Stress-activated signaling pathways mediate the stimulation of pregnancy-associated plasma protein-A expression in cultured human fibroblasts

Pregnancy-associated plasma protein-A (PAPP-A) is an IGF binding protein protease that appears to function as a post-translational modulator of IGF bioavailability in response to injury. A previous study indicated that the proinflammatory cytokines, TNFα and IL-1β, were potent stimulators of PAPP-A expression in cultured human fibroblasts. In this study, we investigated the intracellular signaling pathways mediating cytokine-stimulated PAPP-A expression. Treatment of human fibroblasts with TNFα and IL-1β (1 nM) had little or no effect on phosphatidylinositol 3-kinase and Erk1/2 activation, pathways commonly associated with proliferation. On the other hand, TNFα and IL-1β induced p38, c-Jun N-terminal kinase (JNK), and nuclear factor (NF)κB activation, pathways more closely related to stress response. An inhibitor of p38 activation (SB203580) had no effect on TNFα-or IL-1β-stimulated PAPP-A expression. The JNK inhibitor, SP600125, had no effect on IL-1β- or TNFα-stimulated PAPP-A mRNA expression. However, SP600125 effectively inhibited IL-1β-induced PAPP-A protein expression. MG-132, a proteasome inhibitor that blocked degradation of the intrinsic NFκB inhibitor, IκB, and thereby prevented NFκB activation, was a potent inhibitor of both TNFα- and IL-1β-stimulated PAPP-A mRNA and protein expression and IGF binding protein-4 protease activity. MG-132 had no effect on JNK phosphorylation or p38 activation, and SB203580 and SP600125 had no effect on IκB degradation, documenting inhibitor specificity. BAY11-7082, another inhibitor of NFκB activation, also inhibited TNFα- and IL-1β-stimulated PAPP-A expression and IGF binding protein-4 protease activity. These data indicate that NFκB activation is the primary mediator of cytokine-stimulated PAPP-A expression in human fibroblasts.