Pirger Zsolt, Rácz Boglárka, Kiss Tibor
Department of Experimental Zoology, Balaton Limnological Research Institute, Hungarian Academy of Sciences, Tihany, Hungary.
Biol Cell. 2009 Feb;101(2):105-16. doi: 10.1042/BC20070168.
PCD (programmed cell death) is a common mechanism to remove unwanted and excessive cells from organisms. In several exocrine cell types, PCD mode of release of secretory products has been reported. The molecular mechanism of the release, however, is largely unknown. Our aim was to study the molecular mechanism of saliva release from cystic cells, the specific cell type of snail SGs (salivary glands).
SG cells in active feeding animals revealed multiple morphological changes characteristic of PCD. Nerve stimulation and DA (dopamine) increased the number of TUNEL (terminal deoxynucleotidyl transferase-mediated dUTP nick-end labelling)-positive cells both in inactive and feeding animals. The DA-induced PCD was prevented by TEA (tetraethylammonium chloride) and eticlopride, emphasizing the role of K channels and D2 receptors in the PCD of cystic cells. DA enhanced cyto-c (cytochrome c) translocation into the cytosol and methyl-beta-cyclodextrin prevented it, suggesting apoptosome formation and ceramide involvement in the PCD linking of the surface DA receptor to mitochondria. Western blot analysis revealed that the release of cyto-c was under the control of Bcl-2 and Bad. DA also increased the active caspase-3 in gland cells while D2 receptor antagonists and TEA attenuated it.
Our results provide evidence for a type of transmitter-mediated pathway that regulates the PCD of secretory cells in a mitochondrial-caspase-dependent manner. The activation of specific molecules, such as K channels, DA receptors, cyto-c, ceramide, Bcl-2 proteins and caspase-3, but not caspase-8, was demonstrated in cells involved in the DA-induced PCD, suggesting that PCD is a physiological method for the release of saliva from SG cells.
程序性细胞死亡（PCD）是生物体清除不需要的多余细胞的一种常见机制。在几种外分泌细胞类型中，已报道了分泌产物释放的PCD模式。然而，这种释放的分子机制在很大程度上尚不清楚。我们的目的是研究蜗牛唾液腺（SGs）的特定细胞类型——囊状细胞中唾液释放的分子机制。
活跃进食动物的SG细胞显示出多种PCD特征性的形态变化。神经刺激和多巴胺（DA）增加了非活跃和进食动物中TUNEL（末端脱氧核苷酸转移酶介导的dUTP缺口末端标记）阳性细胞的数量。TEA（四乙铵氯化物）和依替必利可阻止DA诱导的PCD，强调了钾通道和D2受体在囊状细胞PCD中的作用。DA增强了细胞色素c（cyto-c）向细胞质的转位，而甲基-β-环糊精可阻止这种转位，表明凋亡小体形成以及神经酰胺参与了表面DA受体与线粒体的PCD连接。蛋白质免疫印迹分析表明，cyto-c的释放受Bcl-2和Bad的控制。DA还增加了腺细胞中活化的半胱天冬酶-3，而D2受体拮抗剂和TEA可使其减弱。
我们的结果为一种递质介导的途径提供了证据，该途径以线粒体-半胱天冬酶依赖性方式调节分泌细胞的PCD。在参与DA诱导的PCD的细胞中，证实了特定分子的激活，如钾通道、DA受体、cyto-c、神经酰胺、Bcl-2蛋白和半胱天冬酶-3，但未发现半胱天冬酶-8的激活，这表明PCD是SG细胞释放唾液的一种生理方式。
