Liu J P, Engler D, Funder J W, Robinson P J
Prince Henry's Institute of Medical Research, Clayton, Victoria, Australia.
Mol Cell Endocrinol. 1992 Sep;87(1-3):35-47. doi: 10.1016/0303-7207(92)90231-t.
These studies were undertaken to evaluate the role of protein kinase C (PKC) in the regulation by arginine vasopressin (AVP) of adrenocorticotropin (ACTH) secretion from the ovine anterior pituitary. AVP caused the rapid translocation of PKC from the cytosol to the cell membrane in ovine anterior pituitary cells that was maximal at 5 min. This phenomenon, which is a known concomitant of C-kinase activation, was produced to a greater extent by phorbol 12-myristate 13-acetate (PMA) but not by corticotropin-releasing factor (CRF). To determine whether AVP activated corticotrope PKC, we assessed the ability of three different PKC inhibitors (H-7, sphingosine, and retinal) to modify basal, AVP-, PMA-, and CRF-stimulated ACTH release. In addition to inhibiting the in vitro activity of purified PKC, each compound also caused in vitro inhibition of the protein kinase A (PKA) catalytic subunit, indicating that none could be considered to be a specific inhibitor of PKC and the PKA catalytic subunit. As determined by the mean IC50 values required for the in vitro inhibition of PKC and the PKA catalytic subunit, sphingosine was judged to be the most selective and H-7 the least selective PKC inhibitor. A 4 h exposure to each inhibitor caused a dose-dependent increase in basal ACTH release and attenuation of both AVP- and PMA-stimulated ACTH release. H-7 and retinal, in concentrations that caused a 20-50% inhibition of PKA, also attenuated CRF-stimulated ACTH release; however, this effect was not observed with sphingosine in concentrations that caused only a 10-20% inhibition of PKA. We conclude that: (1) AVP causes the direct activation of PKC in the ovine anterior pituitary and that C kinase activation is important in mediating the effect of AVP on ACTH release; (2) the finding that inhibition of PKC elevates ACTH suggests that basal ACTH secretion is also partly regulated by PKC; (3) since CRF does not cause PKC translocation in ovine anterior pituitary cells, it is unlikely that PKC plays a physiological role in the action of CRF on the corticotrope; (4) the finding that H-7 and retinal attenuate CRF-stimulated ACTH secretion suggests that CRF activates PKA in corticotropes.
开展这些研究是为了评估蛋白激酶C（PKC）在精氨酸加压素（AVP）对绵羊垂体前叶促肾上腺皮质激素（ACTH）分泌的调节作用中所起的作用。AVP可使绵羊垂体前叶细胞中的PKC迅速从胞质溶胶转位至细胞膜，5分钟时达到最大值。这种现象是已知的C激酶激活的伴随现象，佛波醇12 - 肉豆蔻酸酯13 - 乙酸酯（PMA）能更大程度地引发该现象，但促肾上腺皮质激素释放因子（CRF）则不能。为了确定AVP是否激活促肾上腺皮质激素细胞的PKC，我们评估了三种不同的PKC抑制剂（H - 7、鞘氨醇和视黄醛）对基础状态、AVP、PMA和CRF刺激的ACTH释放的影响。除了抑制纯化的PKC的体外活性外，每种化合物还在体外抑制蛋白激酶A（PKA）催化亚基，这表明没有一种可以被认为是PKC和PKA催化亚基的特异性抑制剂。根据体外抑制PKC和PKA催化亚基所需的平均IC50值判断，鞘氨醇是最具选择性的PKC抑制剂，而H - 7是选择性最低的。每种抑制剂暴露4小时都会导致基础ACTH释放呈剂量依赖性增加，并减弱AVP和PMA刺激的ACTH释放。H - 7和视黄醛在导致PKA抑制20 - 50%的浓度下，也会减弱CRF刺激的ACTH释放；然而，在仅导致PKA抑制10 - 20%的浓度下，鞘氨醇未观察到这种效应。我们得出以下结论：（1）AVP可直接激活绵羊垂体前叶中的PKC，且C激酶激活在介导AVP对ACTH释放的作用中很重要；（2）抑制PKC会升高ACTH这一发现表明基础ACTH分泌也部分受PKC调节；（3）由于CRF不会导致绵羊垂体前叶细胞中的PKC转位，PKC在CRF对促肾上腺皮质激素细胞的作用中不太可能发挥生理作用；（4）H - 7和视黄醛减弱CRF刺激的ACTH分泌这一发现表明CRF可激活促肾上腺皮质激素细胞中的PKA。
