Identification of a novel human kinase supporter of Ras (hKSR-2) that functions as a negative regulator of Cot (Tpl2) signaling.
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-kappaB activation. This inhibition is specific to Cot, because Ras-induced ERK and IkappaB kinase-induced NF-kappaB 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 beta-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-kappaB pathway signaling.
Channavajhala
Padma L
PL
Department of Inflammation, Wyeth Research, 200 Cambridge Park Drive, Cambridge, MA 02140, USA. pchannavajhala@wyeth.com
Wu
Leeying
L
Cuozzo
John W
JW
Hall
J Perry
JP
Liu
Wei
W
Lin
Lih-Ling
LL
Zhang
Yuhua
Y
D001483:Base Sequence; D002460:Cell Line; D003001:Cloning, Molecular; D006801:Humans; D016209:Interleukin-8 / Q000037:antagonists & inhibitors / Q000096:biosynthesis; D020930:MAP Kinase Kinase Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D020935:MAP Kinase Signaling System; D008969:Molecular Sequence Data; D016328:NF-kappa B / Q000378:metabolism; D011233:Precipitin Tests; D011494:Protein Kinases / Q000302:isolation & purification / Q000502:physiology*; D011518:Proto-Oncogene Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism*; D015398:Signal Transduction; D018631:ras Proteins / Q000378:metabolism
D016209:Interleukin-8; D016328:NF-kappa B; D011518:Proto-Oncogene Proteins; D011494:Protein Kinases; C097199:KSR-1 protein kinase; D020930:MAP Kinase Kinase Kinases; C069937:MAP3K8 protein, human; D018631:ras Proteins