IKKα signaling in the nucleus or cytoplasm of keratinocytes leads to opposite skin phenotypes.

The skin exerts essential roles for the organism survival, such as environmental barrier and immune functions. IKKα is known as an essential protein for skin homeostasis. However, the functions performed by IKKα in the skin and the mechanisms it employs are largely unknown, leading to contradictory interpretations and results regarding the consequences of its deregulation in pathologies such as non-melanoma skin cancer (NMSC). Here, using our previously generated transgenic mouse models which express IKKα in the cytoplasm (C-IKKα mice) or in the nucleus (N-IKKα mice) of basal keratinocytes, we demonstrate that at each subcellular localization, IKKα distinctly regulates signaling pathways important for maintaining the balance between keratinocyte proliferation and differentiation, as well as the inflammatory response of the skin. As a result, N-IKKα mice show an atrophic epidermis with exacerbated terminal differentiation, reminiscent of alterations observed in patients with ichthyosis. Conversely, C-IKKα mice display a hyperplastic epidermis with impaired epidermal differentiation and pustular inflammation, resembling patients with pustular psoriasis. Interestingly, C-IKKα keratinocytes are almost devoid of nuclear IKKα due to endogenous IKKα downregulation. However, these changes in the skin of C-IKKα mice do not lead to the development of squamous cell carcinomas (SCCs), unlike N-IKKα mice, which develop spontaneous SCCs.