Inhibition of immunoreactive growth hormone secretion from lymphoid cell lines by dexamethasone

Lymphocyte GH-axis hormones in immunity

The production and utilization of common ligands and their receptors by cells of the immune and neuroendocrine systems constitutes a biochemical information circuit between and within the immune and neuroendocrine systems. The sharing of ligands and receptors allows the immune system to serve as the sixth sense notifying the nervous system of the presence of foreign entities. Within this framework, it is also clear that immune cell functions can be altered by neuroendocrine hormones and that cells of the immune system have the ability to produce neuroendocrine hormones. This review summarizes a part of this knowledge with particular emphasis on growth hormone (GH). The past two decades have uncovered a lot of detail about the actions of GH, acting through its receptor, at the molecular and cellular level and its influence on the immune system. The production and action of immune cell-derived GH is less well developed although its important role in immunity is also slowly emerging. Here we discuss the production of GH, GH-releasing hormone (GHRH) and insulin-like growth factor-1 (IGF-1) and their cognate receptors on cells of the immune system and their influence via endocrine/autocrine/paracrine and intracrine pathways on immune function. The intracellular mechanisms of action of immune cell-derived GH are still largely unexplored, and it is anticipated that further work in this particular area will establish an important role for this source of GH in normal physiology and in pathologic situations.

Pituitary and extrapituitary growth hormone: Pit-1 dependence?

Growth hormone (GH) is primarily produced in pituitary somatotrophs. The synthesis of this hormone is thought to be dependent upon a pituitary-specific transcription factor (Pit-1). However, many extrapituitary tissues are now known to express GH genes. The extrapituitary production of GH may therefore indicate an extrapituitary distribution of the Pit-1 gene. The extrapituitary production of GH may, alternatively, indicate that GH expression occurs independently of Pit-1 in extrapituitary tissues. These possibilities are considered in this brief review.Key words: growth hormone, pituitary, pituitary transcription factor 1.

Stimulatory effects of cocaine and its metabolites on IM-9 human B-lymphoblastoid cells

This study examined the effect of cocaine and its metabolites benzoylecgonine, norcocaine, and cocaethylene on human B-cell proliferation using IM-9 cells. Cells were incubated with 0.01-10 micrograms/ml of cocaine or metabolite in serum-free medium or medium containing 2% FBS for 24 and 48 h, and [3H] thymidine incorporation into DNA was measured using liquid scintillation counting. Results showed incubation with cocaine and metabolites significantly increased IM-9 cell proliferation. With cocaine, maximal stimulation of 148% (compared to drug-free control) occurred at 1.0 micrograms/ml in serum-free medium at 48 h. Benzoylecgonine and norcocaine showed maximal stimulation at 0.1 micrograms/ml with 170% and 150% stimulation, respectively. Cocaethylene showed maximal stimulation of 146% at 10 micrograms/ml. Drug stability was monitored under incubation conditions using high-performance liquid chromatography (HPLC). We have shown that cocaine and its major metabolites have an immunomodulatory effect on B-cell proliferation at concentrations equivalent to serum levels produced during cocaine use in humans. Since the cocaine metabolites also show an immunomodulatory effect, the immune consequences of cocaine use may be significantly prolonged.

Stimulatory effects of immunoreactive growth hormone on proliferation of a human lymphocyte cell line

Previous studies have indicated the secretion of a growth hormone-like molecule by the lymphocyte T-cell line, H9. We examined the autocrine growth-promoting effects of this T-cell derived factor. H9 conditioned medium stimulates proliferation of H9 cells themselves in a dose-dependent fashion. This growth stimulating effect could be blocked by anti-human growth hormone antiserum, but could not be simulated by addition of growth hormone only or interleukin 2 only, or a combination of both. Dexamethasone inhibited H9 growth in low nutrient culture conditions and seemed to somewhat offset the growth promoting effect of the hGH-like molecule. However, the exact role played by dexamethasone in H9 cell growth and death, as well as the exact mechanism by which the hGH-like molecule exerted its growth-promoting action, remain to be elucidated.

Human IM-9 lymphoblasts as a model of the growth hormone-insulin-like growth factor axis: gene expression, and interactions of ligands with receptors and binding proteins

Human IM-9 lymphoblasts bind growth hormone (hGH) and insulin-like growth factors (IGFs). We have systematically examined the IM-9 cells as a valuable model of the interaction of hGH and the IGFs at the cellular level. Cells were cultured in medium with 10% serum and for a subset of experiments cultured in serum-free medium. Binding of [125I]hGH and [125I]IGF-I and -II to intact IM-9 cells was measured: unlabeled hGH inhibited binding of [125I]hGH (half max. 20 ng/ml). Binding of [125I]IGF-I was inhibited by IGF-I (half max. 7.5 ng/ml), IGF-II (half max. 60 ng/ml), and insulin and anti IGF-I receptor antibody (alpha IR3). [125I]IGF-II was inhibited by IGF-II (half max. 15 ng/ml), IGF-I (half max. 500 ng/ml), insulin (half max. 250 ng/ml) but not by alpha IR3. Crosslinking experiments with [125I]IGF-II and DSS as the crosslinking agent and analysis of radioligand-receptor complexes by SDS-PAGE under reducing conditions revealed that [125I]IGF-II bound to a 250 kDa and a 135 kDa receptor species. The latter possibly represents an insulin-type receptor whereas the 250 kDa species had the characteristics of the IGF-II/M6P receptor. When IM-9 cell conditioned medium was analyzed in ligand blotting experiments with either [125I]IGF-I or -II a 30 kDa IGFBP species was detected on the autoradiographs. Also, IGF-II immunoreactivity (approx. 1 ng/ml medium) was measured in the cell conditioned medium using an IGF-BP blocked RIA employing [125I]IGF-II. In a subset of experiments IM-9 cells were homogenized in 4 M guanidinium-thiocyanate and RNA extracted in 5.7 M CsCl. Denatured RNA was electrophoresed on 0.8% agarose gels and transferred to a nylon membrane, fixed and the blots hybridized with cDNA probes. Probes were labeled with [32P]dCTP using a random prime labeling procedure: a Pst I 700 bp fragment of the human IGF-I cDNA, a 554 bp Pst I-Sal I fragment of the IGF-II cDNA, a 614 bp Pst I fragment of the IGF-I receptor cDNA and a 663 bp Pst I fragment of the IGF-II/M6P receptor. Autoradiographs of Northern blots showed specific hybridization with the IGF-I probe at 3.7 kb and with the IGF-II probe at 5.3 kb. No signal was detected with the IGF-I receptor cDNA probe. Hybridization with the IGF-II/M6P receptor probe yielded a 9 kb RNA species.(ABSTRACT TRUNCATED AT 400 WORDS)