Sa. Barber et al., THE SERINE THREONINE PHOSPHATASE INHIBITOR, CALYCULIN-A, INHIBITS ANDDISSOCIATES MACROPHAGE RESPONSES TO LIPOPOLYSACCHARIDE, The Journal of immunology, 155(3), 1995, pp. 1404-1410
LPS-stimulated macrophages (M phi) produce inflammatory mediators that
are largely responsible for the pathophysiology associated with septi
c shock. M phi respond to LPS with rapid protein phosphorylation and d
ephosphorylation 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 inhibit
ors block LPS-induced tyrosine phosphorylation of MAP kinases as well
as TNF-alpha and IL-1 beta production. To investigate a role for serin
e/threonine phosphatases, we evaluated the effect of calyculin A, a po
tent serine/threonine phosphatase inhibitor, on LPS stimulation of mur
ine M phi. Pretreatment of M phi with calyculin A inhibited LPS-induce
d expression of six immediate-early genes: TNF-alpha, IL-1 beta, IFN-b
eta IP-10, IRF-1, and TNFR-2. Calyculin A added 1.5 h after LPS treatm
ent greatly reduced accumulation of IP-10, IRF-1, and TNFR-2 mRNA, but
not TNF-alpha, IL-1 beta, and IFN-beta mRNA. Calyculin A, in the abse
nce or presence of LPS, resulted in sustained tyrosine phosphorylation
of the MAP kinases. These findings suggest that an ''early'' serine/t
hreonine phosphatase activity is essential for LPS stimulation of M ph
i and that the activation of MAP kinases is not sufficient for the ind
uction 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 transducti
on.