Activating transcription factor 3 (ATF3) expression is increased in erythema multiforme and is regulated by IFN-gamma in human keratinocytes. Experimental Dermatology 2010; 19: e310-e313. Abstract: Activating transcription factor 3 (ATF3) is a member of the ATF/cyclic AMP responsive element-binding protein (CREB) family of transcription factors and is involved in the regulation of immune responses, apoptosis, DNA repair and oncogenesis. The epidermal expression of ATF3 in the setting of cutaneous inflammation has not been well characterized. To examine the expression of ATF3 in the setting of inflammatory skin disease, ATF3 protein expression was analysed by immunohistochemistry (IHC). We found diffuse epidermal ATF3 protein expression in skin biopsies of erythema multiforme (EM). Given the role of interferon (IFN)-gamma in erythema multiforme, we sought to examine the impact of IFN-gamma on ATF3 expression in human keratinocytes. IFN-gamma induced ATF3 mRNA and protein in primary human keratinocytes and HaCaT cells. Thus, epidermal ATF3 expression can be increased in the setting of inflammatory skin diseases and is regulated by IFN-gamma in human keratinocytes.