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). A catalytically inactive mutant of MAP3K8 (Tpl2-K167M) was reported to become phosphorylated at Thr290 in transfected HEK-293 cells, suggesting that Thr290 phosphorylation occurs as a result of trans-phosphorylation (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).

Activation of MAP3K8 may also occur trough phosphorylation on Ser62 and Ser400 (Stafford MJ et al. 2006; Roget K et al. 2012).