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The human multidrug resistance 1 promoter has an element that responds to serum starvation
1Department of Biochemistry, Oita Medical University, Japan.
Abstract:
We have previously demonstrated in transient expression assay systems that a human multidrug resistance 1 (MDR1) promoter can be directly activated by cytotoxic anticancer agents. In this study, we examined whether the MDR1 promoter could be regulated in response to growth arrest induced by serum starvation. We have established human and rodent cell lines which stably expressed the chloramphenicol acetyltransferase (CAT) gene driven by various lengths of the MDR1, the viral thymidine kinase (TK) and the simian virus 40 (SV40) promoters. Serum starvation caused enhanced expression of CAT gene with MDR1 promoter, but not with two viral gene promoters in human cancer KB cells. Hydroxyurea activated the MDR1 promoter, but not TK and SV40 promoters. By contrast, the DNA topoisomerase II inhibitor, etoposide, equally activated the MDR1, TK and SV 40 promoters. Increased CAT gene expression by serum starvation was also specifically observed in stable transfectants of human adrenal SW-13 cell lines, but not in stable transfectants of mouse fibroblast NIH3T3 and adrenal Y-1 cell lines when the human MDR1 promoter-CAT was introduced. Etoposide, however, effectively induced CAT activity in both human and rodent cells. Assays with deletion constructs of the MDR1 promoter showed that serum starvation activated the MDR1 promoter carrying -258 approximately +121 base sequence of the promoter, but not -198 approximately +121 of the promoter. These results suggest that the expression of the MDR1 gene induced by serum starvation is regulated at the transcriptional level in a promoter sequence-specific manner in human cells.
Insights
Serum starvation activates the human multidrug resistance 1 (MDR1) gene promoter in a sequence-specific manner. This transcriptional regulation occurs independently of viral promoters, highlighting a unique cellular response to growth arrest.
Area of Science:
- Molecular Biology
- Genetics
- Cancer Research
Background:
- The human multidrug resistance 1 (MDR1) promoter is known to be activated by cytotoxic anticancer agents.
- The regulation of the MDR1 promoter in response to cellular growth arrest, such as serum starvation, remains less understood.
Purpose of the Study:
- To investigate whether the MDR1 promoter is regulated by growth arrest induced by serum starvation.
- To determine the promoter sequence specificity and cell-type specificity of MDR1 gene regulation during serum starvation.
Main Methods:
- Establishment of human and rodent cell lines with stable expression of the chloramphenicol acetyltransferase (CAT) gene under the control of MDR1, thymidine kinase (TK), or simian virus 40 (SV40) promoters.
- Treatment of cell lines with serum starvation and various agents (hydroxyurea, etoposide) to assess promoter activity via CAT gene expression.
- Analysis of deletion constructs of the MDR1 promoter to identify critical sequences involved in serum starvation-induced regulation.
Main Results:
- Serum starvation enhanced CAT gene expression driven by the MDR1 promoter in human cancer KB and adrenal SW-13 cells, but not in viral promoters or in mouse fibroblast NIH3T3 and adrenal Y-1 cells.
- Hydroxyurea specifically activated the MDR1 promoter, while etoposide activated MDR1, TK, and SV40 promoters in both human and rodent cells.
- Deletion analysis indicated that the -258 to +121 region of the MDR1 promoter is crucial for serum starvation-induced activation.
Conclusions:
- The MDR1 gene expression is regulated at the transcriptional level in response to serum starvation-induced growth arrest.
- This regulation is specific to the MDR1 promoter sequence and occurs in a cell-type-specific manner in human cells.
- The findings suggest a distinct mechanism for MDR1 gene control during cellular stress.