Characterization of Bursal Anti-steroidogenic Peptide : an Anti-steroidogenic Peptide derived from the humoral immune system of chickens

Abstract

Phenomenological association of alterations of immune system function at the time of puberty (e.g. involution of the chicken bursa of Fabricius) has led to postulation that the humoral immune system may negatively affect the hypothalamo-adenohypophyseal-gonadal axis of the neonate. The effect of an acidic aqueous bursa of Fabricius extract, derived from prepubescent chickens and purified to a single reverse phase HPLC chromatographic peak, on in vitro basal and LH-stimulated progesterone biosynthesis by isolated chicken ovarian granulosa cells was examined. Inhibitory activity was observed with maximal suppression reaching basal levels. Based on ultrafiltration, the bioactive component was determined to be <5kDA and >3kDA. The bioactive component was observed to be heat labile and sensitive to the endopeptidases chymotrypsin, trypsin and papain. The peptide was not sensitive to the exopeptidase aminopeptidase M. Following removal of the peptide, granulosa cells were capable of LH-stimulated progesterone biosynthesis similar to controls. Bursal extract significantly inhibited cAMP analog-stimulated progesterone biosynthesis. Neither activation nor inhibition of protein kinase C were observed to affect the inhibitory activity of bursa of Fabricius extract. This bursa of Fabricius extract was also observed to significantly inhibit either adrenocorticotropin- or cAMP analog-stimulated corticosteroid biosynthesis from adrenocortical cells derived from chickens, pigs and dogs. A small but significant suppression of corticosteroid production was observed in bursa of Fabricius extract-treated canine adrenocortical carcinoma cells in the present experiments. Paradoxically, bursa of Fabricius extract caused significant increases in intracellular cAMP associated with marked anti-steroidogenic effects in either adrenocortical or ovarian cells. These data indicate that the anti-steroidogenic peptide derived from the chicken bursa of Fabricius is a single heat labile, amino-terminally blocked peptide with bioactivity independent of the gonadotropin or adrenocorticotropin receptor. Bursal Anti-steroidogenic Peptide (BASP) has been proposed for the bioactive peptide characterized in these experiments. In vitro, BASP has bioactivity in avian gonadal and adrenocortical cells and causes significant suppression of corticosteroid production from adrenocortical cells of 2 mammalian species. The second messenger pathway utilized by BASP is unknown. Data from the present experiments would indicate that BASP does not inhibit steroidogenesis through interference with intracellular cAMP nor activation of protein kinase C.