Synergistic induction of IL-23 by TNFα, IL-17A, and EGF in keratinocytes.

IL-23 is an inflammatory cytokine that plays an essential role in Th17 immunity by enhancing Th17 cell proliferation and survival, and Th17 cytokine production. IL-23 has pathogenic roles in the development of Th17-mediated inflammatory diseases including psoriasis. Despite successful treatment of psoriasis by blocking IL-23, the regulation of IL-23 expression in psoriasis patients is largely unknown. Dendritic cells are generally considered to be the primary source of IL-23 in psoriasis. While high levels of IL-23 are found in psoriatic epidermis, IL-23 expression in psoriatic keratinoctyes remains a controversial issue. In this study, we demonstrated that IL-23 production is induced by a combination of TNFα and IL-17A in human keratinocytes. Additionally, this IL-23 induction by TNFα and IL-17A is further increased in psoriatic keratinocytes and is enhanced by EGFR signaling. Although IL-23 is also robustly induced by toll-like receptor agonists in dendritic cells and macrophages, IL-23 expression in these cell types is not regulated by TNFα, IL-17A, and EGFR signaling. Given that IL-23 is essential for maintaining Th17 activation, IL-23 induction by TNFα, IL-17A, and EGF in keratinocytes could play an important pathological role in psoriasis pathogenesis as well as the cutaneous rash associated with EGFR inhibition therapy.

Inverse Correlation of TRIM32 and Protein Kinase C ζ in T Helper Type 2-Biased Inflammation.

Atopic dermatitis (AD) is a T helper (Th)2-biased disease with elevated expression of Th2 cytokines that responds to Th2 signaling blockade. TRIM32 is an E3 ubiquitin ligase with innate antiviral activity. In our previous studies, we showed that Trim32 null mice developed Th2-biased skin inflammation in response to imiquimod and associated a low level of TRIM32 with AD. In this study, we provide evidence that TRIM32 deficiency contributes to enhanced Th2 cell differentiation in vitro. Analysis of TRIM32-associated proteins from public databases identified protein kinase C (PKC)ζ as a TRIM32-associated protein that contributes to the regulation of Th2 signaling. We demonstrated that PKCζ was specifically ubiquitinated by TRIM32 and, further, that PKCζ stability tended to be increased in Th2 cells with a Trim32 null background. Furthermore, Prkcz null mice showed compromised AD-like phenotypes in the MC903 AD model. Consistently, a high PKCζ and low TRIM32 ratio was associated with CD4+ cells in AD human skin compared with those in healthy controls. Taken together, these findings suggest that TRIM32 functions as a regulator of PKCζ that controls the differentiation of Th2 cells important for AD pathogenesis.

Trim32 Deficiency Enhances Th2 Immunity and Predisposes to Features of Atopic Dermatitis.

Altered innate immunity is a feature of certain skin inflammatory diseases such as psoriasis and atopic dermatitis (AD). In this study, we provide evidence that deficiency in Trim32 (a tripartite motif [TRIM] protein with innate antiviral activity) contributes to a T helper type 2 biased response and predisposes to features of AD in mice. On treatment with the toll-like receptor 7 agonist imquimod (IMQ), Trim32 knockout mice displayed compromised psoriasiform phenotypes and defective T helper type 17 response. Instead, IMQ treatment of Trim32 knockout mice induced AD-like phenotypes with enhanced skin infiltration of eosinophils and mast cells, elevation of T helper type 2 cytokines/chemokines expression, and reduced expression of filaggrin protein expression. Furthermore, although the induction of phosphorylated Stat3 and RelA was compromised after IMQ treatment in the knockout mice, phosphorylated Stat6 was elevated. CC chemokine ligand 20 induction by tumor necrosis factor-α and IL-17A was reduced in Trim32-deficient keratinocytes, whereas CC chemokine ligand 5 induction by tumor necrosis factor-α and IL-4 was enhanced. In addition, Trim32 protein levels were elevated in mice treated with IMQ. Unlike Trim32 overexpression in psoriasis, TRIM32 levels were low in patients with AD. Based on Trim32 induction by IMQ, the lower levels of TRIM32 in AD skin compared with healthy control and psoriatic skin suggest a defective TRIM32 pathway in AD pathogenesis.