Stress-inducible, murine protein mSTI1. Characterization of binding domains for heat shock proteins and in vitro phosphorylation by different kinases

• Published in: The Journal of biological chemistry Vol. 272; no. 3; pp. 1876 - 1884
• Main Authors: Lässle, M, Blatch, G L, Kundra, V, Takatori, T, Zetter, B R
• Format: Journal Article
• Language: English
• Published: United States 17.01.1997
• Subjects: 3T3 Cells; Amino Acid Sequence; Animals; Binding Sites; Cell Extracts; Fungal Proteins - biosynthesis; Fungal Proteins - genetics; Fungal Proteins - metabolism; Glutathione Transferase - genetics; HSP70 Heat-Shock Proteins - metabolism; Mice; Molecular Sequence Data; Phosphorylation; Protein Binding; Protein Kinases - metabolism; Recombinant Fusion Proteins - genetics; Recombinant Fusion Proteins - metabolism; Signal Transduction
• ISSN: 0021-9258
• DOI: 10.1074/jbc.272.3.1876

We have recently isolated the cDNA for the murine homologue of the stress-inducible phosphoprotein STI1 (also known as IEF SSP 3521 or p60). STI1 was previously shown to be 2-fold up-regulated in MRC-5 fibroblasts upon viral transformation and to exist in a macromolecular complex with heat shock proteins of the HSP 70 and 90 families. By peptide-sequencing we have identified the two heat shock proteins that bind to murine STI1 (mSTI1) as HSC 70 and HSP 84/86. We describe two separate binding regions within mSTI1 for the two heat shock proteins. In the presence of cell extracts, the N-terminal region of mSTI1 binds preferentially to HSC 70, whereas the C-terminal portion of the molecule promotes the binding of HSP 84/86. Heat treatment caused a strong induction of mSTI1 message without affecting the steady-state level of the protein significantly. In addition, heat treatment led to changes in the isoform-composition of mSTI1. pp70(s6k), pp90(rsk), and mitogen-activated protein kinase-activated protein kinase 2 were tested as possible STI1 kinases in vitro using recombinant mSTI1 as a substrate: only pp90(rsk) was able to phosphorylate recombinant mSTI1. In vitro kinase assays using casein kinase II suggest serine 189 to be a likely phosphorylation site in mSTI1.