Post-translational modifications of MTF-1: Regulation of gene expression

MTF-1 and MT Gene Regulation. Metallothionein transcription is induced following exposure to elevated concentrations of a variety of transition metals. Transcription is mediated via interactions between metal response elements (MREs) and the metal response element-binding transcription factor, MTF-1. It has been proposed that metals initiate intracellular signaling cascades, resulting in altered states of MTF-1 phosphorylation and activation of the MRE/MTF-1 complex. This report demonstrates that antimony, arsenic, cadmium, copper, mercury, silver, and zinc induce MT-I transcription, and that pretreatment with a broad range PKC inhibitor inhibits the response. Real time RT-PCR results indicate that MT-I expression correlates with transcriptional assay results. These metals are located within the 1B, 2B, or 5B categories of the IUPAC periodic table, suggesting that a common electrochemical property of the metals may be responsible for initiating signaling events. In vitro kinase assay results indicate that MTF-1 is phosphorylated by kinases PKC, JNK 1, JNK 2, and CK II. NanoLC-ESI-MS/MS analysis of mouse MTF-1 protein has identified a phosphorylated serine at residue 304, a PKC consensus sequence site. Site-directed mutagenesis of serine 304 was completed, and findings from the transfection of the mutated sequence into cells indicated an increase in MT-I transcript, suggesting that dephosphorylation may result in constituitive activation of MTF-1.; MTF-1 and p53. Metals are persistent and ubiquitous contaminants, continuously introduced into the environment. Understanding mechanisms by which metals affect transcription provides insight into factors influencing metal toxicity in vivo. Metal-activated gene expression of metallothionein is reduced in p53-deficient cells. To determine the influence of p53 on metal-activated metallothionein gene expression, MCF7 (human breast cancer epithelial cells; wild type p53), MCF7 E6, and HCC1806 (p53-deficient breast cancer epithelial cells) were used in a reporter gene assay. Results indicated that metal responsive metallothionein transcription in p53 deficient cells was significantly reduced compared to cells expressing wild-type levels. p53 protein levels increased in MCF7 cells following cadmium and mercury exposure, suggesting that p53 plays a key role in modulating response to metals. Rescue RT-RT-PCR experiments involving p53 transfection into p53-null cells were contradictory, indicating that further studies should be done to interpret the relationship between MTF-1 and p53.