Amaral M C, Casillas A M, Nel A E
Department of Medicine, UCLA School of Medicine 90024-1680.
Immunology. 1993 May;79(1):24-31.
The induction of T-cell growth by the T-cell antigen receptor (TcR) is dependent on a co-ordinated process of phosphorylation and dephosphorylation of intracellular proteins. An intermediary in this signalling pathway is the serine kinase, p42 mitogen-activated protein kinase (p42MAPK), also known as microtubule-associated protein-2 kinase (MAP-2K). MAP-kinase is activated upon the acquisition of tyrosine as well as threonine phosphate groups and removal of either by specific tyrosine or serine/threonine phosphatases abrogates kinase activity. Okadaic acid (OA), a tumour promoter and potent inhibitor of type 1 and 2A serine/threonine protein phosphatases (PP1 and PP2A), induced MAP-kinase activity in Jurkat T cells in a dose-dependent fashion with optimal effect at 1 microM. Compared to rapid activation (peak < 10 min) of MAP-kinase by another tumour promoter, the phorbol ester, PMA, the effect of OA was delayed (> 30 min) and more sustained. In spite of activating a growth-promoting kinase, OA differed from PMA by its lack of mitogenic activity and failure to induce CD25 [interleukin-2R alpha (IL-2R alpha)] expression in normal human T cells. This implies that PP1 and PP2A also act downstream of MAP-kinase to facilitate later cell cycle events. PMA induced a 42,000 MW tyrosine phosphoprotein which co-electrophoresed and co-chromatographed with ERK-2, a p42 MAP-kinase. Although OA induced an identical Mono-Q peak, there was less avid tyrosine phosphorylation of p42. OA also differed from PMA to the extent by which it induced mobility shift of the tyrosine protein kinase, p56lck, which has been implicated in p42MAPK activation in T cells. Taken together, these results indicate that OA and PMA exert both overlapping as well as divergent effects on lymphocyte growth pathways.
T细胞抗原受体（TcR）对T细胞生长的诱导依赖于细胞内蛋白质磷酸化和去磷酸化的协调过程。该信号通路中的一个中间物是丝氨酸激酶，即p42丝裂原活化蛋白激酶（p42MAPK），也称为微管相关蛋白-2激酶（MAP-2K）。MAP激酶在获得酪氨酸以及苏氨酸磷酸基团后被激活，而通过特定的酪氨酸或丝氨酸/苏氨酸磷酸酶去除这些磷酸基团会消除激酶活性。冈田酸（OA）是一种肿瘤促进剂，也是1型和2A型丝氨酸/苏氨酸蛋白磷酸酶（PP1和PP2A）的强效抑制剂，它以剂量依赖的方式诱导Jurkat T细胞中的MAP激酶活性，在1 microM时效果最佳。与另一种肿瘤促进剂佛波酯PMA对MAP激酶的快速激活（峰值<10分钟）相比，OA的作用延迟（>30分钟）且更持久。尽管OA激活了一种促进生长的激酶，但它与PMA不同，缺乏促有丝分裂活性，并且不能在正常人T细胞中诱导CD25 [白细胞介素-2Rα（IL-2Rα）]表达。这意味着PP1和PP2A也作用于MAP激酶的下游，以促进后期的细胞周期事件。PMA诱导了一种42,000 MW的酪氨酸磷酸化蛋白，它与p42 MAP激酶ERK-2共电泳和共色谱。尽管OA诱导了相同的Mono-Q峰，但p42的酪氨酸磷酸化程度较低。OA与PMA的不同之处还在于它诱导酪氨酸蛋白激酶p56lck迁移率变化的程度，p56lck与T细胞中p42MAPK的激活有关。综上所述，这些结果表明OA和PMA对淋巴细胞生长途径既有重叠作用，也有不同作用。
