The activity of tumor progression locus-2 (TPL2, also known as COT and MAP3K8) is regulated by means of phosphorylation (Gantke T 2011).
The catalytic subunit of MAP3K8 (TPL2) was reported to undergo phosphorylation at Thr290 in human embryonic kidney 293 (HEK293) cells transfected with MAP3K8 (Luciano BS et al. 2004; Cho J et al. 2005; Stafford MJ et al. 2006). Mutation of this residue to alanine prevented the LPS-stimulated activation of MAP3K8 in mouse macrophages (Cho J et al. 2005). Experiments with a small-molecule inhibitor of MAP3K8 have suggested that Thr290 is autophosphosphorylated after IL-1 beta stimulation of IL-1R-expressing HEK293T cells (Handoyo H et al. 2009). However, a catalytically inactive mutant of MAP3K8 (Tpl2-K167M) was reported to become phosphorylated at Thr290 in transfected HEK-293 cells, suggesting that Thr290 phosphorylation did not occur as a result of autophosphorylation (Cho J et al. 2005) In addition, the phosphorylation at Thr290 was also reported to be catalysed by IKBKB, based on small interfering RNA(siRNA)-knockdown studies and the use of high concentrations of the IKBKB inhibitor PS1145 (Cho J et al. 2005). However, the other work showed that lower concentrations of PS1145, but nevertheless sufficient to completely inhibit IKBKB, did not affect the IL-1-stimulated phosphorylation of transfected MAP3K8 at Thr290, suggesting that the IL-1 beta stimulated phosphorylation of Thr290 is catalysed by a protein kinase distinct from IKBKB. (Stafford MJ et al. 2006). Thus, phosphorylation at Thr290 is required for the physiological activation of MAP3K8 by external signals, although the mode of the modification remains to be clarified.
Activation of MAP3K8 may also occur trough phosphorylation on Ser62 and Ser400 (Stafford MJ et al. 2006; Roget K et al. 2012).