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.

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)

Prenatal expression of the growth hormone (GH) receptor/binding protein in the rat: a role for GH in embryonic and fetal development?

Although fetal growth is generally considered to be independent of pituitary growth hormone (GH), it is possible that pituitary GH plays a modulatory role in organ development or that a GH-like substance of non pituitary origin may influence fetal growth through the GH receptor. Accordingly, we have used immunohistochemistry, northern blot analysis, the reverse transcriptase-polymerase chain reaction and solution hybridization to study the ontogeny of the GH receptor/binding protein (BP) from the 12-day-old embryo (E12) to the E18 rat fetus. GH receptor/BP immunoreactivity was observed in all major organ systems of the E18 rat fetus and was not preferentially associated with any germ layer derivative. A general increase in GH receptor/BP immunoreactivity was evident from E12 to E18, with a marked increase occurring between E16 and E18. Hemangioblastic tissue was, however, strongly or intensely immunoreactive at all stages of development, as was the placenta. Most noteworthy of the other tissues expressing GH receptor/BP immunoreactivity by day 18 were skeletal and smooth muscle, chondroprogenitor cells, epithelial lining cells, neuronal ganglia, ependymal cells and the adrenal cortex. In the placenta, the most prominent immunoreactivity was associated with decidual cells. Total RNA was isolated from E12 to E18 rat fetuses and adult rat liver. Northern hybridization with a 35S-labelled rat GH receptor cRNA probe revealed that 3.9 kb and 1.2 kb transcripts complementary to the rat GH receptor riboprobe are present from at least E16. The existence of GH receptor mRNA at E12 and E14 was demonstrated by the polymerase chain reaction.(ABSTRACT TRUNCATED AT 250 WORDS)

The nuclear growth hormone receptor binding protein. Antigenic and physicochemical characterization

The mechanisms involved in transcriptional regulation by growth hormone (GH) remain unknown. We report here that GH receptor immunoreactivity can be demonstrated in the nuclei of GH-responsive rat and rabbit tissues at both the light and electron micrograph level using monoclonal antibodies to the receptor extracellular domain. Nuclear staining is heterogeneous and associated with both chromatin and the nuclear membrane. To confirm these observations, nuclei were isolated from rabbit liver by two methods, one involving extensive nonionic detergent washes. Scatchard analysis of nuclear fractions revealed high affinity somatogenic receptor in nuclear membranes, nucleoplasm, and chromatin fractions. A panel of GH receptor monoclonal antibodies was used to further define these nuclear binding sites as being antigenically identical to microsomal receptor in all but one case. In addition, affinity cross-linking experiments showed the somatogenic binding subunit to have a reduced Mr of 67,000, similar to the Mr of the GH binding protein. We propose that the association of a GH binding protein with the nucleus may provide a means whereby GH can regulate the transcription of specific genes either directly or indirectly through nuclear kinase C activation. This speculation is congruent with the recent demonstration of a GH response element by Yoon et al. (Yoon, J. B., Berry, S. A., Seelig, S., and Towle, H. C. (1990) J. Biol. Chem. 265, 19947-19954).

Growth hormone receptor expression in the Dunning R 3327 prostatic carcinoma of the rat

The Dunning R3327 rat carcinoma is an important model for human prostate adenocarcinoma. In the present study this tumor was further characterized by immunohistochemical demonstration of receptors for growth hormone (GH-R). Weak GH-R immunoreactivity was present in the secretory epithelial cells of the tumor acini. Large epithelial cells which were localized at the periphery of the acini and large cells in the stroma, which are probably derived from the epithelium ("Large neoplastic epithelial cells"), displayed a strong staining with one of the monoclonal antibodies (Mab 263) to GH-R. The presence of GH-R receptors in proliferating prostatic tumor cells supports the concept that GH reacts directly on prostate target tissue to facilitate tumor cell growth.

Localization of the growth hormone receptor/binding protein in skin

Acromegaly is characterized by coarsening of facial features, acanthosis nigricans, hypertrichosis and oily skin. To determine the site through which GH exerts these effects, we have used immunohistochemistry to localize the GH receptor/binding protein (BP) in rat, rabbit and human skin. Three monoclonal antibodies (MAb 1, 43, 263) were immunoreactive in identical locations, whereas no immunoreactivity was evident when control monoclonal antibodies (MAb 50.8 and MAb 7 (rat] were used. Skin from neonatal and adult animals was used to determine whether GH receptor/BP expression was developmentally regulated. Immunoreactivity of the GH receptor/BP in the three species was consistently localized in the stratum basale and stratum spinosum. Intermittent staining was observed in the stratum granulosum. Scattered basal epidermal cells often displayed more intense immunoreactivity. This distribution was observed at all maturational stages examined. Intense GH receptor/BP immunoreactivity was observed in all histological layers of the lower one-third of hair follicles and in hair matrix cells of the dermal papillae. Immunoreactivity was also detected in the outer epithelial root sheath of the upper two-thirds of hair follicles, in sebaceous glands and in fibroblasts of the connective tissue sheath surrounding the follicle. GH receptor/BP immunoreactivity was also present in the secretory duct and myoepithelial cells of human eccrine sweat glands. Fibroblasts, Schwann cells of peripheral nerve fascicles, skeletal muscle cells and adipocytes of the dermis were also immunoreactive as were medial smooth muscle and endothelial cells of arteries. These results provide evidence that GH acts locally on the epidermis and epidermal appendages concordant with our recent localization of GH receptor/BP to epithelial cell types of the gastrointestinal and reproductive systems.

Cellular localization of the growth hormone receptor/binding protein in the male and female reproductive systems

We have used immunohistochemistry to localize GH receptor/binding protein (BP) in the male and female reproductive systems of adult rats. Testes and ovaries from neonatal animals were also examined to determine if GH receptor/BP expression in these tissues is developmentally regulated. Two monoclonal antibodies (MAb 43 and 263) were immunoreactive in identical locations whereas no immunoreactivity was evident when control monoclonal antibodies 7 and 50.8 were used. Localization of the receptor/BP was observed in both the nucleus and cytoplasm of immunopositive cells confirming our recent report of a nuclear GH receptor. Intense GH receptor/BP immunoreactivity in the male reproductive system was evident in the epithelium of the vas deferens and coagulating gland, the prostatic epithelium during the secretory phase, and the ductular epithelium of the coagulating and bulbourethral glands, respectively. Strong immunoreactivity was detectable in the Leydig and Sertoli cells, the epithelium of the ductus epididymis and seminal vesicles and smooth muscle of the tunica muscularis of the vas deferens, septae of the seminal vesicles, and in prostatic fibromuscular stroma. Cells of the seminiferous tubules (spermatogonia, primary and secondary spermatocytes, and spermatids) were moderately immunoreactive. No immunoreactivity was detectable in spermatozoa in the ductus epididymis or vas deferens, in scattered epithelial cells of the ductus epididymis, the prostatic epithelium in the nonsecretory phase, and mucous secreting cells of the bulbourethral glands. Leydig cells of 10-day postnatal rat testis were intensely immunoreactive whereas seminiferous tubular cells displayed homogenous immunoreactivity from moderate to strong. Intense GH receptor/BP immunoreactivity in the female reproductive system was evident in the germinal epithelium, the vascular endothelium of the myometrium, the epithelial lining of the fimbriae and oviduct, the endometrial epithelium and scattered endometrial glands, the mesothelium of the perimetrium, and the vascular endothelium of the endometrium. Strong immunoreactivity was exhibited by scattered oocytes, lutein cells of the corpus luteum, scattered endometrial glands, and the vascular endothelium of the endometrium. Moderate immunoreactivity was evident in scattered oocytes, granulosa cells, theca interna and externa, smooth muscle of the oviduct and myometrium, scattered endometrial glands, and luminally placed endometrial stroma cells. Ovarian granulosa cells from 10-day postnatal rats displayed strong immunoreactivity in contrast to moderate immunoreactivity in adult granulosa cells. In conclusion, we report a widespread distribution of the GH receptor/BP in the reproductive system of the rat by which GH may exert a direct action on reproductive function. The distribution is concordant with a role for GH in epithelial function and/or maintenance and also with a possible role for GH in the integrity of the endometrial vasculature.

Growth hormone receptor expression in the rat gastrointestinal tract

We have used immunohistochemistry to define the cellular distribution of GH receptors in the gastrointestinal tract (GIT) and its derivatives. Immunohistochemistry was performed in the adult rat GIT with a panel of characterized monoclonal antibodies to the GH receptor. The most intense and heterogeneous immunoreactivity was observed in epithelial cell subpopulations of GIT mucosa. Mesenchymal elements of the GIT were homogenously and moderately immunoreactive. Intense immunoreactivity was observed in the ductal epithelium of the sublingual gland, scattered basal epidermal cells of the esophageal mucosa, zymogen cells of the gastric glands, scattered surface epithelial cells of the stomach, and scattered peripheral pancreatic acinar groups. Scattered enteroendocrine cells and parietal cells, crypt and villous columnar cells of the small intestine, surface columnar cells of the cecum/colon, crypt base columnar cells of the colon, and contiguous peripheral cords of pancreatic islet cells displayed strong immunoreactivity. No immunoreactivity was detectable in the mucous and serous acini of the sublingual and submandibular gland, respectively, mucous-secreting cells of the base of the cardiac and pyloric glands, surface epithelial cells of the fundus, paneth cells, goblet cells of cecum/colon, or mucous cells at the base of the cecal crypt. Other elements of the GIT were moderately or weakly immunoreactive. In support of our localization we can detect high affinity binding (Ka = 3 x 10(9] of [125I]human GH with ovine GH as displacing ligand to crude homogenates of adult rat stomach and intestine. We conclude that discrete epithelial cell subpopulations of the GIT and its derivatives are directly responsive to GH action. GH may, therefore, act independently of or synergistically with hepatic insulin-like growth factor-I in executing its physiological and/or growth-promoting role in the GIT.