Disturbed progastrin processing in carboxypeptidase E‐deficient fat mice

Abstract

The fat mouse strain exhibits a late-onset obesity syndrome associated with a mutation in the gene encoding carboxypeptidase E (CPE). Since CPE plays a central role in the biosynthesis of a number of regulatory peptides, including gastrin, we examined the biogenesis and processing of progastrin in fatlfat mice by measuring gastrin mRNA, carboxyamidated gastrin and its processing intermediates in the stomach. The tissue concentration of carboxyamidated (i.e. bioactive) gastrin was only slightly reduced (601 ± 28 pmol/g in fatlfat mice vs. 715 ±43 pmol/g in wild-type controls). However, progastrin processing intermediates accumulated excessively with an 86-fold increase in the concentration of the CPE substrate, glycylarginine extended gastrin, and a seven-fold increase in the concentration of glycine-extended gastrin. Accordingly, the total progastrin product was doubled, as was the concentration of gastrin mRNA. Plasma concentrations of carboxyamidated gastrin were, however slightly reduced both in fasted fatlfat mice and postprandially. The results show that the CPE mutation diminishes the efficiency of progastrin processing, but gastrin synthesis is nevertheless increased to maintain an almost normal production of bioactive gastrins. By comparison with other neuroendocrine prohormones, progastrin processing in CPEdeficient mice is unique. Hence, the increase of glycine-extended gastrin in combination with normal levels of carboxyamidated gastrin suggests that G-cells may have another biosynthetic pathway for gastrin. © 1997 Federation of European Biochemical Societies.

Carboxypeptidase�E in rat antropyloric mucosa: distribution in progenitor and mature endocrine cell types

“…We demonstrate that antropyloric gastrin cells are strongly positive for CPE. This agrees with previous data showing that CPE-deficient mice have impaired gastrin processing (Gomez et al 1999;Lacourse et al 1997;Udupi et al 1997). Similarly, our data show that antropyloric somatostatin-producing D cells do not contain detectable levels of CPE.…”

“…Thus, although data on CPEdeficient fat mice suggest a role for CPE in gastrin processing (Lacourse et al 1997;Udupi et al 1997), it has never been determined whether CPE is present in these cells. Moreover, fat/fat mice also have perturbed somatostatin levels (Friis-Hansen and Rehfeld 2000).…”

Relative quantitation of peptides in wild‐type and Cpefat/fat mouse pituitary using stable isotopic tags and mass spectrometry

“…22 Fully processed gastrin in the Cpe fat/fat mouse stomach was reported to be decreased by 65% in one study 23 and by 16% in another. 24 Several of these studies examined the levels of C-terminally extended precursors and found relatively high levels of these processing intermediates in the Cpe fat/fat mouse tissues and either little or no detectable levels of these intermediates in wild-type mouse tissues. A limitation of these previous studies is the radioimmunoassay used to detect the peptides.…”

Analysis of the carboxypeptidase D cytoplasmic domain: Implications in intracellular trafficking*

“…These mice lack carboxypeptidase E activity due to a point mutation within the coding region of the gene [Naggert et al, 1995], but are still able to carry out a reduced amount of neuroendocrine peptide processing [Naggert et al, 1995;Fricker et al, 1996;Rovere et al, 1996;Cain et al, 1997;Lacourse et al, 1997;Udupi et al, 1997]. CPD has carboxypeptidase E-like enzyme properties, but differs in several respects.…”