Identification of a Novel Human Kinase Supporter of Ras (hKSR-2) That Functions as a Negative Regulator of Cot (Tpl2) Signaling

• Published in: The Journal of biological chemistry Vol. 278; no. 47; pp. 47089 - 47097
• Main Authors: Channavajhala, Padma L., Wu, Leeying, Cuozzo, John W., Hall, J. Perry, Liu, Wei, Lin, Lih-Ling, Zhang, Yuhua
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 21.11.2003; American Society for Biochemistry and Molecular Biology
• Subjects: Base Sequence; Cell Line; Cloning, Molecular; Humans; Interleukin-8 - antagonists & inhibitors; Interleukin-8 - biosynthesis; MAP Kinase Kinase Kinases - antagonists & inhibitors; MAP Kinase Kinase Kinases - metabolism; MAP Kinase Signaling System; Molecular Sequence Data; NF-kappa B - metabolism; Precipitin Tests; Protein Kinases - isolation & purification; Protein Kinases - physiology; Proto-Oncogene Proteins - antagonists & inhibitors; Proto-Oncogene Proteins - metabolism; ras Proteins - metabolism; Signal Transduction
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M306002200

Kinase suppressor of Ras (KSR) is an integral and conserved component of the Ras signaling pathway. Although KSR is a positive regulator of the Ras/mitogen-activated protein (MAP) kinase pathway, the role of KSR in Cot-mediated MAPK activation has not been identified. The serine/threonine kinase Cot (also known as Tpl2) is a member of the MAP kinase kinase kinase (MAP3K) family that is known to regulate oncogenic and inflammatory pathways; however, the mechanism(s) of its regulation are not precisely known. In this report, we identify an 830-amino acid novel human KSR, designated hKSR-2, using predictions from genomic data base mining based on the structural profile of the KSR kinase domain. We show that, similar to the known human KSR, hKSR-2 co-immunoprecipitates with many signaling components of the Ras/MAPK pathway, including Ras, Raf, MEK-1, and ERK-1/2. In addition, we demonstrate that hKSR-2 co-immunoprecipitates with Cot and that co-expression of hKSR-2 with Cot significantly reduces Cot-mediated MAPK and NF-κB activation. This inhibition is specific to Cot, because Ras-induced ERK and IκB kinase-induced NF-κB activation are not significantly affected by hKSR-2 co-expression. Moreover, Cot-induced interleukin-8 production in HeLa cells is almost completely inhibited by the concurrent expression of hKSR-2, whereas transforming growth factor β-activated kinase 1 (TAK1)/TAK1-binding protein 1 (TAB1)-induced interleukin-8 production is not affected by hKSR-2 co-expression. Taken together, these results indicate that hKSR-2, a new member of the KSR family, negatively regulates Cot-mediated MAP kinase and NF-κB pathway signaling.