UBE2N/UBE2V1 as a vulnerable link between keratinocytes and myeloid cells

About This Grant

ABSTRACT Epidermis of the skin undergoes continuous self-renewal through a tightly regulated balance of keratinocyte proliferation and terminal differentiation. Disruption of this balance is characteristic of inflammatory skin disorders such a psoriasis, atopic dermatitis, and neutrophilic dermatoses. The etiologies of these skin disorders are complex and heterogeneous, as are the needs for treatments. Our long-term goal is to elucidate how dysregulation of K63-Ub-mediated signal transduction pathways in keratinocytes contribute to skin inflammation. Towards this end, our recent studies have focused on UBE2N, a ubiquitin conjugase that forms heterodimers with an essential noncatalytic partner, UBE2V1 or UBE2V2, to specifically catalyze K63-Ub of target proteins. We demonstrate that conditional knockout of Ube2n in mouse keratinocytes induces psoriasis- like inflammatory skin lesions with a raised and scaly appearance. Transcriptomic and histological analyses identified a diminished epidermal stem cell compartment, a thickened epidermal spinous layer, and an increased infiltration of myeloid-skewed immune cells. This is correlated with increased expressions of myeloid cell chemokines such as CXCL1 and CXCL2 and IL1 family cytokines in keratinocytes and infiltrating myeloid cells. Oral delivery of the small molecule inhibitor of IRAK1/4, common mediators of the IL1R and TLR signaling pathways, alleviated immune infiltration and epidermal defects of the mutant skin. These data highlight a key role for UBE2N in regulation of epidermal and cutaneous immune homeostasis. In line with these animal data, recent GWS studies demonstrate a causal association between UBE2V1 polymorphism and psoriasis. Together, these data support the hypothesis that UBE2N partners with UBE2V1 to restrain keratinocyte recruitment of myeloid cells through suppression of IL1 and CXCL1/2-mediated inflammatory crosstalk between keratinocytes and myeloid cells. We propose 3 specific aims to: 1) validate the importance of UBE2N catalytic function and the role of UBE2V1 in epidermal homeostasis and cutaneous immune homeostasis, 2) determine the contribution of the IL1 signaling pathway in UBE2N-null skin inflammation, and 3) assess the utility of CXCL1/2 receptor antagonists in mitigating neutrophilic dermatosis. We will utilize conditional genetic animal models along with the cutting-edge techniques of single cell transcriptomics and global proteomics to comprehensively analyze mechanistic aspects of UBE2N/UBE2V1-mediated K63-Ub in cutaneous inflammation and therapeutic targeting. Results of these studies will reveal novel mechanisms of epidermal and cutaneous immune homeostasis, as well as insights for therapeutic development.