Membrane localization of acetylated CNK1 mediates a positive feedback on RAF/ERK signaling

Spatiotemporal control is a common mechanism that modulates activity and function of signal transducers in the signaling network. We identified acetylation of CNK1 (connector enhancer of kinase suppressor of Ras-1) as a late step in the activation of CNK1 signaling, accompanied with prolonged stimulation of extracellular signal–regulated kinase (ERK). We identified the acetyltransferase CREB (cyclic adenosine 3',5'-monophosphate response element–binding protein)–binding protein and the deacetylase SIRT2 (sirtuin type 2) as novel binding partners of CNK1, modulating the acetylation state of CNK1. Acetylation of CNK1 at position Lys⁴¹⁴ located in the pleckstrin homology domain drives membrane localization of CNK1 in growth factor–stimulated cells. Inhibition of ERK signaling abolishes CNK1 acetylation. Cosmic database search identified CNK1 mutants at position Arg⁴²⁶ near the acetylation site in several human tumor types. These mutants show constitutive acetylation and membrane localization. CNK1 mutants substituting Arg⁴²⁶, the acetylation mimetic mutant CNK1-K414Q, and membrane-anchored CNK1 mutants all interact with the protein kinase CRAF and stimulate ERK-dependent cell proliferation and cell migration. In RAS-transformed cells, CNK1 is acetylated and membrane-bound and drives cell proliferation. Thus, growth factor–stimulated ERK signaling induces CNK1 acetylation, and acetylated CNK1 promotes ERK signaling, demonstrating a novel function of CNK1 as positive feedback regulator of the RAF/MEK (mitogen-activated protein kinase kinase)/ERK pathway. In addition, acetylation of CNK1 is an important step in oncogenic signaling, promoting cell proliferation and migration.