Mammalian metallothionein (MT) genes are transcriptionally activated by the essential metal zinc as well as by environmental stresses, including toxic metal overload and redox fluctuations. In addition to playing a key role in zinc homeostasis, MT proteins can protect against metal-and oxidant-induced cellular damage, and may participate in other fundamental physiologic and pathologic processes such as cell survival, proliferation, and neoplasia. Previously, our group reported a requirement for metal-responsive transcription factor-1 (MTF-1) in hypoxia-induced transcription of mouse MT-I and human MT-IIA genes. Here, we provide evidence that the protumorigenic hypoxia-inducible transcription factor-1A (HIF-1A) is essential for induction of MT-1 by hypoxia, but not zinc. Chromatin immunoprecipitation assays revealed that MTF-1 and HIF-1A are both recruited to the mouse MT-I promoter in response to hypoxia, but not zinc. In the absence of HIF-1A, MTF-1 is recruited to the MT-I promoter but fails to activate MT-I gene expression in response to hypoxia. Thus, HIF-1A seems to function as a coactivator of MT-I gene transcription by interacting with MTF-1 during hypoxia. Coimmunoprecipitation studies suggest interaction between MTF-1 and HIF-1A, either directly or as mediated by other factors. It is proposed that association of these important transcription factors in a multiprotein complex represents a common strategy to control unique sets of hypoxia-inducible genes in both normal and diseased tissue. (Mol Cancer Res 2008;6(3):483 -90)

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Adenovirus E1A oncoproteins inhibit muscle-specific gene expression and myogenic differentiation by suppressing the transcriptional activating functions of basic helix-loop-helix proteins. As one approach to identifying cardiac-specific gene regulatory proteins, we analyzed the functional regions of E1A proteins that are required for muscle gene repression in cardiac cells. Myocyte-specific promoters, including the ␣-actins and ␣-myosin heavy chain, were selectively and potently inhibited (>90%) by E1A, while the ubiquitously expressed ␤-actin promoter was only partially (ϳ30%) repressed; endogenous gene expression was also affected. Distinct E1A protein binding sites mediated repression of muscle-specific and ubiquitous actin promoters. E1A-mediated inhibition of ␤-actin required both an intact binding site for the tumor repressor proteins pRb and p107 and a second E1A domain (residues 15-35). In contrast, cardiac-specific promoter repression required the E1A amino-terminal residues 2-36. The proximal skeletal actin promoter (3 to base pair ؊153) was a target for repression by E1A. Although E1A binding to p300 was not required for inhibition of either promoter, co-expression of p300 partially reversed E1A-mediated transcriptional repression. We conclude that cardiac-specific and general promoter inhibition by E1A occurs by distinct mechanisms and that cardiac-specific gene expression is modulated by cellular factors interacting with the E1A p300/CBP-binding domain.

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The peroxisome proliferator-activated receptor delta (PPARdelta) is a ligand-activated, nuclear receptor transcription factor that has a documented role in glucose and lipid homeostasis. Recent studies have implicated this nuclear receptor in numerous aspects of oncogenesis. We report herein the characterization of a novel small-molecule (SR13904) that inhibits PPARdelta agonist-induced transactivation and functions as a PPARdelta antagonist. SR13904 also antagonizes PPARgamma transactivation, albeit with much weaker potency. SR13904 displays inhibitory effects on cellular proliferation and survival in several human carcinoma lines, including lung, breast and liver. These inhibitory effects of SR13904 on tumor cells were linked to a G(1)/S cell cycle block and increased apoptosis. Molecular studies show that SR13904 treatment of a lung cancer cell line, A549, results in markedly reduced levels of a number of cell cycle proteins including cyclin A and D, and cyclin dependent kinase (CDK) 2 and 4. The inhibitory effects on CDK2 appear to be transcriptional. Several of these cell cycle-related genes are known to be upregulated by PPARdelta. The antitumor activities of SR13904 suggest that antagonism of PPARdelta-mediated transactivation may inhibit tumorigenesis and that pharmacological inhibition of PPARdelta may be a potential strategy for treatment or prevention of cancer.