McArdle C A, Huckle W R, Conn P M
J Biol Chem. 1987 Apr 15;262(11):5028-35.
The demonstration that activators of the Ca2+-activated, phospholipid-dependent protein kinase (protein kinase C), such as phorbol esters and diacylglycerols, can provoke luteinizing hormone (LH) release from pituitary gonadotropes, suggests a possible role for protein kinase C in stimulus-release coupling. We now report that administration of phorbol myristate acetate (PMA) to pituitary cell cultures causes a sustained reduction in Triton X-100-extracted protein kinase C activity. Further, phorbol ester- and diacylglycerol-stimulated LH release, as well as inhibition by PMA of gonadotropin-releasing hormone (GnRH)-stimulated inositol phosphate production, were reduced by pretreatment with PMA. The effects of phorbol ester pretreatment on PMA-stimulated LH release and protein kinase C activity were dose-dependent, sustained (greater than or equal to 24 h) and specific (no measurable effect with 4 alpha-phorbol didecanoate). The effect on PMA-stimulated LH release was apparently Ca2+-independent. In pituitary cell cultures with reduced protein kinase C activity, the gonadotropes have reduced responsiveness to PMA but release a similar proportion of cellular LH in response to Ca2+-mobilizing secretagogues (GnRH and A23187) as do control cells. The normal responsiveness to GnRH of cells with reduced responsiveness to protein kinase C activators calls into question the requirement for this enzyme for GnRH-stimulated LH release.
钙离子激活的磷脂依赖性蛋白激酶（蛋白激酶C）的激活剂，如佛波酯和二酰基甘油，能够促使垂体促性腺细胞释放促黄体生成素（LH），这表明蛋白激酶C在刺激-释放偶联中可能发挥作用。我们现在报告，向垂体细胞培养物中施用佛波醇肉豆蔻酸酯乙酸酯（PMA）会导致Triton X-100提取的蛋白激酶C活性持续降低。此外，用PMA预处理可降低佛波酯和二酰基甘油刺激的LH释放，以及PMA对促性腺激素释放激素（GnRH）刺激的肌醇磷酸生成的抑制作用。佛波酯预处理对PMA刺激的LH释放和蛋白激酶C活性的影响呈剂量依赖性、持续性（大于或等于24小时）且具有特异性（4α-佛波醇二癸酸酯无明显作用）。对PMA刺激的LH释放的影响显然与钙离子无关。在蛋白激酶C活性降低的垂体细胞培养物中，促性腺细胞对PMA的反应性降低，但与对照细胞一样，对钙离子动员性促分泌素（GnRH和A23187）释放相似比例的细胞内LH。对蛋白激酶C激活剂反应性降低的细胞对GnRH的正常反应性，使人质疑该酶对GnRH刺激的LH释放的必要性。
