Vargas M A, Joseph-Bravo P, Charli J L
Instituto de Biotecnología, Universidad Nacional Autónoma de México, Cuernavaca.
Neuroendocrinology. 1994 Sep;60(3):323-30. doi: 10.1159/000126765.
Pyroglutamyl peptidase II (PPII) is a thyrotropin-releasing hormone (TRH) hydrolyzing ectoenzyme with a narrow specificity. In the adenohypophysis, it is present on lactotropes. This study was undertaken in order to determine whether TRH itself regulates PPII activity in the adenohypophysis. After 5 days in culture, dispersed cells from female pituitaries expressed detectable levels of PPII activity when 10(-8) M 3,3',5'-triiodo-L-thyronine was present throughout the culture. 10(-6) M TRH decreased PPII activity with a maximal effect (down to 46% of initial values) at 16 h and an ED50 of 10(-9) M. [3Me-His2]TRH, a potent agonist of the TRH receptor was effective at lower concentrations (ED50: 1.6 x 10(-10) M). Phorbol-12-myristate-13-acetate (PMA; 10(-6) M), a protein kinase C (PKC) activator, diminished PPII activity to 61% or initial values with an ED50 of 2.2 x 10(-8) M. Maximal effects of PMA and TRH were not additive. Neither PMA nor TRH effects were reversed by inhibitors of protein kinases (1-(5-isoquinolinesulfonyl)-2-methyl-piperazine or sphingosine or staurosporine); TRH-induced downregulation of the enzyme was not modified by PMA pretreatment. TRH had no effect on two other ectopeptidases, endopeptidase 24.11 and dipeptidyl aminopeptidase IV. These data demonstrate that TRH specifically downregulates PPII activity in adenohypophyseal cells through TRH receptor activation and suggest that the activation of a presumably calcium-independent PKC mimics the TRH effect. TRH regulation of PPII activity may contribute to adjust lactotrope responsiveness to TRH.
焦谷氨酸肽酶II（PPII）是一种具有狭窄特异性的促甲状腺激素释放激素（TRH）水解外切酶。在腺垂体中，它存在于催乳细胞上。进行这项研究是为了确定TRH本身是否调节腺垂体中的PPII活性。培养5天后，当在整个培养过程中存在10^(-8) M 3,3',5'-三碘-L-甲状腺原氨酸时，来自雌性垂体的分散细胞表达出可检测水平的PPII活性。10^(-6) M TRH在16小时时降低PPII活性，最大效应（降至初始值的46%），ED50为10^(-9) M。[3Me-His2]TRH是TRH受体的强效激动剂，在较低浓度下有效（ED50：1.6×10^(-10) M）。佛波醇-12-肉豆蔻酸酯-13-乙酸酯（PMA；10^(-6) M）是一种蛋白激酶C（PKC）激活剂，将PPII活性降低至初始值的61%，ED50为2.2×10^(-8) M。PMA和TRH的最大效应不是相加的。蛋白激酶抑制剂（1-(5-异喹啉磺酰基)-2-甲基哌嗪或鞘氨醇或星形孢菌素）均不能逆转PMA和TRH的作用；PMA预处理不会改变TRH诱导的酶下调。TRH对另外两种外肽酶，即内肽酶24.11和二肽基氨基肽酶IV没有影响。这些数据表明TRH通过TRH受体激活特异性下调腺垂体细胞中的PPII活性，并表明推测的钙非依赖性PKC的激活模拟了TRH的作用。TRH对PPII活性的调节可能有助于调节催乳细胞对TRH的反应性。
