The expression of prolyl isomerase Pin1 is expanded in the skin of patients with atopic dermatitis and facilitates IL‐33 expression in HaCaT cells

Atopic dermatitis (AD) is attributable to both a genetic predisposition and environmental factors. Among numerous cytokines involved in the pathogenesis of AD, interleukin‐33 (IL‐33), reportedly escaping exocytotically in response to a scratch, is abundantly expressed in the skin tissues of patients with AD and is postulated to induce inflammatory and autoimmune responses. In this study, we first demonstrated that peptidylprolyl cis/trans isomerase, NIMA‐interacting 1 (Pin1), a unique enzyme which isomerizes the proline residues of target proteins, is abundantly expressed in keratinocytes, and that the areas where it is present in the skin tissues of AD patients became expanded due to hyperkeratosis. Thus, we investigated the effects of Pin1 on the regulation of IL‐33 expression using the human keratinocyte cell line HaCaT. Interestingly, silencing of the Pin1 gene or treatment with Pin1 inhibitors dramatically reduced IL‐33 expressions in HaCaT cells, although Pin1 overexpression did not elevate it. Subsequently, we showed that Pin1 binds to STAT1 and the nuclear factor‐kappaB (NF‐κB) subunit p65. Silencing the Pin1 gene with small interfering RNAs significantly reduced the phosphorylation of p65, while no marked effects of Pin1 on the STAT1 pathway were detected. Thus, it is likely that Pin1 contributes to increased expression of IL‐33 via the NF‐κB subunit p65 in HaCaT cells, at least modestly. Nevertheless, further study is necessary to demonstrate the pathogenic roles of Pin1 and IL‐33 in AD development.