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Oncogenic Ras abrogates MEK SUMOylation that suppresses the ERK pathway and cell transformation

Nat Cell Biol. 2011 Mar;13(3):282-91. Epub 2011 Feb 20.
Kubota Y, O'Grady P, Saito H, Takekawa M.
[1] Department of Molecular Cell Signaling, Institute of Medical Science, The University of Tokyo, 4-6-1 Shirokanedai, Minato-ku, Tokyo 108-8639, Japan [2] Department of Biophysics and Biochemistry, Graduate School of Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan [3] Department of Cell Signaling and Molecular Medicine, Research Institute of Environmental Medicine, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8601, Japan.

The ERK (extracellular signal-regulated kinase) MAPK (mitogen-activated protein kinase) cascade (Raf-MEK-ERK) mediates mitogenic signalling, and is frequently hyperactivated by Ras oncogenes in human cancer. The entire range of activities of multifunctional Ras in carcinogenesis remains elusive. Here we report that the ERK pathway is downregulated by MEK (MAPK-ERK kinase) SUMOylation, which is inhibited by oncogenic Ras. MEK SUMOylation blocked ERK activation by disrupting the specific docking interaction between MEK and ERK. Expression of un-SUMOylatable MEK enhanced ERK activation, cell differentiation, proliferation and malignant transformation by oncogenic ErbB2 or Raf, but not by active Ras. Interestingly, MEK SUMOylation was abrogated in cancer cells harbouring Ras mutations. Oncogenic Ras inhibits MEK SUMOylation by impairing the function of the MEKK1 MAPKKK as a SUMO-E3 ligase specific for MEK. Furthermore, forced enhancement of MEK SUMOylation suppressed Ras-induced cell transformation. Thus, oncogenic Ras efficiently activates the ERK pathway both by activating Raf and by inhibiting MEK SUMOylation, thereby inducing carcinogenesis.