Project description: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.
Project description:Progenitor cells at the basal layer of skin epidermis play an essential role in maintaining tissue homeostasis and enhancing wound repair in skin. The proliferation, differentiation, and cell death of epidermal progenitor cells have to be delicately regulated, as deregulation of this process can lead to many skin diseases, including skin cancers. However, the underlying molecular mechanisms involved in skin homeostasis remain poorly defined. In this study, with quantitative proteomics approach, we identified an important interaction between KDF1 (Keratinocyte Differentiation Factor 1) and IKKα (IκB kinase α) in differentiating skin keratinocytes. Ablation of either KDF1 or IKKα in mice leads to similar but striking abnormalities in skin development, particularly in skin epidermal differentiation. With biochemical and mouse genetics approach, we further demonstrate that the interaction of IKKα and KDF1 is essential for epidermal differentiation. To probe deeper into the mechanisms, we find that KDF1 associates with a deubiquitinating protease, USP7 (Ubiquitin Specific Peptidase 7), and KDF1 can regulate skin differentiation through deubiquitination and stabilization of IKKα. Taken together, our study unravels an important molecular mechanism underlying skin tissue homeostasis and epidermal differentiation.
Project description:Cellular binary fate decisions require the progeny to silence genes associated with the alternative fate. The major subsets of alpha:beta T cells have been extensively studied as a model system for fate decisions. While the transcription factor RUNX3 is required for the initiation of Cd4 silencing in CD8 T cell progenitors, it is not required to maintain the silencing of Cd4 and other helper T lineage genes. The other runt domain containing protein, RUNX1, silences Cd4 in an earlier T cell progenitor, but this silencing is reversed whereas the gene silencing after RUNX3 expression is not reverse. Therefore, we hypothesized that RUNX3 and not RUNX1 recruits other factors that maintains the silencing of helper T lineage genes in CD8 T cells. To this end, we performed a proteomics screen of RUNX1 and RUNX3 to determine candidate silencing factors.
Project description:It has long been known that excessive mitotic activity due to H-Ras can block keratinocyte differentiation and cause skin cancer. It is not clear, however, whether there are any innate surveillants that ensure keratinocytes undergoing terminal differentiation, preventing the disease. IKKα induces keratinocyte terminal differentiation and its reduction promotes skin tumor development. However, its nature function in skin cancer is unknown. Here we found that mice with IKKα deletion in keratinocytes or in hair follicle keratinocytes developed a thickened epidermis and spontaneous squamous cell-like carcinomas. Inactivation of epidermal growth factor receptor (EGFR) or reintroduction of IKKα inhibited excessive mitosis, induced terminal differentiation, and prevented skin cancer through an EGFR-driven autocrine loop in mice. Thus, IKKα serves as an innate surveillant.
