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Effect of POMC1–76, its C‐terminal Fragment γ 3‐MSH and Anti‐POMC1–76 Antibodies on DNA Replication in Lactotrophs in Aggregate Cell Cultures of Immature Rat Pituitary
Author(s) -
Tilemans Diane,
Ramaekers Dirk,
Denef Carl
Publication year - 1997
Publication title -
journal of neuroendocrinology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.062
H-Index - 116
eISSN - 1365-2826
pISSN - 0953-8194
DOI - 10.1046/j.1365-2826.1997.d01-1130.x
Subject(s) - prolactin cell , prolactin , endocrinology , medicine , polyclonal antibodies , biology , receptor , cell culture , somatotropic cell , microbiology and biotechnology , pituitary gland , antibody , hormone , chemistry , immunology , genetics
Treatment of aggregate cell cultures of 14‐day‐old rat pituitary for 40 h with purified human (h) POMC 1–76 dose‐dependently augmented the number of DNA replicating lactotrophs as estimated by autoradiography of []> 3 H]‐thymidine ( 3 H‐T) incorporation in cells immunostained for prolactin (PRL). No such effect was seen on the total number of 3 H‐T labelled cells (the majority of which did not contain any pituitary hormone in a detectable amount) or on the total number of lactotrophs. The effect of hPOMC 1–76 on 3 H‐T incorporation in lactotrophs was blocked by concomitant treatment with anti‐hPOMC 1–76 monoclonal and polyclonal antibodies cross‐reactive with rat POMC 1–74 . The latter anti‐hPOMC 1–76 antibodies also decreased the number of 3 H‐T incorporating lactotrophs in the absence of hPOMC 1–76 . γ 3‐MSH, which is the C‐terminal domain of hPOMC 1–76 , mimicked the effect of hPOMC 1–76 on 3 H‐T incorporation in lactotrophs but its potency was lower than that of hPOMC 1–76 . Other melanocortin (MC) peptides such as α ‐ and β ‐MSH were also effective but were less potent than γ 3‐MSH. The difference in potency was not due to partial degradation of the peptides. hPOMC 1–76 did not affect 3 H‐T incorporation in other pituitary cell types. In contrast γ 3 ‐MSH also augmented the number of 3 H‐T labelled somatotrophs and thyrotrophs. In the embryonic kidney 293 cell line stably transfected with the MC‐3 receptor, γ 3‐MSH (10 nM) augmented cAMP formation up to 30 times. In contrast, hPOMC 1–76 (100 nM) was inactive in this test system, indicating this peptide is not an agonist at the MC‐3 receptor. The present investigation further supports the role of rat POMC 1–74 as a paracrine growth factor in the development of lactotrophs. The active core of POMC 1–76 does not seem to be restricted to its C‐terminal domain γ 3‐MSH as the latter peptide displays a growth promoting effect that is different from that of POMC 1–76 : it is less potent, it is not specific for lactotrophs and whereas the effect of γ 3‐MSH may be mediated by the MC‐3 receptor that of POMC 1–76 is not.