title: Serum-dependent phosphorylation of human MAP4 at Ser696 in cultured mammalian cells.
abstract: In the previous paper (Ookata et al., (1997) Biochemistry, 36: 249-259), we identified two mitotic cdc2 kinase phosphorylation sites (Ser696 and Ser787) in the proline-rich region of human MAP4. One (Ser696) of them was also phosphorylated during interphase. A protein kinase responsible for interphase phosphorylation of Ser696 could necessarily be distinct from cdc2/cyclin B kinase. To get insights into a physiological role for Ser696 phosphorylation, we searched for a Ser696 kinase and for cellular conditions under which Ser696 is dephosphorylated. Because Ser696 conforms to the MAP kinase phosphorylation consensus motif (PXSP), MAP kinase was tested as a possible kinase phosphorylating Ser696. MAP kinase, in fact, did phosphorylate Ser696 in MTB3, the carboxy-terminal half of human MAP4 in vitro. Phosphorylation of Ser696 in HeLa cell extract was suppressed by a MAP kinase inhibitor, DBTM-0004. Also consistent with the notion that Ser696 is a MAP kinase site were the fact that serum-starvation induced dephosphorylation of Ser696 in HeLa cells, TIG-3 and MRC-5-30 human fibroblasts, while readdition of serum recovered Ser696 phosphorylation, albeit after a surprisingly long interval. Thus, phosphorylation of Ser696 of MAP4, most likely carried out by MAP kinase, may play a role in modulation of MAP4 activity in proliferating versus quiescent cells.
authors.affiliation: Laboratory of Cell and Developmental Biology, Faculty of Biosciences, Tokyo Institute of Technology, 4259 Nagatsuta, Midori-ku, Yokohama 226-8501, Japan.
authors.forename: V
authors.initials: V
authors.lastname: Srsen
authors.forename: H
authors.initials: H
authors.lastname: Kitazawa
authors.forename: M
authors.initials: M
authors.lastname: Sugita
authors.forename: H
authors.initials: H
authors.lastname: Murofushi
authors.forename: J C
authors.initials: JC
authors.lastname: Bulinski
authors.forename: T
authors.initials: T
authors.lastname: Kishimoto
authors.forename: S
authors.initials: S
authors.lastname: Hisanaga
mesh_terms: D000818:Animals; D001345:Autoradiography; D015153:Blotting, Western; D016203:CDC2 Protein Kinase / Q000378:metabolism; D002453:Cell Cycle / Q000502:physiology; D002457:Cell Extracts; D002460:Cell Line; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005347:Fibroblasts / Q000378:metabolism; D006367:HeLa Cells; D006801:Humans; D008858:Microscopy, Phase-Contrast; D008869:Microtubule-Associated Proteins / Q000235:genetics / Q000378:metabolism*; D020928:Mitogen-Activated Protein Kinases / Q000235:genetics / Q000378:metabolism; D010766:Phosphorylation / Q000187:drug effects; D010768:Phosphoserine / Q000378:metabolism; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism; D012694:Serine / Q000378:metabolism*; D044967:Serum / Q000166:cytology / Q000502:physiology*
chemical_list: D002457:Cell Extracts; D004791:Enzyme Inhibitors; D008869:Microtubule-Associated Proteins; D011994:Recombinant Proteins; D010768:Phosphoserine; D012694:Serine; D016203:CDC2 Protein Kinase; D020928:Mitogen-Activated Protein Kinases