Aquaporin 1 is important for maintaining secretory granule biogenesis in endocrine cells
Aquaporin 1 is important for maintaining secretory granule biogenesis in endocrine cells
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DOI：
10.1210/me.2007-0434
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发表时间：
2008-08-01
影响因子：
--
通讯作者：
Loh, Y. Peng
中科院分区：
文献类型：
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作者：
Arnaoutova, Irina;Cawley, Niamh X.;Loh, Y. Peng
水通道蛋白（Aquaporins, AQPs）是上皮细胞中表达的一个水通道家族，其功能是双向运输水，促进上皮液的吸收和分泌。此外，AQP1和AQP5存在于胰腺酶原颗粒和突触囊泡中，参与外分泌细胞和神经元的囊泡肿胀和胞吐。我们发现AQP1存在于垂体和肾上腺髓质的内分泌组织致密核分泌颗粒（DCSG）膜中。通过将AQP1反义RNA稳定转染垂体细胞系AtT20细胞，下调AQP1的表达，研究了AQP1在内分泌细胞功能中的必要性。这些AQP1-缺陷细胞的DCSG缺失超过60%，DCSG蛋白水平显著降低，包括proopiomelanocotin/pro-ATCH和prohormone convertase 1/3，但非DCSG蛋白水平未见下降。脉冲追踪研究显示，尽管DCSG蛋白的合成不受影响，但大约50%新合成的propropiomelanocortin在1小时内被降解。刺激后释放低水平的ACTH，表明在残留AQP1存在的情况下产生的少量DCSG具有胞吐功能。AQP1基因敲除小鼠的垂体前叶分析显示，与野生型小鼠相比，激素原转化酶1/3、羧肽酶E和ACTH水平降低，这表明我们在AtT20细胞中观察到的结果可以推广到动物模型中。因此，AQP1对于维持DCSG生物发生和垂体内分泌细胞正常水平的激素分泌非常重要。
Aquaporins (AQPs), a family of water channels expressed in epithelial cells, function to transport water in a bidirectional manner to facilitate transepithelial fluid absorption and secretion. Additionally, AQP1 and AQP5 are found in pancreatic zymogen granules and synaptic vesicles and are involved in vesicle swelling and exocytosis in exocrine cells and neurons. Here, we show AQP1 is in dense- core secretory granule (DCSG) membranes of endocrine tissue: pituitary and adrenal medulla. The need for AQP1 in endocrine cell function was examined by stable transfection of AQP1 antisense RNA into AtT20 cells, a pituitary cell line, to down- regulate AQP1 expression. These AQP1- deficient cells showed more than 60% depletion of DCSGs and significantly decreased DCSG protein levels, including proopiomelanocotin/pro-ATCH and prohormone convertase 1/3, but not non-DCSG proteins. Pulse-chase studies revealed that whereas DCSG protein synthesis was unaffected, approximately 50% of the newly synthesized proopiomelanocortin was degraded within 1 h. Low levels of ACTH were released upon stimulation, indicating that the small number of DCSGs that were made in the presence of the residual AQP1 were functionally competent for exocytosis. Analysis of anterior pituitaries from AQP1 knockout mice showed reduced prohormone convertase 1/3, carboxypeptidase E, and ACTH levels compared to wild- type mice demonstrating that our results observed in AtT20 cells can be extended to the animal model. Thus, AQP1 is important for maintaining DCSG biogenesis and normal levels of hormone secretion in pituitary endocrine cells.