Cloning and Characterization of a Human Protein Kinase with Homology to Ste20

doi:10.1074/jbc.270.37.21695

Cloning and Characterization of a Human Protein Kinase with Homology to Ste20 (*)

From the Fox Chase Cancer Center, Philadelphia, Pennsylvania 19111

^§To whom correspondence should be addressed:
Fox Chase Cancer Center, 7701 Burholme Ave., Philadelphia, PA 19111.
Tel.: 215-728-5320; Fax: 215-728-3616; chernoff{at}boggy.ptp.fccc.edu

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.

Footnotes

↵* This work was supported in part by National Institutes of Health Grant RO1 CA58836 (to J. C.) and Postdoctoral Training Grant CA-09035 (to C. L. C.), and by W. W. Smith Foundation Grant C9201 (to J. C.). The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore by hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

The nucleotide sequence(s) reported in this paper has been submitted to the GenBank(TM)/EMBL Data Bank with accession number(s) U18297[GenBank].
↵¹ The abbreviations used are

MAPK

mitogen-activated protein kinase

ERK

extracellular-signal regulated kinase

MEK MAP kinase/ERK-activating kinase; MEKK

MEK kinase

DMEM

Dulbecco's modified Eagle's medium

MBP

myelin basic protein

PAGE

polyacrylamide gel electrophoresis

EGF

epidermal growth factor

bp

base pair(s)

kb

kilobase pair(s)

HA

hemagglutinin

SAPK

stress-activated protein kinase

HOG

high osmolarity glycerol).
↵²M. A. Sells, U. G. Knaus, S. Bagrodia, D. Ambrose, G. M. Bokoch, and J. Chernoff, manuscript submitted for publication.
- Received May 5, 1995.
- Revision received July 10, 1995.