Marth J D, Cooper J A, King C S, Ziegler S F, Tinker D A, Overell R W, Krebs E G, Perlmutter R M
Howard Hughes Medical Institute, Seattle, Washington.
Mol Cell Biol. 1988 Feb;8(2):540-50. doi: 10.1128/mcb.8.2.540-550.1988.
The lck proto-oncogene encodes a lymphocyte-specific member of the src family of protein tyrosine kinases. Here we demonstrate that pp56lck is phosphorylated in vivo at a carboxy-terminal tyrosine residue (Tyr-505) analogous to Tyr-527 of pp60c-src. Substitution of phenylalanine for tyrosine at this position resulted in increased phosphorylation of a second tyrosine residue (Tyr-394) and was associated with an increase in apparent kinase activity. In addition, this single point mutation unmasked the oncogenic potential of pp56lck in NIH 3T3 cell transformation assays. Viewed in the context of similar results obtained with pp60c-src, it is likely that the enzymatic activity and transforming ability of all src-family protein tyrosine kinases can be regulated by carboxy-terminal tyrosine phosphorylation. We further demonstrate that overexpression of pp56lck in the murine T-cell lymphoma LSTRA as a result of a retroviral insertion event produces a kinase protein that despite wild-type primary structure is nevertheless hypophosphorylated at Tyr-505. Thus, control of normal growth in this lymphoid cell line may have been abrogated through acquisition of a posttranslationally activated version of pp56lck.
lck原癌基因编码src蛋白酪氨酸激酶家族的一个淋巴细胞特异性成员。在此我们证明，pp56lck在体内可在一个羧基末端酪氨酸残基（Tyr-505）处发生磷酸化，该残基类似于pp60c-src的Tyr-527。在此位置用苯丙氨酸取代酪氨酸导致第二个酪氨酸残基（Tyr-394）的磷酸化增加，并与表观激酶活性的增加相关。此外，在NIH 3T3细胞转化试验中，这个单点突变揭示了pp56lck的致癌潜力。结合对pp60c-src获得的类似结果来看，所有src家族蛋白酪氨酸激酶的酶活性和转化能力可能都受羧基末端酪氨酸磷酸化的调节。我们进一步证明，由于逆转录病毒插入事件，pp56lck在鼠T细胞淋巴瘤LSTRA中过表达，产生了一种激酶蛋白，尽管其一级结构为野生型，但Tyr-505处仍发生低磷酸化。因此，通过获得一个翻译后激活形式的pp56lck，该淋巴细胞系中的正常生长控制可能已被消除。
