Cot kinase activates tumor necrosis factor-alpha gene expression in a cyclosporin A-resistant manner.

Cot kinase is a protein serine/threonine kinase, classified as a mitogen-activated protein kinase kinase kinase, implicated in T lymphocyte activation. Here we show that an increase in Cot kinase expression promotes tumor necrosis factor-alpha (TNF-alpha) production in Jurkat T cells stimulated by soluble anti-CD3 or by low concentrations of phorbol 12,13-dibutyrate (PDBu) and calcium ionophore. Overexpression of Cot kinase in Jurkat cells activates TNF-alpha gene expression. Cot kinase promotes TNF-alpha promoter activation to a similar extent as calcium ionophore and PDBu or soluble anti-CD28 and PDBu. Neither phorbol esters nor calcium ionophore can replace Cot kinase on TNF-alpha promoter-driven transcription. Expression of a dominant negative form of Cot kinase inhibits TNF-alpha promoter activation induced by stimulation with either calcium ionophore and PDBu, soluble anti-CD28 and PDBu, or soluble anti-CD3 and PDBu. TNF-alpha promoter-driven transcription by Cot kinase is partially mediated by MAPK/ERK kinase and is cyclosporin A-resistant. Cot kinase increases at least the AP-1 and AP-2 response elements. These data indicate that Cot kinase plays a critical role in TNF-alpha production.

Cot kinase regulation of IL-2 production in Jurkat T cells.

tpl-2 is a rat gene that encodes a serine/threonine protein kinase that can act as a novel mitogen-activated protein (MAP) kinase kinase kinase. Tpl-2 is activated in Moloney murine leukemia virus-induced rat T lymphomas, due to a truncation in the C-terminal region of the protein. cot is a very closely related gene, if not the human homologue. The truncated form of Cot has been shown to have a higher transforming activity than the nontruncated form. In this paper we show that an increase in truncated Cot kinase expression correlates with an increase in IL-2 production in anti-CD3-treated Jurkat cells. Truncated Cot expression also cooperates with PHA or phorbol 12,13-dibutyrate (PDBu) and calcium ionophore for IL-2 production in Jurkat cells. Both the truncated and nontruncated Cot forms increased IL-2 transcription because they enhanced transcription of a reporter gene linked to the IL-2 promoter. The expression of a dominant negative form of Cot inhibits transcription directed by the IL-2 promoter in Jurkat cells stimulated by PDBu and ionophore. These data suggest a role of Tpl-2/Cot kinase in IL-2 production during T lymphocyte activation and could also explain its role in Moloney murine leukemia virus-induced lymphomagenesis.

Interleukin-2 induces gamma-S-adenosyl-L-methionine synthetase gene expression during T-lymphocyte activation.

The regulation of expression of the gamma-S-adenosyl-L-methionine (AdoMet) synthetase gene was investigated in T-cells during G0/G1 transition, as well as throughout the G1 phase. Stimulation of G0 T-lymphocytes with concanavalin A induces AdoMet synthetase gene expression, starting 8 h after stimulation. Interleukin-2 (IL-2) stimulates the induction of this gene expression and AdoMet synthetase activity in G1 lymphoblasts, in part by an increase in the transcription rate of the gene. Phorbol esters, which also stimulate the proliferation of G1 lymphoblasts, show a similar kinetics of AdoMet synthetase mRNA induction. In contrast, the mRNA levels of the S-adenosyl-L-homocysteine hydrolase, another enzyme of the methionine cycle, remain unchanged upon IL-2 or phorbol 12,13-dibutyrate treatment. Dexamethasone and 8Br-cAMP, both inhibitors of lymphocyte proliferation, are able to block the expression of the AdoMet synthetase gene and, consequently, AdoMet synthetase activity. Together these findings indicate that the AdoMet synthetase gene is subject to cell-cycle regulation in T-lymphocytes.