Nucleotide sequence and analysis of the mouse SPC3 promoter region

Regulation of pancreatic PC1 and PC2 associated with increased glucagon-like peptide 1 in diabetic rats

The pancreatic processing enzymes, PC1 and PC2, convert proinsulin to insulin and convert proglucagon to glucagon and glucagon-like peptide 1 (GLP-1). We examined the effect of streptozotocin (STZ) treatment on the regulation of these enzymes and the production of insulin, glucagon, and GLP-1 in the rat. Pancreatic PC1 and PC2 mRNA increased >2-fold and >4-fold, respectively, in rats receiving intraperitoneal STZ (50 mg/kg) daily for 5 days. Immunocytochemistry revealed that, although pancreatic islet cells in the STZ-treated rats were sparse and atrophic PC1, PC2, glucagon, and GLP-1 immunoreactivity increased dramatically in the remaining islet cells. Heightened PC1 and PC2 expression was seen in cells expressing glucagon but not in insulin-expressing cells. Furthermore, in STZ-treated rats, bioactive GLP-1(7-36 amide) accumulated in pancreatic extracts and serum 3- and 2.5-fold, respectively, over control animals. This treatment also caused a 2-fold increase in the ratio of amidated forms of GLP-1 immunoreactivity to total glucagon immunoreactivity in the pancreas but did not affect the ratio of proinsulin to insulin. We conclude that hyperglycemic rats have an increased expression of prohormone converting enzymes in islet alpha cells, leading to an increase in amidated GLP-1, which can then exert an insulinotropic effect on the remaining beta cells.

Pilocarpine-induced seizures are accompanied by a transient elevation in the messenger RNA expression of the prohormone convertase PC1 in rat hippocampus: comparison with nerve growth factor and brain-derived neurotrophic factor expression

Several prohormone convertases that are involved in the posttranslational processing of precursor proteins, including neuropetides, hormones and neurotrophic factors, are produced in the central nervous system. These include enzymes named furin, PC1, PC2, PC5 and PACE4. To understand better the potential role played by prohormone convertases in the central nervous system we studied the expression of their messenger RNAs in the hippocampus of rats with pilocarpine-induced seizures. Moreover, we compared their expression patterns with those of neurotrophins such as nerve growth factor and brain-derived neurotrophic factor, which are up-regulated in the hippocampus during seizures. Pilocarpine (380 mg/kg, i.p.) induced seizure activity that appeared within the first hour and persisted for approximately 8 h. In situ hybridization showed transient increases in messenger RNA for nerve growth factor and brain-derived neurotrophic factor that peaked at 120 min in the hippocampus. Among the convertases studied, only PC1 messenger RNA displayed up-regulation, with temporal and topographic features comparable to those of nerve growth factor and brain-derived neurotrophic factor messenger RNA. The expression of furin, PC2 and PC5 messenger RNA changed little, while PACE4 was not expressed at all, both before and after pilocarpine administration. The highest increase in PC1 messenger RNA expression was found in granule cells of the dentate gyrus and, to a lesser extent, in the pyramidal layer of CA1 and CA3 subfields. Thus, in the rat hippocampus, the epileptiform activity induced by pilocarpine mediates a co-ordinated expression of messenger RNAs for PC1, nerve growth factor and brain-derived neurotrophic factor. Our findings suggest the involvement of PC1 in the processing of precursor proteins during seizure activity.

Kainic acid increases the expression of the prohormone convertases furin and PC1 in the mouse hippocampus

Prohormone convertases (PCs) belong to the mammalian family of subtilisin/kexin-like enzymes which have been implicated in the posttranslational processing of precursor proteins. Several PCs are produced in the central and peripheral nervous system, and only a few specific precursor-substrates have been identified in vivo. In the nervous system, PCs may be involved in intracellular processing of precursors for neuropeptides, hormones and neurotrophic factors, including nerve growth factor (NGF) and brain-derived neurotrophic factor (BDNF). To study the interrelationships between the convertases furin, PC1 and PC2, and the neurotrophins NGF, BDNF and NT-3, we compared their mRNA distribution in different tissues. We also examined their expression in the hippocampus of mice undergoing kainic acid-induced seizures. In this experiment, in situ hybridization (ISH) demonstrated that the levels of mRNA for furin, PC1 and BDNF increased maximally at 3 h after kainic acid administration, followed by a decline to normal levels by 96 h. NGF showed small changes, while NT-3 was downregulated with minimal expression levels between 3 to 12 h. Double ISH with radioactively-labeled riboprobes and digoxigenin-labeled riboprobes demonstrated colocalization of furin with NGF and BDNF in the mouse submaxillary gland, and of furin and PC1 with BDNF in the trigeminal ganglion. Based on colocalization studies and evidence of coordinate expression with NGF and BDNF, we suggest the involvement of furin in processing of proNGF, and of both furin and PC1 in processing of proBDNF.

Specific co-ordinated regulation of PC3 and PC2 gene expression with that of preproinsulin in insulin-producing beta TC3 cells

Short-term (less than 2 h) glucose stimulation of isolated pancreatic islets specifically increases the biosynthesis of proinsulin and its converting enzymes PC2 and PC3 at the translation level. To determine whether gene expression of PC2 and PC3 was also regulated by longer-term (more than 6 h) glucose stimulation along with that of preproinsulin, studies were performed with the beta TC3 insulin-producing cell line. By Northern blot analysis, glucose maintained PC2 and PC3 mRNA levels in parallel with those of preproinsulin. After 48 h, mRNA levels of preproinsulin, PC2 and PC3 were, respectively, 2.9 (P < 0.05), 3.0 (P < 0.005) and 5.3 (P < 0.001) times greater in the presence of glucose than in beta TC3 cells cultured in the absence of glucose. Glucose-regulated PC2 and PC3 gene expression, like that of preproinsulin, was maximal at glucose concentrations above 5.5 mM. Studies of mRNA stability showed that the half-lives of PC2 (9 h) and PC3 (5 h) mRNA were much shorter than that of preproinsulin mRNA (over 24 h), but little effect of glucose on stability of these mRNAs was observed. Nuclear run-off analysis indicated that transcription of preproinsulin, PC2 and PC3 was modestly induced after 1 h exposure to 16.7 mM glucose. Therefore preproinsulin, PC2 and PC3 mRNA levels in beta TC3 cells were most probably maintained at the level of gene transcription. In contrast, elevation of cyclic AMP by forskolin had no effect on mRNA levels or gene transcription of preproinsulin, PC2 and PC3, despite a cyclic-AMP-induced phosphorylation of the cyclic AMP response element binding protein that correlated with a marked increase in cJun and cFos gene transcription in the same beta-cells. These results suggest that preproinsulin, PC2 and PC3 gene transcription can be specifically glucose-regulated in a mechanism that is unlikely to involve a key role for cyclic AMP. The co-ordinate increase in PC2 and PC3 mRNA levels with that of preproinsulin mRNA in response to chronic glucose represents a long-term means of catering for an increased demand on proinsulin conversion.