Cain Brian M, Connolly Kelly, Blum Alissa, Vishnuvardhan Daesety, Marchand James E, Beinfeld Margery C
Department of Pharmacology and Experimental Therapeutics, Tufts University School of Medicine, Boston, Massachusetts 02111, USA.
J Comp Neurol. 2003 Dec 15;467(3):307-25. doi: 10.1002/cne.10924.
During posttranslational processing to generate CCK 8, pro-cholecystokinin (CCK) undergoes endoproteolytic cleavage at three sites. Several studies using endocrine and neuronal tumor cells in culture and recombinant enzymes and synthetic substrates in vitro have pointed to the subtilisin/kexin-like enzymes prohormone convertase (PC) 1, PC2, and PC5 as potential candidates for these endoproteolytic cleavages. In these experimental models, they all appear to be able to cleave pro-CCK to make the correct products. One rodent model has provided information about the role of PC2. PC2 knockout mouse brains had less CCK 8 than wild-type, although a substantial amount of CCK was still present. The degree to which CCK levels were reduced in these mice was regionally specific. These data indicated that PC2 is important for normal production of CCK but that it is not the only endoprotease that is involved in CCK processing. To evaluate whether PC1 and PC5 are possible candidates for the other enzymes involved in CCK processing, the distribution of PC1, PC2, and PC5 mRNA was studied in rat brain. Their colocalization with CCK mRNA was examined using double-label in situ hybridization. PC2 was the most abundant of these enzymes in terms of the intensity and number of cells labeled. It was widely colocalized with CCK. PC1 and PC5 mRNA-positive cells were less abundant, but they were also widely distributed and strongly colocalized with CCK in the cerebral cortex, hippocampus, amygdala, ventral tegmental area, and substantia nigra zona compacta. The degree of colocalization of the enzymes with CCK was regionally specific. It is clear that PC1 and PC5 are extensively colocalized with CCK and could be participating in CCK processing in the rat brain and may be able to substitute for PC2 in its absence. These three enzymes may represent a redundant system to ensure production of biologically active CCK.
在生成胆囊收缩素-8（CCK 8）的翻译后加工过程中，前胆囊收缩素（CCK）在三个位点进行内切蛋白水解切割。多项利用培养的内分泌和神经肿瘤细胞以及体外重组酶和合成底物的研究指出，枯草杆菌蛋白酶/克新样酶激素原转化酶（PC）1、PC2和PC5是这些内切蛋白水解切割的潜在候选酶。在这些实验模型中，它们似乎都能够切割前CCK以产生正确的产物。一种啮齿动物模型提供了有关PC2作用的信息。PC2基因敲除小鼠的大脑中CCK 8比野生型少，尽管仍存在大量的CCK。这些小鼠中CCK水平降低的程度具有区域特异性。这些数据表明，PC2对CCK的正常产生很重要，但它不是参与CCK加工的唯一内切蛋白酶。为了评估PC1和PC5是否是参与CCK加工的其他酶的可能候选者，研究了大鼠脑中PC1、PC2和PC5 mRNA的分布。使用双标记原位杂交检查它们与CCK mRNA的共定位。就标记的细胞强度和数量而言，PC2是这些酶中最丰富的。它与CCK广泛共定位。PC1和PC5 mRNA阳性细胞较少，但它们也广泛分布，并在大脑皮层、海马体、杏仁核、腹侧被盖区和黑质致密部与CCK强烈共定位。这些酶与CCK的共定位程度具有区域特异性。很明显，PC1和PC5与CCK广泛共定位，可能参与大鼠脑中的CCK加工，并且在没有PC2的情况下可能能够替代PC2。这三种酶可能代表一个冗余系统，以确保产生生物活性CCK。
