LPS-stimulated macrophages (Mφ) produce inflammatory mediators that are largely responsible for the pathophysiology associated with septic shock. Mφ respond to LPS with rapid protein phosphorylation and dephosphorylation on serine, threonine, and tyrosine residues. If these events are critical for the cellular response to LPS, the kinases and/or phosphatases involved may be vulnerable targets for pharmacologic intervention. Recent studies demonstrated that tyrosine kinase inhibitors block LPS-induced tyrosine phosphorylation of MAP kinases as well as TNF-α and IL-1β production. To investigate a role for serine/threonine phosphatases, we evaluated the effect of calyculin A, a potent serine/threonine phosphatase inhibitor, on LPS stimulation of murine Mφ. Pretreatment of Mφ with calyculin A inhibited LPS-induced expression of six immediate-early genes: TNF-α, IL-1β, IFN-β, IP-10, IRF-1, and TNFR-2. Calyculin A added 1.5 h after LPS treatment greatly reduced accumulation of IP-10, IRF-1, and TNFR-2 mRNA, but not TNF-α, IL- 1β, and IFN-β mRNA. Calyculin A, in the absence or presence of LPS, resulted in sustained tyrosine phosphorylation of the MAP kinases. These findings suggest that an 'early' serine/threonine phosphatase activity is essential for LPS stimulation of Mφ and that the activation of MAP kinases is not sufficient for the induction of these immediate-early genes. The requirement for a 'late' phosphatase activity for expression of a subset of LPS-inducible genes dissociates at least two regulatory pathways in LPS signal transduction.
|Original language||English (US)|
|Number of pages||7|
|Journal||Journal of Immunology|
|State||Published - 1995|
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