Effects of RING-SH2Grb², a chimeric protein containing the E3 ligase domain of Cbl, on the EGFR pathway.

The E3 ubiquitin-protein ligase Casitas B-lineage lymphoma protein (Cbl) negatively regulates epidermal growth factor receptor (EGFR) signaling pathway in many organisms, and has crucial roles in cell growth, development and human pathologies, including lung cancers. RING-SH2Grb² a chimeric protein of 215 amino acids containing the RING domain of Cbl that provides E3 ligase activity, and the SH2 domain of Grb2 that serves as an adaptor for EGFR. In this study, we demonstrated that RING-SH2Grb² could promote the ubiquitinylation and degradation of EGFR in a human non-small cell lung carcinoma cell line H1299. Moreover, we discovered that the RING-SH2Grb² chimera promoted the internalization of ligand-bound EGFR, inhibited the growth of H1299 cells, and significantly suppressed tumor growth in a xenograft mouse model. In summary, our results revealed a potential new cancer therapeutic approach for non-small cell lung cancer.