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EGR-1 induction is required for maximal radiosensitivity in A375-C6 melanoma cells
M M Ahmed1, K Venkatasubbarao, S M Fruitwala
1Department of Radiation Medicine, University of Kentucky, Lexington, Kentucky 40536, USA.
Abstract:
Exposure to ionizing radiation leads to induction of the immediate-early gene, early growth response-1 (Egr-1). Previous studies have suggested distinct cell type- and inducer-specific roles for EGR-1 protein in cellular growth inhibition. The present study was undertaken to determine the functional role of EGR-1 in growth inhibition caused by exposure of tumor cells to ionizing radiation. Exposure to ionizing radiation caused induction of EGR-1 protein in human melanoma cells A375-C6. Inhibition of either the function of EGR-1 protein by stable transfection with a dominant-negative mutant or the expression of EGR-1 by transient transfection with an antisense oligomer resulted in a diminished growth-inhibitory response to ionizing radiation. Because previous studies have suggested that mutations in the tumor-suppressor gene p53 confer radio-resistance, we examined the p53 status of A375-C6 cells. Interestingly, both the parental and the transfected A375-C6 cells showed trisomy for wild-type p53 alleles. Exposure to ionizing radiation resulted in induction of p53 protein that localized to the nucleus in A375-C6 cells. These data suggest that inhibition of EGR-1 function confers radio resistance despite the induction of wild-type nuclear p53. Thus, EGR-1 is required for the growth-inhibitory response to ionizing radiation in A375-C6 cells.
Insights
Early growth response-1 (EGR-1) is crucial for the growth-inhibitory effects of ionizing radiation on melanoma cells. Inhibiting EGR-1 function reduces this response, even with functional p53 present.
Area of Science:
- Molecular Biology
- Oncology
- Radiation Biology
Background:
- Ionizing radiation induces the immediate-early gene early growth response-1 (EGR-1).
- EGR-1 protein has proposed roles in cell growth inhibition, but its specific function in radiation-induced growth suppression remains unclear.
- The tumor suppressor gene p53 is known to influence radio-resistance.
Purpose of the Study:
- To investigate the functional role of EGR-1 in the growth inhibition of tumor cells exposed to ionizing radiation.
- To determine if EGR-1 is necessary for the radiation-induced growth-inhibitory response in human melanoma cells.
Main Methods:
- Exposure of human melanoma cells (A375-C6) to ionizing radiation.
- Inhibition of EGR-1 function using a dominant-negative mutant via stable transfection.
- Inhibition of EGR-1 expression using an antisense oligomer via transient transfection.
- Analysis of p53 status and protein localization in response to radiation.
Main Results:
- Ionizing radiation induced EGR-1 protein in A375-C6 melanoma cells.
- Inhibition of EGR-1 function or expression led to a reduced growth-inhibitory response to ionizing radiation.
- A375-C6 cells possessed wild-type p53 alleles, and radiation induced nuclear p53 localization.
- EGR-1 inhibition conferred radio resistance, irrespective of wild-type nuclear p53 induction.
Conclusions:
- EGR-1 is essential for the growth-inhibitory effects of ionizing radiation in human melanoma cells.
- The requirement of EGR-1 for radiation-induced growth inhibition is independent of p53 status.
- Targeting EGR-1 may represent a strategy to modulate cellular responses to radiation therapy.