Matozaki T, Sakamoto C, Nagao M, Nishizaki H, Baba S
Second Department of Internal Medicine, Kobe University School of Medicine.
Nihon Naibunpi Gakkai Zasshi. 1988 Jun 20;64(6):523-30. doi: 10.1507/endocrine1927.64.6_523.
Our previous study concerning guanine nucleotides regulation of labeled somatostatin binding has suggested that somatostatin receptors on pancreatic acinar cell membranes probably couple with the inhibitory guanine nucleotide regulatory protein (Ni). In order to clarify the possible role of Ni in mediating signal transduction of somatostatin in the pancreas, we further examined the effect of pretreatment with islet activating protein (IAP) on the inhibition of VIP-stimulated cellular cyclic AMP content by somatostatin in isolated rat pancreatic acini. Increasing concentrations of somatostatin decreased VIP-stimulated cellular content of cyclic AMP in the acini, with a maximal inhibition at 10(-8) M somatostatin. When pancreatic acini were pretreated with varying concentrations of IAP for 4 hours, the somatostatin-induced inhibition of cyclic AMP content was attenuated in a dose dependent manner by IAP pretreatment. Incubation of pancreatic acinar membrane with preactivated IAP and [32P] NAD resulted in labeling of a Mr = 41,000 protein band, consistent with alpha-subunit of Ni in many other cell types previously reported. On the other hand, a Mr = 41,000 protein band on SDS gel was reduced in a dose dependent fashion by IAP pretreatment, when acini were pretreated with increasing concentrations of IAP. These results suggest that only the Mr = 41,000 protein is a specific substrate in pancreatic acinar membranes for IAP-induced ADP-ribosylation. Furthermore, the reduction of 32P incorporation to Mr = 41,000 protein by IAP pretreatment occurred in parallel to decreases in somatostatin-induced inhibition of cellular cyclic AMP contents in pancreatic acini.(ABSTRACT TRUNCATED AT 250 WORDS)
我们先前关于鸟嘌呤核苷酸对标记生长抑素结合的调节作用的研究表明，胰腺腺泡细胞膜上的生长抑素受体可能与抑制性鸟嘌呤核苷酸调节蛋白（Ni）偶联。为了阐明Ni在介导胰腺中生长抑素信号转导中的可能作用，我们进一步研究了用胰岛激活蛋白（IAP）预处理对生长抑素抑制离体大鼠胰腺腺泡中血管活性肠肽（VIP）刺激的细胞环磷酸腺苷（cAMP）含量的影响。生长抑素浓度增加可降低腺泡中VIP刺激的细胞cAMP含量，在10^(-8) M生长抑素时抑制作用最大。当用不同浓度的IAP预处理胰腺腺泡4小时时，IAP预处理以剂量依赖性方式减弱了生长抑素诱导的cAMP含量抑制。用预激活的IAP和[32P]NAD孵育胰腺腺泡膜导致一条分子量为41,000的蛋白带被标记，这与先前报道的许多其他细胞类型中的Niα亚基一致。另一方面，当用浓度递增的IAP预处理腺泡时，SDS凝胶上分子量为41,000的蛋白带会因IAP预处理而以剂量依赖性方式减少。这些结果表明，只有分子量为41,000的蛋白是胰腺腺泡膜中IAP诱导的ADP核糖基化的特异性底物。此外，IAP预处理使32P掺入分子量为41,000的蛋白的减少与胰腺腺泡中生长抑素诱导的细胞cAMP含量抑制的降低同时发生。（摘要截短于250字）
