Transcriptional regulation of the mouse ferritin H gene - Involvement of p300/CBP adaptor proteins in FER-1 enhancer activity

We previously identified a major enhancer of the mouse ferritin H gene (FER -1) that is central to repression of the ferritin H gene by the adenovirus E1A oncogene (Tsuji, Y,, Akebi, N,, Lam, T, K,, Nakabeppu, Y,, Torti, S. V, , and Torti, F, M, (1995) Mel. Cell. Biol, 15, 5152-5164), To dissect the m olecular mechanism of transcriptional regulation of ferritin H, E1A mutants were tested for their ability to repress FER-1 enhancer activity using cot ransfection with ferritin H-chloramphenicol acetyltransferase (CAT) reporte r constructs. Here we report that p300/CBP transcriptional adaptor proteins are involved in the regulation of ferritin H transcription through the FER -1 enhancer element. Thus, ELA mutants that failed to bind p300/CBP lost th e ability to repress FER-1, whereas mutants of E1A that abrogated its inter action with Rb, p107, or p130 were fully functional in transcriptional repr ession. Transfection with EIA did not affect endogenous p300/CBP levels, su ggesting that repression of FER-1 by E1A is not due to repression of p300/C BP synthesis, but to E1A and p300/CBP interaction. In addition, we have dem onstrated that transfection of a p300 expression plasmid significantly acti vated ferritin H-CAT containing the FER-1 enhancer, but had a marginal effe ct on ferritin H-CAT with FER-1 deleted, Furthermore, both wild-type p300 a nd a p300 mutant that failed to bind E1A but retained an adaptor function r estored FER-1 enhancer activity repressed by E1A. Sodium butyrate, an inhib itor of histone deacetylase, mimicked p300/CBP function in activation of fe rritin H-CAT and elevation of endogenous ferritin H mRNA, suggesting that t he histone acetyltransferase activity of p300/CBP or its associated protein s may contribute to the activation of ferritin H transcription, Recruitment of these broadly active transcriptional adaptor proteins for ferritin H sy nthesis may represent an important mechanism by which changes in iron metab olism are coordinated with other cellular responses mediated by p300/CBP.