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Molecular and Cellular Biology, February 1999, p. 1569-1581, Vol. 19, No. 2
0270-7306/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.

The MKK7 Gene Encodes a Group of c-Jun NH2-Terminal Kinase Kinases

Cathy Tournier, Alan J. Whitmarsh, Julie Cavanagh, Tamera Barrett, and Roger J. Davis*

Howard Hughes Medical Institute and Program in Molecular Medicine and Department of Biochemistry and Molecular Biology, University of Massachusetts Medical School, Worcester, Massachusetts 01605

Received 27 April 1998/Returned for modification 3 June 1998/Accepted 4 November 1998

The c-Jun NH2-terminal protein kinase (JNK) is a member of the mitogen-activated protein kinase (MAPK) group and is an essential component of a signaling cascade that is activated by exposure of cells to environmental stress. JNK activation is regulated by phosphorylation on both Thr and Tyr residues by a dual-specificity MAPK kinase (MAPKK). Two MAPKKs, MKK4 and MKK7, have been identified as JNK activators. Genetic studies demonstrate that MKK4 and MKK7 serve nonredundant functions as activators of JNK in vivo. We report here the molecular cloning of the gene that encodes MKK7 and demonstrate that six isoforms are created by alternative splicing to generate a group of protein kinases with three different NH2 termini (alpha , beta , and gamma  isoforms) and two different COOH termini (1 and 2 isoforms). The MKK7alpha isoforms lack an NH2-terminal extension that is present in the other MKK7 isoforms. This NH2-terminal extension binds directly to the MKK7 substrate JNK. Comparison of the activities of the MKK7 isoforms demonstrates that the MKK7alpha isoforms exhibit lower activity, but a higher level of inducible fold activation, than the corresponding MKK7beta and MKK7gamma isoforms. Immunofluorescence analysis demonstrates that these MKK7 isoforms are detected in both cytoplasmic and nuclear compartments of cultured cells. The presence of MKK7 in the nucleus was not, however, required for JNK activation in vivo. These data establish that the MKK4 and MKK7 genes encode a group of protein kinases with different biochemical properties that mediate activation of JNK in response to extracellular stimuli.

* Corresponding author. Mailing address: Howard Hughes Medical Institute, Program in Molecular Medicine, University of Massachusetts Medical School, 373 Plantation St., Worcester, MA 01605. Phone: (508) 856-6054. Fax: (508) 856-3210. E-mail: roger.davis{at}ummed.edu.

Molecular and Cellular Biology, February 1999, p. 1569-1581, Vol. 19, No. 2
0270-7306/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.


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