Abstract
17β-Hydroxysteroid dehydrogenases (17HSDs) catalyze
the reactions between 17-hydroxy and 17-keto steroids. In the present
study, the enzyme activities and tissue distribution of 17HSD type
1, type 2 and type 4 were characterized. Furthermore, the role of
17HSD type 1 in estrogen-dependent growth was studied in MCF-7 breast
cancer cells which were stably transfected with type 1 cDNA.
Endogenous oxidative 17HSD activity found in COS-m6 monkey
kidney cells was first compared with that of human placental 17HSD.
Cultured COS-m6 cells exclusively possessed oxidative 17HSD activity,
converting estradiol (E2) to less active estrone (E1). When placental
17HSD was transfected into these cells, highly reductive activity
appeared. The 17HSD enzyme in COS-m6 cells also catalyzed the conversion
of testosterone to androstenedione, whereas the placental enzyme
was estrogen-specific. These results further proved the existence
of different 17HSD isoenzymes.
The enzymatic properties and cell- and tissue-specific expression
of 17HSD type 1, type 2 and oxidative type 4 were further characterized.
The data confirmed that in cultured cells the direction of 17HSD
activity is determined by the expression of different isoenzymes
and not by the intracellular environment. In addition, the 17HSD
type 1 gene expresses two mRNA signals, 1.3 kb and 2.3 kb in size.
The expression of 1.3 kb mRNA, but not 2.3 kb mRNA was related to
enzyme concentration in all the cell types studied. The type 1 enzyme
was expressed in the placenta, ovary and in some breast cancer specimens
and in the cell lines originated from these tissues. 17HSD type
2 was more widely expressed in both steroidogenic and in target
tissues of steroid action. 17HSD type 4 was expressed in almost
all cell lines and in all tissues studied, but no correlation with
17HSD activity was detected. These results suggest that 17HSD type
1 is involved in E2 production in females and 17HSD type 2 is responsible
for inactivation of sex steroids. However, the oxidation of 17β-hydroxysteroids
seems not to be the primary activity of 17HSD type 4.
The mRNAs for 17HSD type 1, type 2 and type 4 were found to
be expressed in human mammary epithelial cells. In breast tissue
samples both 17HSD type 1 and type 2 were detected by in
situ hybridization. Despite the presence of 17HSD type
1 mRNA in human mammary epithelial cells, only oxidative 17HSD activity
was detected. The reason for the lack of reductive activity is not
yet known.
Finally, MCF-7 breast cancer cells were stably transfected
with 17HSD type 1 cDNA in order to study the effect of 17HSD type
1 on estrogen-dependent growth. In wild type MCF-7 cells, very low 17HSD
activity was detected and E1 did not have any effect on cell growth.
In the cells expressing 17HSD type 1, E1 was rapidly converted to
E2. Hence in these cells E1 had a similar growth-promoting effect
as E2 as a result of the action of 17HSD type 1. The presence of
17HSD type 1 in breast cancer cells may thus be an important factor
regulating estrogen exposure and the estrogen-responsive growth
of breast cancer tissue.
| Identifer | oai:union.ndltd.org:oulo.fi/oai:oulu.fi:isbn951-42-5416-3 |
| Date | 15 October 1999 |
| Creators | Miettinen, M. (Minna) |
| Publisher | University of Oulu |
| Source Sets | University of Oulu |
| Language | English |
| Detected Language | English |
| Type | info:eu-repo/semantics/doctoralThesis, info:eu-repo/semantics/publishedVersion |
| Format | application/pdf |
| Rights | info:eu-repo/semantics/openAccess, © University of Oulu, 1999 |
| Relation | info:eu-repo/semantics/altIdentifier/pissn/0355-3221, info:eu-repo/semantics/altIdentifier/eissn/1796-2234 |
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