Proteomics analysis of in vitro protein methylation during Src-induced transformation

Src, a nonreceptor tyrosine kinase, was the first oncogene identified from an oncogenic virus. Mechanistic studies of Src-induced transformations aid in understanding the pathologic processes underlying tumorigenesis and may provide new strategies for cancer therapy. Although several pathways and protein modifications are reportedly involved in Src-induced transformation, the detailed mechanisms of their regulation remain unclear. Protein methylation is an important PTM that is widely involved in cellular physiology. In this study, we determined if protein methylation was involved in Src activation and which methylated proteins were associated with this activity. Using in vitro methylation and 2-DE analysis of viral Src (v-Src)-transformed rat kidney epithelial cells (RK3E), several known and novel methylated proteins were identified based on their changes in methylation signal intensity upon transformation. Among these, elongation factor 2 (EF-2), heterogeneous nuclear ribonucleoprotein K (hnRNP K), and beta-tubulin protein expressions remained unchanged, indicating that their altered methylation levels were due to Src activation. In addition, the altered expression of beta-actin, vimentin, and protein phosphatase 2, catalytic subunit (PPP2C) as well as protein phosphatase 2, catalytic subunit methylation were also confirmed in RK3E cells transformed with a human oncogenic Src mutant (Src531), supporting their association with Src-induced transformation in human cancer. Together, we showed putative involvement of protein methylation in Src activation and our identification of methylated proteins provides important targets for extensively studying Src-induced transformations.