Src Activation Requires Coordinative Acetylation In Both Unique And Catalytic Domains

v-Src (virus-Src), the first oncogene identified in Rous sarcoma virus(RSV), was associated with the development of sarcoma. c-Src (cellular-Src), which is highly homologous with v-Src, is widely expressed in eukaryotes. The oncogenic protein coded by c-Src is one kind of nonreceptor tyrosine kinase that regulates multiple cellular functions including:growth, proliferation, differentiation, apoptosis, as well as mediating various signal transduction pathways. Kinds of carcinomas (breast cancer and hepatocellular carcinoma, etc.) are related with the Src over-expression or aberrant Src kinase activity. Functionally, Src can be divided into four domains:the N-terminal region includes the unique domain, the SH3 domain, and the SH2 domain, while the C-terminal region contains the catalytic domain. The most conserved SH2 domain is very important for signal transduction via inter/intra-molecular binding with phosphorylated tyrosine residue. Src can be activated by several types of receptors, such as epithelial growth factor receptor (EGFR), G-protein-coupled receptor and integrin bound to extracellular matrix. When associated with the plasma membrane, Src would catalyse proximal membrane substrates through self structure alteration. Also, Src could dissociate from the plasma membrane and target more substrates in the cytosal or cellular compartments (such as endoplasmic reticulum, mitochondria and nucleus). Src cell membrane association requires both hydrophobic insertion of its myristate into the hydrocarbon interior of the membrane and nonspecific electrostatic interaction of its N-terminal positively charged cluster(s) of basic residues with the overall negatively charged cell membrane acidic phospholipids. In this thesis, we studied the relationship between Src acetylation and its kinase activity. We demonstrated that CBP, as one of the histone acetyltransferases (HATs), bound and then acetylated Src with EGF treatment. Acetylation neutralized Src N-terminal lysine clusters, especially for lysine7, resulting in Src dissociation from plasma membrane for reduced electrostatic attraction. In the other hand, acetylation of Src C-terminal lysine clusters, especially for lysine 427, enhanced the interaction between Src and Stat3. As a result, Stat3 was phosphorylated on tyrosine 705 in its C-terminal region, as well as tyrosine 45 and 68 in the N-terminal region. Finally, an enhanceosome including phosphorylated STAT3 and acetylated Src, was formed which bound to DNA and increased STAT3 transcriptional activity to the maximal. Our findings here established a close link between acetylation and protein tyrosine kinase activity, which served as a central step in signal transduction and transcriptional regulation in response to environmental changes. Besides, this study is an important supplement to the mechanism of cancer development induced by aberrant Src and STAT3 activity.