Identification of MAPKAP kinase 2 as a major enzyme responsible for the phosphorylation of the small mammalian heat shock proteins

Abstract

MAP kinase-activated protein kinase-2 (MAPKAP kinase-2) phosphorylates the serine residues in murine heat shock protein 25 (hsp25) and human heat shock protein 27 (hsp27) which are phosphorylated in vivo in response to growth factors and heat shock, namely Ser 15 and Ser 40 (hsp25) and Ser 15, Ser 78 and Ser 82 (hsp27). Se 86 of hsp25 and the equivalent residue in hsp27 (Ser 82) are phosphorylated preferentially in vitro. The small heat shock protein is present in rabbit skeletal muscle and hsp25 kinase activity in skeletal muscle extracts co-purifies with MAPKAP kinase-2 activity throughout the purification of the latter enzyme. These results suggest that MAPKAP kinase-2 is the enzyme responsible for the phosphorylation of these small heat shock proteins in mammalian cells.