Department of Biochemistry, College of Medicine, University of Saskatchewan, Saskatoon, Canada.
FEBS J. 2013 Sep;280(18):4539-59. doi: 10.1111/febs.12420. Epub 2013 Aug 19.
SRMS (Src-related tyrosine kinase lacking C-terminal regulatory tyrosine and N-terminal myristoylation sites) belongs to a family of nonreceptor tyrosine kinases, which also includes breast tumour kinase and Fyn-related kinase. SRMS, similar to breast tumour kinase and Fyn-related kinase, harbours a Src homology 3 and Src homology 2, as well as a protein kinase domain. However, unlike breast tumour kinase and Fyn-related kinase, SRMS lacks a C-terminal regulatory tail but distinctively possesses an extended N-terminal region. Both breast tumour kinase and Fyn-related kinase play opposing roles in cell proliferation and signalling. SRMS, however, is an understudied member of this family. Although cloned in 1994, information on the biochemical, cellular and physiological roles of SRMS remains unreported. The present study is the first to explore the expression pattern of SRMS in breast cancers, its enzymatic activity and autoregulatory elements, and the characterization of docking protein 1 as its first bonafide substrate. We found that, similar to breast tumour kinase, SRMS is highly expressed in most breast cancers compared to normal mammary cell lines and tissues. We generated a series of SRMS point and deletion mutants and assessed enzymatic activity, subcellular localization and substrate recognition. We report for the first time that ectopically-expressed SRMS is constitutively active and that its N-terminal region regulates the enzymatic activity of the protein. Finally, we present evidence indicating that docking protein 1 is a direct substrate of SRMS. Our data demonstrate that, unlike members of the Src family, the enzymatic activity of SRMS is regulated by the intramolecular interactions involving the N-terminus of the enzyme and that docking protein 1 is a bona fide substrate of SRMS.
SRMS（Src 相关酪氨酸激酶缺乏 C 端调节性酪氨酸和 N 端豆蔻酰化位点）属于非受体酪氨酸激酶家族，该家族还包括乳腺癌激酶和 Fyn 相关激酶。SRMS 与乳腺癌激酶和 Fyn 相关激酶相似，具有Src 同源结构域 3 和 Src 同源结构域 2，以及蛋白激酶结构域。然而，与乳腺癌激酶和 Fyn 相关激酶不同，SRMS 缺乏 C 端调节尾巴，但具有独特的延伸 N 端区域。乳腺癌激酶和 Fyn 相关激酶在细胞增殖和信号转导中发挥相反的作用。然而，SRMS 是该家族中研究较少的成员。尽管它于 1994 年被克隆，但关于 SRMS 的生化、细胞和生理作用的信息仍未报道。本研究首次探讨了 SRMS 在乳腺癌中的表达模式、其酶活性和自身调节元件，以及鉴定 docking protein 1 作为其第一个真正的底物。我们发现，与乳腺癌激酶相似，SRMS 在大多数乳腺癌中高度表达，而在正常乳腺细胞系和组织中表达较低。我们生成了一系列 SRMS 点突变和缺失突变体，并评估了酶活性、亚细胞定位和底物识别。我们首次报道了外源性表达的 SRMS 是组成性激活的，其 N 端区域调节蛋白的酶活性。最后，我们提供了证据表明 docking protein 1 是 SRMS 的直接底物。我们的数据表明，与 Src 家族成员不同，SRMS 的酶活性受涉及酶的 N 端的分子内相互作用调节，并且 docking protein 1 是 SRMS 的真正底物。
