Role of putative membrane receptors in the effect of androgens on human vascular cell growth

Abstract

We have reported previously that dihydrotestosterone (DHT) induces a biphasic effect on DNA synthesis in human vascular smooth muscle cells (VSMC), i.e. stimulation at low concentrations and inhibition at high concentrations. In contrast, DHT dose-dependently stimulated [ 3 H]thymidine incorporation in a human endothelial cell line (ECV304). Additionally, DHT increased the specific activity of creatine kinase (CK) in both vascular cell types. In the present study, we have determined whether some of these effects are exerted via membrane-binding sites. We measured changes in DNA synthesis and CK after treatment with DHT and the membrane-impermeant testosterone-3-carboxymethyl oxime conjugated to bovine serum albumin (BSA) (T-BSA). High concentrations of either DHT or T-BSA inhibited VSMC proliferation (by 52+22% and 51+25% respectively). DHT as well as T-BSA increased DNA synthesis in ECV304 cells dose-dependently. In contrast, T-BSA did not affect CK in either cell type. In both cell types, DHT as well as T-BSA increased mitogen-activated protein kinase (MAPK) kinase activity as measured by total phosphorylated MAPK. Further, the inhibitory effect of either the free or protein-bound androgens on DNA synthesis was blocked by UO126, an inhibitor of MAPK kinase activity. T-BSA conjugate labeled with Europium showed binding to whole VSMC, which could be displaced by excess T-BSA, but not by estradiol-BSA or the free hormones. Finally, using T-BSA linked to the fluorescent dye Cy3·5, we directly demonstrated the presence of membrane-binding sites for androgen in VSMC. Hence, the inhibitory effects of testosterone on DNA synthesis in VSMC are apparently exerted by membranebinding sites for androgen, do not require intracellular entry of the hormone and its binding to the classical nuclear receptors and are linked to MAPK activation.

Role of androgen and vitamin D receptors in endothelial cells from benign and malignant human prostate

“…Although possibly not a phenomenon general in all human organs, this concept has been validated in other human endothelial cell models (92,93). A recent study in primary cultures of human aortic endothelial cells showed that AR activation led to moderate (a less than 2-fold increase) upregulation of VEGF-A, cyclin A, and cyclin D1 mRNA expression measured by real-time PCR; the latter two factors are involved in cell cycle progression (9).…”

Hormonal effects on blood vessels

“…Hanke et al 113 reported, using an ex vivo organ culture system, that testosterone at 10-100 ng ml -1 significantly inhibited neointima formation in association with increased expression of AR in endothelium-denuded rabbit aortic rings after 21 days of incubation. Somjen et al 114 demonstrated the dose-dependent inhibitory effects of dihydrotestosterone and membrane-impermeable testosterone on DNA synthesis in cultured VSMCs derived from the human umbilical artery, suggesting a role for membrane AR. The above-mentioned study by Tharp et al 94 showed that the expressions of protein kinase C delta and p27 (kip1) were increased in coronary artery sections of testosterone-treated swine.…”

Activation of Membrane Androgen Receptors in Colon Cancer Inhibits the Prosurvival Signals Akt/Bad In Vitro and In Vivo and Blocks Migration via Vinculin/Actin Signaling

“…Recent studies established the expression of functional membrane androgen receptors (mARs) inducing rapid nongenomic androgen actions in tumors, including prostate (1,2), breast (3,4) and colon (5) as well as in other cell types such as macrophages and T cells (6,7), C6 (8) and vascular smooth muscle cells (9). The exact molecular identity of mAR remains unknown.…”