GADD45 regulates G2/M arrest, DNA repair, and cell death in keratinocytes following ultraviolet exposure

GADD45 is a multifunctional protein that is regulated by p53. p53 plays an important role in regulating DNA repair and in the response to ultraviolet light in keratinocytes. This study investigates the role of GADD45 in the response to ultraviolet B. Cell cycle analysis demonstrated that wild-type and Gadd45-deficient cells have transient G2/M arrest, but only in the wild-type cells was arrest sustained. Cdc2 kinase activity in immunoprecipitates from normal and Gadd45-deficient cells decreases after irradiation in normal cells but not in Gadd45-deficient cells. An immunofluorescent study with Cdc2 antibody demonstrated diffuse cellular fluorescence before ultraviolet irradiation in both Gadd45-deficient and wild-type cells, but upon ultraviolet irradiation only Gadd45-proficient cells showed Cdc2 sequestration in the cytoplasm. Gadd45-deficient cells also have a slower rate of nucleotide excision repair. The lack of G2/M arrest coupled with reduced DNA repair leads to a higher ultraviolet sensitivity of Gadd45-deficient cells. These results reveal that GADD45 promotes G2/M arrest via nuclear export and kinase activity of Cdc2, increases global genomic DNA repair, and inhibits cell death in keratinocytes. Thus, GADD45 plays an important role in maintaining genomic integrity in ultraviolet-exposed skin.