Maruyama S, Kurosaki T, Sada K, Yamanashi Y, Yamamoto T, Yamamura H
Department of Biochemistry, Fukui Medical School, Matsuoka, Fukui 910-11, Japan.
J Biol Chem. 1996 Mar 22;271(12):6631-5. doi: 10.1074/jbc.271.12.6631.
Human leukemic cell line K562 is induced to differentiate into the megakaryocytic lineage by stimulation with 12-O-tetradecanoylphorbol-13-acetate (TPA). We demonstrate here that TPA stimulation increases tyrosine phosphorylation of an 80-kDa protein at an early stage of megakaryocytic differentiation and that this 80-kDa protein is identical with cortactin. Since tyrosine kinase Syk was activated by TPA stimulation, we examined the possibility that cortactin is a potential substrate of Syk in K562 cells. TPA-induced tyrosine phosphorylation of cortactin was decreased profoundly by overexpression of dominant-negative Syk. Furthermore, cortactin was associated with Syk even before TPA stimulation. Since cortactin was previously referred as an 80/85-kilodalton pp60src substrate, we examined the association between Src and cortactin, whereas its association could not be detected. These data suggest that Syk phosphorylates cortactin in K562 cells upon TPA treatment.
人白血病细胞系K562通过12 - O - 十四烷酰佛波醇 - 13 - 乙酸酯（TPA）刺激诱导分化为巨核细胞系。我们在此证明，TPA刺激在巨核细胞分化早期增加了一种80 kDa蛋白的酪氨酸磷酸化，并且这种80 kDa蛋白与皮层肌动蛋白相同。由于酪氨酸激酶Syk被TPA刺激激活，我们研究了皮层肌动蛋白是否是K562细胞中Syk的潜在底物。显性负性Syk的过表达显著降低了TPA诱导的皮层肌动蛋白酪氨酸磷酸化。此外，甚至在TPA刺激之前，皮层肌动蛋白就与Syk相关联。由于皮层肌动蛋白以前被称为80/85千道尔顿的pp60src底物，我们研究了Src与皮层肌动蛋白之间的关联，但未检测到其关联。这些数据表明，在TPA处理后，Syk在K562细胞中使皮层肌动蛋白磷酸化。
