Conditional ablation of C/EBPβ demonstrates its keratinocyte-specific requirement for cell survival and mouse skin tumorigenesis

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Abstract
The CCAAT/enhancer binding protein β (C/EBPβ) is implicated in the regulation of many different molecular and physiological processes. Mice with a germline deletion of C/EBPβ (C/EBPβ−/−) display phenotypes in a multitude of cell types and organ systems, including skin where C/EBPβ−/− mice exhibit increased apoptosis in epidermal keratinocytes in response to carcinogen treatment and are completely resistant to carcinogen-induced skin tumorigenesis. To determine the contribution of systemic versus cell autonomous functions of C/EBPβ to specific phenotypes, mice with a conditional ‘floxed’ C/EBPβ null allele were generated. Epidermal-specific deletion of C/EBPβ was achieved by Cre recombinase expression from a keratin 5 (K5) promoter. Similar to C/EBPβ−/− mice, K5-Cre;C/EBPβfl/fl mice were completely refractory to 7,12 dimethylbenz[a]anthracene (DMBA)-induced skin tumorigenesis and these mice displayed increased DMBA-induced apoptosis in epidermal keratinocytes compared to wild-type mice. In contrast, mice lacking the related gene, C/EBPδ, were not resistant to DMBA-induced skin tumorigenesis, indicating a unique role of C/EBPβ in skin tumor development. Our findings demonstrate that C/EBPβ exerts an essential, keratinocyte-intrinsic role in cell survival in response to carcinogen treatment and the elimination of C/EBPβ in keratinocytes is sufficient to confer complete resistance of the skin to chemical carcinogenesis.