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Search for other papers by J Finidori in
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Introduction
Cytokines are chemical mediators that include interleukins, polypeptide hormones and other growth factors. They regulate growth, differentiation and specific cellular functions by interacting with their cognate receptors. Cytokine receptors, which contain no tyrosine kinase domain in their cytoplasmic regions, have been grouped into different classes (Bazan 1990, Kitamura et al. 1994). The haematopoietic or cytokine/growth hormone/prolactin receptor family (Class I) and the interferon family (Class II) share both structural features and newly identified common signal transduction pathways. In the last 2 years, it has been demonstrated that both classes of receptors are associated with various members of the Janus kinase (JAK) family and activate a new family of transcription factors that couple ligand binding to the activation of gene expression and are thus termed signal transducers and activators of transcription (STATs) (Shuai et al. 1993a).
Structure of cytokine receptors
Class I and Class II cytokine receptors appear to
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Abstract
The expression of mRNA encoding the long and short forms of the prolactin receptor (PRLR) in the fetal rat was examined using the method of reverse transcription-PCR. A 742 bp PCR product encoding the extracellular and transmembrane domains of the PRLR was detected in maternal and fetal liver and in fetal adrenal, kidney, small intestine, pancreas, brain, pituitary, thymus, lung and skin but not in fetal heart. Highest levels of the 742 bp PRLR transcript were detected in fetal adrenal (45·2% of levels in maternal liver), kidney (27·2%), small intestine (21·7%), pancreas (18·3%) and liver (10·8%), and tissue levels of the 742 bp product correlated positively (r=0·92, P<0·01) with the specific binding of the fetal lactogenic hormone rat placental lactogen II (rPL-II). These findings suggest that the PRLR may serve as a physiological binding protein for rPL-II in the rat fetus. There were striking differences in the relative expression of mRNA encoding the long and short forms of the PRLR. The long form of the receptor was expressed in maternal liver and placenta and in all fetal tissues studied except fetal heart. The short form of the receptor was also detected in maternal liver and placenta and fetal adrenal, kidney, small intestine, liver and thymus; in contrast, there was limited expression of the short-form of the receptor in fetal pancreas, pituitary and brain and no short form transcripts were detected in fetal lung, skin or heart. The results of these studies indicate widespread expression of the rat PRLR in fetal and uteroplacental tissues, implicating diverse roles for the placental prolactin-like proteins in fetal development.
Journal of Endocrinology (1995) 144, 285–292
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Abstract
Previous reports demonstrated that prolactin receptors (PRL-R) are widely expressed on cells of the immune system. We analyzed a possible regulation of PRL-R expression on human mononucleated blood cells by prolactin (PRL) itself. PRL-R expression was analyzed by immunofluorescence on T and B lymphocytes and monocytes from peripheral blood mononucleated cells (PBMC) of patients with hyperprolactinemia or acromegaly compared with sex- and age-matched control subjects. The frequency of PRL-R positive cells and the intensity of PRL-R expression was only modified among the CD8+ T cell population of hyperprolactinemic patients with macroadenoma. No correlation was reported between PRL-R expression and circulating PRL levels. The percentage of PRL-R+ cells on B or T lymphocytes and monocytes as well as the capacity of PBMC to proliferate in response to T cell mitogens were not significantly different in bromocriptine-treated compared with untreated patients. These findings suggest that factors other than pituitary PRL play the major role in regulating PRL-R expression on cells of the immune system.
Journal of Endocrinology (1995) 147, 353–359
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Search for other papers by P. A. KELLY in
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SUMMARY
Radioreceptor assays for prolactin-like (lactogenic) activity and growth hormone (GH)-like activity have been used to study concentrations of caprine placental lactogen (PL) in the circulation during pregnancy. Both lactogenic and GH-like activities increased from less than 100 ng/ml (ovine prolactin- and human GH-equivalents) about 60 days after mating to reach peak levels (400–1600 ng/ml) between days 110 and 130 of pregnancy. The levels of both activities increased in essentially the same fashion but during the last 15 days of pregnancy, lactogenic activity declined less than GH-like activity. This divergence was most pronounced at parturition when levels of lactogenic activity increased (∼ 700 ng/ml) despite very low (< 200 ng/ml) levels of GH-like activity being measured and this probably reflected increased secretion of pituitary prolactin near parturition. When serum from a pregnant goat or a simple alkaline extract of placental cotyledons was fractionated on a column packed with Sephadex G-100, lactogenic and GH-like activities eluted together with distribution coefficients of approximately 0·5–0·6. The possibility that caprine PL serves physiologically as a luteotrophin and/or mammotrophin during pregnancy in goats is discussed.
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Abstract
The red deer is a seasonally breeding mammal with a circannual cycle of prolactin secretion which reaches its peak during the non-breeding season. This study investigated expression of the prolactin receptor gene in red deer tissues collected in the breeding and non-breeding seasons. A 562 bp fragment of the extracellular domain of the red deer prolactin receptor cDNA was amplified from red deer liver poly(A)+ RNA by reverse transcriptase-polymerase chain reaction (RT-PCR) using primers designed from the human sequence. Northern blots were prepared using 10–20 μg poly(A)+ RNA. The blots were hybridized to the 562 bp cDNA labelled by random priming with α32P-dCTP. A main transcript of 3·5 kb was expressed in liver, heart, kidney and testis throughout the year and in epididymis during the breeding season only. In the testis an additional major transcript of 1·7 kb was present during the breeding and non-breeding seasons. Competitive binding assays using 125I-ovine prolactin (125I-oPRL) were performed on microsomal membrane fractions prepared from liver. Scatchard analyses confirmed the presence of a single class of lactogen-binding receptor with a mean Ka of 0·87 ± 0·12 × 109 m −1 and a Bmax of 73·6 ± 9·8 fmol/mg protein (n=5). Cross-linking of 125I-oPRL to liver microsomes with 0·5 mm disuccinimidyl suberate followed by SDS-PAGE revealed a major band of molecular mass 56 kDa which was displaced by ovine prolactin, suggesting a specific lactogen-binding entity of 33 kDa. This study confirms the expression of the red deer prolactin receptor gene throughout the year, characterizes the prevalent form of receptor in the liver and demonstrates the expression of a separate, short form in the testis.
Journal of Endocrinology (1995) 146, 313–321
