title: Endoplasmic reticulum stress-inducible protein GRP94 is associated with an Mg2+-dependent serine kinase activity modulated by Ca2+ and GRP78/BiP.
abstract: The 94-kDa glucose-regulated protein (GRP94) is a glycoprotein in the endoplasmic reticulum (ER). It has been characterized as a Ca2+-binding protein and a molecular chaperone. In this report we show that highly purified GRP94 exhibits an active Mg2+-dependent serine kinase activity (termed 94-kinase). The 94-kinase can be recovered from ER membrane fractions and is able to phosphorylate both the constitutive and stress-induced forms of GRP94, correlating with their induction kinetics. The 94-kinase activity is distinct from casein kinase II. In contrast to the heat-stable, Ca2+-dependent autophosphorylation activity recently reported for GRP94, the labile 94-kinase activity is inhibited by Ca2+. We determined that the phosphopeptide map of in vitro phosphorylated GRP94 by the 94-kinase resembles that of the in vivo phosphorylated GRP94. Further, the 94-kinase activity can be specifically stimulated by GRP78, a coregulated protein in the ER known to interact with GRP94.
authors.affiliation: Department of Biochemistry and Molecular Biology, University of Southern California School of Medicine, Norris Cancer Center, Los Angeles 90033, USA.
authors.forename: M
authors.initials: M
authors.lastname: Ramakrishnan
authors.forename: A H
authors.initials: AH
authors.lastname: Schönthal
authors.forename: A S
authors.initials: AS
authors.lastname: Lee
mesh_terms: D000818:Animals; D015153:Blotting, Western; D002118:Calcium / Q000494:pharmacology*; D002352:Carrier Proteins / Q000378:metabolism*; D002460:Cell Line; D004721:Endoplasmic Reticulum / Q000378:metabolism*; D000091342:Endoplasmic Reticulum Chaperone BiP; D018840:HSP70 Heat-Shock Proteins / Q000378:metabolism*; D006367:HeLa Cells; D006360:Heat-Shock Proteins / Q000378:metabolism*; D006801:Humans; D007668:Kidney; D007951:Leukemia, Myeloid; D008274:Magnesium / Q000494:pharmacology*; D008565:Membrane Proteins / Q000378:metabolism*; D018832:Molecular Chaperones / Q000378:metabolism*; D010449:Peptide Mapping; D010748:Phosphopeptides / Q000737:chemistry / Q000302:isolation & purification; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D051381:Rats; D013347:Subcellular Fractions / Q000378:metabolism
chemical_list: D002352:Carrier Proteins; D000091342:Endoplasmic Reticulum Chaperone BiP; D018840:HSP70 Heat-Shock Proteins; C000717247:HSPA5 protein, human; D006360:Heat-Shock Proteins; D008565:Membrane Proteins; D018832:Molecular Chaperones; D010748:Phosphopeptides; C018551:glucose-regulated proteins; D017346:Protein Serine-Threonine Kinases; D008274:Magnesium; D002118:Calcium