Metallothionein Induction by Hypoxia Involves Cooperative Interactions between Metal-Responsive Transcription Factor-1 and Hypoxia-Inducible Transcription Factor-1α

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-1α (HIF-1α) is essential for induction of MT-1 by hypoxia, but not zinc. Chromatin immunoprecipitation assays revealed that MTF-1 and HIF-1α are both recruited to the mouse MT-I promoter in response to hypoxia, but not zinc. In the absence of HIF-1α, MTF-1 is recruited to the MT-I promoter but fails to activate MT-I gene expression in response to hypoxia. Thus, HIF-1α 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-1α, 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)