Negative regulation of interleukin-1β-activated neutral sphingomyelinase by protein kinase C in rat mesangial cells

Abstract

Endogenous ceramide is produced by the action of acidic or neutral sphingomyelinases (SMase) in response to stimuli such as proinflammatory cytokines or other inducers of stress. Interleukin-1β (IL-1β) is known to stimulate ceramide formation in rat renal mesangial cells; however, the respective subtype of SMase and its regulation have not been investigated. We found that IL-1β induced an increase in endogenous ceramide levels via the action of a neutral SMase but not an acidic SMase in rat mesangial cells. Cytokine-induced activation of neutral SMase was inhibited by stimulation of protein kinase C (PKC) by the phorbol ester TPA which caused a reduction of ceramide back to control levels. This inhibitory effect of TPA was reversed by the specific PKC-inhibitor Ro-318220. Long-term incubation (24 h) of mesangial cells with TPA, which downregulates PKC-α, -δ, and -ϵ isoenzymes, resulted in a recovery of IL-1β-stimulated neutral SMase activity as well as ceramide formation. These data implicate an important modulatory function of PKC in ceramide production in IL-1β-activated mesangial cells.