Maxwell A P, Goldberg H J, Tay A H, Li Z G, Arbus G S, Skorecki K L
Department of Medicine, University of Toronto, Ontario, Canada.
Biochem J. 1993 Nov 1;295 ( Pt 3)(Pt 3):763-6. doi: 10.1042/bj2950763.
We have previously shown that phospholipase A2 (PLA2) activity is rapidly activated by epidermal growth factor (EGF) and phorbol 12-myristate 13-acetate (PMA) in renal mesangial cells and other cell systems in a manner that suggests a covalent modification of the PLA2 enzyme(s). This PLA2 activity is cytosolic (cPLA2) and is distinct from secretory forms of PLA2, which are also stimulated in mesangial cells in response to cytokines and other agonists. However, longer-term regulation of cPLA2 in renal cells may also occur at the level of gene expression. Cultured rat mesangial cells were used as a model system to test the effects of EGF and PMA on the regulation of cPLA2 gene expression. EGF and PMA both produced sustained increases in cPLA2 mRNA levels, with a parallel increase in enzyme activity over time. Inhibition of protein synthesis by cycloheximide increased basal cPLA2 mRNA accumulation in serum-starved mesangial cells, and the combination of EGF and cycloheximide resulted in super-induction of cPLA2 gene expression compared with EGF alone. Actinomycin D treatment entirely abrogated the effect of EGF on cPLA2 mRNA accumulation. These findings suggest that regulation of cPLA2 is achieved by factors controlling gene transcription and possibly mRNA stability, in addition to previously characterized posttranslational modifications.
我们之前已经表明，在肾系膜细胞和其他细胞系统中，磷脂酶A2（PLA2）活性可被表皮生长因子（EGF）和佛波酯12-肉豆蔻酸酯13-乙酸酯（PMA）迅速激活，其激活方式提示PLA2酶存在共价修饰。这种PLA2活性是胞质型的（cPLA2），与分泌型PLA2不同，分泌型PLA2在系膜细胞中也会因细胞因子和其他激动剂而被刺激。然而，肾细胞中cPLA2的长期调节也可能发生在基因表达水平。培养的大鼠系膜细胞被用作模型系统，以测试EGF和PMA对cPLA2基因表达调节的影响。EGF和PMA均使cPLA2 mRNA水平持续升高，且酶活性随时间平行增加。用放线菌酮抑制蛋白质合成可增加血清饥饿的系膜细胞中基础cPLA2 mRNA的积累，与单独使用EGF相比，EGF与放线菌酮联合使用可导致cPLA2基因表达的超诱导。放线菌素D处理完全消除了EGF对cPLA2 mRNA积累的影响。这些发现表明，除了先前已确定的翻译后修饰外，cPLA2的调节还通过控制基因转录以及可能的mRNA稳定性的因素来实现。
