Intracellular transformation of prolactin following internalization into rat liver

• Published in: Molecular and cellular endocrinology Vol. 35; no. 1; pp. 25 - 31
• Main Authors: Ferland, Louis H., Djiane, Jean, Houdebine, Louis-M., Kelly, Paul A.
• Format: Journal Article
• Language: English
• Published: Shannon Elsevier Ireland Ltd 01.04.1984; Elsevier
• Subjects: Animals; Biological and medical sciences; Cell Membrane - metabolism; Chromatography, Gel; Female; Fundamental and applied biological sciences. Psychology; Golgi Apparatus - metabolism; Golgi complex; Growth Hormone - metabolism; hormone-receptor complex; Hormones and neuropeptides. Regulation; Hypothalamus. Hypophysis. Epiphysis. Urophysis; In Vitro Techniques; intracellular receptors; Liver - metabolism; lysosome; Lysosomes - metabolism; Molecular Weight; prelysosome; Prolactin - analysis; Prolactin - metabolism; prolactin processing; Rats; Rats, Inbred Strains; Receptors, Cell Surface - metabolism; Receptors, Prolactin; Vertebrates: endocrinology; prolactin processing; prelysosome; hormone-receptor complex; intracellular receptors; Golgi complex; lysosome; Cell organelle; Rat; Rodentia; Lysosome; Gonadotropin; Biological activity; Golgi apparatus; Processing; Protein hormone; Vertebrata; Mammalia; Hepatocyte; Prolactin; Hormone receptor complex; Intracellular; Hormonal receptor
• DOI: 10.1016/0303-7207(84)90026-1
• ISSN: 0303-7207

We investigated prolactin (PRL) degradation in rat liver lysosomes both in vivo and in vitro. In previous studies we showed that, in addition to the Golgi apparatus, PRL is internalized towards lysosomes and light, lysosome-like vesicles which we identified as ' prelysosomes'. Injected [ 125I]oPRL that localized in lysosomes and prelysosomes at times varying from 0 to 45 min showed significant differences from fresh and plasma membrane- (PM) or Golgi-bound hormone. First, it was more easily dissociable by 3 M MgCl 2 than Golgi- but less than PM-bound [ 125I]oPRL. Second, it was only in lysosomal fractions that, as time following injection increased, a significant part of dissociable radioactivity became non-TAC-precipitable. When MgCl 2-extracted [ 125I]oPRL was subjected to gel filtration on a Sephadex G-75 fine column, some of the radioactivity, and especially that extracted from prelysosomal or lysosomal fractions, eluted as a high molecular weight (HMW) entity, most co-migrated with fresh [ 125I]oPRL, and a little was found in small fragments. Only the central peak had any rebinding activity, which was comparable to that of fresh hormone. In an in vitro study we incubated [ 125I]hGH with lysosomal fractions for 16 h at 25°C. After centrifugation, an aliquot of supernatant hormone was assayed for its binding capacity to standard receptor preparations and the rest subjected to gel filtration. Peak fractions were also tested in binding assay. [ 125I]hGH that had been in contact with prelysosomes lost almost all of its ability to bind to standard receptors and totally migrated in the HMW peak, at the void volume of the column. Hormone incubated with lysosomes bound about 65% as well as the fresh hormone and, correspondingly, 35–40% of the radioactivity was found in the HMW peak and a little as small fragments. It is possible that in lysosomes, and especially in prelysosomes, binding of the hormone to its receptor becomes irreversible and the hormone-receptor complex may become partially solubilized.