Abstract
A human protein kinase (termed MST1) has been cloned and characterized. The MST1 catalytic domain is most homologous to Ste20 and other Ste20-like kinases (62-65% similar). MST1 is expressed ubiquitously, and the MST1 protein is present in all human cell lines examined. Biochemical characterization of MST1 catalytic activity demonstrates that it is a serine/threonine kinase, and that it can phosphorylate an exogenous substrate as well as itself in an in vitro kinase assay. Further characterization of the protein indicates MST1 activity increases approximately 3-4-fold upon treatment with PP2A, suggesting that MST1 is negatively regulated by phosphorylation. MST1 activity decreases approximately 2-fold upon treatment with epidermal growth factor; however, overexpression of MST1 does not affect extracellular signal-regulated kinase-1 and -2 activation. MST1 is unaffected by heat shock or high osmolarity, indicating that it is not involved in the stress-activated or high osmolarity glycerol signal transduction pathways. Thus MST1, although homologous to a member of a yeast MAPK cascade, is not involved in the regulation of a known mammalian MAPK pathway and potentially regulates a novel signaling cascade.
Highlights
The nucleotide sequence(s) reported in this paper has been submitted to the GenBankTM/EMBL Data Bank with accession number(s) U18297
MST1 does not function in the mitogen-activated protein kinase (MAPK) signal transduction cascade nor is its activity increased in response to growth factors, heat shock or high osmolarity suggesting that it is involved in an as yet unidentified signal transduction pathway
While Ste20 expressed at high levels is able to complement a ste20 null allele, MST1 expressed from the same promoter does not complement, indicating that these genes are not functionally homologous
Summary
The nucleotide sequence(s) reported in this paper has been submitted to the GenBankTM/EMBL Data Bank with accession number(s) U18297. Cloning and Sequencing MST1—Degenerate oligonucleotide primers, corresponding to conserved amino acids present in the catalytic domains of serine/threonine kinases, were used to amplify cDNA from a human lymphocyte cDNA library [30].
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