Biomedical subjects

J Blaisdell

Publications and source records attributed to J Blaisdell.

23 records · Page 2Linked to original sources

PubMed1987

Transforming growth factor-beta inhibits Leydig cell steroidogenesis in primary culture.

The effects of transforming growth factor (TGF) on Leydig cell steroidogenesis in primary culture were investigated. Basal testosterone levels were 3.7 +/- 0.54 ng/ml (mean +/- SE, N = 7). In the presence of hCG (10 ng/ml), testosterone levels increased to 22.77 +/- 3.05 ng/ml. TGF-beta caused a dose dependent inhibition of hCG-stimulated testosterone formation but without effects on basal levels. TGF-beta also inhibited 8-bromo cyclic AMP-induced testosterone formation and hCG-stimulated cyclic AMP formation. In contrast, TGF-alpha had no effect on either basal or hCG-stimulated testosterone formation and did not modify the inhibitory effect of TGF-beta. Present study indicates that TGF-beta can modulate Leydig cell steroidogenesis.

8-Bromo Cyclic Adenosine Monophosphate↗

PubMed1987

Inconsistent effects of all-trans retinoic acid on different clones of chemically transformed rat liver epithelial cells.

The effects of all-trans retinoic acid (RA) on the growth and biochemical properties of five clonal strains of neoplastically transformed rat liver epithelial cells were studied. These cell strains were derived clonally from a single line of normal diploid rat liver epithelial cells that had been transformed by treatment with N-methyl-N'-nitro-N-nitrosoguanidine. The results show that RA induces inconsistent alterations in selected phenotypic properties of these five different cell strains. Retinoic acid either depressed, enhanced or produced no effect on the colony-forming ability in soft agar, on the activity of gamma-glutamyl transpeptidase, on the amount of cell-associated fibronectin, and on the binding capacity of 125I-epidermal growth factor (EGF). The only consistent correlation observed among cell strains was between the cellular ability to grow in soft agar and the amount of cell-associated fibronectin. Enhancement of anchorage-independent growth by retinoic acid was not mediated through changes in the number of EGF receptors. Our data demonstrate that the responses to retinoic acid of clonal subpopulations of chemically transformed rat liver epithelial cells are inconsistent, even when the clonal subpopulations are derived from a common precursor.

Animals↗

PubMed1986

Epidermal growth factor (EGF) stimulates EGF receptor synthesis.

Epidermal growth factor (EGF) binds to the extracellular domain of a specific 170,000-dalton transmembrane glycoprotein; this results in rapid removal of both ligand and receptor from the cell surface. In WB cells, a rat hepatic epithelial cell line, ligand-directed receptor internalization leads to receptor degradation. We tested whether the EGF receptor was replenished at a constitutive or enhanced rate following EGF binding by immunoprecipitating biosynthetically labeled EGF receptor from cells cultured with [35S]methionine. EGF stimulated receptor synthesis within 2 h in a dose-dependent manner; this was particularly evident when examining the nascent form of the receptor. To determine the site of EGF action, total WB cell RNA was transferred to nitrocellulose paper after electrophoresis and was hybridized to cDNA probes from both the external and cytoplasmic coding regions of the human EGF receptor. EGF increased receptor mRNA by 3-5-fold. Therefore, at least in some cells, the surface action of EGF that leads to EGF receptor degradation is counterbalanced by a positive effect on receptor synthesis.

Animals↗

PubMed1984

Dimethyl sulfoxide decreases specific EGF binding.

Dimethyl sulfoxide (DMSO) stimulates tyrosine phosphorylation of the hepatic EGF receptor in isolated membrane preparations. To determine whether DMSO affects EGF binding, primary cultures of rat hepatocytes were incubated with 1-10% DMSO for 30 min prior to the addition of 125I-EGF. DMSO (1-2%) reduced specific 125I-EGF binding; the effect was maximal (a 40-60% reduction) at 5-7.5% DMSO and was reversed by removing the DMSO. Scatchard analysis showed that the reduction in binding was due to a change in receptor affinity. The decrease in binding was not seen when other, slightly less polar, solvents (eg, acetone and ethanol) were tested. DMSO also reduced 125I-EGF binding to purified rat liver plasma membranes. This reduction was seen in the absence of added ATP and in membranes that had been pretreated with TLCK, a tyrosine kinase inhibitor. Thus, completion of the receptor autophosphorylation reaction was not necessary to effect the change. The data are consistent with a DMSO-induced alteration of receptor conformation that reversibly reduces receptor affinity.

Animals↗

PubMed1984

Insulin inhibits the glucocorticoid-mediated increase in hepatocyte EGF binding.

Hydrocortisone and dexamethasone produced a time-dependent increase [125I]epidermal growth factor [( 125I]EGF) binding in primary cultures of isolated rat hepatocytes. Maximally effective doses of glucocorticoids resulted in a 70-100% increase in binding. The effect was similar when hepatocytes were maintained on collagen-coated plates or directly on culture dishes. The glucocorticoid-mediated increase in [125I]EGF binding could be detected after 4 h exposure to glucocorticoid and was substantial by 8 h. The major effect of glucocorticoid appeared to be to increase the number of EGF receptors. While insulin (100 nM) had no effect on basal [125I]EGF binding, it significantly inhibited the increase produced by the glucocorticoid. Since the inhibitory effect of insulin was only observed when insulin was added with the inducing glucocorticoid, insulin appears to inhibit an early hydrocortisone-mediated event.

Animals↗