Novel phosphorylation target in the serum response factor MADS box regulates α-actin transcription

Iyer, Dinakar, Belaguli, Narasimhaswamy, Flüeck, Martin, Rowan, Brian G., Wei, Lei, Weigel, Nancy L., Booth, Frank W., Epstein, Henry F., Schwartz, Robert J. and Balasubramanyam, Ashok (2003) Novel phosphorylation target in the serum response factor MADS box regulates α-actin transcription. Biochemistry, 42 (24). pp. 7477-7486. ISSN 1943-295X

File not available for download.

Abstract

Serum response factor (SRF) is a phosphoprotein that regulates skeletal and cardiac α-actin gene transcription. Myotonic dystrophy protein kinase (DMPK), a muscle- and neuron-restricted kinase, enhanced SRF-mediated promoter activity of the skeletal and cardiac α-actin genes in C2C12 myoblasts as well as in nonmyogenic cells. DMPK phosphorylated SRF in vitro in the αI coil of the DNA-binding domain in the MADS box, a highly conserved region required for DNA binding, dimerization, and co-activator interaction in COS and CV1 cells. Threonine 159 in the MADS box αI coil was a specific phosphorylation target in vitro as well as in vivo of both DMPK and protein kinase C-α. Substitution of threonine 159 with the nonphosphorylatable residue alanine markedly diminished activation of the cardiac α-actin promoter in the presence of kinase, while its substitution with aspartic acid, to introduce a negative charge and mimic phosphorylation, restored activation completely. Phosphorylation of the MADS box may constitute a novel mechanism for regulation of SRF-dependent actin gene transcription.