Low cell cholesterol levels increase NFκB activity through a p38 MAPK-dependent mechanism

Cholesterol, p38 MAPK and NFκB have been shown to participate in inflammation and cellular differentiation. Here, we examined the effect of cholesterol on NFκB-dependent transcription and the mechanisms underlying this effect in NIH3T3 cells. We show that chronic cholesterol depletion achieved with lipoprotein-deficient serum (LPDS) and 25-hydroxycholesterol (25-HC) treatment resulted in a significant increase in NFκB-dependent transcription, NFκB–DNA binding, IκBα degradation and p65/NFκB translocation to the nucleus, and the addition of exogenous cholesterol reversed these effects. Previously, we have shown that low cell cholesterol levels activate p38 MAPK. Here, we found that inhibition of p38 MAPK with the specific inhibitor SB203580 blocked the increase in NFκB activity, IκBα degradation and p65/NFκB translocation to the nucleus induced by cholesterol depletion. Moreover, the inhibition of the p38 MAPK downstream effector MSK1 with the specific inhibitor H89, or the overexpression of a kinase defective MSK1 abrogated the NFκB-dependent transcription induced by cholesterol depletion. On the other hand, the transactivation potential of p65/NFκB depends on phosphorylation of S276 by MSK1. We observed that cholesterol depletion increased the p65/NFκB transactivation capacity. This effect was reversed by cell cholesterol repletion or incubation with the SB203580 inhibitor. Moreover, the expression of a p65/NFκB S276A mutant was insensitive to cholesterol depletion. Together, our results demonstrate that cholesterol depletion induces NFκB transcriptional activity, not only by affecting the IκBα degradation and the translocation of p65/NFκB to the nucleus, but also regulating the p65/NFκB transactivating potential through a p38 MAPK/MSK1 mediated pathway.