Goppelt-Struebe M, Fickel S, Reiser C O
Medizinische Klinik IV, Universität Erlangen-Nürnberg, Loschgestrasse 8, D-91054 Erlangen, Germany.
Biochem J. 2000 Jan 15;345 Pt 2(Pt 2):217-24.
In renal mesangial cells, activation of protein tyrosine kinase receptors may increase the activity of mitogen-activated protein (MAP) kinases and subsequently induce expression of prostaglandin G/H synthase-2 (PGHS-2, cyclo-oxygenase-2). As examples, platelet-derived growth factor (PDGF) and epidermal growth factor (EGF) were shown to transiently enhance p42/44 MAP kinase activity, which was an essential step in the induction of PGHS-2 mRNA and protein. Inhibitors of receptor kinase activities, tyrphostins AG1296 and AG1478, specifically inhibited the effects of PDGF and EGF respectively. Activation of p42/44 and p38 MAP kinases and PGHS-2 induction were also mediated by lysophosphatidic acid (LPA), which binds to pertussis-toxin-sensitive G-protein-coupled receptors. LPA stimulation was inhibited by AG1296, but not AG1478, indicating involvement of the PDGF receptor kinase in LPA-mediated signalling. This was confirmed by pertussis-toxin-sensitive tyrosine phosphorylation of the PDGF receptor by LPA, whereas no phosphorylation of the EGF receptor was detected. For comparison, 5-hydroxytryptamine ('serotonin')-mediated signalling was only partially inhibited by AG1296, and also not affected by AG1478. A strong basal AG1296-sensitive tyrosine phosphorylation of the PDGF receptor and a set of other proteins was observed, which by itself was not sufficient to induce p42/44 MAP kinase activation, but played an essential role not only in LPA- but also in phorbol ester-mediated activation. Taken together, the PDGF receptor, but not the EGF receptor, is involved in LPA-mediated MAP kinase activation and PGHS-2 induction in primary mesangial cells, where both protein kinase receptors are present and functionally active.
在肾系膜细胞中，蛋白酪氨酸激酶受体的激活可能会增加丝裂原活化蛋白（MAP）激酶的活性，并随后诱导前列腺素G/H合酶-2（PGHS-2，环氧化酶-2）的表达。例如，血小板衍生生长因子（PDGF）和表皮生长因子（EGF）已被证明可短暂增强p42/44 MAP激酶活性，这是诱导PGHS-2 mRNA和蛋白的关键步骤。受体激酶活性抑制剂 tyrphostins AG1296和AG1478分别特异性抑制了PDGF和EGF的作用。p42/44和p38 MAP激酶的激活以及PGHS-2的诱导也由溶血磷脂酸（LPA）介导，LPA与百日咳毒素敏感的G蛋白偶联受体结合。AG1296可抑制LPA刺激，但AG1478不能，这表明PDGF受体激酶参与了LPA介导的信号传导。LPA对PDGF受体的百日咳毒素敏感酪氨酸磷酸化证实了这一点，而未检测到EGF受体的磷酸化。作为对照，5-羟色胺（“血清素”）介导的信号传导仅被AG1296部分抑制，且不受AG1478影响。观察到PDGF受体和一组其他蛋白存在强烈的基础AG1296敏感酪氨酸磷酸化，其本身不足以诱导p42/44 MAP激酶激活，但不仅在LPA介导的激活中，而且在佛波酯介导的激活中都发挥了重要作用。综上所述，在同时存在两种蛋白激酶受体且功能活跃的原代系膜细胞中，PDGF受体而非EGF受体参与了LPA介导的MAP激酶激活和PGHS-2诱导。
