Differential regulation of ferritin H by TNF-alpha in normal and transformed cells.

摘要

Ferritin, the primary cellular storage protein for iron, is a polymer of H and L subunits. The inflammatory cytokines tumor necrosis factor alpha (TNF-alpha) and IL-1 alpha regulate ferritin composition through selective induction of H subunit mRNA, leading to H enriched protein. The role of ferritin H in rapid iron uptake suggests that selective induction of ferritin H by TNF is a cytoprotective mechanism. Consistent with this hypothesis, TNF is cytotoxic to some transformed cells (i.e. L929 cells) that fail to induce ferritin H in response to TNF. This dissertation explores the cis- and trans-acting factors involved in the differential regulation of ferritin H transcription in cytokine-treated transformed and non-transformed cells.; Ferritin H TNF responsiveness is mediated through the FER2 enhancer element that binds the transcription factor, NF-kappaB. The FER2 element is both necessary and sufficient for TNF responsiveness of ferritin H transcription in NIH3T3 mesenchymal cells. However, fully transformed L929 cells fail to induce ferritin H despite activation of NF-kappaB. Further, NF-kappaB can drive transcriptional activation of a ferritin H chimeric gene in which the FER2 element is ligated to a minimal ferritin H promoter, indicating functionality of the activated NF-kappaB in L929 cells. These results suggest the presence of a cis-acting repressor element within the ferritin H promoter through which L929 cells repress ferritin H induction despite NF-kappaB activation.; The adenoviral oncogene E1A alters cellular events and phenotype through interaction with cellular regulatory proteins. E1A renders TNF resistant cells sensitive to TNF cytotoxicity and represses ferritin H induction in response to TNF. NF-kappaB is activated in E1A transfectants, suggesting that TNF dependent induction of ferritin H requires a coactivating protein in conjunction with NF-kappaB. The E1A binding proteins, pRB and p300 were found to be dispensable as coactivators of NF-kappaB in TNF dependent ferritin H transcription. Rather, a domain of E1A (a.a. residues 23--36) that binds to p400 and p21 was implicated in TNF dependent induction of ferritin H. Thus, transformed cells exhibit novel modes of ferritin H regulation in response to TNF.