Regulation of the activity of MEK kinase 1 (MEKK1) by autophosphorylation within the kinase activation domain.
MEK kinase 1 (MEKK1) shares sequence identity with the yeast kinases Ste11 and Byr2, and is capable of phosphorylation and activation of both mitogen-activated protein/extracellular signal-related protein kinase (MAP/ERK) kinase (MEK) and stress-activated protein kinase (SAPK)/ERK kinase (SEK) in vitro. In vivo, however, MEKK1 predominantly activates the SEK/SAPK kinase cascade. Mechanisms of activation of MEKK1 are unclear. We have identified a major site of autophosphorylation (Thr-575) within the 'activation loop' of MEKK1 between the kinase subdomains VII and VIII. Phosphatase treatment of a constitutively active MEKK1 decreased kinase activity by 59%. Dephosphorylated T575 was rapidly re-(auto)phosphorylated by MEKK1. Mutation of T575 to alanine decreased MEKK1 transphosphorylation activity with a SEK substrate to approx. 30% of wild-type. Mutation of a second threonine residue (Thr-587) to alanine eliminated the phosphorylation of MEK or SEK substrate but not autophosphorylation. MEKK1 autophosphorylation is an intramolecular reaction because active MEKK1 cannot transphosphorylate a kinase-inactive MEKK1. Inactive MEKK1 was not phosphorylated on Thr-575 within cells, suggesting that the phosphorylation of Thr-575 in vivo results from autophosphorylation rather than phosphorylation by an upstream kinase. Autoactivation of MEKK1 via autophosphorylation of Thr-575 might be an immediate response to initial kinase activation through non-phosphorylation mechanisms.
Deak
J C
JC
Institute of Pathology, Case Western Reserve University, Cleveland OH 44106, USA.
Templeton
D J
DJ
D000595:Amino Acid Sequence; D000818:Animals; D002460:Cell Line; D004789:Enzyme Activation / Q000235:genetics; D000882:Haplorhini; D007668:Kidney; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism*; D017434:Protein Structure, Tertiary
D017346:Protein Serine-Threonine Kinases