Large variations in the proteolytic formation of a chromogranin A-derived peptide (GE-25) in neuroendocrine tissues

Abstract

We have established a radioimmunoassay for GE-25, a peptide present in the C-terminal end of the primary amino acid sequence of chromogranin A where it is flanked by typical proteolytic cleavage sites. Gel-filtration HPLC was used to characterize the molecular sizes of the immunoreactive molecules. The antiserum recognized not only the free peptide but also larger precursors including the proprotein chromogranin A. The tissues with the highest levels of GE-25 immunoreactivity were in decreasing order: the adrenal medulla, the three lobes of the pituitary gland, intestinal mucosa, pancreas and various brain regions. In adrenal medulla and parathyroid gland most of the immunoreactivity was found to be present as intact chromogranin A and some intermediate-sized peptides, without significant amounts of the free peptide. In anterior pituitary, and even more so in intestine, a shift to smaller peptides was seen. In the posterior and intermediate pituitary and in pancreas the predominant immunoreactive material was apparently represented by the free peptide GE-25. In reverse-phase chromatography this peptide eluted exactly like the synthetic standard, which allows a tentative identification as GE-25. In brain tissue the processing of chromogranin A was intermediate, with significant amounts of immunoreactivity corresponding to GE-25 as well as precursor proteins being present. We suggest that in those organs (endocrine pancreas, intermediate and posterior pituitary) where the major hormones are proteolytically processed there is also a concomitant proteolysis of further susceptible peptides. Since GE-25 is apparently formed in vivo and is well conserved between species it seems a good candidate for having specific physiological functions.

Subcellular Localization of Chromogranins, Calcium ChanneAmine Carriers, and Proteins of the Exocytotic Machinery in Bovine Splenic Nerve

“…The following rabbit polyclonal antisera raised against synthetic peptides were used : GE‐25 for chromogranin A (Kirchmair et al, 1995), PE‐11 for chromogranin B (Kroesen et al, 1996), secretoneurin for secretogranin II (Kirchmair et al, 1993), GAIPIRRH for NESP55 (Ischia et al, 1997), peptide 592‐610 for endoprotease PC2 (Egger et al, 1994), C‐terminal end of VMAT2 for VMAT2 (Weihe et al, 1995), and affinity‐purified N434II for the NET (S. Schroeter, S. Apparsundaram, E. Giovanetti, and R. D. Blakely, manuscript in preparation). The antiserum against VAMP was kindly provided by Dr. C. Shone.…”

Chromogranin A in gastric neuroendocrine tumours: an immunohistochemical and biochemical study with region-specific antibodies

“…Various CgA-related peptides have been identified biochemically and they are, from the N-terminal to the C-terminal region of the molecule, vasostatins (amino acid sequences 1-17/113) [6,13], chromostatin (124-143) [10], chromacin [35], pancreastatin (250-301) [36], WE-14 (316-329) [5], catestatin (361-372) [19], parastatin (347-419) [9] and GE-25 (367-391) [15]. The immunohistochemical expression of various CgA epitopes has been shown to vary in different human NE cells and tumours and may be of help in the characterization of some neuroendocrine tumours [22][23][24][25].…”

Presence of chromogranins and regulation of their synthesis and processing in a neuroendocrine prostate tumor cell line

“…These proteases are glycoproteins consisting of soluble and membrane-bound components [5]. The 439 amino-acid chromogranin A is a substrate for the endoproteases PC1 and PC2, and its cleavage leads to the generation of various peptides, such as pancreastatin, ␤-granin, parastatin, vasostatin, and GE-25 [6][7][8][9][10][11]. In chromogranin B, 18 cleavage sites for the enzymes PC1 and PC2 have been identified along the protein chain (657 amino acids), and small peptides are generated by processing at both the N-terminus and C-terminus [12].…”