Relative amounts and molecular forms of NESP55 in various bovine tissues

NESP55 (neuroendocrine secretory protein with M-r 55,000) comprises a novel chromogranin-like protein, which is paternally imprinted at the genomic le vel. We used antisera raised against GAIPIRRH, a peptide present at the C-t erminus of this protein, and against TC-14, a peptide located in the N-term inal half of NESP55. Radioimmunoassay, gel-filtration chromatography and im munoblotting were used to determine the levels and the molecular forms of N ESP55 in different bovine organs. The tissues with the highest levels of GA IPIRRH immunoreactivity were, in decreasing order: the adrenal medulla, the anterior pituitary, the posterior pituitary, various brain regions, and th e intestine. The degree of proteolytic processing revealed differences amon g the tissues analyzed. The lowest processing was detected in the anterior pituitary and in the brain where only a peak corresponding to the intact pr ecursor was present. This was also true for cerebrospinal fluid (CSF). In t he posterior pituitary and in the intestine, the free peptide GAIPIRRH was the predominant molecular form. GAIPIRRH-IR, as in the CSF, is present in s erum mainly as an intact precursor. A relatively high concentration of GAIP IRRH-IR was found in the kidney medulla, probably due to an endocytotic re- uptake of this molecule from the tubuli after filtration in the glomeruli. The present study is consistent with the concept that NESP55, like the othe r chromogranins, becomes proteolytically processed. The function of this ne w chromogranin-like protein, therefore, might be to represent a precursor o f biologically active peptides. (C) 1999 Elsevier Science B.V. All rights r eserved.