MST/MLK2, a Member of the Mixed Lineage Kinase Family, Directly Phosphorylates and Activates SEK1, an Activator of c-Jun N-terminal Kinase/Stress-activated Protein Kinase

doi:10.1074/jbc.272.24.15167

MST/MLK2, a Member of the Mixed Lineage Kinase Family, Directly Phosphorylates and Activates SEK1, an Activator of c-Jun N-terminal Kinase/Stress-activated Protein Kinase*

From the ^‡Department of Molecular Biology, Yokohama City University School of Medicine, 3-9, Fukuura, Kanazawa-ku, Yokohama 236, Japan, the ^¶Genetics Division, National Cancer Center Research Institute, Tsukiji 5-chome, Chuo-ku, Tokyo 104, Japan, the ^‖Diabetes Unit and Medical Services, Massachusetts General Hospital East, and the Department of Medicine, Harvard Medical School, Charlestown, Massachusetts 02129, and the ^**Dana-Farber Cancer Institute, Harvard Medical School, Boston, Massachusetts 02115

Abstract

c-Jun N-terminal kinases/stress-activated protein kinases (JNKs/SAPKs) are mitogen-activated protein kinase (MAPK)-related protein kinases that are involved in several cellular events, including growth, differentiation, and apoptosis. Mixed lineage kinases (MLKs) form a family of protein kinases sharing two leucine zipper-like motifs and a kinase domain whose primary structure is similar to both the tyrosine-specific and the serine/threonine-specific kinase classes. We have reported that a member of the MLK family, MUK/DLK/ZPK, can activate JNK/SAPK in vivo, and here we show that another member of the MLK family, MST/MLK2, activates JNK/SAPK. Both MUK/DLK/ZPK and MST/MLK2 cause a slight activation of p38/Mpk2 when overexpressed in COS-1 cells, whereas MST/MLK2, but not MUK/DLK/ZPK, activates extracellular response kinase (ERK) to a certain degree. The activity of SEK1/MKK4/JNKK, a MAPK kinase class protein kinase designated as a direct activator of JNK/SAPK, is also induced by MUK/DLK/ZPK or MST/MLK2 overexpression. Furthermore, recombinant MST/MLK2 produced in bacteria directly phosphorylates and activates SEK1/MKK4/JNKK in vitro, showing that MST/MLK2 acts like a MAPK kinase kinase. Taken together, these results suggest that MLK family members are MAPK kinase kinases preferentially acting on the JNK/SAPK pathway.

Footnotes

↵* This work was supported in part by grants-in-aid for scientific research from the Ministry of Education, Science, Sports, and Culture of Japan, the Cell Science Foundation, and the Naito Foundation.The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
↵§ To whom correspondence should be addressed. Tel.: 81-45-787-2596/2597; Fax: 81-45-785-4140; E-mail:sh3312{at}med.yokohama-cu.ac.jp.
↵1 The abbreviations used are: MAPK, mitogen-activated protein kinase; MAPKK, MAPK kinase; MAPKKK, MAPK kinase kinase; ERK, extracellular response kinase; JNK/SAPK, c-Jun N-terminal kinase/stress-activated protein kinase; MEK, MAPK/ERK kinase; MEKK, MEK kinase; MLK, mixed lineage kinase; GST, glutathioneS-transferase; HA, hemagglutinin; MBP, myelin basic protein; PAGE, polyacrylamide gel electrophoresis.
↵2 S.-i. Hirai, unpublished data.
- Received November 14, 1996.
- Revision received March 24, 1997.