Laboratory of Molecular Carcinogenesis , National Institute of Environmental Health Sciences , National Institutes of Health , Research Triangle Park , North Carolina 27709 .
Mol Carcinog 7 : 249-56 ( 1993)
Abstract
Immortal , nontumorigenic cell lines of Syrian hamster embryo ( SHE ) cells with different tumor-suppressing activity were isolated .
Subclones from the parental cells were isolated that either had retained ( supB+ ) or lost ( supB- ) the ability to suppress tumorigenicity after hybridization with tumor cells .
The growth properties of these cells were studied to determine how this tumor-suppressor gene function influences cell growth .
When the cells were grown on plastic , their growth properties were similar , and neither cell type grew in soft agar containing 10% serum , which supported the growth of tumorigenic cells .
However , in agar supplemented with growth factors and 10% serum , supB- cells formed colonies whereas supB+ cells did not .
Efficient growth ( colony-forming efficiencies greater than 20% ) of supB- cells was obtained in agar supplemented with serum and a combination of epidermal growth factor ( EGF ) , platelet-derived growth factor ( PDGF ) , and insulin ( EPI ) or with serum and basic fibroblast growth factor ( bFGF ) .
The effect of EPI and bFGF together was additive .
supB+ cells failed to grow under any of these conditions , suggesting that the suppressor gene function blocked the growth response of the cells to multiple growth factors when the cells were suspended in agar .
In SupB- cells , transforming growth factor-beta 1 and retinoic acid inhibited anchorage-independent growth response to EPI but not the growth response to bFGF .
These observations are consistent with the hypothesis that bFGF stimulates the growth of supB- cells by a signal transduction pathway that differs from the pathway stimulated by EGF or PDGF .
Thus , this suppressor gene function may regulate anchorage-independent growth at some common point in signal transduction for multiple mitogens .
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Department of Surgery , UCLA School of Medicine , Torrance 90509 .
J Steroid Biochem Mol Biol 45 : 333-43 ( 1993)
Abstract
Androgens down-regulate the levels of androgen receptors ( AR ) and AR mRNA in the penis and prostate of castrated rats , and are assumed to cause their decrease during sexual maturation in the penile smooth muscle of intact rats .
In order to determine whether these effects occur directly at the target cell level , and to what extent they are due to testosterone ( T ) or to their metabolites , we have measured AR mRNA in cultures of smooth muscle cells from the adult rat corpora cavernosa treated in vitro with sex steroids .
T at high concentrations ( 100 nM ) acted like dihydrotestosterone ( DHT ) in increasing moderately the levels of AR mRNA in both proliferating and contact-inhibited cells .
However , when conversion of T to DHT was blocked by the 5-alpha reductase inhibitor finasteride , the levels of AR mRNA were considerably down-regulated by T ( 10-500 nM ) , particularly in the contact-inhibited cells .
Finasteride by itself was inactive .
These effects in both types of cultures were inhibited by platelet derived growth factor ( PDGF ) ( 20 ng/ml ) , a growth factor that up-regulates AR mRNA levels , and by fadrozole ( 100 nM ) , an aromatase inhibitor of the T/estrogen conversion .
Estradiol ( 50 nM ) was even more potent than T in decreasing AR mRNA levels .
With the exception of PDGF none of the treatments affected significantly cell growth , as measured by DNA synthesis and content .
Our results indicate that it is possible to modulate in vitro AR mRNA levels in the penile smooth muscle cells , and that under normal conditions DHT and T act as moderate up-regulators .
When DHT formation is inhibited , the aromatization pathway of T to estradiol will prevail and induce a pronounced down-regulation of AR mRNA levels .
We assume that the in vivo AR down-regulation in the penile smooth muscle by androgens is an indirect effect mediated by a paracrine or endocrine mechanism elicited in another tissue .