Activation of MEK Kinase 1 by the c-Abl Protein Tyrosine Kinase in Response to DNA Damage

Abstract

The c-Abl protein tyrosine kinase is activated by certain DNA-damaging agents and regulates induction of the stress-activated c-Jun N-terminal protein kinase (SAPK). Here we show that nuclear c-Abl associates with MEK kinase 1 (MEKK-1), an upstream effector of the SEK1→SAPK pathway, in the response of cells to genotoxic stress. The results demonstrate that the nuclear c-Abl binds to MEKK-1 and that c-Abl phosphorylates MEKK-1 in vitro and in vivo. Transient-transfection studies with wild-type and kinase-inactive c-Abl demonstrate c-Abl kinase-dependent activation of MEKK-1. Moreover, c-Abl activates MEKK-1 in vitro and in response to DNA damage. The results also demonstrate that c-Abl induces MEKK-1-mediated phosphorylation and activation of SEK1-SAPK in coupled kinase assays. These findings indicate that c-Abl functions upstream of MEKK-1-dependent activation of SAPK in the response to genotoxic stress.

ACKNOWLEDGMENTS

This work was supported by Public Health Service grants CA75216 (S.K.) and CA55241 (D.K.) awarded by the National Cancer Institute, U.S. Department of Health and Human Services.

pEBG-SAPK, pEBG-SEK1, pEBG-SEK1(K-R) cDNAs were provided by Len Zon and Jim Woodgett. N17 Rac-1, N17 Cdc42Hs, and dominant-negative PAK-1 were provided by Jonathan Chernoff. MEKK-1 CF and the MEKK-1 CF(K-R) mutant were provided by Dennis Tempelton. Full-length HA–MEKK-1 was provided by Melanie Cobb. Wild-type c-Abl and kinase-inactive c-Abl(K-R) were provided by Charles Sawyers and Ruibao Ren. GST-SAPK, GST–SEK1(K-R), and GST-SEK1 were provided by Jim Woodgett.