Chiang G G, Sefton B M
Molecular Biology and Virology Laboratory, The Salk Institute for Biological Studies, La Jolla, California 92037, USA.
J Biol Chem. 2000 Mar 3;275(9):6055-8. doi: 10.1074/jbc.275.9.6055.
Exposure of cells to oxidants increases the phosphorylation of the Src family tyrosine protein kinase Lck at Tyr-394, a conserved residue in the activation loop of the catalytic domain. Kinase-deficient Lck expressed in fibroblasts that do not express any endogenous Lck has been shown to be phosphorylated at Tyr-394 following H(2)O(2) treatment to an extent indistinguishable from that seen with wild type Lck. This finding indicates that a kinase other than Lck itself is capable of phosphorylating Tyr-394. Because fibroblasts express other Src family members, it remained to be determined whether the phosphorylation of Tyr-394 was carried out by another Src family kinase or by an unrelated tyrosine protein kinase. We examined here whether Tyr-394 in kinase-deficient Lck was phosphorylated following exposure of cells devoid of endogenous Src family kinase activity to H(2)O(2). Strikingly, treatment of such cells with H(2)O(2) led to the phosphorylation of Tyr-394 to an extent identical to that seen with wild type Lck, demonstrating that Src family kinases are not required for H(2)O(2)-induced phosphorylation of Lck. Furthermore, this efficient phosphorylation of Lck at Tyr-394 in non-lymphoid cells suggests the existence of an ubiquitous activator of Src family kinases.
将细胞暴露于氧化剂会增加Src家族酪氨酸蛋白激酶Lck在Tyr-394位点的磷酸化，Tyr-394是催化结构域激活环中的一个保守残基。在不表达任何内源性Lck的成纤维细胞中表达的激酶缺陷型Lck，经H₂O₂处理后，已被证明在Tyr-394位点发生磷酸化，其程度与野生型Lck难以区分。这一发现表明，除Lck自身外，还有一种激酶能够磷酸化Tyr-394。由于成纤维细胞表达其他Src家族成员，因此仍有待确定Tyr-394的磷酸化是由另一种Src家族激酶还是由一种不相关的酪氨酸蛋白激酶完成的。我们在此研究了缺乏内源性Src家族激酶活性的细胞在暴露于H₂O₂后，激酶缺陷型Lck中的Tyr-394是否会发生磷酸化。令人惊讶的是，用H₂O₂处理这些细胞会导致Tyr-394磷酸化，其程度与野生型Lck相同，这表明H₂O₂诱导的Lck磷酸化不需要Src家族激酶。此外，非淋巴细胞中Lck在Tyr-394位点的这种高效磷酸化表明存在一种普遍存在的Src家族激酶激活剂。
