Damholt A B, Buchan A M, Holst J J, Kofod H
Beta Cell Biology, Novo Nordisk A/S, Novo Allé, Bagsvaerd, Denmark.
Endocrinology. 1999 Oct;140(10):4800-8. doi: 10.1210/endo.140.10.7068.
The tissue-specific differential processing of proglucagon (Pg) yields glucagon in pancreatic A cells and glucagon-like peptide-1 (GLP-1), GLP-2, and glicentin in intestinal L cells. It has been suggested that the difference in Pg cleavage in A and L cells is due to the presence of distinct prohormone convertases (PC) in the two cell types, PC1/3 in the L cell and PC2 in the A cell. PC2 has been shown to cleave the N-terminal part of Pg, being essential for glucagon formation and PC1/3 to cleave the C-terminal part of Pg, leading to the formation of GLP-1. However, some of the cleavage sites in Pg have not proven to be substrates exclusively for either PC2 or PC1/3, and the cleavage profile of Pg in a primary cultured L cell has not yet been correlated with the actual presence of PC2 and PC1/3 in the L cell. We demonstrate here the presence of PC1/3, PC2, and the PC2 chaperone 7b2, in L cells using light immunohistochemistry on sections from canine ileum and on a canine intestinal cell culture enriched for L cells. Analysis of the cultured L cells, using gel chromatography and RIA, confirms the classical intestinal cleavage profile of Pg, resulting in mainly glicentin, oxyntomodulin, GLP-1-(7-37), and GLP-2. Despite the presence of 7b2 and mature PC2, as demonstrated by Western blot, absolute minimal amounts of glucagon were detected. These data show that the presence of intracellular PC2 and 7b2 in a primary cell possessing Pg does not have to lead to the formation of glucagon. This formation must then require an additional element to occur, or alternatively, the results could be explained by a canine specific organization of PC2 and Pg into separate compartments, which would prevent interaction.
胰高血糖素原（Pg）的组织特异性差异加工在胰腺A细胞中产生胰高血糖素，在肠道L细胞中产生胰高血糖素样肽-1（GLP-1）、GLP-2和胃泌酸调节素。有人提出，A细胞和L细胞中Pg裂解的差异是由于两种细胞类型中存在不同的激素原转化酶（PC），L细胞中为PC1/3，A细胞中为PC2。已表明PC2可裂解Pg的N端部分，这对胰高血糖素的形成至关重要，而PC1/3可裂解Pg的C端部分，导致GLP-1的形成。然而，Pg中的一些裂解位点尚未被证明是PC2或PC1/3的专属底物，并且原代培养的L细胞中Pg的裂解谱尚未与L细胞中PC2和PC1/3的实际存在情况相关联。我们在此使用光免疫组织化学方法，对犬回肠切片和富含L细胞的犬肠道细胞培养物进行研究，证明了L细胞中存在PC1/3、PC2和PC2伴侣蛋白7b2。使用凝胶色谱法和放射免疫分析法对培养的L细胞进行分析，证实了Pg的经典肠道裂解谱，主要产生胃泌酸调节素、胃动素、GLP-1-(7-37)和GLP-2。尽管通过蛋白质印迹法证明存在7b2和成熟的PC2，但检测到的胰高血糖素绝对量极少。这些数据表明，在含有Pg的原代细胞中，细胞内PC2和7b2的存在不一定会导致胰高血糖素的形成。那么这种形成必然需要一个额外的因素才能发生，或者，结果可以用犬特异性的PC2和Pg组织到不同区室来解释，这将阻止它们相互作用。
