Prostate cancer (PCa) is the second leading cause of cancer-associated death in men. Inflammation has been recognized as a risk factor for this disease. Heme oxygenase 1 (HO-1), the inducible isoform of the rate-limiting enzyme in heme degradation, counteracts oxidative and inflammatory damage. Here, we investigated the regulated expression of HO-1 and its functional consequences in PCa. We studied the effect of genetic and pharmacologic disruption of HO-1 in the growth, invasion, and migration in androgen-sensitive (MDA PCa2b and LNCaP) and androgen-insensitive (PC3) PCa cell lines. Our results show that HO-1 levels are markedly decreased in PC3 compared with MDA PCa2b and LNCaP. Hemin treatment increased HO-1 at both protein and mRNA levels in all cell lines and decreased cell proliferation and invasion. Furthermore, overexpression of HO-1 in PC3 resulted in markedly reduced cell proliferation and migration. Accordingly, small interfering RNA–mediated silencing of HO-1 expression in MDA PCa2b cells resulted in increased proliferation and invasion. Using reverse transcription-quantitative PCR–generated gene array, a set of inflammatory and angiogenic genes were upregulated or downregulated in response to HO-1 overexpression identifying matrix metalloprotease 9 (MMP9) as a novel downstream target of HO-1. MMP9 production and activity was downregulated by HO-1 overexpression. Furthermore, PC3 cells stably transfected with HO-1 (PC3HO-1) and controls were injected into nu/nu mice for analysis of in vivo tumor xenograft phenotype. Tumor growth and MMP9 expression was significantly reduced in PC3HO-1 tumors compared with control xenografts. Taken together, these results implicate HO-1 in PCa cell migration and proliferation suggesting its potential role as a therapeutic target in clinical settings. (Mol Cancer Res 2009;7(11):1745–55)

Alterations in BRCA1 transcription can contribute to sporadic forms of breast cancer. Now the dynamics between transcriptional coactivators and co-repressors at the BRCA1 promoter reveal a central role for the metabolic sensor CtBP in the response to estrogen or cellular metabolic status Though the linkages between germline mutations of BRCA1 and hereditary breast cancer are well known, recent evidence suggests that altered BRCA1 transcription may also contribute to sporadic forms of breast cancer. Here we show that BRCA1 expression is controlled by a dynamic equilibrium between transcriptional coactivators and co-repressors that govern histone acetylation and DNA accessibility at the BRCA1 promoter. Eviction of the transcriptional co-repressor and metabolic sensor, C terminal–binding protein (CtBP), has a central role in this regulation. Loss of CtBP from the BRCA1 promoter through estrogen induction, depletion by RNA interference or increased NAD+/NADH ratio leads to HDAC1 dismissal, elevated histone acetylation and increased BRCA1 transcription. The active control of chromatin marks, DNA accessibility and gene expression at the BRCA1 promoter by this 'metabolic switch' provides an important molecular link between caloric intake and tumor suppressor expression in mammary cells.

Alkylphospholipids (ALKs) are a novel class of antitumor agents with an unknown mechanism of action. The first ALK tested in the clinic, miltefosine, has been approved recently in Europe for the local treatment of patients with cutaneous metastasis. Perifosine, the only available oral ALK, is being studied currently in human cancer clinical trials. We have shown previously that perifosine induces p21^waf1/cip1 in a p53-independent fashion and that induction of p21^waf1/cip1 is required for the perifosine-induced cell cycle arrest because cell lines lacking p21^waf1/cip1 are refractory to perifosine. In this report, we investigated the mechanism by which perifosine induces p21^waf1/cip1 protein expression. We observed that perifosine induces the accumulation of p21^waf1/cip1 mRNA without affecting p21^waf1/cip1 mRNA stability. Using several p21^waf1/cip1 promoter-driven luciferase reporter plasmids, we observed that perifosine activates the 2.4-kb full-length p21^waf1/cip1 promoter as well as a p21 promoter construct lacking p53-binding sites, suggesting that perifosine activates the p21^waf1/cip1 promoter independent of p53. The minimal p21 promoter region required for perifosine-induced p21 promoter activation contains four consensus Sp1-binding sites. Mutations in each particular Sp1 site block perifosine-induced p21^waf1/cip1 expression. Moreover, we showed that perifosine activates the mitogen-activated protein/extracellular signal-regulated kinase pathway, and this activation promotes the phosphorylation of Sp1 in known mitogen-activated protein kinase residues (threonine 453 and 739), thereby leading to increased Sp1 binding and enhanced p21^waf1/cip1 transcription. These results represent a novel mechanism by which alkylphospholipids modulate transcription, and may contribute to the discovery of new signal transduction pathways crucial for normal and neoplastic cell cycle control.

The BRCA1 gene product plays numerous roles in regulating genome integrity. Its role in assembling supermolecular complexes in response to DNA damage has been extensively studied; however, much less is understood about its role as a transcriptional coregulator. Loss or mutation is associated with hereditary breast and ovarian cancers, whereas altered expression occurs frequently in sporadic forms of breast cancer, suggesting that the control of BRCA1 transcription might be important to tumorigenesis. Here, we provide evidence of a striking linkage between the roles for BRCA1 as a transcriptional coregulator with control of its expression via an autoregulatory transcriptional loop. BRCA1 assembles with complexes containing E2F-1 and RB to form a repressive multicomponent transcriptional complex that inhibits BRCA1 promoter transcription. This complex is disrupted by genotoxic stress, resulting in the displacement of BRCA1 protein from the BRCA1 promoter and subsequent upregulation of BRCA1 transcription. Cells depleted of BRCA1 respond by upregulating BRCA1 transcripts, whereas cells overexpressing BRCA1 respond by downregulating BRCA1 transcripts. Tandem chromatin immmunoprecipitation studies show that BRCA1 is regulated by a dynamic coregulatory complex containing BRCA1, E2F1, and Rb at the BRCA1 promoter that is disrupted by DNA-damaging agents to increase its transcription. These results define a novel transcriptional mechanism of autoregulated homeostasis of BRCA1 that selectively titrates its levels to maintain genome integrity in response to genotoxic insult. Cancer Res; 70(2); 532–42