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Identification of genes whose expression is altered during mitosuppression in livers of ethinyl estradiol-treated
J Chen1, D A Schwartz, T A Young
1Johns Hopkins University, The School of Hygiene and Public Health, Baltimore, MD 21205-2179, USA.
Abstract:
In this study, our goal was to identify genes whose expression in liver is altered in female F-344 rats during mitosuppression induced by 42 days of ethinyl estradiol (EE) treatment (Yager et al., Carcinogenesis, 15, 2117-2123, 1994). Northern analysis demonstrated that the mRNA levels for transforming growth factor-beta1 (TGF-beta1) and the mannose 6-phosphate/insulin-like growth factor II receptor were significantly increased by EE treatment. Ten cDNA clones representing mRNAs whose expression was increased two- to four-fold in the mitosuppressed livers were identified by differential display. Sequence analysis revealed that one was homologous to the S-24 ribosomal protein and another to mitochondrial ATPase subunit e. The remaining clones showed no homology to known genes in GenBank. However, the expression of clones 15, 16 and 17 was increased in HepG2 cells following treatment with doxorubicin suggesting their induction by oxidative DNA damage. These results suggest that two independent but interrelated signalling pathways, one mediated through transforming growth factor-beta and the other through oxidative DNA damage, may contribute to hepatic mitosuppression caused by EE, perhaps through activation of cyclin-dependent kinase inhibitors.
Insights
Ethinyl estradiol (EE) treatment in rats suppressed liver cell division. This study identified genes involved in EE-induced liver mitosuppression, implicating transforming growth factor-beta and oxidative DNA damage pathways.
Area of Science:
- Hepatology
- Molecular Biology
- Toxicology
Background:
- Ethinyl estradiol (EE) is known to induce liver mitosuppression in female rats.
- Understanding the molecular mechanisms behind EE-induced liver changes is crucial for assessing its toxicological impact.
Purpose of the Study:
- To identify specific genes and signaling pathways involved in liver mitosuppression caused by ethinyl estradiol (EE) treatment.
- To elucidate the molecular underpinnings of EE-induced hepatic cellular changes.
Main Methods:
- Differential display was used to identify genes with altered expression in rat livers after 42 days of EE treatment.
- Northern blot analysis was performed to confirm changes in mRNA levels for specific genes.
- Sequence analysis of cDNA clones was conducted to identify homologous genes.
- HepG2 cells were treated with doxorubicin to investigate gene induction by oxidative DNA damage.
Main Results:
- EE treatment significantly increased mRNA levels of transforming growth factor-beta1 (TGF-beta1) and the mannose 6-phosphate/insulin-like growth factor II receptor.
- Ten cDNA clones representing mRNAs with 2- to 4-fold increased expression were identified.
- One clone was homologous to S-24 ribosomal protein, another to mitochondrial ATPase subunit e.
- Clones 15, 16, and 17 showed increased expression in HepG2 cells after doxorubicin treatment, suggesting induction by oxidative DNA damage.
Conclusions:
- Two signaling pathways, one involving transforming growth factor-beta and another involving oxidative DNA damage, may contribute to EE-induced hepatic mitosuppression.
- These pathways might activate cyclin-dependent kinase inhibitors, leading to suppressed cell division.
- The identified genes provide insights into the molecular mechanisms of EE toxicity in the liver.