpressing VHL displayed a reduced growth rate (70% inhibition) compared to the parental cell line when subcutaneously implanted in athymic (nu/nu) mice. Growth inhibition was associated with a 50% reduction in the number of tumor vessels and a 60% increase in tumor cell apoptosis, due in part to downregulation of HIF-1, VEGF, and the antiapoptotic factor Bcl-2, respectively. Gene transfer of VHL suppressed the growth of established C6 gliomas, and synergized with antisense HIF-1 to completely eradicate tumors. The data suggest that VHL gene therapy and/or agents that increase VHL expression could have utility in the treatment of gliomas, particularly when combined with agents that inhibit the expression or function of HIF-1.

Under-expression of VHL and over-expression of HDAC-1, HIF-1?, LL-37, and IAP-2 in affected skin biopsies of patients with psoriasis

BACKGROUND

A feature of psoriasis is the rapid proliferation of keratinocytes, during which apoptosis is blocked and angiogenesis starts. It is known that tumor hypoxic cells produce histone deacetylase-1 (HDAC-1), which up-regulates hypoxia-inducible factor-1alpha (HIF-1alpha) and down-regulates von Hippel-Lindau (VHL) protein by up-regulating vascular endothelial growth factor (VEGF) expression. It has been reported recently that the porcine peptide PR39 (homologous to human LL-37) has angiogenic and antiapoptotic activity. Thus, LL-37, induced by insulin-like growth factor-1 (IGF-1), could help in the production of VEGF. PR39 also induces the expression of inhibitor of apoptosis protein-2 (IAP-2), which blocks apoptosis. The purpose of this work was to analyze whether these genes and their proteins are expressed in psoriatic biopsies.

METHODS

Using semiquantitative reverse transcriptase-polymerase chain reaction (RT-PCR) messenger RNA (mRNA) expression and immunohistochemical staining, we studied VHL, IAP-2, and related genes in skin biopsies from psoriatic patients and healthy subjects.

RESULTS

An over-expression of the mRNA for HDAC-1, HIF-1alpha, LL-37, and IGF-1 in psoriatic skin, in comparison with skin from healthy subjects, was found. The antiangiogenic VHL mRNA and protein were under-expressed in psoriatic skin and highly expressed in healthy skin. The antiapoptotic IAP-2 was over-expressed in dermal endothelial cells from psoriatic skin. The pro-apoptotic Bax, Fas, and FasL mRNAs were expressed.

CONCLUSIONS

These findings suggest that there could be an association of HDAC-1, HIF-1alpha, LL-37, VHL, and IAP-2 with angiogenic and apoptotic mechanisms in psoriasis.

Primary cilium formation requires von hippel-lindau gene function in renal-derived cells

Biallelic inactivation of the von Hippel-Lindau tumor suppressor gene, VHL, occurs in the majority of renal clear cell carcinomas (RCC). VHL's function, regulating the degradation of hypoxia-inducible factor alpha (HIFalpha) subunits, explains the angiogenic nature of these tumors, but not tumor initiation. Because the development of renal cysts precedes tumor formation, and because the dysfunction of primary cilium is a common pathogenic mechanism in polycystic kidney diseases, we determined whether kidney-derived VHL- cells required VHL for the generation of cilium. Ectopic expression of VHL in RCC(VHL-) cells induced increased polarization and primary cilium formation. Cilium formation correlated directly with the expression of both wild-type VHL isoforms and a VHL mutant not associated with RCC development, whereas expression of RCC-associated VHL mutants did not support ciliogenesis. Requirement of VHL for ciliogenesis was independent of HIFalpha abundance. These data indicate separable independent functions for VHL (HIFalpha degradation and differentiation) and suggest a mechanism whereby disruption of both functions is required for renal carcinogenesis.

Regulation of E-cadherin expression by VHL and hypoxia-inducible factor

Mutations in von Hippel-Lindau tumor suppressor gene (VHL) underlie the VHL hereditary cancer syndrome and also occur in most sporadic clear cell renal cell cancers (CCRCC). Currently, the mechanism(s) by which VHL loss of function promotes tumor development in the kidney are not fully elucidated. Here, we show that VHL inactivation in precancerous lesions in kidneys from patients with VHL disease correlates with marked down-regulation of the intercellular adhesion molecule E-cadherin. Moreover, in VHL-defective cell lines (RCC4 and RCC10) derived from sporadic CCRCC, reexpression of VHL was found to restore E-cadherin expression. The product of the VHL gene has multiple reported functions, the best characterized of which is its role as the recognition component of an ubiquitin E3 ligase complex responsible for mediating oxygen-dependent destruction of hypoxia-inducible factor-alpha (HIF-alpha) subunits. We show that HIF activation is necessary and sufficient to suppress E-cadherin in renal cancer cells. Given the fundamental role of E-cadherin in controlling epithelial behavior, our findings give insight into how VHL inactivation/HIF activation may lead to kidney cancer and also indicate a mechanism by which reduced oxygenation could alter E-cadherin expression in other cancers and influence normal homeostasis in other epithelia.

Hypoxia-inducible factor-1-dependent repression of E-cadherin in von Hippel-Lindau tumor suppressor-null renal cell carcinoma mediated by TCF3, ZFHX1A, and ZFHX1B

A critical event in the pathogenesis of invasive and metastatic cancer is E-cadherin loss of function. Renal clear cell carcinoma (RCC) is characterized by loss of function of the von Hippel-Lindau tumor suppressor (VHL), which negatively regulates hypoxia-inducible factor-1 (HIF-1). Loss of E-cadherin expression and decreased cell-cell adhesion in VHL-null RCC4 cells were corrected by enforced expression of VHL, a dominant-negative HIF-1alpha mutant, or a short hairpin RNA directed against HIF-1alpha. In human RCC biopsies, expression of E-cadherin and HIF-1alpha was mutually exclusive. The expression of mRNAs encoding TCF3, ZFHX1A, and ZFHX1B, which repress E-cadherin gene transcription, was increased in VHL-null RCC4 cells in a HIF-1-dependent manner. Thus, HIF-1 contributes to the epithelial-mesenchymal transition in VHL-null RCC by indirect repression of E-cadherin.

[HIF-1alpha, HIF-2alpha and VHL mRNA expression in different cell lines during hypoxia]

Hypoxia inducible factor-1alpha (HIF-1alpha) mRNA expression is significantly decreased under hypoxia in different cell lines exposed directly to hypoxia or treated with dimethyloxalylglycine which mimics hypoxic effects under normoxic conditions. However, the decreased expression of HIF-1alpha mRNA is accompanied by an increase of HIF-1alpha protein (pHIF-1alpha) level as well as by overexpression of known HIF-dependent genes (VEGF, Glut1, PFKFB-3 and PFKFB-4) under hypoxic conditions or with the use of dimethyloxalylglycine. Expression of HIF-1alpha mRNA also depends on iron because desferrioxamine and cobalt chloride produce similar to hypoxia effects on the levels of this mRNA. It was shown that HIF-1alpha mRNA expression did not change significantly in some cell lines (SKBR3, MDA-MB468 and BT549) under hypoxia. However, in these cell lines hypoxia decreases expression of HIF-2alpha mRNA, another member of HIF-alpha gene family, as a result of cell specific regulation of HIF-alpha genes under hypoxia. Moreover, hypoxia slightly induces expression of PFKFB-4 mRNA in SKBR3, MDA-MB468 and BT549 as compared to other cell lines where this effect of hypoxia was much stronger and adaptation to hypoxia is controlled by HIF-1alpha. Hypoxia slightly reduces expression of tumor suppressor VHL which targets HIF-1alpha for ubiquitination. Thus, our results clearly demonstrated down regulation of HIF-1alpha or HIF-2alpha in different cell lines by hypoxia.

von Hippel-Lindau Tumor Suppressor Protein Regulates the Assembly of Intercellular Junctions in Renal Cancer Cells through Hypoxia-Inducible Factor–Independent Mechanisms

Inactivation of the von Hippel-Lindau (VHL) tumor suppressor gene is responsible for the development of renal cell cancers (RCC), pheochromocytomas, and tumors in other organs. The best known function of VHL protein (VHL) is to target the hypoxia-inducible factor (HIF) for proteasome degradation. VHL is also required for the establishment of an epithelial-like cell shape in otherwise fibroblastic-like RCC cell lines. However, the underlying mechanisms and whether this is linked to HIF remain undetermined. Because the breakage of intercellular junctions induces a fibroblastic-like phenotype in multiple cancer cell models, we hypothesized that VHL may be required for the assembly of intercellular junctions in RCC cells. Our experiments showed that VHL in RCC cell lines is necessary for the normal organization of adherens and tight intercellular junctions, the maintenance of cell polarity, and control of paracellular permeability. Additionally, 786-O cells reconstituted with wild-type VHL and with a constitutively active form of HIF-2alpha did not reproduce any of the phenotypic alterations of VHL-negative cells. In summary, we show that VHL inactivation in RCC cells disrupts intercellular junctions and cell shape through HIF-independent events, supporting the concept that VHL has additional functions beside its role in the regulation of HIF.

Interplay between VHL/HIF1α and Wnt/β-catenin pathways during colorectal tumorigenesis

Activation of the Wnt signaling pathway initiates the transformation of colorectal epithelial cells, although the transition to metastatic cancer requires angiogenesis. We have investigated the expression of the von Hippel-Lindau (VHL) tumor suppressor in the intestines from humans and mice. Here, we show that VHL expression is regulated by TCF4 and is restricted to the proliferative compartment at the bottom of intestinal crypts. Accordingly, VHL is completely absent from the proliferative intestinal pockets of Tcf4(-/-) perinatal mice. We observed complementary staining of the hypoxia-inducible factor (HIF) 1alpha to VHL in normal intestinal epithelium as well as in all stages of colorectal cancer (CRC). To the best of our knowledge, this is the first report demonstrating the presence of nuclear HIF1alpha in normoxic healthy adult tissue. Although we observed upregulated levels of VHL in very early CRC lesions from sporadic and familial adenomatous polyposis patients - presumably due to activated Wnt signaling - a clear reduction of VHL expression is observed in later stages of CRC progression, coinciding with stabilization of HIF1alpha. As loss of VHL in later stages of CRC progression results in stabilization of HIF, these data provide evidence that selection for VHL downregulation provides a proangiogenic impulse for CRC progression.