Vervoordeldonk M J, Schalkwijk C G, Pfeilschifter J, van den Bosch H
Centre for Biomembranes and Lipid Enzymology, Ultrecht, The Netherlands.
Biochem J. 1996 Apr 15;315 ( Pt 2)(Pt 2):435-41. doi: 10.1042/bj3150435.
The expression of 14 kDa group II phospholipase A2 [also referred to as secretory PLA2 (sPLA2)] is induced in rat glomerular mesangial cells by exposure to inflammatory cytokines and forskolin, a cAMP elevating agent. Previously we have shown that dexamethasone and transforming growth factor-beta 2 (TGF-beta 2) suppress sPLA2 protein synthesis and enzyme activity induced by cytokines and forskolin. The regulation of sPLA2 by pro-inflammatory cytokines suggests that the enzyme may play a role in glomerular inflammatory reactions. In order to understand the regulation of sPLA, in more detail, we investigated whether dexamethasone and TGF-beta 2 also suppress sPLA, mRNA after its induction by either interleukin-1 beta (IL-1 beta) or forskolin. We found that IL-1 beta-induced sPLA2 mRNA in rat mesangial cells is not down-regulated by pretreatment of the cells with dexamethasone, even at a concentration of 10 microM, which dramatically decreases sPLA2 protein levels and activity. Metabolic labelling experiments indicated that the decreased sPLA2 levels under these conditions can be explained by inhibition of the rate of sPLA2 synthesis from the elevated mRNA levels. In contrast, the forskolin-induced elevation of sPLA, mRNA is inhibited by dexamethasone in a concentration-dependent manner. Likewise, TGF-beta 2 inhibits the elevation of sPLA, mRNAs induced by either IL-1 beta or forskolin. The decrease in sPLA2 mRNA caused by TGF-beta 2 corresponds with the decrease in sPLA2 enzyme levels and activity. These data suggest that cytokine- and forskolin-induced sPLA2, expression is tightly controlled via both transcriptional and post-transcriptional mechanisms. Furthermore, we show that pretreatment of mesangial cells with epidermal growth factor prior to stimulation with IL-1 beta or forskolin had no suppressing effect on sPLA2 levels or enzyme activity, as has been reported previously for osteoblasts.
14 kDa的II组磷脂酶A2（也称为分泌型磷脂酶A2，即sPLA2）的表达，在大鼠肾小球系膜细胞中可通过暴露于炎性细胞因子和福斯可林（一种能提高cAMP水平的试剂）而被诱导。此前我们已表明，地塞米松和转化生长因子-β2（TGF-β2）可抑制由细胞因子和福斯可林诱导的sPLA2蛋白合成及酶活性。促炎细胞因子对sPLA2的调控表明该酶可能在肾小球炎症反应中起作用。为了更详细地了解sPLA2的调控机制，我们研究了地塞米松和TGF-β2在白细胞介素-1β（IL-1β）或福斯可林诱导sPLA2后，是否也会抑制其mRNA水平。我们发现，即使在浓度为10 μM时，用地塞米松预处理大鼠系膜细胞，也不会下调IL-1β诱导的sPLA2 mRNA水平，而该浓度能显著降低sPLA2蛋白水平和活性。代谢标记实验表明，在这些条件下sPLA2水平的降低可通过从升高的mRNA水平抑制sPLA2合成速率来解释。相反，地塞米松以浓度依赖的方式抑制福斯可林诱导的sPLA2 mRNA升高。同样，TGF-β2可抑制由IL-1β或福斯可林诱导的sPLA2 mRNA升高。TGF-β2导致的sPLA2 mRNA降低与sPLA2酶水平和活性的降低相对应。这些数据表明，细胞因子和福斯可林诱导的sPLA2表达通过转录和转录后机制受到严格控制。此外，我们还表明，如先前在成骨细胞中所报道的那样，在系膜细胞用IL-1β或福斯可林刺激之前，先用表皮生长因子进行预处理，对sPLA2水平或酶活性没有抑制作用。
