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Fig. 2.
Effects of NF-kB or MAPK inhibitor on TNF-α-induced lipin-1A and -1B gene suppression. Serum-starved 3T3-L1 adipocytes (Day 14) were cultured in the presence of SN50 (SN, 18 μM) (A,B), U0126 (U, 10 μM), SB202190 (SB, 10 μM), or SP600125 (SP, 20 μM) (C,D) for 1 h before TNF-α (TNF, 0.2 nM, 8 h) was added. At the end of the treatment, specific mRNA was quantified. Data are calculated by fold change vs. DMSO control and expressed as the mean ± SE (n = 3–4). ??P HA14-1 were exposed to C2-Ceramide, a cell-permeable ceramide analog, at a concentration of 50 or 100 μM for 8 h. C2-Ceramide did not affect on both the lipin-1A and -1B mRNA expression (Fig. 3A and B). Because ceramide is synthesized from sphingomyelin by sphingomyelinase, we additionally examined the effect of desipramine, a sphingomyelinase inhibitor, on the reduced expression of lipin-1 mRNA by TNF-α. As shown in Fig. 3C and D, TNF-α significantly inhibited mRNA expression of lipin-1A and -1B in 3T3-L1 adipocytes that had been pretreated with desipramine. To test the involvement of a β-catenin/TCF pathway in the TNF-α-induced lipin-1 suppression, we used an inhibitor for glycogen synthase kinase-3β (GSK-3β), which inhibits β-catenin by phosphorylation and degradation. Fig. 3E and F showed that GSK-3β inhibitor VIII did not affect on both the lipin-1A and -1B gene expression either in the absence or presence of TNF-α.