Metabolism of parathyroid hormone by isolated rat Kupffer cells and hepatocytes.
Metabolism of parathyroid hormone by isolated rat Kupffer cells and hepatocytes.
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DOI：
10.1172/jci110053
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发表时间：
1981-02
期刊：
影响因子：
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通讯作者：
G. Segre;A. S. Perkins;L. Witters;J. Potts
中科院分区：
文献类型：
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作者：
G. Segre;A. S. Perkins;L. Witters;J. Potts
来自多个实验室的数据表明，肝脏机制可能在完整激素分泌后的代谢中具有独特的作用，这一过程至少部分解释了循环甲状旁腺激素的异质性。因此，我们研究了分离的大鼠库普弗细胞和肝细胞对完整激素的蛋白水解作用。库普弗细胞（10（6）细胞/ml）和肝细胞（10（7）细胞/ml）与未标记和（125）I标记的牛甲状旁腺激素在37℃下孵育长达2小时。当与 Kupffer 细胞一起孵育时，完整的激素在 12+/-4 分钟的 t((1/2)) 内消失。使用序列特异性抗血清的放射免疫测定表明，在培养基中回收的主要激素片段的表观分子量约为 6,000，缺乏氨基末端抗原决定簇，并且在特异性识别完整激素羧基末端部分决定簇的测定中发生反应。还检测到高浓度的氨基末端片段，特别是在短孵育期后。 (125)I 标记的牛甲状旁腺激素与 Kupffer 细胞一起孵育产生的放射性碘化片段与未标记的完整激素代谢产生的片段具有相同的表观大小；当通过 Edman 降解分析时，完整激素序列的第 34 和 37 位是这些主要羧基末端片段的氨基末端氨基酸。肝细胞不水解激素。因此，库普弗细胞对甲状旁腺激素的代谢导致介质中出现碎片，这些碎片在免疫化学上与静脉注射完整激素时在血浆中发现的碎片无法区分，并且在化学上相同。这表明体外观察到的蛋白水解准确地反映了体内激素的代谢情况。检测到的氨基末端片段的浓度几乎等于羧基末端片段的浓度，表明完整激素的裂解最初是通过内肽酶进行的。库普弗细胞可能是可以表征水解甲状旁腺激素的特定蛋白酶的来源，特别是在酶特异性和抑制要求方面。对甲状旁腺激素与这些细胞孵育期间的细胞和分子事件的详细分析可能有助于阐明激素外周代谢的生物学意义。
Data from several laboratories indicate that hepatic mechanisms may have a distinctive role in the metabolism of intact hormone after secretion, a process that accounts, at least partly, for the heterogeneity of circulating parathyroid hormone. Accordingly, we studied the proteolysis of intact hormone by isolated rat Kupffer cells and hepatocytes. Kupffer cells (10(6) cells/ml) and hepatocytes (10(7) cells/ml) were incubated with unlabeled and (125)I-labeled bovine parathyroid hormone at 37 degrees C for periods ranging up to 2 h. When incubated with Kupffer cells, intact hormone disappeared with a t((1/2)) of 12+/-4 min. Radio-immunoassays using sequence-specific antisera showed that the dominant hormonal fragments recovered in the medium have an apparent molecular weight of approximately 6,000, lack amino-terminal antigenic determinants, and react in assays that specifically recognize determinants in the carboxy-terminal portion of the intact hormone. Amino-terminal fragments also were detected in high concentrations, particularly after short incubation periods. Radioiodinated fragments resulting from incubation of (125)I-labeled bovine parathyroid hormone with Kupffer cells had the same apparent size as fragments derived from the metabolism of unlabeled, intact hormone; when analyzed by Edman degradation, positions 34 and 37 of the intact hormone sequence were the amino-terminal amino acids of these dominant carboxy-terminal fragments. Hepatocytes did not hydrolyze the hormone. Thus, metabolism of parathyroid hormone by Kupffer cells results in the appearance of fragments in the media that are immunochemically indistinguishable from, and chemically identical with, those found in plasma when intact hormone is injected intravenously. This indicates that the proteolysis observed in vitro accurately reflects the metabolism of the hormone in vivo. The detection of amino-terminal fragments in concentrations nearly equal to those of carboxy-terminal fragments indicates that cleavage of intact hormone is, initially, by an endopeptidase(s). Kupffer cells may be a source from which specific protease(s) that hydrolyze parathyroid hormone can be characterized, particularly in terms of enzymic specificity and requirements for inhibition. Detailed analysis of the cellular and molecular events during incubation of parathyroid hormone with these cells may help to clarify the biologic significance of the peripheral metabolism of the hormone.