Submitted to: Journal of Endocrinology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/31/2002
Publication Date: N/A
Citation: Interpretive Summary: We identified glandular kallikrein (GK), an enzyme potentially capable of processing prolactin into biologically active compounds, in the carp, Cyprinus carpio. Using antibody against bass GK, kallikrein-related proteins were found in the gills, kidney, and pituitary gland of the carp. The enzyme was present in intermuscular cells, in cells lining the gills, and in specific cells in the pituitary gland. The presence of GK in these tissues suggests a function for this enzyme in maintaining osmotic (water) balance within the tissues of the carp. Prolactin, a protein hormone, was found in three sizes in the pituitary gland and in fish plasma. The presence of prolactin and GK in the same tissues within the pituitary gland suggests that GK may be required to process prolactin into more biologically active forms. The addition of estrogen to male carp during the winter months caused an increase in the levels of prolactin, but there was no change in the levels of GK in the gills or muscle tissue of estrogen-treated fish. There was a substantial increase in the levels of GK and prolactin in the kidneys.
Technical Abstract: We examined glandular kallikrein (GK), a putative prolactin processing protease, in the carp, Cyprinus carpio. When employing an anti-Centropristis striata GK antibody, proteins of 39 kDa in muscle, 52 kDa in gill, 52 kDa in kidney and two proteins of 46 and 72 kDa in the pituitary gland were detected. Immunoreactive kallikreins were recognized in intermuscle cell tissue, epithelial gill cells, apical regions of tubular cells and prolactin producing lactotrophs in the pituitary gland, suggesting an osmoregulatory role for this enzyme. We found three prolactin (PRL) variants using anti-tilapia PRL antibodies, in pituitary gland 23 kDa and 16 kDa, and in plasma 23 kDa and 22 kDa forms. Co-localization of GK and PRL in lactotrophs might indicate involvement in PRL processing to specific forms in the circulation. In winter-acclimatized male carp, where the pituitary PRL level is low, 17-beta estradiol treatment increased PRL but not GK immunoreactivity. In contrast to GK and PRL co-regulation by estrogen in mammalian pituitary gland, no similar effect on immunoreactive PRL and GK was observed in the ichtyc pituitary. No changes in GK immunostaining occurred in gill or muscle tissue in response to estrogen treatment. These results, taken with the observation of significantly increased GK immunoreactivity in the apical region of kidney tubular cells in estrogen-treated male carp, indicate that the regulation of GK expression in the pituitary and kidney could be different between fish and mammals. The regulation of GK levels may be through a process of proenzyme activation in fish pituitary, gill, and muscle tissues.