The heregulin family of polypeptides arise as splice variants from a single gene and share a conserved epidermal growth factor (EGF)-like domain thought to be the major determinant of their biological activities. We report here the cloning of a novel member of this family, termed sensory and motor neuron-derived factor or SMDF, which is highly expressed in sensory and motor neurons in human and rodent species. It contains a C-terminal beta-type EGF-like domain and an unique N-terminal sequence which lacks an Ig-like domain and is distinct from all known heregulin variants. Mammalian cell-expressed SMDF activates tyrosine phosphorylation of a 185-kDa protein in cell lines expressing p185erbB2, indicating that it is biologically active. Analyses of expression patterns suggest that, unlike other heregulin variants, SMDF is expressed mainly in the nervous system. In situ hybridization signals with the unique SMDF sequence probe and with a probe to the conserved EGF-like domain are comparable, suggesting that SMDF is the predominant isoform expressed in sensory and motor neurons. Expression of SMDF is maintained in both adult motor neurons and dorsal root ganglion neurons. These findings suggest that SMDF may mediate biological responses such as Schwann cell proliferation and acetylcholine receptor induction in the peripheral nervous system.
Relaxin is a member of the insulin family of polypeptide hormones and exerts its best understood actions in the mammalian reproductive system. Using a biologically active 32P-labeled human relaxin, we have previously shown by in vitro autoradiography specific relaxin binding sites in rat uterus, cervix, and brain tissues. Using the same approach, we describe here a detailed localization of human relaxin binding sites in the rat brain. Displaceable relaxin binding sites are distributed in discrete regions of the olfactory system, neocortex, hypothalamus, hippocampus, thalamus, amygdala, midbrain, and medulla of the male and female rat brain. Characterization of the relaxin binding sites in the subfornical organ and neocortex reveals a single class of high-affinity sites (Kd = 1.4 nM) in both regions. The binding of relaxin to two of the circumventricular organs (subfornical organ and organum vasculosum of the lamina terminalis) and the neurosecretory magnocellular hypothalamic nuclei (i.e., paraventricular and supraoptic nuclei) provides the anatomical and biochemical basis for emerging physiological evidence suggesting a central role for relaxin in the control of blood pressure and hormone release. We conclude that specific, high-affmity relaxin binding sites are present in discrete regions of the rat brain and that the distribution of some of these sites may be consistent with a role for relaxin in control of vascular volume and blood pressure.Relaxin belongs to the insulin family of polypeptide hormones and is best known for its biological activities on various parts ofthe mammalian reproductive system, notably elongation of the public ligament, inhibition of uterine contraction, and softening of the cervix (for reviews, see refs. 1 and 2). The effects of relaxin on nonreproductive tissues remain to be established (2).The biological actions of relaxin are probably mediated through specific receptors located on the target cells. Receptors for relaxin have previously been partially characterized in rat and porcine uterine and porcine cervical membranes by using 125I-labeled porcine relaxin (3-5). Using a biologically active 32P-labeled human relaxin (32P-relaxin), we have shown by ligand autoradiography specific relaxin binding sites in rat uterus, cervix, and brain (6). In this paper, we describe the localization and partial characterization of 32p-relaxin binding sites in the rat brain and discuss the physiological implications of these findings. MATERIALS AND METHODSMaterials. Synthetic human relaxin was supplied by E. Rinderknecht (Genentech). It was active in the mouse pubic symphysis assay (7) and a cAMP bioassay (6,8). The concentration of relaxin was determined by amino acid analysis. Human insulin (Humulin) was obtained from Eli Lilly. Synthetic human angiotensin II and atrial natriuretic peptide were obtained from Sigma. Rat nerve growth factor was from Biomedical Technologies (Stoughton, MA).Phosphorylation of Relaxin. Phosphorylation of relaxin with the catalytic subunit of cAMP-dependent pro...
Relaxin is a member of the insulin family of polypeptides that is best known as a reproductive hormone. In an effort to elucidate the mechanism of action of relaxin we previously localized the specific binding sites of a 32P-labeled relaxin in the rat uterus and brain. These studies suggested that, in addition to its classical role in pregnancy, relaxin might have other physiological functions. In the present paper we describe the specific and high-afminity binding of relaxin to the cardiac atrium of both male and female rats. The relaxin binding could not be displaced by peptides belonging to the same family [insulin, insulin-like growth factor I (IGF-I)] or by peptides that were identified in the atrium or were known to have cardiovascular functions (atrial natriuretic peptide, angiotensin II). The dissociation constant for relaxin in the atrium was estimated to be 1.4 nM, which was similar to that found in the uterus (1.3 nM) and the brain (1.4 nM). In view of the close association of relaxin with reproduction, an experiment was also performed to compare the relaxin binding in the uterus and heart after gonadectomy and sex steroid treatment. It was found that the relaxin binding in the rat uterus was diminished by 53% overall following ovariectomy but was restored to 90% of normal levels when treated with estrogen (but not with testosterone). In contrast, the relaxin binding in the rat heart was not affected by castration or sex steroid treatment. We conclude that specific and high-affinity relaxin receptors exist in the atrium of both the male and female rat heart and that these are regulated differently than the relaxin receptors in the uterus.Relaxin is structurally related to insulin and insulin-like growth factors and is best known as a pregnancy-associated hormone (1, 2). In addition to its classical actions on cervical ripening, uterine contraction, and pubic symphysis elongation (1, 2), relaxin has been suggested to participate in the regulation of blood pressure (3-8) and neuropeptide release, notably oxytocin and vasopressin (9-13). However, the results from these studies were conflicting, and the site of action of relaxin was undetermined. Biochemical support for these hypotheses was provided when it was shown that, in addition to the uterus and cervix (14), relaxin bound with specificity and high affinity (Kd 1 nM) to several sites in the male and female rat brain (15). Some of these sites, in particular two of the circumventricular organs (subfornical organ and organum vasculosum of the lamina terminalis) and the magnocellular hypothalamic nuclei (paraventricular and supraoptic nucleus) are known to be involved in the control of blood pressure, fluid balance, and the release of neuropeptides. To further investigate the mechanism of action of relaxin, we continued the search for relaxin target tissues and were surprised to observe the specific and high-affinity binding of relaxin to the atrium of the rat heart. We also show that the atrial binding is regulated differently than the uterus. ...
Within 2 min following the intravenous injection of sheep erythrocytes (sRBC) there occurs 20 to 80-fold increase in prostaglandin (PG) F2alpha in the spleen. This burst of synthesis is followed by a slow decline to control levels over the next 1-4 hr. No increase in splenic PGF2alpha levels is observed between 24 and 72 hr after injection. Injection of colloidal carbon results in a small increase, approximately 20% of the increase in PGF2alpha observed with sRBC. The early increase in splenic PGF2alpha levels stimulated by sRBC is also dependent upon thymus-derived (T) cells, since the increase is small or nonexistent in athymic mice and NZB mice. Also, the elevation of splenic PGF2alpha levels is blocked by the administration of indomethacin or Ro 20-5720, both of which block the synthesis of prostglandin. A small increase (2-fold) in PGF2alpha levels occurs in the thymus. A soluble antigen, bovine gamma globulin, stimulated a bimodal increase in splenic PGF2alpha levels, the early peak occurring at 2 hr and the later increase occurring at 48 hr. Using inhibitors of prostaglandin synthesis, it is possible to enhance the appearance of cells forming 19S antibody against sRBC, both in vivo and in vitro. Furthermore, inhibition of prostaglandin synthesis enhances DNA synthesis induced in a two-way mixed-lymphocyte reaction only in whole spleen cell cultures and not in cultures of spleen cells purified by passage over glass wool. Based on this evidence, it is proposed that the prostaglandins represent a major soluble mediator in the control of T cell-T cell interactions and also play an important part in T-B (bone-marrow derived) cell interactions.
Relaxin is known for its function in parturition and has been suggested to participate in the regulation of blood pressure, heart rate, and the release of neuropeptides such as oxytocin and vasopressin. Consistent with the physiological roles of relaxin, high affinity relaxin receptors have been demonstrated in the rat uterus, brain, and cardiac atrium. Here we report the binding and cross-linking of a biologically active, 32P-labeled human relaxin to a human uterine cell line and primary rat atrial cardiomyocytes. Relaxin binding to the human uterine cells consisted of a single class of high affinity sites (Kd = approximately 0.44 nM) with approximately 1082 +/- 62 binding sites/cell. Binding and cross-linking of relaxin to the human uterine cells and rat atrial cardiomyocytes followed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis revealed that the putative relaxin receptor showed a major component with an apparent M(r) greater than 220 kilodaltons and a minor component of approximately 36 kilodaltons, and was not disulfide linked. The binding and cross-linking of [32P]relaxin could be displaced by unlabeled relaxin in a concentration-dependent manner, but not by a 1000-fold molar excess of insulin, insulin-like growth factor I (IGF-I), or IGF-II. These data suggested that the relaxin receptor was similar in size but distinct from the insulin, IGF-I, and IGF-II receptors.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.