LPS-induced production of TNF-α and IL-6 in mast cells is dependent on p38 but independent of TTP.

The production of the proinflammatory cytokines TNF-α and IL-6 is regulated by various mRNA-binding proteins, influencing stability and translation of the respective transcripts. Research in macrophages has shown the importance of the p38-MK2-tristetraprolin (TTP) axis for regulation of TNF-α mRNA stability and translation. In the current study we examined a possible involvement of p38 and TTP in LPS-induced cytokine production in bone marrow-derived mast cells (BMMCs). Using pharmacological inhibitors we initially found a strong dependence of LPS-induced TNF-α and IL-6 production on p38 activation, whereas activation of the Erk pathway appeared dispensable. LPS treatment also induced p38-dependent expression of the TTP gene. This prompted us to analyze the proinflammatory cytokine response in BMMCs generated from TTP-deficient mice. Unexpectedly, there were no significant differences in cytokine production between TTP-deficient and WT BMMCs in response to LPS. Gene expression and cytokine production of TNF-α and IL-6 as well as stability of the TNF-α transcript were comparable between TTP-deficient and WT BMMCs. In contrast to TTP mRNA expression, TTP protein expression could not be detected in BMMCs. While we successfully precipitated and detected TTP from lysates of LPS-stimulated RAW 264.7 macrophages, this was not accomplished from BMMC lysates. In contrast, we found mRNA and protein expressions of the other TIS11 family members connected to regulation of mRNA stability, BRF1 and BRF2, and detected their interaction with 14-3-3 proteins. These data suggest that control of cytokine mRNA stability and translation in MCs is exerted by proteins different from TTP.