The presence and in vivo biosynthesis of fragments of CPP (the C-terminal glycopeptide of the rat vasopressin precursor) in the hypothalamo-neurohypophyseal system

Abstract

SEGER, M. A. AND J. P. H. BURBACH. The presence and in vivo biosynthesis of fragments of CPP (the C-terminal glycopeptide of the rat vasopressin precursor) in the hypothalamo-neurohypophyseal system. PEP'rIDES 8(5) 757-762,1987.--The existence and rate of formation of fragments of the 39-residue C-terminal glycopeptide of propressophysin (CPPI-aa) was investigated in the hypothalamo-neurohypophyseal system. Newly-prepared antisera to CPP were used to confirm the existence of smaller C-terminal fragments derived from CPPI-sg. Radiolabelled fucose was injected into rats in vivo into the area of the supraoptic nucleus, and the labelled peptides formed in the neurohypophysis were examined at various time intervals up to five weeks after the injection. The products derived from the neurohypophyseal hormone precursors were separated by high-performance liquid chromatography. The level of the major immunoreactive C-terminal fragment (CPP22-a~) was constant and represented about 5% of the intact CPP1_39 in the neurohypophysis. The appearance of newly-synthesized N-terminal fragment of CPP1-39 occurred only after 3 or 4 days. This fucose labelled fragment increased slowly thereafter until it reached the same level as the CPP C-terminal fragment immunoreactivity between 21 and 28 clays after injection. The results suggest that CPPI-z9 is extremely stable in the hypothalamo-neurohypophyseal neurons, and that the cleavage at Arg2~-Leu22 is a delayed proteolytic event in the magnocellular neurons of the SON. . These studies suggested the existence of two distinct neurophysins (NPI and NPID cosynthesized in the precursor proteins with oxytocin (OT) and vasopressin (VP) respectively, and the existence of a unique giycopeptide in propressophysin. In both precursors, OT or VP are located at the extreme N-terminus and are followed by their respective neurophysins beginning in position 13. The location of the giycopeptide at the C-terminus of the vasopressin precursor (and hence the name CPP for C-terminal peptide of propressophysin) was confirmed by the cDNA sequence analysis of the RNAs encoding the two precursors from the bovine hypothalamus [12,13].

Mass spectrometric charting of bovine posterior/intermediate pituitary peptides.

“…Full-length CPP has been reported to stimulate the release of prolactin (40). Biological activity of the CPP fragments may also be anticipated because their in vivo biosynthesis has recently been shown for the rat (41,42) [CPP (1-19/20) and CPP (22-37/39)]. By analogy, the bovine counterparts found in this study are likely to be processing products rather than artifacts of the isolation procedure.…”

Removal of PSA from NCAM affects the survival of magnocellular vasopressin‐ and oxytocin‐producing neurons in organotypic cultures of the paraventricular nucleus

“…Vasopressin was also localized with a rabbit antiserum against the C‐terminal glycopeptide (GP) of the vasopressin precursor molecule (gift from M. Seger, dilution 1 : 100). This antibody has been previously characterized (Seger & Burbach, 1987). A similar staining pattern was obtained inside the explants with these two antibodies.…”

Electron microscopic and immunocytochemical study of rapidly frozen, freeze-substituted neural lobes of rats

“…Its staining in tissue is removed with prior absorption to either purified human or bovine NP. The C3 antiserum was raised against synthetic CPP22-3,) and recognizes its C-terminus (Seger & Burbach, 1987). This antiserum showed no cross-reactivity with VP, OT, or their respective NPs in liquid phase assay.…”