Fusaki N, Iwamatsu A, Iwashima M, Fujisawa J i
Department of Microbiology, Kansai Medical University, 10-15 Fumizono-cho, Moriguchi-shi, Osaka 570, Japan.
J Biol Chem. 1997 Mar 7;272(10):6214-9. doi: 10.1074/jbc.272.10.6214.
The Src family protein-tyrosine kinase, Fyn, is associated with the T cell receptor (TCR) and plays an important role in TCR-mediated signaling. We found that a human T cell leukemia virus type 1-infected T cell line, Hayai, overexpressed Fyn. To identify the molecules downstream of Fyn, we analyzed the tyrosine phosphorylation of cellular proteins in the cells. In Hayai, a 68-kDa protein was constitutively tyrosine-phosphorylated. The 68-kDa protein was coimmunoprecipitated with various signaling proteins such as phospholipase C gamma1, the phosphatidylinositol 3-kinase p85 subunit, Grb2, SHP-1, Cbl, and Jak3, implying that the protein might function as an adapter. Purification and microsequencing of this protein revealed that it was the RNA-binding protein, Sam68 (Src associated in mitosis, 68 kDa). Sam68 was associated with the Src homology 2 and 3 domains of Fyn and also those of another Src family kinase, Lck. CD3 cross-linking induced tyrosine phosphorylation of Sam68 in uninfected T cells. These data suggest that Sam68 participates in the signal transduction pathway downstream of TCR-coupled Src family kinases Fyn and Lck in lymphocytes, that is not only in the mitotic pathway downstream of c-Src in fibroblasts.
Src家族蛋白酪氨酸激酶Fyn与T细胞受体（TCR）相关，并在TCR介导的信号传导中发挥重要作用。我们发现，一株感染了1型人类T细胞白血病病毒的T细胞系Hayai中，Fyn表达上调。为了鉴定Fyn下游的分子，我们分析了该细胞中细胞蛋白的酪氨酸磷酸化情况。在Hayai细胞中，一种68 kDa的蛋白持续发生酪氨酸磷酸化。该68 kDa蛋白能与多种信号蛋白共免疫沉淀，如磷脂酶Cγ1、磷脂酰肌醇3激酶p85亚基、Grb2、SHP-1、Cbl和Jak3，这表明该蛋白可能作为一种衔接蛋白发挥作用。对该蛋白进行纯化和微量测序后发现，它是RNA结合蛋白Sam68（有丝分裂中与Src相关的68 kDa蛋白）。Sam68与Fyn的Src同源结构域2和3相关，也与另一种Src家族激酶Lck的同源结构域相关。在未感染的T细胞中，CD3交联可诱导Sam68发生酪氨酸磷酸化。这些数据表明，Sam68参与淋巴细胞中TCR偶联的Src家族激酶Fyn和Lck下游的信号转导途径，而不仅参与成纤维细胞中c-Src下游的有丝分裂途径。
