Tumor suppressor protein VHL is induced at high cell density and mediates contact inhibition of cell growth

Ultrasound Microbubble-Mediated VHL Regulates the Biological Behavior of Ovarian Cancer Cells

According to the literature, the von Hippel-Lindau (VHL) gene has a certain correlation with ovarian cancer. In this study, we investigated the effect and mechanism of ultrasound microbubble-mediated VHL on the biological function of ovarian cancer cells. Non-targeting lipid microbubbles and targeted lipid microbubbles were prepared. OVCAR-3 cells were treated with VHL mediated by ultrasound and microbubbles alone or together. Expressions of VHL, Akt, epithelial-mesenchymal-transition-related proteins and apoptosis-related proteins were detected by Western blot and quantitative real-time polymerase chain reaction as needed. The effect of ultrasound microbubble-mediated VHL on the proliferation, apoptosis, cell cycle, migration and invasion of OVCAR-3 cells was examined by Cell Counting Kit-8, flow cytometry, wound-healing assay and Transwell. Compared with other treatment methods, ultrasound microbubble mediation enhanced VHL expression in OVCAR-3 cells. Overexpression of liposome-mediated VHL inhibited the proliferation and migration; caused cell-cycle arrest; promoted apoptosis: downregulated the expressions of MMP2, MMP9, E-cadherin, Akt and Bcl-2; and upregulated the expressions of VHL and BCL2-associated X protein (BAX) in OVCAR-3 cells. The effect of microbubble-treated VHL was similar to liposome-mediated regulation, while ultrasound treatment enhanced the effect of VHL on OVCAR-3 cells. More interestingly, ultrasound microbubble-mediated VHL had the most obvious regulatory effect on OVCAR-3 cells. Ultrasound microbubble technology increases the transfection efficiency of VHL into OVCAR-3 cells and enhances the effect of VHL gene on the biological function of OVCAR-3 cells.

Hypermethylation and loss of retinoic acid receptor responder 1 expression in human choriocarcinoma

Background

Human placental development resembles tumorigenesis, due to the invasive and fusogenic potential of trophoblasts. However, these features are tightly controlled in trophoblasts. Disturbance of this spatial and temporal regulation is thought to contribute to the rare formation of choriocarcinomas. Promoter hypermethylation and loss of the tumor suppressor Retinoic acid receptor responder 1 (RARRES1) were shown to contribute to cancer progression. Our study investigated the epigenetic and transcriptional regulation of RARRES1 in healthy human placenta in comparison to choriocarcinoma cell lines and cases.

Methods

Three choriocarcinoma cell lines (Jeg-3, JAR and BeWo) were treated with three different retinoic acid derivates (Am580, Tazarotene and all-trans retinoic acid) and 5-aza-2′-deoxycytidine. We analyzed RARRES1 promoter methylation by pyrosequencing and performed realtime-PCR quantification to determine RARRES1 expression in placental tissue and trophoblastic cell lines. Additionally, RARRES1 was stained in healthy placentas and in biopsies of choriocarcinoma cases (n = 10) as well as the first trimester trophoblast cell line Swan71 by immunofluorescence and immunohistochemistry.

Results

In the choriocarcinoma cell lines, RARRES1 expression could not be induced by sole retinoic acid treatment. Stimulation with 5-aza-2′-deoxycytidine significantly induced RARRES1 expression, which then could be further increased with Am580, Tazarotene and all-trans retinoic acid. In comparison to healthy placenta, choriocarcinoma cell lines showed a hypermethylation of the RARRES1 promoter, which correlated with a reduced RARRES1 expression. In concordance, RARRES1 protein expression was lost in choriocarcinoma tissue. Additionally, in the trophoblastic cell line Swan71, we found a significant induction of RARRES1 expression with increased cell density, during mitosis and in syncytial knots.

Conclusions

Our findings showed that RARRES1 expression is absent in choriocarcinoma due to promoter methylation. Based on our analysis, we hypothesize that RARRES1 might exert tumor suppressive functions in multiple cellular processes (e.g. cell cycle regulation, adhesion, invasion and apoptosis).

Electronic supplementary material

The online version of this article (10.1186/s13046-017-0634-x) contains supplementary material, which is available to authorized users.

Cell type- and density-dependent effect of 1 T static magnetic field on cell proliferation

Increasing evidence shows that static magnetic fields (SMFs) can affect cell proliferation but mixed results have been reported. Here we systematically examined the effects of 1 T (Tesla) SMF, which is close to the SMF intensity that patients are exposed to MRI (magnetic resonance imaging) scanners in hospitals, for its effect on 15 different cell lines, including 12 human and 3 rodent cell lines. Our results show that 1 T SMF does not have apparent impact on cell cycle or cell death. However, at higher cell density, it reduced cell numbers in six out of seven solid human cancer cell lines. We found that both cell type and cell density had evident impacts on SMF effects. Moreover, the EGFR-Akt-mTOR pathway, which varies significantly between different cell types and densities, contributes to the differential effects of SMF. In addition, SMF also increases the efficacy of Akt inhibitors on cancer cell growth inhibition. Therefore 1 T SMF affects cell proliferation in a cell type- and cell density-dependent manner, and the inhibition effect of 1 T SMF on multiple cancer cells at higher cell density may indicate its clinical potential in late stage cancer therapy.

Choosing the right cell line for renal cell cancer research

Cell lines are still a tool of choice for many fields of biomedical research, including oncology. Although cancer is a very complex disease, many discoveries have been made using monocultures of established cell lines. Therefore, the proper use of in vitro models is crucial to enhance our understanding of cancer. Therapeutics against renal cell cancer (RCC) are also screened with the use of cell lines. Multiple RCC in vitro cultures are available, allowing in vivo heterogeneity in the laboratory, but at the same time, these can be a source of errors. In this review, we tried to sum up the data on the RCC cell lines used currently. An increasing amount of data on RCC shed new light on the molecular background of the disease; however, it revealed how much still needs to be done. As new types of RCC are being distinguished, novel cell lines and the re-exploration of old ones seems to be indispensable to create effective in vitro tools for drug screening and more.

An Immunohistochemical and Ultrastructural Study of Pancreatic Microcystic Serous Cyst Adenoma with Special Reference to Tumor-Associated Microvasculature and Vascular Endothelial Growth Factor in Tumor Cells

Pancreatic microcystic serous cyst adenomas are rare exocrine tumors composed of small cysts lined by glycogen-rich cells. The disease may be sporadic or present as part of von Hippel-Lindau (VHL) syndrome. Four sporadic cases of pancreatic serous cyst adenoma were examined by conventional histological, immunohistochemical, and ultrastructural methods. In the present study, new findings include the immunohistochemical identification of vascular endothelial growth factor (VEGF) and the lack of PDX-1 (putative master transcriptional factor in pancreatic stem cells) in the epithelial tumor cells. Ultrastructurally, many small blood vessels were intimately associated with epithelial tumor cells and adjacent fibroblastic cells. The observations suggest the possibility that VEGF-containing tumor cells act in a paracrine fashion to stimulate neovascularization; that peripheral blood in the vascular lumen might be filtered or processed by the endothelial and epithelial tumor cells; and that filtrates might therefore be stored as serous inclusions. It is hypothesized that pancreatic serous cyst adenomas might be under the abnormal regulation of the VHL gene, just like VHL disease itself and certain types of renal cell carcinoma, showing the distinctive histology of a rich vascularity intimately related to epithelial lining cells of cysts accompanied by stromal fibroblasts/myofibroblasts and collagenous stroma.

VHL promotes E2 box-dependent E-cadherin transcription by HIF-mediated regulation of SIP1 and snail

The product of the von Hippel-Lindau gene (VHL) acts as the substrate-recognition component of an E3 ubiquitin ligase complex that ubiquitylates the catalytic alpha subunit of hypoxia-inducible factor (HIF) for oxygen-dependent destruction. Although emerging evidence supports the notion that deregulated accumulation of HIF upon the loss of VHL is crucial for the development of clear-cell renal cell carcinoma (CC-RCC), the molecular events downstream of HIF governing renal oncogenesis remain unclear. Here, we show that the expression of a homophilic adhesion molecule, E-cadherin, a major constituent of epithelial cell junctions whose loss is associated with the progression of epithelial cancers, is significantly down-regulated in primary CC-RCC and CC-RCC cell lines devoid of VHL. Reintroduction of wild-type VHL in CC-RCC (VHL(-/-)) cells markedly reduced the expression of E2 box-dependent E-cadherin-specific transcriptional repressors Snail and SIP1 and concomitantly restored E-cadherin expression. RNA interference-mediated knockdown of HIFalpha in CC-RCC (VHL(-/-)) cells likewise increased E-cadherin expression, while functional hypoxia or expression of VHL mutants incapable of promoting HIFalpha degradation attenuated E-cadherin expression, correlating with the disengagement of RNA polymerase II from the endogenous E-cadherin promoter/gene. These findings reveal a critical HIF-dependent molecular pathway connecting VHL, an established "gatekeeper" of the renal epithelium, with a major epithelial tumor suppressor, E-cadherin.

Proteomic identification of a role for the von Hippel Lindau tumour suppressor in changes in the expression of mitochondrial proteins and septin 2 in renal cell carcinoma

The von Hippel Lindau (VHL) tumour suppressor gene, VHL, plays a central role in development of sporadic conventional renal cell carcinomas (RCCs). Studying VHL function may, therefore, increase understanding of the pathogenesis of RCC and identify markers/therapeutic targets. Comparison of 2-DE protein profiles of VHL-defective RCC cells (UMRC2) transfected with control vector or wild-type VHL showed differences in 30 proteins, including several novel changes. One of the findings confirmed by Western blotting was up-regulation of the mitochondrial protein ubiquinol cytochrome c reductase complex core protein 2 following VHL transfection, a change that was also observed in two other cell line backgrounds. A marked decrease in expression of this and several other mitochondrial proteins was demonstrated in RCC tissues and using VHL-transfectants, several were shown to exhibit VHL-dependent regulation. Thus, VHL may contribute to the decreased mitochondrial function seen in RCC. A form of septin 2 down-regulated following VHL transfection was also identified. Septin 2 was up-regulated in 12/16 RCCs, while alteration of the form present was also observed in 1/3 tumours analysed. Thus, increased expression of septin 2 is a common event in RCC and protein modification may also alter septin 2 function in a subset of tumours.

E2-EPF UCP targets pVHL for degradation and associates with tumor growth and metastasis

The von Hippel-Lindau tumor suppressor, pVHL, forms part of an E3 ubiquitin ligase complex that targets specific substrates for degradation, including hypoxia-inducible factor-1alpha (HIF-1alpha), which is involved in tumor progression and angiogenesis. It remains unclear, however, how pVHL is destabilized. Here we show that E2-EPF ubiquitin carrier protein (UCP) associates with and targets pVHL for ubiquitin-mediated proteolysis in cells, thereby stabilizing HIF-1alpha. UCP is detected coincidently with HIF-1alpha in human primary liver, colon and breast tumors, and metastatic cholangiocarcinoma and colon cancer cells. UCP level correlates inversely with pVHL level in most tumor cell lines. In vitro and in vivo, forced expression of UCP boosts tumor-cell proliferation, invasion and metastasis through effects on the pVHL-HIF pathway. Our results suggest that UCP helps stabilize HIF-1alpha and may be a new molecular target for therapeutic intervention in human cancers.

Formation of primary cilia in the renal epithelium is regulated by the von Hippel-Lindau tumor suppressor protein

Growing evidence points to defects in the primary cilium as a critical mechanism underlying renal cyst development. Inactivation of the VHL gene is responsible for the autosomal dominant condition von Hippel-Lindau (VHL) disease and is implicated in most sporadic clear cell renal carcinomas. Manifestations of VHL disease include cysts in several organs, particularly in the kidney. Here it is shown that VHL inactivation is associated with abrogation of the primary cilium in renal cysts of patients with VHL disease and in VHL-defective cell lines. Complementation of VHL-defective clear cell renal carcinoma cell lines with wild-type VHL restored primary cilia. Moreover, it is shown that the effects of VHL on the primary cilium are mediated substantially via hypoxia-inducible factor. The effect of VHL status on the primary cilium provides a potential mechanism for renal cyst development in VHL disease and may help in the understanding of how VHL acts as a tumor suppressor.

Inactivation of von Hippel-Lindau gene induces constitutive phosphorylation of MET protein in clear cell renal carcinoma

It is well known that inactivation of von Hippel-Lindau (VHL) gene predisposes for human clear cell renal carcinoma (CCRC). However, details about critical roles of VHL inactivation during tumorigenesis are still unknown. MET protein is a tyrosine kinase receptor for hepatocyte growth factor/scatter factor (HGF/SF), which regulates cell growth, cell morphology, and cell motility. We showed that MET protein overexpressed in CCRC cells was phosphorylated without HGF/SF. This constitutive phosphorylation of MET protein in CCRC cells was inhibited by the rescue of exogenous wild-type VHL gene without a decrease in expression level of MET protein. Interestingly, wild-type VHL gene suppressed the phosphorylation of MET protein only under high cell density conditions. Additionally, MET protein activated by the inactivation of VHL gene modified cell adherence, including N-cadherin and beta-catenin. When activation of MET protein in CCRC cells was inhibited by the MET inhibitor K252a, the growth of CCRC cells in vitro and the tumorigenesis induced by CCRC cells in nude mice were suppressed. From these results, we concluded that inactivation of VHL gene induced constitutive phosphorylation of MET protein and modified intercellular adherence structure to trigger the cell growth released from contact inhibition, finally resulting in tumorigenesis. This is one of the mechanisms of CCRC oncogenesis, and MET protein has potential as a molecular target for novel CCRC therapies.

Induction of the von Hippel-Lindau tumor suppressor gene by late hypoxia limits HIF-1 expression

Hypoxia-inducible factor (HIF) remains the central focus of oxygen sensing during hypoxia. HIF is a heterodimeric transcription factor consisting of an oxygen-regulated alpha- and a constitutively expressed beta subunit. The von Hippel-Lindau tumor suppressor (pVHL) is a component of the E3 ubiquitin ligase complex and targets HIF-alpha to proteasomal degradation, but also is known to exert a significant control on HIF transactivation activity. However, the understanding of the full interaction between HIF and pVHL has been hindered by a lack in the understanding of pVHL regulation. Here, we report that pVHL itself is induced in prolonged hypoxia in a kinetic that parallels the observed downregulation of HIF-1alpha protein under such conditions. In addition, we document direct HIF-1alpha binding to the VHL promoter and identify a functional hypoxia response element (HRE) within the VHL promoter. Such induction of pVHL in hypoxia furthermore has functional implications for the HIF dependent hypoxic response, implicating a physiologically relevant feedback mechanism. These results provide an intriguing model, whereby HIF self-regulates expression through VHL and highlight the role of pVHL as a unifying mechanism of HIF regulation.

Engineering microenvironment for expansion of sensitive anchorage-dependent mammalian cells

Tissue engineering involves ex vivo seeding of anchorage-dependent mammalian cells onto scaffolds, or transplanting cells in vivo. The cell expansion currently requires repeated cell detachment from solid substrata by enzymatic, chemical or mechanical means. The report here presents a high yield three-dimensional culture and harvest system circumventing the conventional detachment requirements. Cells mixed with dilute cationic collagen were microencapsulated within an ultra-thin shell of synthetic polymers. The cationic collagen could rapidly form a conformal layer of collagen fibers around cells to support cell proliferation and functions. The collagen could be readily removed from cells with a buffer rinse after harvesting from the fragile microcapsules. The cells harvested from this system demonstrate improved attachment, morphology and functions over conventionally cultured cells, upon binding to ligand-conjugated polymer surfaces. The harvested cells can be re-encapsulated and allowed to proliferate again, or used immediately in applications.

Cellular quiescence induced by contact inhibition or serum withdrawal in C3H10T1/2 cells

Either confluence or serum withdrawal may cause growth arrest of cultured non-transformed cells. Here, we compared sparsely populated and confluent C3H10T1/2 cells with and without serum-containing medium. The following proliferation-relevant end points were examined: cell-cycle distribution, Ki-67 antigen presence, the level of the von Hippel-Lindau (VHL) protein, and gene expression, determined using a microarray approach. In sparse/logarithmic cultures, the fraction of cells in G(0)/G(1) phase increased from 55 to 85% following serum withdrawal. Moreover, the fraction of Ki-67 positive cells dropped from 89 to 47%. In confluent cultures, the majority of cells (80%) were in G(0)/G(1) phase and only 25-30% were Ki-67 positive, regardless of serum presence. In both serum-deprived and contact-inhibited cultures, significant and distinct changes in gene expression were observed. Serum deprivation of sparsely cultured cells resulted in significant over-expression of several transcription factors, while confluent cells showed elevated expression of genes coding for Wnt6, uPar, Tdag51, Egr1, Ini1a and Mor1. These results indicate that contact inhibition and serum withdrawal lead to cellular quiescence through distinct genetic and molecular mechanisms.

Loss of the von Hippel Lindau Tumor Suppressor Disrupts Iron Homeostasis in Renal Carcinoma Cells

Given the modulation of iron metabolism by hypoxia and the high iron requirement of neoplastic cells, we investigated iron metabolism in a human renal cancer cell line with a mutated von Hippel Lindau (VHL) tumor suppressor gene (RCC10) and in a transfectant clone with wild-type VHL (RCC63). The loss of VHL strongly up-regulated transferrin receptor expression in RCC10 cells as a result of hypoxia inducible factor-1 (HIF-1)-mediated transcriptional activation, leading to an increased uptake of transferrin-bound 55Fe. Increased iron availability did not compromise the resistance of VHL-defective cells to oxidative stress or promote faster cell multiplication. Surprisingly, the content of ferritin H and L subunits and ferritin mRNA levels were considerably lower in the RCC10 than in the RCC63 cells. Despite the similarities between HIF-1 and iron regulatory protein 2 (IRP2), we found no evidence of specific regulation of IRP2 by VHL. However, both IRP2 and IRP1 were slightly activated in RCC10 cells, thus indicating that this cell line has a somewhat reduced labile iron pool (LIP). The finding that RCC10 cells had a lower ferritin content but more ferritin-associated 55Fe than RCC63 explains why VHL-lacking cells may have a smaller LIP despite increased iron uptake. We also found a correlation between cytoprotection from iron-mediated damage and efficient incorporation into ferritin of both transferrin and non-transferrin-bound 55Fe. This study shows that, like oncogene activation, the loss of an oncosuppressor rearranges the expression pattern of the genes of iron metabolism to increase iron availability. However, in the case of VHL loss, mechanisms affecting iron handling by ferritin somehow counteract the effects that the reduced content of this protective protein may have on proliferation and oxidant sensitivity.

Jade-1, a candidate renal tumor suppressor that promotes apoptosis

Medical therapies are lacking for advanced renal cancer, so there is a great need to understand its pathogenesis. Most renal cancers have defects in the von Hippel-Lindau tumor suppressor pVHL. The mechanism by which pVHL protein functions in renal tumor suppression remains unclear. Jade-1 is a short-lived, kidney-enriched transcription factor that is stabilized by direct interaction with pVHL. Loss of Jade-1 stabilization by pVHL correlates with renal cancer risk, making the relationship between Jade-1 and renal cancer compelling. We report that Jade-1 expression was barely detectable in all tested renal cancer cell lines, regardless of VHL status. Strikingly, proteasome inhibitor treatment increased endogenous Jade-1 expression up to 10-fold. Jade-1 inhibited renal cancer cell growth, colony formation, and tumor formation in nude mice. Intriguingly, Jade-1 also affected the pattern of cell growth in monolayer culture and 3D culture. Jade-1 increased apoptosis by 40-50% and decreased levels of antiapoptotic Bcl-2. Antisense Jade-1-expressing cells confirmed these results. Therefore, Jade-1 may suppress renal cancer cell growth in part by increasing apoptosis. Jade-1 may represent a proapoptotic barrier to proliferation that must be overcome generally in renal cancer, perhaps initially by pVHL inactivation and subsequently by increased proteasomal activity. Therefore, Jade-1 may be a renal tumor suppressor.

The role of von Hippel–Lindau protein in the differentiation of neural progenitor cells under normoxic and anoxic conditions

Von Hippel-Lindau protein (pVHL) normally functions to cause ubiquitin-mediated degradation of hypoxia-inducible factor-1alpha (HIF-1alpha) under normoxic but not under hypoxic conditions, and induces neuronal differentiation of neural progenitor cells. However, the role of pVHL in the differentiation of neural progenitor cells under either condition has not been fully elucidated. Herein, we show that under the anoxic condition the expression of pVHL and neuronal markers in neural progenitor cells was inhibited, while HIF-1alpha was induced. In addition, neural progenitor cells expressing pVHL following gene transfer showed distinct neuronal differentiation and no induction of HIF-1alpha under the normoxic condition but not under the anoxic condition. In conclusion, neuronal differentiation induced by pVHL is associated with degradation of HIF-1alpha and occurs normally under the normoxic condition but not under the anoxic condition. Differentiation of neuronal progenitor cells may thus depend on oxygen density.

In vitroandIn vivoModels Analyzing von Hippel-Lindau Disease-Specific Mutations

Mutations in the von Hippel-Lindau (VHL) tumor suppressor gene cause tissue-specific tumors, with a striking genotype-phenotype correlation. Loss of VHL expression predisposes to hemangioblastoma and clear cell renal cell carcinoma, whereas specific point mutations predispose to pheochromocytoma, polycythemia, or combinations of hemangioblastoma, renal cell carcinoma, and/or pheochromocytoma. The VHL protein (pVHL) has been implicated in many cellular activities including the hypoxia response, cell cycle arrest, apoptosis, and extracellular matrix remodeling. We have expressed missense pVHL mutations in Vhl(-/-) murine embryonic stem cells to test genotype-phenotype correlations in euploid cells. We first examined the ability of mutant pVHL to direct degradation of the hypoxia inducible factor (HIF) subunits HIF1alpha and HIF2alpha. All mutant pVHL proteins restored proper hypoxic regulation of HIF1alpha, although one VHL mutation (VHL(R167Q)) displayed impaired binding to Elongin C. This mutation also failed to restore HIF2alpha regulation. In separate assays, these embryonic stem cells were used to generate teratomas in immunocompromised mice, allowing independent assessment of the effects of specific VHL mutations on tumor growth. Surprisingly, teratomas expressing the VHL(Y112H) mutant protein displayed a growth disadvantage, despite restoring HIFalpha regulation. Finally, we observed increased microvessel density in teratomas derived from Vhl(-/-) as well as VHL(Y112H), VHL(R167Q), and VHL(R200W) embryonic stem cells. Together, these observations support the hypothesis that pVHL plays multiple roles in the cell, and that these activities can be separated via discrete VHL point mutations. The ability to dissect specific VHL functions with missense mutations in a euploid model offers a novel opportunity to elucidate the activities of VHL as a tumor suppressor.

Effect of Radiation and Ibuprofen on Normoxic Renal Carcinoma Cells Overexpressing Hypoxia-Inducible Factors by Loss of von Hippel–Lindau Tumor Suppressor Gene Function

PURPOSE

Tumor hypoxia is a major limiting factor for radiation therapy. Hypoxia-inducible factors (HIFs) are overexpressed in several human cancers and are considered prognostic markers and potential targets for cancer therapy. The purpose of the present study was to investigate the impact of HIFs on radiosensitivity.

EXPERIMENTAL DESIGN

Renal clear cell carcinoma (RCC) cell lines overexpressing HIFs under normoxic conditions because of inactivation of von Hippel-Lindau tumor suppressor gene function (VHL-ve) and their matched pairs in which overexpression of HIFs was abolished by expression of functional VHL (VHL+ve) were irradiated. Radiosensitivity was determined by clonogenic assay. HIF and VHL protein levels were evaluated by Western blot analysis. RCC cells were also treated with ibuprofen, a radiosensitizer and HIF inhibitor in prostate cancer cells. The effect of ibuprofen on radiosensitization and HIF and VHL proteins was compared in RCC matched-pair cell lines.

RESULTS

The data showed only small differences in the radiosensitivity between the cells overexpressing HIFs and cells with basal HIF levels. The dose-modifying factors for C2, 786-0, and A498 RCC cells were 1.14, 1.14 and 1.15, respectively. Radiation did not alter HIF or VHL protein levels. Ibuprofen inhibited HIFs in VHL+ve cells expressing basal levels of HIFs. In VHL-ve cells overexpressing HIFs, the inhibition was very modest. Ibuprofen radiosensitized C2 RCC cells to the same extent irrespective of their HIF status.

CONCLUSIONS

Overexpression of HIFs in RCC cells harboring VHL mutations has only a modest effect on the radiosensitivity. Radiosensitization by ibuprofen appears to be independent of HIF status.

Lavendustin A enhances axon elongation in VHL gene-transfected neural stem cells

Axonal elongation is necessary for neuronal regeneration of the spinal cord after spinal injury. Recently neural stem cells have been proposed as hopeful graft donors for regeneration of the central nervous system. However, most grafted stem cells are not able to differentiate into neurons, and grafted stem cells cannot usually grow axons. Here, we show the effect of the protein tyrosine kinase inhibitor lavendustin A on axonal growth of neurons differentiated from neural stem cells obtained from adult rat hippocampal cells transfected with the von Hippel-Lindau (VHL) gene. Significantly greater axonal outgrowth was observed for the transfected cells treated with the inhibitor than for those not so treated. Thus, protein-tyrosine kinase inhibition is effective for axonal outgrowth of neurons differentiated from neural stem cells and may prove to be useful for neuronal regeneration via transplanted stem cells, particularly in the case of spinal cord injuries.

p53 mediates density-dependent growth arrest

While the stress-response-associated importance of the p53 tumor suppressor is well established, recent studies have also linked p53 with several basic parameters in the normal behavior of cells. Here, we present evidence that basal p53 expression in WI38 human embryonic lung fibroblasts restricts growth rate and mediates density-dependent inhibition of growth and the associated G1 phase arrest of the cell cycle by affecting the density-dependent regulation of p16/INK4a. Additionally, we show that prolonged culturing of hTert-immortalized WI38 cells leads to a loss of density-dependent growth inhibition that correlates with p27/KIP deregulation as well as the previously shown INK4a locus silencing, and to an onset of contact-induced, p53-dependent cell death.

von Hippel-Lindau protein complex is regulated by cell density

Mutations in the von Hippel-Lindau (VHL) gene are involved in the VHL family cancer syndrome and sporadic renal cell carcinoma. Previous studies indicated that VHL-induced growth arrest required high cell density and growth on extracellular matrix. In the present study, VHL protein (pVHL) levels were observed to be dramatically increased in cells grown to high cell density compared to cells grown at low cell density. Reverse transcription-polymerase chain reaction and Northern blot analysis indicated that VHL mRNA levels were equivalent in sparse and dense cells. The pVHL was rapidly degraded when cell-cell contact was disturbed by trypsinization or EDTA release. Treatment of cells with a proteasome inhibitor blocked the degradation of pVHL. Using a set of VHL deletions fused to GFP, a cell density-dependent region (CDDR) was identified and localized to the c-terminus of pVHL. In addition, other members of the VBC protein complex also showed a cell density-dependent regulation similar to pVHL. Cell density regulation of VHL did not require elongin binding and density-dependent regulation of other VBC components was not dependent on pVHL. In addition, hypoxia inducible factor-2alpha protein levels were elevated in sparse cells with low levels of pVHL and reduced or absent in confluent cells containing abundant VHL. These results indicate that pVHL levels and thus function are tightly regulated by cell-cell signaling. In addition, care must be taken when interpreting studies of VHL function and subcellular localization of cells grown at subconfluent conditions.

A Case of Renal Cell Carcinoma with Bone and Lymph Node Metastases

We present a rare case of renal cell carcinoma (RCC) with a metastatic, mainly osteoblastic lesion of the skull and spread to the lymph nodes. Renal tumors are often associated with bone metastases; these are most often of the osteolytic type, while osteoblastic metastases are extremely rare. In the case presented here, the primary metastasis was a large osteoblastic lesion of the skull that spread to the lymph nodes. The patient has undergone treatment for 20 months with interleukin-2: 3 million IU/day (subcutaneous) for six consecutive days once every four weeks, ie a total weekly dose of 18 million IU.

Loss of von Hippel-Lindau protein causes cell density dependent deregulation of CyclinD1 expression through hypoxia-inducible factor

Loss of the von Hippel-Lindau gene (VHL) expression ca-uses deregulation of contact inhibition of cell growth, which might be one of the bases of the tumor suppressor function of VHL. Here we show that this function of the VHL gene product (pVHL) depends on cell autonomous events. To identify the target gene of pVHL, which is directly involved in the contact inhibition, we compared the gene expression profile between VHL-deficient renal carcinoma 786-O cells and those infected with an adenovirus vector encoding VHL. In addition to known pVHL-regulated genes, such as vascular endothelial growth factor and carbonic anhydrase, we found cyclinD1 as a new target of pVHL at a high cell density. In VHL-expressing cells (VHL (+) cells), the cyclinD1 mRNA expression level diminishes at a high cell density, while it remains at a relatively high level in VHL-deficient cells (VHL (-) cells). The cyclinD1 expression level was also abnormally high in VHL (-) cells at a high cell density. Consequently, the phosporylation level of the retinoblastoma (Rb) protein remained high in these cells, whereas there was no phosporylated Rb in VHL (+) cells under the contact inhibition. The abnormal expression of cyclinD1 at a high cell density was observed even in VHL (+) cells under the hypoxic state. Moreover, ectopic expression of a HIF mutant resistant to pVHL-mediated proteolysis causes the abnormal cyclinD1 expression in VHL (+) cells. Taken together, these observations indicate that VHL is required for the downregulation of cyclinD1 at a high cell density through HIF.

Regulation of tumor suppressors by nuclear-cytoplasmic shuttling

Tumor suppressor proteins control the proliferation and survival of normal cells; consequently, their inactivation by gene mutations can initiate or drive cancer progression. Most tumor suppressors have been identified by genetic screening, and in many cases their function and regulation are poorly understood. Ten such proteins were recently shown to contain nuclear transport signals that facilitate their "shuttling" between the nucleus and cytoplasm. This type of dynamic intracellular movement not only regulates protein localization, but also often impacts on function. Here, we review the pathways by which tumor suppressors such as APC, p53, VHL, and BRCA1 cross the nuclear envelope and the impact of regulated nuclear import/export on protein function.

Practical uses for ecdysteroids in mammals including humans: an update

Ecdysteroids are widely used as inducers for gene-switch systems based on insect ecdysteroid receptors and genes of interest placed under the control of ecdysteroid-response elements. We review here these systems, which are currently mainly used in vitro with cultured cells in order to analyse the role of a wide array of genes, but which are expected to represent the basis for future gene therapy strategies. Such developments raise several questions, which are addressed in detail. First, the metabolic fate of ecdysteroids in mammals, including humans, is only poorly known, and the rapid catabolism of ecdysteroids may impede their use as in vivo inducers. A second set of questions arose in fact much earlier with the pioneering "heterophylic" studies of Burdette in the early sixties on the pharmacological effects of ecdysteroids on mammals. These and subsequent studies showed a wide range of effects, most of them being beneficial for the organism (e.g. hypoglycaemic, hypocholesterolaemic, anabolic). These effects are reviewed and critically analysed, and some hypotheses are proposed to explain the putative mechanisms involved. All of these pharmacological effects have led to the development of a wide array of ecdysteroid-containing preparations, which are primarily used for their anabolic and/or "adaptogenic" properties on humans (or horses or dogs). In the same way, increasing numbers of patents have been deposited concerning various beneficial effects of ecdysteroids in many medical or cosmetic domains, which make ecdysteroids very attractive candidates for several practical uses. It may be questioned whether all these pharmacological actions are compatible with the development of ecdysteroid-inducible gene switches for gene therapy, and also if ecdysteroids should be classified among doping substances.

Spatially resolved monitoring of cellular metabolic activity with a semiconductor-based biosensor

Metabolic activity of cultured cells can be monitored by measuring changes in the pH of the surrounding medium caused by metabolic products such as protons, carbon dioxide or lactic acid. Although many systems designed for this purpose have been reported, almost all of them are based on bulk measurements, where the average metabolic activity of all cells in contact with the device is recorded. Here, we report on a novel biosensor, based on a modified light-addressable potentiometric sensor (LAPS) device, which enables the metabolic activity of cultured cells to be measured with spatial resolution. This is demonstrated here by detecting the differential sensitivity to a cholinergic receptor agonist of two different co-cultured cellular populations. By making simultaneous measurements of the metabolic activity of different cell types seeded on different segments of one sensor, this device not only provides a rapid means of assessing cellular specificity of pharmaceutical compounds but also has the potential of being used to non-invasively monitor humoral as well as synaptic communication between different cell populations in co-culture. The temporal and spatial resolution of the device were investigated and are discussed.

Molecular characterization of mouse gastric epithelial progenitor cells

The adult mouse gastric epithelium undergoes continuous renewal in discrete anatomic units. Lineage tracing studies have previously disclosed the morphologic features of gastric epithelial lineage progenitors (GEPs), including those of the presumptive multipotent stem cell. However, their molecular features have not been defined. Here, we present the results of an analysis of genes and pathways expressed in these cells. One hundred forty-seven transcripts enriched in GEPs were identified using an approach that did not require physical disruption of the stem cell niche. Real-time quantitative RT-PCR studies of laser capture microdissected cells retrieved from this niche confirmed enriched expression of a selected set of genes from the GEP list. An algorithm that allows quantitative comparisons of the functional relatedness of automatically annotated expression profiles showed that the GEP profile is similar to a dataset of genes that defines mouse hematopoietic stem cells, and distinct from the profiles of two differentiated GEP descendant lineages (parietal and zymogenic cell). Overall, our analysis revealed that growth factor response pathways are prominent in GEPs, with insulin-like growth factor appearing to play a key role. A substantial fraction of GEP transcripts encode products required for mRNA processing and cytoplasmic localization, including numerous homologs of Drosophila genes (e.g., Y14, staufen, mago nashi) needed for axis formation during oogenesis. mRNA targeting proteins may help these epithelial progenitors establish differential communications with neighboring cells in their niche.

The von Hippel-Lindau tumor suppressor stabilizes novel plant homeodomain protein Jade-1

The von Hippel-Lindau disease gene (VHL) is the causative gene for most adult renal cancers. However, the mechanism by which VHL protein functions as a renal tumor suppressor remains largely unknown. To identify low occupancy VHL protein partners with potential relevance to renal cancer, we screened a human kidney library against human VHL p30 using a yeast two-hybrid approach. Jade-1 (gene for Apoptosis and Differentiation in Epithelia) encodes a previously uncharacterized 64-kDa protein that interacts strongly with VHL protein and is most highly expressed in kidney. Jade-1 protein is short-lived and contains a candidate destabilizing (PEST) motif and plant homeodomains that are not required for the VHL interaction. Jade-1 is abundant in proximal tubule cells, which are clear-cell renal cancer precursors, and expression increases with differentiation. Jade-1 is expressed in cytoplasm and the nucleus diffusely and in speckles, where it partly colocalizes with VHL. VHL reintroduction into renal cancer cells increases endogenous Jade-1 protein abundance up to 10-fold. Furthermore, VHL increases Jade-1 protein half-life up to 3-fold. Thus, direct protein stabilization is identified as a new VHL function. Moreover, Jade-1 protein represents a novel candidate regulatory factor in VHL-mediated renal tumor suppression.

Domains of type 1 protein phosphatase inhibitor-2 required for nuclear and cytoplasmic localization in response to cell-cell contact

Inhibitor-2 of type 1 protein phosphatase is a phosphoprotein conserved among all eukaryotes, and it appears in both the nucleus and cytoplasm of tissue culture cells. We discovered that endogenous inhibitor-2 is concentrated in the nucleus of cells cultured at low density, whereas cells growing at high density excluded inhibitor-2 from the nucleus. There was rapid redistribution of inhibitor-2 when cells were replated at low or high density. Localization of myc-tagged forms of inhibitor-2 showed that residues 119-197 were required for nuclear accumulation in low-density cells and residues 78-119 were required for cytoplasmic localization in high-density cells. Fusion of inhibitor-2 residues 78-119 to green fluorescent protein was sufficient to produce cytoplasmic retention. Inhibitor-2 fused to triple tandem green fluorescent protein (100 kDa) was imported into the nucleus of low-density cells but was not excluded from the nucleus when cells reached high density, implying that inhibitor-2 was actively imported into the nucleus but exited by passive diffusion instead of active export. We conclude that inhibitor-2 contains two separate domains that control its localization in the nucleus or cytoplasm. This change in inhibitor-2 localization may direct inhibitor-2 to different forms of protein phosphatase 1 or change the localization of protein phosphatase, as part of the cellular response to cell-cell contacts at high density.

Obligate roles for p16(Ink4a) and p19(Arf)-p53 in the suppression of murine pancreatic neoplasia

Epithelial tumors of the pancreas exhibit a wide spectrum of histologies with varying propensities for metastasis and tissue invasion. The histogenic relationship among these tumor types is not well established; moreover, the specific role of genetic lesions in the progression of these malignancies is largely undefined. Transgenic mice with ectopic expression of transforming growth factor alpha (TGF-alpha) in the pancreatic acinar cells develop tubular metaplasia, a potential premalignant lesion of the pancreatic ductal epithelium. To evaluate the cooperative interactions between TGF-alpha and signature mutations in pancreatic tumor genesis and progression, TGFalpha transgenic mice were crossed onto Ink4a/Arf and/or p53 mutant backgrounds. These compound mutant mice developed a novel pancreatic neoplasm, serous cystadenoma (SCA), presenting as large epithelial tumors bearing conspicuous gross and histological resemblances to their human counterpart. TGFalpha animals heterozygous for both the Ink4a/Arf and the p53 mutation showed a dramatically increased incidence of SCA, indicating synergistic interaction of these alleles. Inactivation of p16(Ink4a) by loss of heterozygosity, intragenic mutation, or promoter hypermethylation was a common feature in these SCAs, and correspondingly, none of the tumors expressed wild-type p16(Ink4a). All tumors sustained loss of p53 or Arf, generally in a mutually exclusive fashion. The tumor incidence data and molecular profiles establish a pathogenic role for the dual inactivation of p16(Ink4a) and p19(Arf)-p53 in the development of SCA in mice, demonstrating that p16(Ink4a) is a murine tumor suppressor. This genetically defined model provides insights into the molecular pathogenesis of SCA and serves as a platform for dissection of cell-specific programs of epithelial tumor suppression.

Von Hippel-Lindau disease: gene to bedside

Von Hippel-Lindau is an autosomal dominant familial tumor syndrome with a risk of developing central nervous system and retinal hemangioblastomas, kidney cysts and clear cell carcinoma, cyst adenomas of other organs and pheochromocytoma. Despite continued elaboration of the neurobiologic role of the von Hippel-Lindau protein, the mainstay of management remains the definitive clinical diagnosis of von Hippel-Lindau syndrome (as distinct from sporadic cases of single von Hippel-Lindau-associated tumors), clinical monitoring and preemptive intervention by surgical or ablative therapy. Specific pharmacologic treatment awaits further biologic understanding of critical pathogenic components. Increasingly sensitive imaging and surgical techniques allow for optimum clinical management and intervention. This article will review von Hippel-Lindau molecular genetics, genotype-phenotype correlations and clinical classification, current understanding of the biology of the von Hippel-Lindau protein, its role in the pathophysiology of this disorder and the consequent implications for future therapeutic/interventional strategies. Central nervous system manifestations will be highlighted.

The von Hippel-Lindau tumor suppressor protein mediates ubiquitination of activated atypical protein kinase C

The von Hippel-Lindau tumor-suppressor protein (pVHL) forms a protein complex (VCB-Cul2) with elongin C, elongin B, Cul-2, and Rbx1, which functions as a ubiquitin-protein ligase (E3). The alpha-subunits of the hypoxia-inducible factors have been identified as targets for the VCB-Cul2 ubiquitin ligase. However, a variety of cellular defects caused by the depletion of pVHL cannot be explained solely by the ubiquitin-mediated degradation of hypoxia-inducible factor-alpha. We show here that a member of the atypical protein kinase C (PKC) group, PKClambda, is ubiquitinated by the pVHL-containing E3 enzyme. An active PKClambda mutant is ubiquitinated more extensively than wild-type PKClambda in HEK293 cells, and the ubiquitination is further enhanced by the overexpression of pVHL. The activation of wild-type PKClambda by serum stimulation of cells enhances the ubiquitination of the protein, supporting the notion that active PKClambda is preferentially ubiquitinated by VCB-Cul2 ubiquitin ligase. Furthermore, we show that PKClambda can be ubiquitinated in vitro in a cell-free ubiquitination assay using purified recombinant components including VCB-Cul2. Given the known function of aPKC in the regulation of cell polarity and cell growth, PKClambda may be a target of pVHL in its function as a tumor suppressor.