| J ENDOCRINOLOGY 180:97-106,2004 |
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| Role of putative membrane receptors in androgens′ effects on human
vascular cell growth |
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| Dalia Somjen, Fortune Kohen1, Batya Gayer1, Tikva Kulik1, Esther
Knoll and Naftali Stern |
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| Institute of Endocrinology, Metabolism and Hypertension, Tel Aviv
Sourasky Medical Center and Sackler Faculty of Medicine, Tel Aviv University,
Tel Aviv, Israel |
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We 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 human endothelial cell line (ECV- 304). Additionally, DHT increased
the specific activity of creatine kinase (CK) in both vascular cell
types. In the present study we determine 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 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
dose– dependently DNA synthesis in ECV-304 cells. In contrast, T-BSA
did not affect CK in either cell type. In cell types, DHT as well as
T-BSA increased MAP- kinase- 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 MAP- kinase- 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 membrane binding 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.
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