Aganna Ebun, Burrin Jacky M, Hitman Graham A, Turner Mark D
Centre for Diabetes and Metabolic Medicine, Institute of Cell and Molecular Science, Barts and The London, Queen Mary's School of Medicine and Dentistry, University of London, Whitechapel, London E1 2AT, UK.
J Endocrinol. 2006 Sep;190(3):R1-7. doi: 10.1677/joe.1.06737.
The requirement for Ca(2+) to regulate hormone secretion from endocrine cells is long established, but the precise function of Ca(2+) sensors in stimulus-secretion coupling remains unclear. In the current study, we examined the expression of calpain and synaptotagmin in INS-1 pancreatic and GH3 and AtT20 pituitary cells, and investigated the sensitivity of hormone secretion from these cells to inhibition of the calpain family of cysteine proteases. Little difference in expression of mu-calpain was observed between the different endocrine cells. However, AtT20 cells did exhibit an extremely low abundance of both m-calpain and the 54 kDa isoform of calpain-10 relative to their expression in INS-1 and GH3 cells. Interestingly, secretagog-stimulated secretion from both INS-1 and GH3 cells was completely abolished following pre-incubation with the cysteine protease inhibitor E64, whereas stimulated secretion from AtT20 cells was modest and completely insensitive to E64 inhibition. These results are in stark contrast to synaptotagmin data. Synaptotagmin expression in AtT20 cells is abundant, whereas INS-1 cells express extremely low levels of this Ca(2+) sensor, relative to the pituitary cells. We hypothesize that the expression pattern of calpain and synaptotagmin isoforms may reflect alternative mechanisms of stimulus-secretion coupling in excitable endocrine cells.
钙离子对调节内分泌细胞激素分泌的需求早已确立，但钙离子传感器在刺激-分泌偶联中的精确功能仍不清楚。在本研究中，我们检测了钙蛋白酶和突触结合蛋白在INS-1胰腺细胞、GH3和AtT20垂体细胞中的表达，并研究了这些细胞的激素分泌对抑制半胱氨酸蛋白酶钙蛋白酶家族的敏感性。在不同的内分泌细胞之间，μ-钙蛋白酶的表达差异不大。然而，相对于它们在INS-1和GH3细胞中的表达，AtT20细胞中m-钙蛋白酶和钙蛋白酶-10的54 kDa亚型的丰度极低。有趣的是，用半胱氨酸蛋白酶抑制剂E64预孵育后，INS-1和GH3细胞中促分泌剂刺激的分泌完全被消除，而AtT20细胞中刺激的分泌适度且对E64抑制完全不敏感。这些结果与突触结合蛋白的数据形成鲜明对比。相对于垂体细胞，AtT20细胞中突触结合蛋白表达丰富，而INS-1细胞中这种钙离子传感器的表达水平极低。我们推测，钙蛋白酶和突触结合蛋白亚型的表达模式可能反映了可兴奋内分泌细胞中刺激-分泌偶联的替代机制。
