Ultraviolet A (UVA) radiation is an oxidizing agent that strongly induces the heme oxygenase 1(HO-1) expression in cultured human skin fibroblasts, but weakly induces it in skin keratinocytes. Here, we report that low basal levels of HO- 1 and much higher basal levels of HO-2 protein were observed in keratinocytes compared with fibroblasts. Silencing of Bach1 strongly increased HO-1 levels in HaCaT transformed keratinocytes and these HO-1 levels were not further increased by either UVA irradiation or silencing of HO-2. This is consistent with the conclusion that high constitutive levels of HO-2 expression in keratinocytes are responsible for the resistance of these cells to HO-1 induction by UVA radiation and that Bach1 plays a predominant role in influencing the lack of HO-1 expression in keratinocytes. Bach1 inhibition reduced the 500 kJ/m2 UVA-induced cell damage by LDH membrane integrity and MTS viability assays. These results suggest that Bach1 inhibition protect against high dose of UVA irradiation induced damage in keratinocytes.© (2010) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.