The Cell-Specific Pattern of Cholecystokinin Peptides in Endocrine Cells Versus Neurons Is Governed by the Expression of Prohormone Convertases 1/3, 2, and 5/6

Abstract

Most peptide hormone genes are, in addition to endocrine cells, also expressed in neurons. The peptide hormone cholecystokinin (CCK) is expressed in different molecular forms in cerebral neurons and intestinal endocrine cells. To understand this difference, we examined the roles of the neuroendocrine prohormone convertases (PC) 1/3, PC2, and PC5/6 by measurement of proCCK, processing intermediates and bioactive, alpha-amidated, and O-sulfated CCK peptides in cerebral and jejunal extracts of null mice, controls, and in the PC5/6-expressing SK-N-MC cell-line. In PC1/3 null mice, the synthesis of bioactive CCK peptide in the gut was reduced to 3% of the translational product, all of which was in the form of alpha-amidated and tyrosine O-sulfated CCK-22, whereas the neuronal synthesis in the brain was largely unaffected. This is opposite to the PC2 null mice in which only the cerebral synthesis was affected. SK-N-MC cells, which express neither PC1/3 nor PC2, synthesized alone the processing intermediate, glycine-extended CCK-22. Immunocytochemistry confirmed that intestinal endocrine CCK cells in wild-type mice express PC1/3 but not PC2. In contrast, cerebral CCK neurons contain PC2 and only little, if any, PC1/3. Taken together, the data indicate that PC1/3 governs the endocrine and PC2 the neuronal processing of proCCK, whereas PC5/6 contributes only to a modest endocrine synthesis of CCK-22. The results suggest that the different peptide patterns in the brain and the gut are due to different expression of PCs.

Genetic deficiency for proprotein convertase subtilisin/kexin type 2 in mice is associated with decreased adiposity and protection from dietary fat-induced body weight gain

“…Pro-CCK processing is reportedly impaired in the neurons, but not in the intestine of Pcsk2 À/À mice. 34 It remains to be determined whether impaired processing of neuronal pro-CCK contributes to lowering of circulating leptin levels in these mice. In the periphery, the most significant peptidergic alteration in Pcsk2 À/À mice documented so far has been the absence of pancreatic glucagon.…”

Nonsulfated cholecystokinins in the small intestine of pigs and rats

“…In secretory and synaptic vesicles, proCCK is cleaved at multiple mono-and dibasic sites, to an extent depending on the site of synthesis [14,25]. From mouse knockout models it is known that prohormone convertase 1/3 (PC-1/3) is an important endopeptidase operating in the endocrine I-cells of the intestinal mucosa, whereas, PC-2 mainly cleaves proCCK in cerebral CCK neurons [25].…”

Cell-Specific Precursor Processing

“…Thus, the synthesis of hormonally active CCK is almost entirely blocked in the small intestine of PC1 knockout mice (Rehfeld et al 2008b). In contrast, the intestinal synthesis of bioactive CCK peptides is intact in PC2 knockout mice (Rehfeld et al 2002b).…”

“…In addition, a variety of procholecystokinin (proCCK)-derived peptides of different lengths have been identified from extracts of both the small intestine and the brain (Blanke et al 1993;Eberlein et al 1992;Eng et al 1984;Rehfeld and Hansen 1986). Combination of these results with those of knockout of prohormone convertase genes in mice and general knowledge about peptide hormone synthesis has given a picture of the cellspecific proCCK processing, both in intestinal I-cells and cerebral CCK neurons (Rehfeld et al 2008b). …”

“…The cerebral processing of proCCK is only marginally affected in PC1 knockout mice (Rehfeld et al 2008b), whereas lack of PC2 profoundly disturbs the neuronal processing (Rehfeld et al 2002b). PC5/6 is expressed also in CCK neurons and can cleave proCCK (Cain et al 2003).…”