Background: The genetic locus CDKN2A has been linked to familial melanoma, and mutations or deletions in its coding sequence are seen in some cases of sporadic and familial melanomas. The protein encoded by CDKN2A, p16(INK4a), functions as a negative regulator of cell cycle progression and as a tumor suppressor, but the regulatory mechanisms involved in controlling its expression remain poorly defined.
Objective: This study tested the hypothesis that UVB irradiation, which transiently inhibits the growth of human melanocytes, is one of the regulators of p16(INK4a) expression.
Methods: Cultured human melanocytes were irradiated with UVB over a sublethal dosage range, and p16(INK4a) protein and mRNA levels were quantified at varying times thereafter by quantitative immunostaining and by Western and Northern blotting.
Results: Levels of p16(INK4a) protein in melanocytes increased significantly after sublethal UVB irradiation as compared with nonirradiated cells. Northern analysis indicated that p16(INK4a) messenger RNA coordinately increased in a dose-dependent manner more than 2-fold in irradiated cells at the tested doses.
Conclusion: UVB irradiation transcriptionally activates the expression of p16(INK4a) in cultured human melanocytes. Therefore the growth arrest that occurs with irradiation of melanocytes could be mediated, in part, by upregulation of p16(INK4a). This transient arrest may allow repair of UVB-induced DNA damage before cell division. Conversely, hereditary or acquired defects in CDK4A that give rise to functional insufficiency of p16(INK4a) could permit the premature propagation of melanocytes harboring potentially carcinogenic DNA damage.