Serum-Dependent Phosphorylation of Human MAP4 at Ser696 in Cultured Mammalian Cells

• Published in: Cell Structure and Function Vol. 24; no. 5; pp. 321 - 327
• Main Authors: Srsen, Vlastimil, Kitazawa, Hidefumi, Sugita, Minoru, Murofushi, Hiromu, Bulinski, Jeannette Chloe, Kishimoto, Takeo, Hisanaga, Shin-ichi
• Format: Journal Article
• Language: English
• Published: Japan Japan Society for Cell Biology 1999; Japan Science and Technology Agency
• Subjects: Animals; Autoradiography; Blotting, Western; CDC2 Protein Kinase - metabolism; cell cycle; Cell Cycle - physiology; Cell Extracts; Cell Line; Enzyme Inhibitors - pharmacology; Fibroblasts - metabolism; HeLa Cells; Humans; MAP4; Microscopy, Phase-Contrast; microtubule; Microtubule-Associated Proteins - genetics; Microtubule-Associated Proteins - metabolism; Mitogen-Activated Protein Kinases - genetics; Mitogen-Activated Protein Kinases - metabolism; phosphorylation; Phosphorylation - drug effects; Phosphoserine - metabolism; Recombinant Proteins - genetics; Recombinant Proteins - metabolism; Serine - metabolism; Serum - cytology; Serum - physiology; serum starvation
• ISSN: 0386-7196; 1347-3700
• DOI: 10.1247/csf.24.321

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.