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Expression of c-fos in human and murine multidrug-resistant cells
A Bhushan1, R Abramson, J F Chiu
1Department of Pharmacology, University of Vermont College of Medicine, Burlington 05405.
Abstract:
In both mouse sarcoma 180 and human KB cells selected for the multiple drug resistance (MDR) phenotype, there is an elevation in the steady state mRNA level of c-fos. There is no detectable gene amplification for c-fos, nor is there any significant change in the rate of mRNA transcription or degradation, suggesting that other factors are responsible for the increased expression level in resistance. Cells selected for resistance to methotrexate, a drug not in the MDR group, do not have an increase in c-fos mRNA expression. When drug-sensitive cells are exposed for 30 min to an ED50 concentration of vinblastine, Adriamycin, colchicine, or VP-16, but not to methotrexate or cisplatin, there is a 3-6-fold induction in the level of c-fos message. Because the former drugs are members of the MDR class and the latter are not, the results are consistent with the hypothesis that induction of c-fos by low levels of cytotoxic drugs may be an early event in the acquisition of the MDR phenotype. If this were the case, then c-fos would be expected to act in concert with c-jun to control transcription by binding to a specific DNA regulatory site. Consistent with this explanation is the existence of an AP-1 sequence in the promotor region for the P-glycoprotein gene (mdr1), as well as the fact that c-jun is also overexpressed in MDR cells.
Insights
Elevated c-FOS mRNA levels are observed in multidrug-resistant cells, suggesting its role in acquired drug resistance. This induction by specific cytotoxic drugs may be an early event in developing multidrug resistance (MDR).
Area of Science:
- Molecular Biology
- Cancer Research
- Cell Biology
Background:
- Multidrug resistance (MDR) is a major challenge in cancer chemotherapy.
- The c-FOS proto-oncogene's role in MDR is not fully understood.
Purpose of the Study:
- To investigate the expression of c-FOS in drug-resistant cells.
- To determine if c-FOS induction is associated with the acquisition of the MDR phenotype.
Main Methods:
- Analysis of c-FOS mRNA levels in mouse sarcoma 180 and human KB cells with MDR phenotype.
- Exposure of drug-sensitive cells to various cytotoxic drugs (vinblastine, Adriamycin, colchicine, VP-16, methotrexate, cisplatin).
- Measurement of c-FOS mRNA induction following drug exposure.
Main Results:
- Elevated steady-state c-FOS mRNA levels were found in MDR cells.
- No gene amplification or significant changes in c-FOS transcription/degradation rates were detected.
- Specific MDR drugs, but not non-MDR drugs, induced c-FOS mRNA in sensitive cells.
- c-JUN was also found to be overexpressed in MDR cells.
Conclusions:
- Induction of c-FOS by low-level cytotoxic MDR drugs may be an early event in acquiring the MDR phenotype.
- c-FOS likely collaborates with c-JUN to regulate genes involved in MDR, such as P-glycoprotein (mdr1).
- These findings provide insights into the molecular mechanisms underlying multidrug resistance.