Serum response factor (SRF) is a transcription factor, which binds to a serum response element (SRE) associated with a variety of genes including (i)immediate early genes such as c-fos, fosB, junB, egr-1 and -2, (ii)neuronal genes such as nurr1 and nur77, and (iii)muscle genes such as actins and myosins. By regulating expression of these genes, SRF controls cell growth and differentiation, neuronal transmission as well as muscle development and function. SRF can be activated by serum, lysophosphatidic acid (LPA), lipopolysaccharide (LPS), 12-O-tetradecanoylphorbol-13-acetate (TPA), cytokines, tumor necrosis factor-alpha (TNFalpha), agents that increase intracellular Ca2+, T-cell virus1 activator protein, hepatitis B virus activator proteins pX, activated oncogenes and protooncogenes and extracellular stimuli such as antioxidant and UV light. In serum-starved cells, MAL is predominantly cytoplasmic where it is sequestered by actin monomers. Upon serum stimulation, Rho becomes active and, through its interaction with ROCK and mDia1, causes an accumulation of F-actin and a commensurate decrease in the level of G-actin. As a consequence, MAL is no longer sequestered and is free to translocate to the nucleus where it associates with SRF and activates SRE-mediated gene expression.
