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M J Waters

Publications and source records attributed to M J Waters.

At least 91 records · Page 5Linked to original sources
PubMed1994

Signal transduction by the growth hormone receptor.

It has been proposed that dimerization of identical receptor subunits by growth hormone (GH) is the mechanism of signal transduction across the cell membrane. We present here data with analogs of porcine GH (pGH), with GH receptors (GHR) mutated in the dimerization domain and with monoclonal antibodies to the GHR which indicate that dimerization is necessary but not sufficient for transduction. We also report nuclear uptake of GH both in vivo and in vitro, along with nuclear localization of the receptor and GH-binding protein (GHBP). This suggests that GH acts directly at the nucleus, and one possible target for this action is a rapid increase in transcription of C/EBP delta seen in 3T3-F442A cells in response to GH. This tyrosine kinase-dependent event may be an archetype for induction of other immediate early gene transcription factors which then interact to determine the programming of the subsequent transcriptional response to GH.

Animals↗
PubMed1994

Serum growth hormone binding protein and hepatic GH binding sites in the Lewis dwarf rat: effects of IGF-I and GH.

A radioimmunoassay (RIA) for the rat growth hormone binding protein (GHBP) was developed using a synthetic peptide (corresponding to the hydrophilic carboxyl-terminal sequence of mouse GHBP) as standard and a monoclonal antibody (MAb 4.3) reactive with this peptide as the primary antibody. The values for GHBP concentration obtained for normal rats using this assay compare favourably with those obtained by gel filtration and ELISA methods. The concentration of GHBP in normal male rats at 11 weeks of age (680 +/- 30 ng/ml, SEM, n = 9) was significantly less than the concentration in normal females (943 +/- 47 ng/ml, SEM, n = 25). In 11-week-old dwarf male rats the concentration of GHBP was 423 +/- 35 ng/ml (n = 8); less than in dwarf females (542 +/- 32, P < 0.05, n = 9) and normal males (680 +/- 30, P < 0.001, n = 9). The GHBP concentration in dwarf rats was not age-dependent, whereas in normal females the concentration of GHBP increased with age. The availability of an RIA which is not susceptible to interference by endogenous GH, will facilitate further studies on hormonal and nutritional regulation of the rat GHBP. The assay was applied to studying the effects of IGF-I infusion (240 micrograms/day for 1 week) and GH injection (65 micrograms/100 g body weight, twice daily for 1 week and 4 weeks) on the serum concentration of GHBP in 11-week-old Lewis dwarf rats. Hepatic GH binding sites were also measured in desaturated membranes from the same animals.(ABSTRACT TRUNCATED AT 250 WORDS)

Aging↗
PubMed1994

Insulin-like growth factor-I receptor in the cell biology of the ameloblast: an immunohistochemical study on the rat incisor.

The distribution of IGF-I receptor is reported in the odontogenic epithelium and mesenchyme of the continuously erupting mandibular incisor of the rat by immunohistochemistry using a polyclonal antibody specific to the IGF-I receptor. Odontogenic epithelium is a unique odontogenic sequence in that all stages of the complex life cycle of the ameloblast are represented along the length of the enamel-forming aspect of the tooth. Pre-ameloblasts become post-mitotic before secreting enamel matrix. When the full thickness of the enamel has been formed, a remarkable transition in phenotype takes place in the ameloblast. It changes from a protein secretory cell to one active in maturation of enamel matrix by removal of water and protein from the increasingly mineralized matrix. The distribution and intensity of IGF-I receptor expression varied with the phenotypic stages of the ameloblasts. Diffuse cellular staining for IGF-I receptor was found during the active secretory phase of amelogenesis. However, towards the end of this phase, the staining was confirmed to granular or vesicular structures within the cytoplasm. These granular deposits gradually decreased as the ameloblasts made the transition towards enamel maturation. This transition is accompanied by programmed cell death (apoptosis) of approximately 25% of the ameloblasts and cells in this zone did not stain for IGF-I receptor. With the onset of enamel maturation, diffuse staining of the ameloblast layer was re-established gradually and staining remained evident right up to the reduced enamel epithelium, which joins with the oral epithelium. Strong IGF-I receptor immunoreactivity was observed in the stratum basale and stratum spinosum of the adjacent labial gingival epithelium.(ABSTRACT TRUNCATED AT 250 WORDS)

Ameloblasts↗
PubMed1993

Localization and ontogeny of growth hormone receptor gene expression in the central nervous system.

There is literature evidence that both growth hormone (GH) and its mediator, insulin-like growth factor 1 (IGF-1), are able to act upon neuronal and glial cells in the brain. We report here the location of the GH receptor in the brain of the rat and rabbit. Receptor distribution was determined by immunohistochemistry with GH receptor/binding protein (BP) specific monoclonal antibodies and by in situ hybridization with a [35S]riboprobe. GH receptor/BP immunoreactivity in the rat was most prominent in the neonate and declined with postnatal age. Receptor immunoreactivity was generalised with variation in immunoreactivity in regional areas. In the rat, strongest immunoreactivity was seen in layers 2, 3, 5 and especially layer 6 of the cerebral cortex, in neurones of the thalamus and hypothalamus, in Purkinje cells of the cerebellum, in neurones of the trapezoid body of the brainstem, and in retinal ganglion cells. Glial cells, notably astrocytes were also strongly reactive, along with ependyma of the choroid plexus, ventricular lining and pia mater. In the neonatal rabbit, strongest immunoreactivity was evident in layers 2 and 3 of the cerebral cortex, in pyramidal cells of the hippocampus, and in neurones of the inferior and superior colliculi, brain stem reticular formation, dorsal thalamus and hypothalamus. A similar distribution of GH receptor mRNA was seen by in situ hybridization. The ontogeny of GH receptor/BP mRNA in whole rat brain was quantified by solution hybridization-RNAse protection assay. Contrary to its ontogeny in the liver (Endocrinology, 113 (1983) 1325-1329) receptor mRNA decreased with postnatal age.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1993

A bromodeoxyuridine immunocytochemical and morphometric study of the influence of growth hormone on cell proliferation in odontogenic mesenchyme of the Lewis dwarf rat.

Cell proliferation was studied in pre-odontoblasts, and in cells of the dental papilla and lingual dental follicle using bromodeoxyuridine immunocytochemistry and morphometry in Bouin's perfused and paraffin-embedded, undemineralized maxillary incisors. Cells in DNA synthesis, as shown by this technique, or in mitosis, were counted. Significantly fewer labelled nuclei, unlabelled nuclei and total nuclei were found in the tissues of growth hormone-deficient dwarf rats than in normal tissues. However, in dwarf rats treated for 6 days with bovine growth hormone, their numbers were equivalent to, or in some instances greater than those in normal tissues. The bromodeoxyuridine labelling index, the ratio of positive to negative nuclei and the mitotic index of pre-odontoblasts in dwarf rats were consistently lower than in normal rats, and were reversible by growth hormone. Growth hormone thus plays a part in odontogenic mesenchymal proliferation.

Ameloblasts↗
PubMed1993

Different modes of growth hormone (GH) administration do not change GH binding protein activity in man.

OBJECTIVE: Studies in rodents have shown GH binding protein (GHBP) levels to be dependent on the mode of GH administration. The aim is to determine whether GHBP levels in man are also modulated by the pattern of GH administration. PATIENTS: Six GH deficient subjects participated in a randomized study in which 2 IU GH were administered either as (i) a continuous 24-hour infusion, (ii) two intravenous boluses or (iii) eight intravenous boluses every 3 hours. In a second study, six normal men received a single subcutaneous injection of 0.2 U/kg GH and GHBP activity was measured over 24 hours. Control data were obtained from an untreated group of six age-matched normal men. MEASUREMENTS: GHBP activity was measured by immunoprecipitation using a monoclonal antibody that recognizes the human GHBP, and expressed as percentage specific binding of 125I-GH in 50 microliters of serum. RESULTS: GHBP activity was not significantly different between the GH deficient and normal subjects. GHBP activity did not rise significantly during GH administration with each of the three intravenous patterns of delivery nor were there any significant differences between treatments. In the second study, GHBP activity did not change significantly following subcutaneous GH injection nor did results differ from untreated normal controls. CONCLUSIONS: The level of GHBP in man is not dependent on GH secretory status or altered by short-term GH treatment or the mode of administration. These findings stand in contrast to GH treatment effects in rodents and suggest that GH regulation of GHBP may be different between species.

Adult↗
PubMed1993

Regulation of growth hormone binding protein in man: comparison of gel chromatography and immunoprecipitation methods.

GH circulates in part bound to a high affinity binding protein (GHBP). Gel chromatography is the established method for measuring GH binding activity in plasma, but is slow and tedious. The separation of bound from free GH by immunoprecipitation using a monoclonal antibody to the GH receptor may be a more practical alternative. We have examined the effects of GH and estrogen status on GHBP measured in 24-h pool samples and compared results obtained from gel filtration and immunoprecipitation. GHBP activity (percent specific binding of [125I]GH) was measured in normal, GH-deficient, and acromegalic subjects; and in two groups of postmenopausal women before and after oral (ethinyl estradiol 20 micrograms daily) or transdermal (17 beta-estradiol 100 micrograms daily) estrogen therapy. GHBP activity was not significantly different between normal, GH-deficient, and acromegalic subjects matched for age and sex. Neither GH administration to GH-deficient and normal subjects, nor octreotide treatment of patients with acromegaly, significantly altered GHBP activity. Oral estrogen treatment significantly increased GHBP activity. This change was associated with an increase in binding capacity (P = 0.001) but not affinity, as revealed by Scatchard analysis. GHBP activity did not change significantly with transdermal estrogen therapy. GHBP activity obtained by the two methods was significantly correlated (n = 70, r = 0.92, P = 0.001) although values for the antibody method were 25% higher. Similarly, capacity estimates were highly correlated (r = 0.90, P = 0.0001), with values by immunoprecipitation being 40% higher. We conclude that GH secretory status is not a determinant of GHBP. Oral estrogens increase GHBP activity through an increase in capacity and not affinity. The estrogen effect is route dependent and the oral response is likely to reflect a first pass hepatic effect. The higher binding activity and capacity estimated from immunoprecipitation are likely to reflect a more rapid separation process thereby minimizing dissociation of GHBP complex. Immunoprecipitation offers the advantages of simplicity, convenience, and accuracy for the measurement of GH binding activity and GHBP concentrations in serum.

Acromegaly↗
PubMed1993

Growth hormone (GH) receptors are expressed on human fetal mesenchymal tissues--identification of messenger ribonucleic acid and GH-binding protein.

The role of GH in the fetus remains unclear, in spite of high circulating levels. In order to determine potential sites of action of GH in the human fetus, we have used a combination of immunocytochemistry and northern blotting to examine human fetal tissues for GH receptor or binding protein and its messenger RNA. Human fetal abortus tissues of 15-20 weeks gestation were obtained for sternum and skin. Decalcified paraffin sections, were prepared for immunostaining with a monoclonal antibody to the GH receptor or control antibodies. Chondrocytes were digested from sternum and costal cartilage for primary culture in monolayers for up to 14 days. Skin fibroblasts were similarly cultured and studied at passages 5-10. Polyadenylated mRNA was prepared from cultured chondrocytes and fibroblasts for subsequent northern blotting with a complementary DNA probe to the hGH receptor. Positive immunostaining for GH receptor was seen in growth plate, including chondrocytes in the proliferative and hypertrophic zones, perichondrium, osteoblasts, and erythroid precursor cells. GH receptor immunostaining was also seen in skin sections throughout epidermis, including sebaceous and sweat glands, and vessels and fibroblasts in the dermis. Cultured chondrocytes showed patchy staining, with colonies of immunopositive cells proliferating in culture. Skin fibroblasts showed uniform GH receptor immunostaining. Control sections and cultured cells did not stain. Cultured chondrocytes showed specific binding of 125I-hGH(1-3%), with a typical displacement curve for GH receptor. As for immunostaining, binding increased with time in culture. Finally, northern blotting revealed a single 5.1 kilodalton band representing GH receptor mRNA in both chondrocytes and skin fibroblasts. This study has demonstrated the presence of GH receptor protein and mRNA on human fetal tissues including growth plate chondrocytes and osteoblasts, as well as skin epidermal structures and dermal fibroblasts. These receptors are capable of binding hGH, raising the possibility that, in contrast to current dogma, GH receptors play a functional role in the human fetus by 15 weeks gestation.

Antibodies, Monoclonal↗
PubMed1993

Prolactin receptor expression in the gastrointestinal tract: characterization of the prolactin receptor of gastric mucosa.

There is evidence that prolactin (PRL) influences gastrointestinal function. However, the sites at which prolactin exerts these effects are not known. A monoclonal antibody was therefore generated against the rabbit mammary gland prolactin receptor (MAb 218) and used to study the distribution of the prolactin receptor in the rabbit gastrointestinal tract (GIT) by immunohistochemistry. MAb 218 is an IgG1 kappa-precipitating antibody which precipitates major affinity cross-linked mammary gland prolactin receptor subunits of molecular masses 45 and 80 kDa. It has an affinity of 0.8 x 10(9) mol/l for the prolactin receptor and does not react with GH or insulin receptors in precipitation assays. MAb 218 immunoreactivity was observed in classical prolactin target cells such as mammary gland epithelium, and this immunoreactivity was abolished by preincubation of MAb 218 with purified prolactin receptor but not by preincubation with purified GH receptor. In the GIT, the most intense immunoreactivity was associated with the oesophageal epithelium, chief (zymogenic) cells of the fundic mucosa, pancreatic islets of Langerhans and surface epithelial cells of the duodenum and jejunum. Other specific elements of the GIT were immunoreactive at lower levels or were immunonegative. No immunoreactivity was observed in these locations with a control monoclonal antibody (MAb 50.8) of identical isotype to 218. To support the immunohistochemical findings, rabbit gastric mucosal membranes were used to show the presence of lactogen-specific binding. Scatchard analysis of 125I-labelled human GH binding to the gastric mucosal membranes with rat prolactin as displacing ligand yielded an affinity constant (Ka) of 1.0 +/- 0.2 x 10(9) mol/l with a capacity of 3.5 +/- 0.4 fmol/mg protein. Affinity cross-linking and sodium dodecyl sulphate-polyacrylamide gel electrophoresis of the gastric receptor revealed lactogenic hormone-binding subunits of molecular masses 43, 68 and 83 kDa. The 68 kDa subunit was not seen in rabbit mammary gland or ovarian tissue, and may be unique to gastric mucosa. In conclusion, we have demonstrated the presence of a high affinity lactogenic receptor in specific epithelial cell subpopulations of the GIT. This localization of the prolactin receptor in the GIT will assist in further functional assignment of prolactin to gastrointestinal physiology.

Animals↗
PubMed1993

Expression and regulation of insulin-like growth factor-I in the rat incisor.

Growth factors play an important role in the regulation of cell growth, division and differentiation. In this study the distribution and regulation of insulin-like growth factor-I (IGF-I) in the continuously erupting rat incisor was determined by immunohistochemistry. Results were evaluated both visually and with a computer-based image analysis system. The distribution and intensity of IGF-I immunoreactivity varied with developmental stage of the rat incisor. Strong IGF-I immunoreactivity was observed in differentiating odontoblasts and ameloblasts. The most intense immunoreactivity was observed in secretory ameloblasts, secretory odontoblasts and in maturation ameloblasts. Staining was weak or absent in post-secretory ameloblasts but persisted in post-secretory odontoblasts. Weak to moderate immunoreactivity was also seen in cells of the stratum intermedium and in the reduced enamel epithelium. Surrounding alveolar bone showed strong IGF-I immunoreactivity in osteoblasts and in the stratum basale and stratum spinosum of the adjacent labial gingival epithelium. In order to assess the role of GH in IGF-I expression, GH (65 micrograms/100 g bw) was administered for six days to dwarf GH deficient rats, producing a significant increase in body weight (P < 0.01). Measurements at different stages of odontogenesis showed that the staining intensity of secretory ameloblasts (P < 0.01) and maturation ameloblasts (P < 0.001) was significantly different between untreated and treated animals. These results indicate that IGF-I is present in cell populations of the enamel organ of the rat incisor found previously to exhibit growth hormone receptors, and that expression of IGF is GH dependent.(ABSTRACT TRUNCATED AT 250 WORDS)

Ameloblasts↗
PubMed1993

Nonlinear regression analysis of the time course of ligand binding experiments.

The binding and release of hormones and growth factors are often relatively slow processes under biological conditions. Consequently, a knowledge of the underlying rate constants may be of greater physiological relevance than the equilibrium constant. Here we show how, by following a single time course of binding, the rate constants for both binding and release can be determined. The ratio of these rate constants allows the binding constant to be calculated. A nonlinear regression computer program is described which facilitates these calculations and which provides estimates and standard errors of the constants determined. The method is illustrated by the binding of human growth hormone to the human growth hormone binding protein, and the binding of ovine prolactin to the rabbit prolactin receptor.

Animals↗
PubMed1992

Expression of growth hormone receptor by immunocytochemistry in rat molar root formation and alveolar bone remodeling.

Growth hormone (GH) may regulate tooth formation and bone remodeling associated with tooth eruption. This study reports the distribution of growth hormone receptor/binding protein in developing rat molars and adjacent alveolar bone by immunocytochemistry using well-characterized anti-growth hormone receptor monoclonal antibodies. These tissues represent an excellent model for studying the ontogenic changes that occur in odontogenic and osteogenic cells, as these cells are found in linear arrays displaying the various stages of morphological and functional differentiation, and differentiated function. Immunoreactivity was first seen in precementoblasts in contact with the epithelial root sheath, and preodontoblasts. However, growth hormone receptor immunoreactivity was associated primarily with the cytoplasm of odontogenic and osteogenic cells forming their respective matrices. Thus, cementoblasts and odontoblasts at sites of new matrix formation showed intense immunoreactivity whereas cementocytes and mature odontoblasts at later stages of tooth development were nonreactive. Osteoblasts engaged in intramembranous ossification in the alveolar bone were positive, although osteocytes and endosteal cells were immunonegative. Osteoclasts at sites of alveolar bone remodeling resorption were also immunopositive. These patterns of receptor expression parallel the ontogenic sequences of odontogenic and osteogenic cells and suggest that GH promotes the functional state of these cells. Our results also imply that GH may influence differentiation or differentiated functions associated with odontogenesis, osteogenesis, and bone remodeling independent of systemic insulin-like GF-I.

Alveolar Process↗
PubMed1992

Immunocytochemical localization of growth hormone receptor in rat maxillary teeth.

To address the question of what role growth hormone may have in stimulating tooth formation, the distribution of its receptor/binding protein in developing rat incisors and molars was studied immunocytochemically using well-characterized monoclonal antibodies. Ten female 45-day-old Wistar rats were perfused with 4% paraformaldehyde. Five-microns paraffin sections of the growing end of maxillary incisors and molars were cut, deparaffinized and incubated with mouse anti-growth hormone receptor antibodies or control antibodies. A three-layer streptavidin peroxidase technique was used to detect bound antibody. Immunoreaction product was associated primarily with the cytoplasm of cells at certain stages of differentiation. Dividing cells, differentiating preameloblasts and preodontoblasts, secretory ameloblasts and odontoblasts showed immunoreactivity. Undifferentiated dental epithelium cells, stellate reticulum, external dental epithelial cells, mature odontoblasts, and most of cells in the dental papilla were non-reactive. However, at certain stages of tooth development, the stratum intermedium and the external dental epithelium also stained positively. The presence of growth hormone receptor/binding protein in tooth cells at different stages of their development indicates that growth hormone may influence cell proliferation, differentiation and differentiated functions of ameloblasts, odontoblasts and cementoblasts independent of a systemic mediator, and thus may be involved in stimulating odontogenesis directly.

Ameloblasts↗
PubMed1992

Growth hormone regulates nucleolar organizer regions during odontogenesis in the rat.

Nucleolar organizers are major sites of ribosomal RNA synthesis and provide an index of transcriptional activity. In order to further define growth hormone actions on nucleolar organizer regions in tooth forming cells, hypophysectomized rats treated with growth hormone for 4 and 24 h, hypophysectomized and sham-operated animals were used. After demineralization and standard paraffin embedding, longitudinal sections of maxillary incisors were stained by a silver stain technique to reveal nucleolar organizer regions. The area of these regions per nucleus was measured using a modified microdensitometer. Analyses of variance of the resulting data showed that preameloblasts and preodontoblasts have greater silver stained nucleolar organizer region values than ameloblasts and odontoblasts. Hypophysectomy reduced and growth hormone partly restored the level of nucleolar organizer regions in preameloblasts and preodontoblasts, but not in mature ameloblasts or odontoblasts. In the case of the younger preameloblasts and preodontoblasts, the effect of growth hormone was seen within 4 h of growth hormone injection. In conclusion, rRNA synthesis, as revealed by the specific silver staining of nucleolar organizer regions in tooth forming cells, appears to be regulated by growth hormone over a relatively short time frame.

Ameloblasts↗
PubMed1992

The influence of growth hormone on cell proliferation in odontogenic epithelia by bromodeoxyuridine immunocytochemistry and morphometry in the Lewis dwarf rat.

For investigation of how growth hormone affects tooth development, bromodeoxyuridine immunocytochemistry and morphometry were used for the study of cell proliferation in odontogenic epithelial cell layers. The number of cells in the S phase, as revealed by this technique, and in mitosis, were counted in Bouin's-perfused and paraffin-embedded undecalcified maxillary incisor enamel organs of normal rats, in growth-hormone-deficient dwarf rats, and in dwarf rats treated with growth hormone (66 micrograms/100 g body wt) twice daily for six days. Significantly fewer labeled nuclei, unlabeled nuclei, and total nuclei of various odontogenic epithelia were found in dwarf rats, but in dwarf rats treated with growth hormone, numbers of labeled nuclei equivalent to normal were found in the internal enamel epithelium, stratum intermedium, and Hertwig root sheath. Moreover, the mitotic index for pre-ameloblasts was 1.64 in normal rats, 0.92 for dwarf rats, and 1.66 for growth-hormone-treated dwarf rats (SD, 0.10). Other parameters--such as the labeling index and the ratio of positive to negative nuclei--were similarly related to GH status. Thus, growth hormone may play a role in the proliferation of the odontogenic epithelia in the rat.

Ameloblasts↗
PubMed1992

Growth hormone (GH) regulation of gastric structure and function in the GH-deficient rat: up-regulation of intrinsic factor.

In a recent study we identified GH receptor/binding protein in cells of the gastric mucosa. In order to define the role of the GH receptor/binding protein in gastric function, we have investigated the effect of GH on gastric structure and function in the GH-deficient Lewis (dwarf) rat. Bovine GH, 65 micrograms/100 g body wt, was administered twice daily to adult male dwarf rats for 6 days (DW+) while control animals received vehicle only (DW-). Administration of GH produced a significant increase in body wt (P less than 0.001), stomach wt (P less than 0.01), and stomach to body wt ratio (P less than 0.05). GH administration also resulted in increased total gastric DNA, RNA, and protein content but did not produce significant differences in DNA, RNA, or protein content when normalized to stomach wt. Morphometric analysis of the gastric mucosa revealed a significantly (P less than 0.05) increased gastric epithelial height and mucosal surface area along with an increase in the proportion of nuclei with multiple nucleoli (P less than 0.01). The number of gastric mucosal cells in S-phase was determined by immunohistochemical detection of nuclear 5'-bromo-2'-deoxyuridine (BrdU) incorporated during a 2 h pulse of BrdU. GH treatment resulted in a 74% increase (P less than 0.05) in the number of BrdU-labeled nuclei/mm2 mucosa relative to vehicle-injected control animals. A modification of Zimmerman's method for the differential staining of gastric mucosa was used to delineate cell type for morphometric analysis. This showed that the density of differentiated (parietal and chief) cell types was not significantly different between DW- and to DW+ animals. Soluble extracts of gastric mucosa were prepared for estimation of pepsinogen content and [57Co]cyanocobalamin (vitamin B12) binding. GH administration produced no significant change in pepsinogen content per mg protein and did not affect the relative levels of pepsinogen isoenzymes as determined by polyacrylamide gel electrophoresis. GH administration did however result in an 86% increase (P less than 0.01) in [57Co]cyanocobalamin binding per mg protein. The increase in binding was totally displaceable by 1 microgram/ml unlabeled cyanocobalamin but not by 1 microgram/ml cobinamide dicyanide indicating it was the result of increased intrinsic factor rather than R protein. Sephadex S-300 gel filtration of mucosal extracts revealed an elution profile for [57Co]cyanocobalamin identical to that of purified porcine intrinsic factor and different from that of human salivary R protein. In conclusion, we have demonstrated that GH stimulates proliferation and enlargement of the gastric mucosa without significant alteration in cellular composition.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1992

Cellular localization of the growth hormone binding protein in the rat.

In the rat a GH-binding protein (GHBP) exists that is derived from the GH receptor gene by an alternative messenger RNA splicing mechanism such that the transmembrane and intracellular domains of the GH receptor are replaced by a hydrophilic carboxy terminus. Previous immunohistochemical studies detailing the localization of the GH receptor binding protein (BP) have used monoclonal antibodies that recognize extracellular region-specific epitopes common to both the GH receptor and GHBP. In this study we have used a monoclonal antibody (MAb 4.3) specific for the carboxy terminus of the rat GHBP to map its somatic distribution in the rat and have compared this distribution with that of a MAb recognizing both the BP and the GH receptor. A variety of tissues including the skeletal and muscular systems, the gastrointestinal tract and derivatives, the male and female reproductive systems, skin, central and peripheral nervous systems, and the 18 day gestation fetus were investigated. The distribution of GHBP immunoreactivity (MAb 4.3) was widespread and identical to that previously reported for the extracellular region of the GH receptor (MAbs 263 and 43). Immunoreactivity was both cytoplasmic and nuclear, indicating a possible role for the GHBP in intracellular function. GHBP immunoreactivity was predominantly associated with epithelial/endothelial cell subtypes and with mesenchymal elements such as muscle, chondrocytes, and osteoblasts, as previously described for the GH receptor extracellular region. We also report here the distribution of the GH receptor/GHBP in the kidney, cardiovascular, and respiratory systems. The most prominent immunoreactivity (MAbs 4.3 and 263) was associated with the distal convoluted tubules and collecting ducts of the kidney, with the epithelium and smooth muscle of the broncho-alveolar tree (including type I and II pneumocytes), with the Purkinje and myocardial fibers of the heart and with the endothelium and smooth muscle of blood vessels. Thus we have identified sites of direct GH action in the cardiovascular, renal, and respiratory systems. In conclusion, the extensive cellular distribution of the GHBP in the rat indicates physiological function(s) other than the binding of GH in plasma. Since GHBP mRNA has also been reported in a number of tissues, it may be that the GHBP is synthesized locally to mediate intracellular transport of GH and/or transcriptional regulation by GH in a variety of target tissues.

Amino Acid Sequence↗