Relative amounts and molecular forms of NESP55 in various bovine tissues

NESP55 (neuroendocrine secretory protein with Mr 55,000) comprises a novel chromogranin-like protein, which is paternally imprinted at the genomic level. We used antisera raised against GAIPIRRH, a peptide present at the C-terminus of this protein, and against TC-14, a peptide located in the N-terminal half of NESP55. Radioimmunoassay, gel-filtration chromatography and immunoblotting were used to determine the levels and the molecular forms of NESP55 in different bovine organs. The tissues with the highest levels of GAIPIRRH immunoreactivity were, in decreasing order: the adrenal medulla, the anterior pituitary, the posterior pituitary, various brain regions, and the intestine. The degree of proteolytic processing revealed differences among the tissues analyzed. The lowest processing was detected in the anterior pituitary and in the brain where only a peak corresponding to the intact precursor was present. This was also true for cerebrospinal fluid (CSF). In the posterior pituitary and in the intestine, the free peptide GAIPIRRH was the predominant molecular form. GAIPIRRH-IR, as in the CSF, is present in serum mainly as an intact precursor. A relatively high concentration of GAIPIRRH-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 other chromogranins, becomes proteolytically processed. The function of this new chromogranin-like protein, therefore, might be to represent a precursor of biologically active peptides.