Srsen V, Kitazawa H, Sugita M, Murofushi H, Bulinski J C, Kishimoto T, Hisanaga S
Laboratory of Cell and Developmental Biology, Faculty of Biosciences, Tokyo Institute of Technology, 4259 Nagatsuta, Midori-ku, Yokohama 226-8501, Japan.
Cell Struct Funct. 1999 Oct;24(5):321-7. 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.
在前一篇论文中（大形等人，（1997年）《生物化学》，36卷：249 - 259页），我们在人源MAP4富含脯氨酸的区域鉴定出两个有丝分裂期cdc2激酶磷酸化位点（Ser696和Ser787）。其中一个位点（Ser696）在间期也会发生磷酸化。负责Ser696间期磷酸化的蛋白激酶必然与cdc2/细胞周期蛋白B激酶不同。为了深入了解Ser696磷酸化的生理作用，我们寻找Ser696激酶以及Ser696发生去磷酸化的细胞条件。由于Ser696符合MAP激酶磷酸化共有基序（PXSP），因此测试了MAP激酶作为可能磷酸化Ser696的激酶。事实上，MAP激酶在体外确实能使MTB3（人源MAP4的羧基末端一半）中的Ser696发生磷酸化。HeLa细胞提取物中Ser696的磷酸化被MAP激酶抑制剂DBTM - 0004抑制。血清饥饿诱导HeLa细胞、TIG - 3和MRC - 5 - 30人成纤维细胞中Ser696去磷酸化，而重新添加血清后Ser696磷酸化得以恢复，尽管间隔时间长得惊人，这也与Ser696是MAP激酶位点的观点一致。因此，MAP4的Ser696磷酸化很可能由MAP激酶完成，它可能在增殖细胞与静止细胞中MAP4活性的调节中发挥作用。
