Purpose: First, to investigate whether TP53 status and/or radiation-induced G1 arrest are associated with radiosensitivity, and, second, to detect possible associations between protein levels of p53, myc, ras or raf and radiosensitivity and to investigate whether hypoxia-induced changes in the levels of these proteins are related to hypoxia-induced changes in radiosensitivity in human melanoma lines.
Materials and methods: Radiosensitivity was assessed by clonogenic assays. TP53 status was investigated at the genomic level by constant denaturant gel electrophoresis and at the cDNA level by sequencing. G1 arrest was investigated by flow cytometric analysis of DNA. Protein expression of hypoxia-treated and untreated cells was assessed by flow cytometric measurements and Western blotting.
Results: Considerable differences in radiosensitivity were detected among melanoma lines with wild-type TP53. Only a fraction of the melanoma cells, differing between the lines, was arrested in G1. No association between the fraction of arrested cells and radiosensitivity was detected. Protein levels of p53, myc, ras or raf were not associated with radiosensitivity. Hypoxia-induced changes in p53, ras and raf levels were detected in all cell lines. Changes in the level of myc protein were detected for two of the four cell lines, while hypoxia-induced changes in radiosensitivity were observed only for one.
Conclusions: Differences in radiosensitivity among melanoma lines cannot be elucidated by TP53 status, differences in G1 arrest or different levels of p53, myc, ras or raf proteins. Hypoxia-induced changes in p53, myc, ras or raf levels do not seem to be related to hypoxia-induced changes in radiosensitivity.