Gaisano H Y, Sheu L, Foskett J K, Trimble W S
Department of Medicine, University of Toronto, Ontario, Canada.
J Biol Chem. 1994 Jun 24;269(25):17062-6.
Pancreatic acinar cells, a model cell type for the study of exocytosis in non-excitable cells, were used here to test the hypothesis that molecular mechanisms regulating exocytosis from neuronal and neuroendocrine cells may also be utilized in exocrine cells. Using specific antisera raised against vesicle-associated membrane protein (VAMP) isoforms 1 and 2, we have identified VAMP-2, but not VAMP-1, immunoreactive proteins on rat pancreatic acinar cell secretory (zymogen) granules. This 18-kDa protein co-migrated with rat brain synaptic vesicle VAMP-2. Tetanus toxin (TeTx) light chain caused complete cleavage of this protein, which was prevented by the addition of EDTA. This toxin also inhibited in a dose-dependent manner Ca(2+)-stimulated enzyme secretion by up to approximately 30% in streptolysin O-permeabilized acini. This effect of TeTx on secretion was prevented by the zinc endopeptidase inhibitor captopril or by boiling the toxin. Incomplete inhibition of secretion by TeTx may suggest that TeTx-insensitive or VAMP-2-independent mechanisms also regulate exocytosis. In support, TeTx light chain was without effect on Rab3AL (effector domain peptide of Rab3)-mediated potentiation of Ca(2+)-stimulated secretion. These results indicate that a TeTx-sensitive VAMP-2-like protein on zymogen granules participates in Ca(2+)-regulated pancreatic enzyme secretion and that undefined Rab3AL-activated mechanisms may act independently to regulate exocytosis.
胰腺腺泡细胞是用于研究非兴奋性细胞胞吐作用的一种典型细胞类型，本文利用它来检验下述假说：调节神经元和神经内分泌细胞胞吐作用的分子机制也可能在外分泌细胞中发挥作用。我们使用针对囊泡相关膜蛋白（VAMP）亚型1和2制备的特异性抗血清，在大鼠胰腺腺泡细胞分泌（酶原）颗粒上鉴定出了VAMP - 2免疫反应性蛋白，但未鉴定出VAMP - 1。这种18 kDa的蛋白与大鼠脑突触小泡VAMP - 2共同迁移。破伤风毒素（TeTx）轻链导致该蛋白完全裂解，而加入乙二胺四乙酸（EDTA）可阻止这种裂解。这种毒素还以剂量依赖的方式抑制链球菌溶血素O通透的腺泡中钙（Ca²⁺）刺激的酶分泌，抑制率高达约30%。TeTx对分泌的这种作用可被锌内肽酶抑制剂卡托普利或通过煮沸毒素所阻止。TeTx对分泌的不完全抑制可能表明，TeTx不敏感或VAMP - 2非依赖的机制也参与调节胞吐作用。作为支持，TeTx轻链对Rab3AL（Rab3的效应结构域肽）介导的钙（Ca²⁺）刺激分泌的增强作用没有影响。这些结果表明，酶原颗粒上一种对TeTx敏感的VAMP - 2样蛋白参与了钙（Ca²⁺）调节的胰腺酶分泌，并且未明确的Rab3AL激活机制可能独立发挥作用来调节胞吐作用。
