Cot protooncoprotein activates the dual specificity kinases MEK-1 and SEK-1 and induces differentiation of PC12 cells

Abstract

Mitogenic signals initiated at the plasma membrane are transmitted to the nucleus through an intricate signalling network. We identi®ed the protooncoprotein Cot as a new component of mitogenic signalling cascades, which activates both the classic cytoplasmic cascade and the SAPK stress pathway. Wildtype and activated Cot phosphorylate and activate MEK-1 and SEK-1 in vitro. These ®ndings are consistent with the sequence homology between Cot and the rat gene Tpl-2. Expression of oncogenic Cot in 293, NIH3T3 and PC12 cells leads to in vivo phosphorylation of endogenous c-Jun and Erk-1/2 suggesting that the serine/threonine kinase Cot functions beside c-Raf-1 and Mos as a direct activator of MEK-1. Furthermore, we have examined the biological e ects of Cot on the phenotype of ®broblastic and neuronal cells. In order to test a potential c-Raf-1 dependency of Cot transformation, the e ect of oncogenic Cot on Raf revertant CHP25 cells was determined. Cot could restore the transformed phenotype indicating that Cot transformation is not dependent on active c-Raf-1 and that Cot is not a target for the putative Raf inhibitor, which is presumably active in the revertant cell line. Expression of oncogenic versions of Raf as well as v-Mos leads to di erentiation of PC12 cells. Cot also induces neurite outgrowth of PC12 cells. These data are consistent with the role of Cot in the classic mitogenic cascade and suggest that the simultaneously activated JNK/SAPK stress pathway has no antagonistic e ects in this context.

A different function for a critical tryptophan in c-Raf and Hck

“…The Ras to Raf to MEK to MAPK pathway has been thought to be a simple linear pathway. Recently, COT1 has been shown to activate MEK (Hagemann et al, 1999), TC21 has been shown to activate Raf (Rosario et al, 1999), MKP-1 regulates c-Raf and MAPK (Shapiro and Ahn, 1998). Clearly there are`branches' in the pathway and it may be that other molecules may also participate in the MAPK cascade in ways that have not been observed to date.…”

Cot Kinase Induces Cyclooxygenase-2 Expression in T Cells through Activation of the Nuclear Factor of Activated T Cells

“…It has been shown previously that Cot kinase activates AP-1 (10,12,14) so we next decided to study the role of this transcription factor in the up-regulation of the COX-2 promoter by Cot kinase. For this, Jurkat cells were cotransfected with P2-274 and pEF-BOS trunc-Cot in the presence of a dominant negative version of c-Jun, named TAM67.…”

“…Cot/Tpl-2 kinase plays an important role in T cell activation, promoting tumor necrosis factor-␣ and interleukin-2 production by activating the transcription of these genes (13)(14)(15). Cot/Tpl-2 regulation of gene transcription occurs mainly through activation of several transcription factors such as AP-1 1 (10,12,14), NFAT (14 -16), and NF-B (16 -18). Two enzymes, cyclooxygenase-1 (COX-1) and cyclooxygenase-2 (COX-2), catalyze the rate-limiting step in the synthesis of prostaglandins (for review, see Ref.…”

p27kif Protein Levels and E2F Activity Are Targets of Cot Kinase During G1 Phase Progression in T Cells

“…Cot kinase has been classified as an MAP3K that activates the ERK1, c-Jun N-terminal kinase, p38␥ (ERK6), and ERK5 signal transduction pathways (19 -22) and up-regulates the activity of NF-B and AP-1 transcription factors (21,24,33,34). The contribution of the different signal pathways regulated by Cot kinase in promoting E2F activation has not been elucidated.…”

“…Cot kinase up-regulates the activity of the AP-1 and NF-B transcription factors (16,21,23,24). Cot kinase also participates in the IL-2 and TNF-␣ secretion in T lymphocytes (23,25,26).…”