IL-17A Promotes Psoriasis-Associated Keratinocyte Proliferation through ACT1-Dependent Activation of YAP–AREG Axis

Psoriasis is a recurrent inflammatory skin disorder characterized by epidermal hyperplasia, which is primarily driven by IL-17A. The Hippo-YAP signaling pathway plays a vital role in cell survival and tissue growth, and its target gene, AREG, has been reported to promote the development of psoriasis. However, whether IL-17A promotes keratinocyte proliferation through regulating Hippo-YAP signaling has not been explored. In this study, we show that the YAP-AREG pathway is activated in human psoriatic skin and is suppressed by IL-17A antagonist secukinumab and that imiquimod and IL-17A administration activates the YAP-AREG axis in mice epidermis. In vitro studies using HaCaT and normal human epidermal keratinocyte cells suggest that IL-17A enhances AREG expression and keratinocyte proliferation by activating Hippo-YAP signaling. Mechanistically, IL-17A stimulates the recruitment of MST1 to ACT1 in keratinocytes, which leads to reduced MST1-LATS1 interaction and YAP dephosphorylation. Together, our findings reveal a previously unknown mechanism in which IL-17A promotes keratinocyte proliferation in psoriasis, namely through activating YAP-AREG signaling.