Differential Activation of P53 Downstream Genes in Malignant Melanoma Cells with Different Genetic Contexts

Abstract

This work aims to understand the differential activation of P53 and its downstream genes in response to UV irradiation in different genetic contexts of braf and p53. Human melanoma SK-MEL-28 (mutant BRAF and mutant P53), A375 (mutant BRAF and wild type P53), WM3211 (wild type BRAF and mutant P53), WM3918 (wild type BRAF and wild type P53), and melanocyte cells were irradiated by UV light. The total RNAs were then extracted from cells that were exposed to the UV irradiation (50 J/m2) and collected at 6 time points (0, 0.5, 1, 2, 3 and 4 hours) after the UV irradiation. Real-time PCR was employed to measure the expression of the p53 gene and its downstream genes mdm2, p21, p16, bcl2 and bax at the mRNA level. For all of the four melanoma cell lines, p53 and mdm2 expression at the mRNA level were downregulated in response to UV irradiation. After UV exposure, the p21 gene expression levels were down-regulated, but the relative ratio of bax/bcl2 gene expression level increased, indicating cells prefer to induce apoptosis rather than cell cycle arrest. In the melanocyte, the transcription level of p53 slightly declined after UV light irradiation. A decreasing expression level of mdm2 in both melanocytes and melanoma might predict the same pattern of response to UV light in all melanin-producing cells. The upregulating level of p16 and decreased ratio of bax/bcl2 demonstrate that in response to UV exposure, normal melanocyte cells are prone to stop the cell cycle and repair DNA damage instead of triggering apoptosis. Understanding the deregulation of the P53 network in melanoma cells with different genetic contexts will help identify novel drug targets that restore the function of the P53 network.