Horwitz S B, Shen H J, He L, Dittmar P, Neef R, Chen J, Schubart U K
Department of Molecular Pharmacology, Albert Einstein College of Medicine, Bronx, New York 10461, USA.
J Biol Chem. 1997 Mar 28;272(13):8129-32. doi: 10.1074/jbc.272.13.8129.
Metablastin (also called p19, stathmin, prosolin, p18, Lap18, and oncoprotein 18) is a highly conserved, cytosolic 149-amino acid polypeptide that is expressed in immature vertebrate cells and undergoes extracellular factor- and cell cycle-regulated serine phosphorylation. The protein was shown recently to destabilize microtubules in vitro (Belmont, L., and Mitchison, T. J. (1996) Cell 84, 623-631). Here we demonstrate that microinjection of recombinant metablastin induces a loss of microtubules in COS-7 cells. This effect is enhanced by serine-to-alanine mutations at several phosphorylation sites and virtually abolished by aspartate substitution at a single site, Ser-63. We also show that stoichiometric amounts of metablastin prevent assembly and promote disassembly of microtubules in vitro. Interestingly, the phosphorylation site mutations of metablastin that have dramatic differential effects in intact cells do not alter the ability of metablastin to block tubulin assembly in vitro. The data suggest that phosphorylation of metablastin controls its microtubule-destabilizing activity in vivo but that this regulation may require additional cellular factors. This control mechanism is poised to play a critical role in the dynamic reorganization of the cellular microtubule network that occurs during morphogenesis and mitosis.
变构菌素（也称为p19、微管解聚蛋白、前溶胶蛋白、p18、Lap18和癌蛋白18）是一种高度保守的、存在于细胞质中的149个氨基酸的多肽，在未成熟的脊椎动物细胞中表达，并经历细胞外因子和细胞周期调节的丝氨酸磷酸化。最近的研究表明，该蛋白在体外可使微管不稳定（贝尔蒙特，L.，和米奇森，T. J.（1996年）《细胞》84卷，623 - 631页）。在此我们证明，显微注射重组变构菌素会导致COS - 7细胞中的微管丢失。几个磷酸化位点的丝氨酸突变为丙氨酸会增强这种效应，而单个位点Ser - 63处的天冬氨酸替代则几乎可消除这种效应。我们还表明，化学计量的变构菌素在体外可阻止微管组装并促进其解聚。有趣的是，变构菌素的磷酸化位点突变在完整细胞中具有显著的差异效应，但并不改变变构菌素在体外阻断微管蛋白组装的能力。这些数据表明，变构菌素的磷酸化在体内控制其微管去稳定化活性，但这种调节可能需要其他细胞因子。这种控制机制在形态发生和有丝分裂过程中细胞微管网络的动态重组中可能起着关键作用。
