Alexei Goltsov

Caveolin-1 is regulated by c-myc and suppresses c-myc-induced apoptosis

Recent data indicating that overexpression of caveolin-1 as well as c-myc are relatively common features of advanced prostate cancer prompted us to test for potential cooperative interactions between caveolin-1 and c-myc that would be consistent with malignant progression. We used the well-characterized Rat1AmycERTM cells to show that the caveolin-1 gene is down-regulated at the level of transcription by c-myc. By maintaining relatively high levels of caveolin-1 with an adenoviral vector or in stably transfected clones we show that caveolin-1 can suppress c-myc-induced apoptosis. Further we established human prostate cancer cell lines with the mycERTM construct and show that clones with increased caveolin-1 are more resistant to myc-induced apoptosis and have increased capacity for growth in soft agar when c-myc is activated.

Disruption of the Caveolin-1 Gene Impairs Renal Calcium Reabsorption and Leads to Hypercalciuria and Urolithiasis

Using LoxP/Cre technology, we generated a knockout mouse homozygous for a null mutation in exon 2 of Cav1. In male Cav1-/- animals, we observed a dramatic increase in the incidence of urinary calcium stone formation. In 5-month-old male mice, the incidence of early urinary calculi was 67% in Cav1-/- mice compared to 19% in Cav1+/+ animals. Frank stone formation was observed in 13% of Cav1-/- males but was not seen in Cav1+/+ mice. Urine calcium concentration was significantly higher in Cav1-/- male mice compared to Cav1+/+ mice. In Cav1-/- mice, distal convoluted tubule cells were completely devoid of Cav1 and the localization of plasma membrane calcium ATPase was disrupted. Functional studies confirmed that active calcium absorption was significantly reduced in Cav1-/- compared to Cav1+/+ male mice. These results demonstrate that disruption of the Cav1 gene promotes the progressive steps required for urinary calcium stone formation and establish a new mouse model for urinary stone disease.

Tumor Cell–Secreted Caveolin-1 Has Proangiogenic Activities in Prostate Cancer

Caveolin, a major structural component of specialized plasma membrane invaginations (caveolae) that participate in diverse cellular activities, has been implicated in the pathogenesis of several human diseases, including cancer. We showed in earlier studies that caveolin-1 (cav-1) is consistently and strongly overexpressed in metastatic prostate cancer and is secreted in a biologically active form by virulent prostate cancer cells. Using both in vitro and in vivo model systems, we now present evidence supporting a proangiogenic role for cav-1 in prostate cancer development and progression. Recombinant cav-1 (rcav-1) was taken up by cav-1(-/-) endothelial cells through either a lipid raft/caveolae- or clathrin-dependent mechanism, leading to specific angiogenic activities (tubule formation, cell migration, and nitric oxide production) that were mediated by rcav-1 stimulation of the PI3K-Akt-eNOS signaling module. Pathologic angiogenesis induced by cav-1 in prostate cancer-bearing mice correlated with an increased frequency, number, and size of lung metastases. We propose that in addition to its antiapoptotic role, cav-1 secreted by prostate cancer cells functions critically as a proangiogenic factor in metastatic progression of this tumor. These new insights into cav-1 function in prostate cancer may provide a base for the design of clinically applicable therapeutic strategies.

The role of caveolin-1 in prostate cancer: Clinical implications

Caveolin-1 (cav-1) is reportedly overexpressed in prostate cancer cells and is associated with disease progression. Specific oncogenic activities of cav-1 associated with Akt activation also occur in prostate cancer. A membrane-associated protein, cav-1, is nonetheless secreted by prostate cancer cells; results of recent studies showed that secreted cav-1 can stimulate cell survival and angiogenic activities, defining a role for cav-1 in the prostate cancer microenvironment. Serum cav-1 levels were also higher in prostate cancer patients than in control men without prostate cancer, and the preoperative serum cav-1 concentration had prognostic potential in men undergoing radical prostatectomy. Secreted cav-1 is therefore a potential biomarker and therapeutic target for prostate cancer.

The Role Of Caveolin-1 In Androgen Insensitive Prostate Cancer

PURPOSE We summarize the literature regarding androgen insensitive prostate cancer and caveolin-1. Caveolin-1 is a major structural component of caveolae, membrane micro-domains known to have important roles in signal transduction and lipid transport. MATERIALS AND METHODS A review of the literature relevant to androgen insensitive caveolin-1 and prostate cancer included the first published report in 1998 through those published in March 2002. RESULTS Caveolin-1 expression is increased in primary and metastatic human prostate cancer with highest levels observed after androgen ablation therapy. Recent studies have documented that caveolin-1 is secreted by prostate cancer cells and can be detected in the serum of men with prostate cancer. CONCLUSIONS The results presented in this review establish that caveolin-1 is an autocrine/paracrine factor associated with androgen insensitive prostate cancer. They show the potential for caveolin-1 as a biomarker therapeutic target for this important malignancy.

mRTVP-1, a novel p53 target gene with proapoptotic activities

ABSTRACT We identified a novel mouse gene, mRTVP-1, as a p53 target gene using differential display PCR and extensive promoter analysis. The mRTVP-1 protein has 255 amino acids and differs from the human RTVP-1 (hRTVP-1) protein by two short in-frame deletions of two and nine amino acids. RTVP-1 mRNA was induced in multiple cancer cell lines by adenovirus-mediated delivery of p53 and by gamma irradiation or doxorubicin both in the presence and in the absence of endogenous p53. Analysis of RTVP-1 expression in nontransformed and transformed cells further supported p53-independent gene regulation. Using luciferase reporter and electrophoretic mobility shift assays we identified a p53 binding site within intron 1 of the mRTVP-1 gene. Overexpression of mRTVP-1 or hRTVP-1 induced apoptosis in multiple cancer cell lines including prostate cancer cell lines 148-1PA, 178-2BMA, PC-3, TSU-Pr1, and LNCaP, a human lung cancer cell line, H1299, and two isogenic human colon cancer cell lines, HCT116 p53+/+ and HCT116 p53−/−, as demonstrated by annexin V positivity, phase-contrast microscopy, and in selected cases 4′,6′-diamidino-2-phenylindole staining and DNA fragmentation. Deletion of the signal peptide from the N terminus of RTVP-1 reduced its apoptotic activities, suggesting that a secreted and soluble form of RTVP-1 may mediate, in part, its proapoptotic activities.

RTVP-1, a Tumor Suppressor Inactivated by Methylation in Prostate Cancer

We previously identified and characterized a novel p53-regulated gene in mouse prostate cancer cells that was homologous to a human gene that had been identified in brain cancers and termed RTVP-1 or GLIPR. In this report, we document that the human RTVP-1 gene is also regulated by p53 and induces apoptosis in human prostate cancer cell lines. We show that the expression of the human RTVP-1 gene is down-regulated in human prostate cancer specimens compared with normal human prostate tissue at the mRNA and protein levels. We further document epigenetic changes consistent with RTVP-1 being a tumor suppressor in human prostate cancer.

Caveolin-1, a metastasis-related gene that promotes cell survival in prostate cancer

Metastasis represents the ultimate target in cancer therapy as this complex biological process is the direct cause of mortality for a variety of human malignancies. The current high level of mortality from prostate cancer results in large part from the inexorable growth of overt or occult metastasis present at the time of diagnosis. Currently, there are no curative therapies for metastatic prostate cancer. To better understand the metastatic phenotype in prostate cancer, we developed a strategy to identify mRNAs that are expressed differentially in cell lines derived from primary versus metastatic mouse prostate cancer using differential display-PCR. In using this system a number of metastasis-related sequences were identified including a cDNA that encodes caveolin-1. Caveolin-1 was found to be overexpressed not only in metastatic mouse prostate cancer, but also in human metastatic disease. Recent studies have indicated that suppression of caveolin-1 expression induces androgen sensitivity in high caveolin-1, androgen-insensitive mouse prostate cancer cells derived from metastases. Conversely, overexpression of caveolin-1 leads to androgen insensitivity in low caveolin, androgen-sensitive mouse prostate cancer cells. Caveolin-1, therefore, is both a metastasis-related gene as well as a candidate androgen resistance gene for prostate cancer in man. Interestingly, recent studies also point to a potential role for caveolin-1 in the resistance of various malignancies to multiple antineoplastic agents. The linkage of caveolin-1 expression with the androgen-resistant phenotype in prostate cancer and the multidrug resistance phenotype in various solid tumors establishes a novel paradigm for understanding these clinically important and now potentially related processes in malignant progression.

Glioma Pathogenesis-Related Protein 1 Exerts Tumor Suppressor Activities through Proapoptotic Reactive Oxygen Species–c-Jun–NH2 Kinase Signaling

Glioma pathogenesis-related protein 1 (GLIPR1), a novel p53 target gene, is down-regulated by methylation in prostate cancer and has p53-dependent and -independent proapoptotic activities in tumor cells. These properties suggest an important tumor suppressor role for GLIPR1, yet direct genetic evidence of a tumor suppressor function for GLIPR1 is lacking and the molecular mechanism(s), through which GLIPR1 exerts its tumor suppressor functions, has not been shown. Here, we report that the expression of GLIPR1 is significantly reduced in human prostate tumor tissues compared with adjacent normal prostate tissues and in multiple human cancer cell lines. Overexpression of GLIPR1 in cancer cells leads to suppression of colony growth and induction of apoptosis. Mice with an inactivated Glipr1 gene had significantly shorter tumor-free survival times than either Glipr1(+/+) or Glipr1(+/-) mice in both p53(+/+) and p53(+/-) genetic backgrounds, owing to their development of a unique array of malignant tumors. Mechanistic analysis indicated that GLIPR1 up-regulation increases the production of reactive oxygen species (ROS) leading to apoptosis through activation of the c-Jun-NH(2) kinase (JNK) signaling cascade. Thus, our results identify GLIPR1 as a proapoptotic tumor suppressor acting through the ROS-JNK pathway and support the therapeutic potential for this protein.

Caveolin-1 Promotes Autoregulatory, Akt-Mediated Induction of Cancer-Promoting Growth Factors in Prostate Cancer Cells

Caveolin-1 (cav-1) and the cancer-promoting growth factors vascular endothelial growth factor (VEGF), transforming growth factor β1 (TGF-β1), and fibroblast growth factor 2 (FGF2) are often found to be upregulated in advanced prostate cancer and other malignancies. However, the relationship between cav-1 overexpression and growth factor upregulation remains unclear. This report presents, to our knowledge, the first evidence that in prostate cancer cells, a positive autoregulatory feedback loop is established in which VEGF, TGF-β1, and FGF2 upregulate cav-1, and cav-1 expression, in turn, leads to increased levels of VEGF, TGF-β1, and FGF2 mRNA and protein, resulting in enhanced invasive activities of prostate cancer cells, i.e., migration and motility. Our results further show that cav-1–enhanced mRNA stability is a major mechanism underlying the upregulation of these cancer-promoting growth factors, and that PI3-K-Akt signaling is required for forming this positive autoregulatory feedback loop.(Mol Cancer Res 2009;7(11):1781–91)