1. ¹Department of Molecular Cellular Oncology and Microbiology, Graduate School, Tokyo Medical and Dental University, Bunkyo-ku, Tokyo, Japan
2. ²Division of Genetics, Institute of Medical Science, University of Tokyo, Minato-ku, Tokyo, Japan
3. ³Division of Oncology, Institute of Medical Science, University of Tokyo, Minato-ku, Tokyo, Japan
4. ⁴Division of Diabetes and Digestive and Kidney Diseases, Department of Clinical Molecular Medicine, Kobe University Graduate School of Medicine, Chuo-ku, Kobe, Japan

Correspondence: Dr N Gotoh, Institute of Medical Science, University of Tokyo, 4-6-1 Shirokanedai, Minato-ku, Tokyo 108-8639, Japan. E-mail: ngotoh@ims.u-tokyo.ac.jp; Dr N Tsuchida, Tokyo Medical and Dental University, 1-5-45 Yushima, Bunkyo-ku, Tokyo 113-8510, Japan. E-mail: tsuchida.mcom@tmd.ac.jp

⁵Present address: Chemotherapy Division of Cancer Proteomics Project, National Cancer Research Institute, 5-1-1 Tsukiji, Chuo-ku, Tokyo 104-0045, Japan

⁶These authors contributed equally to this work.

Received 1 December 2005; Revised 31 March 2006; Accepted 3 April 2006; Published online 15 May 2006.

Abstract

The membrane-linked docking protein SNT-2/FRS2/FRS3 becomes tyrosine phosphorylated in response to fibroblast growth factors (FGFs) and neurotrophins and serves as a platform for recruitment of multiple signaling proteins, including Grb2 and Shp2, to FGF receptors or neurotrophin receptors. We previously reported that SNT-2 is not tyrosine phosphorylated significantly in response to epidermal growth factor (EGF) but that it inhibits ERK activation via EGF stimulation by forming a complex with ERK2. In the present report, we show that expression of SNT-2 suppressed EGF-induced cell transformation and proliferation, and expression level of SNT-2 is downregulated in cancer. The activities of the major signaling molecules in EGF receptor (EGFR) signal transduction pathways, including autophosphorylation of EGFR, were attenuated in cells expressing SNT-2 but not in cells expressing SNT-2 mutants lacking the ERK2-binding domain. Furthermore, SNT-2 constitutively bound to EGFR through the phosphotyrosine binding (PTB) domain both with and without EGF stimulation. Treatment of cells with MEK inhibitor U0126 partially restored the phosphorylation levels of MEK and EGFR in cells expressing SNT-2. On the basis of these findings, we propose a novel mechanism of negative control of EGFR tyrosine kinase activity with SNT-2 by recruiting ERK2, which is the site of negative-feedback loop from ERK, ultimately leading to inhibition of EGF-induced cell transformation and proliferation.