Human tumor antigens Tn and sialyl Tn arise from mutations in Cosmc.

Neoplastic lesions typically express specific carbohydrate antigens on glycolipids, mucins, and other glycoproteins. Such antigens are often under epigenetic control and are subject to reversion and loss upon therapeutic selective pressure. We report here that two of the most common tumor-associated carbohydrate antigens, Tn and sialyl Tn (STn), result from somatic mutations in the gene Cosmc that encodes a molecular chaperone required for formation of the active T-synthase. Diverse neoplastic lesions, including colon cancer and melanoma-derived cells lines, expressed both Tn and STn antigen due to loss-of-function mutations in Cosmc. In addition, two human cervical cancer specimens that showed expression of the Tn/STn antigens were also found to have mutations in Cosmc and loss of heterozygosity for the cross-linked Cosmc locus. This is the first example of somatic mutations in multiple types of cancers that cause global alterations in cell surface carbohydrate antigen expression.

Androgens stimulate hypoxia-inducible factor 1 activation via autocrine loop of tyrosine kinase receptor/phosphatidylinositol 3'-kinase/protein kinase B in prostate cancer cells.

PURPOSE: Androgen deprivation is implicated in reducing neoangiogenesis in prostate cancer (PCA). Androgens regulate the expression of the vascular endothelial growth factor (VEGF); hypoxia stimulates VEGF expression through the activation of the transcriptional factor, hypoxia-inducible factor 1 (HIF-1). We tested the hypothesis that an effect of androgens on VEGF expression is regulated directly by HIF-1 and HIF-2, and antiandrogens block HIF function. EXPERIMENTAL DESIGN: Androgen and antiandrogen effects were evaluated on HIF-1alpha protein and HIF-1 transcriptional activation in human PCA cells. RESULTS: Dihydrotestosterone (DHT) activates HIF-1alpha nuclear protein expression in LNCaP cells but not in androgen receptor-negative PC-3 cells. HIF-1alpha expression is correlated with the transactivation of a hypoxia-responsive element-driven reporter gene and with the production of VEGF protein. The effect of DHT on HIF-1 was blocked by nonsteroidal antiandrogens, flutamide and bicalutamide. DHT does not affect HIF-1alpha mRNA levels but regulates HIF-1alpha protein expression through a translation-dependent pathway. PC-3 cells when incubated with increasing amounts of conditioned medium from LNCaP cells treated with DHT experienced a dose-dependent increase in HIF-1alpha. This induction was not seen either when LNCaP cells were treated with flutamide or conditioned medium were pretreated with antibody to the epidermal growth factor (EGF). HIF-1 activation by DHT was blocked by LY294002, a potent inhibitor of the phosphatidylinositol 3'-kinase signaling pathway, whereas HIF-1 activation by EGF, as ligand, was not inhibited by flutamide. In contrast, HIF-2alpha protein was not affected by androgens or antiandrogens. CONCLUSION: Androgens activate HIF-1, driving VEGF expression in androgen-sensitive LNCaP cells. This regulation is mediated through an autocrine loop involving EGF/phosphatidylinositol 3'-kinase/protein kinase B, which in turn activate HIF-1alpha and HIF-1-regulated gene expression. Therapeutic actions of antiandrogens in PCA include inhibition of HIF-1 function.

2ME2 inhibits tumor growth and angiogenesis by disrupting microtubules and dysregulating HIF.

Inhibition of angiogenesis is an important new modality for cancer treatment. 2-methoxyestradiol (2ME2) is a novel antitumor and antiangiogenic agent, currently in clinical trials, whose molecular mechanism of action remains unclear. Herein, we report that 2ME2 inhibits tumor growth and angiogenesis at concentrations that efficiently disrupt tumor microtubules (MTs) in vivo. Mechanistically, we found that 2ME2 downregulates hypoxia-inducible factor-1 (HIF) at the posttranscriptional level and inhibits HIF-1-induced transcriptional activation of VEGF expression. Inhibition of HIF-1 occurs downstream of the 2ME2/tubulin interaction, as disruption of interphase MTs is required for HIF-alpha downregulation. These data establish 2ME2 as a small molecule inhibitor of HIF-1 and provide a mechanistic link between the disruption of the MT cytoskeleton and inhibition of angiogenesis.

Dibenzoylmethane, a natural dietary compound, induces HIF-1 alpha and increases expression of VEGF.

Hypoxia-inducible factor 1 (HIF-1) is the major transcription factor activated during hypoxia. It is composed of HIF-1 alpha and HIF-1 beta subunits. While HIF-1 beta is constitutively expressed, HIF-1 alpha is targeted to proteasome degradation under normoxic conditions. Under hypoxia, HIF-1 alpha is stabilized and heterodimerizes with HIF-1 beta. Iron chelators have also been reported to stabilize HIF-1 alpha protein and activate HIF-1. In this study, we investigated the effects of dibenzoylmethane (DBM), a natural dietary compound and an iron chelator, on HIF-1 pathway. We found that DBM increases HIF-1 alpha protein levels in a dose- and time-dependent manner. This induction was accompanied with activation of HIF-1, measured by reporter gene assay and increased production of its downstream target, the vascular endothelial growth factor. Mechanistically, HIF-1 alpha was stabilized by DBM at a step prior to ubiquitination. The effect of DBM on HIF-1 and its low toxicity profile might be therapeutically beneficial in ischemic diseases.

Geldanamycin induces degradation of hypoxia-inducible factor 1alpha protein via the proteosome pathway in prostate cancer cells.

Hypoxia-inducible factor 1 (HIF-1) is a heterodimeric transcription factor composed of alpha and beta subunits. HIF-1 is critically involved in cellular responses to hypoxia, glycolysis, and angiogenesis. Here, we show that treatment of prostate cancer PC-3 and LNCaP cells with the benzoquinone ansamycin geldanamycin, an Hsp90-specific inhibitor, induced degradation of HIF-1alpha protein in a dose- and time-dependent manner under both normoxia and hypoxia. This inhibition was also shown in other common cancer types tested. Rapid degradation of nuclear HIF-1alpha protein levels was accompanied by respective inhibition in HIF-1alpha functional transcription activity of VEGF. No difference between HIF-1alpha mRNA levels before or after geldanamycin treatment was found. Moreover, [35S]methionine pulse-chase analysis revealed that HIF-1alpha protein half-life was markedly decreased in the presence of geldanamycin compared with that in control. The geldanamycin-induced degradation of HIF-1alpha was reversed by proteosome inhibitors lactacystin and MG-132. We conclude that geldanamycin induces reduction of HIF-1alpha levels and its downstream transcriptional activity by accelerating protein degradation independent of O2 tension. Thus, benzoquinone ansamycin drugs and their derivatives, such as 17-allyl-aminogeldanamycin, are excellent candidates as small molecule drug inhibitors of HIF-1 overexpression in cancer cells.

Idiotypes expressed early in experimental Schistosoma mansoni infections predict clinical outcomes of chronic disease.

In murine Schistosoma mansoni infections, schistosome-specific cross-reactive idiotypes (CRI) are present in the sera of mice with moderate splenomegaly syndrome (MSS) at 20 wk after infection. In contrast, sera from animals that have the more severe hypersplenomegaly syndrome (HSS) at 20 wk of infection do not express these CRI in their sera. To examine when these regulatory CRI first appear in mice that eventually develop MSS, sera from infected animals were monitored for CRI from 1.5 to 20 wk of infection. In mice that eventually developed MSS, CRI were detected by 5 to 6 wk after infection, plateaued by 8 to 10 wk, and persisted through 20 wk of infection. Animals that developed HSS pathology or that died before 20 wk of infection never expressed CRI. Moreover, CRI levels present in the sera of mice at 6 wk of infection were inversely correlated with splenomegaly and hepatic fibrosis, but not with parasitologic measures, at 20 wk after infection. These results suggest that critical events occur very early in some schistosome infections that induce the production of regulatory idiotypes and that the presence or absence of these idiotypes predicts, and possibly determines, subsequent morbidity.