Premium
The orphan nuclear receptor, alpha‐fetoprotein transcription factor (FTF), is phosphorylated by protein kinases
Author(s) -
Stroup Diane,
Nnamani Mauris C.
Publication year - 2006
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.20.4.a525-b
Subject(s) - phosphorylation , protein kinase a , transcription factor , kinase , chemistry , microbiology and biotechnology , protein phosphorylation , biochemistry , biology , gene
FTF, and its splicing variant, cholesterol 7alpha‐hydroxylase promoter factor (CPF), are transcription factors related to SF‐1. Promoter/reporter studies of the cholesterol 7alpha‐hydroxylase gene (CYP7A1) promoter indicated that the activity of FTF may have been modified post‐translationally. Previous work in our laboratory has shown that this transcription factor was the target of protein kinases in vitro. FTF was phosphorylated by c‐Jun N‐terminal kinase (JNK) and protein kinase A (PKA). Multiple sites of phosphorylation by PKA and JNK were found by screening for the transfer of 32P label to affinity‐purified 6XHIS fusion polypeptides and synthetic peptides. Phosphorylation by AMP‐activated protein kinase (AMPK) and nine protein kinase Cs (PKCs) were detectable, but weaker and less‐specific. Here, we report further studies examining the DNA‐binding activity of recombinant full‐length FTF or its DNA binding domain following phosphorylation by PKA, JNK, Erk1 and Erk2; as determined by gel mobility shift assays (EMSA). Fourier transform infrared spectroscopy indicated an increase in alpha‐helix solvation following phosphorylation, consistent with structural changes and mapping of the phosphorylation sites on computer models of FTF structure based on published X‐ray crystallographic data indicated that the amino acids phosphorylated by PKA and JNK are solvent accessible in the folded protein. These results are consistent with differential regulation of FTF by PKA and JNK and may explain previously reported data on FTF activities. Though not excluding ligand binding and control at the level of transcription, phosphorylation of FTF is a potential mechanism for rapid modulation of the activity of this transcription factor in the absence of ligand. (DK069368)