Ramsdell J S, Pettit G R, Tashjian A H
J Biol Chem. 1986 Dec 25;261(36):17073-80.
Phorbol ester tumor promoters such as 12-O-tetradecanoylphorbol acetate (TPA) activate the calcium- and phospholipid-dependent protein kinase C and enhance three biological responses (prolactin release, prolactin synthesis, and cell stretching) in GH4C5 rat pituitary cells. We have examined several actions on GH4C5 cells of TPA and two other classes of protein kinase C activators, synthetic cell permeant dioleins and bryostatins isolated from the marine bryozoan Bugula neritina. Bryostatins 1 and 2 (B1 and B2, respectively) competed for [3H]phorbol 12,13-dibutyrate binding to the protein kinase C complex in intact cells nearly equipotently with TPA. B1 and B2, 1-oleoyl-2-acetylglycerol (OAG) and 1,2-dioctanoylglycerol (Di8) as well as TPA each activated partially purified protein kinase C from GH4C5 cells. B1, B2, and TPA each enhanced the acute release of prolactin from GH4C5 cells to a similar maximal extent. B1, B2, and TPA also enhanced prolactin synthesis. However, B1 and B2 were only partial agonists because they enhanced prolactin synthesis to a lesser maximal extent than did TPA and, given in combination, they reduced TPA-enhanced prolactin synthesis. OAG and Di8 stimulated prolactin release (to a lesser maximal extent than TPA) and did not stimulate prolactin synthesis. Pretreatment with OAG did not reduce TPA-stimulated prolactin release or synthesis. B2 and TPA induced cell stretching in GH4C5 cells, whereas B1, OAG, and Di8 induced little if any stretching. B1, but not B2, given in combination with TPA antagonized TPA-induced stretching but did not reduce thyrotropin-releasing hormone- or epidermal growth factor-induced stretching. We conclude that the bryostatins, phorbol esters, and dioleins bind to the same site on the protein kinase C complex to activate the enzyme, but they alter three biological responses in GH4C5 cells with selectivities and efficacies that differ. We propose that different activators of protein kinase C (such as bryostatins, dioleins, and phorbol esters) may elicit different cellular responses by altering the substrate specificity or activating multiple forms of the kinase.
佛波酯肿瘤促进剂，如12 - O - 十四酰佛波醇 - 13 - 乙酸酯（TPA），可激活钙和磷脂依赖性蛋白激酶C，并增强GH4C5大鼠垂体细胞中的三种生物学反应（催乳素释放、催乳素合成和细胞伸展）。我们研究了TPA以及另外两类蛋白激酶C激活剂（合成的细胞渗透性二油精和从海洋苔藓虫Bugula neritina中分离出的苔藓抑素）对GH4C5细胞的几种作用。苔藓抑素1和2（分别为B1和B2）在完整细胞中与[3H]佛波醇12,13 - 二丁酸酯竞争结合蛋白激酶C复合物，其能力与TPA几乎相当。B1、B2、1 - 油酰 - 2 - 乙酰甘油（OAG）和1,2 - 二辛酰甘油（Di8）以及TPA均能激活从GH4C5细胞中部分纯化的蛋白激酶C。B1、B2和TPA各自将GH4C5细胞中催乳素的急性释放增强到相似的最大程度。B1、B2和TPA也增强了催乳素的合成。然而，B1和B2只是部分激动剂，因为它们增强催乳素合成的最大程度低于TPA，并且联合使用时，它们会降低TPA增强的催乳素合成。OAG和Di8刺激催乳素释放（最大程度低于TPA），但不刺激催乳素合成。用OAG预处理不会降低TPA刺激的催乳素释放或合成。B2和TPA诱导GH4C5细胞伸展，而B1、OAG和Di8几乎不诱导伸展。B1与TPA联合使用时可拮抗TPA诱导的伸展，但不降低促甲状腺激素释放激素或表皮生长因子诱导的伸展。我们得出结论，苔藓抑素、佛波酯和二油精与蛋白激酶C复合物上的同一位点结合以激活该酶，但它们在GH4C5细胞中改变三种生物学反应的选择性和效力不同。我们提出，蛋白激酶C的不同激活剂（如苔藓抑素、二油精和佛波酯）可能通过改变底物特异性或激活激酶的多种形式引发不同的细胞反应。
