Neutrophil-dominant psoriasis-like skin inflammation induced by epidermal-specific expression of Raf in mice

Raf is one of the downstream effectors of Ras GTPases. The induction of Raf in the epidermis causes the proliferation of keratinocytes and epidermal hyperplasia. However, skin inflammation accompanying Ras-induced epidermal reactions has not been fully delineated.

The aim of this study was to characterize inflammatory reactions induced by epidermal-specific Raf expression and to elucidate its role in skin inflammation.

K14-Raf:ER transgenic mice, in which the 4-hydroxytamoxifen (4OHT)-responsive mutant estrogen receptor (ER) ligand binding domain-Raf fusion gene was expressed under control of the keratin 14 promoter, were used to characterize inflammatory reactions induced by Raf expression in the epidermis.

A single topical application of 4OHT induced the expression of phosphorylated extracellular signal-related kinase 1/2 and elicited neutrophil-dominant inflammatory infiltrates in the skin. The Raf expression also rapidly induced the production of several cytokines and chemokines, including VEGF and CXCL1, by keratinocytes and in mouse skin in vivo. Furthermore, CD4-positive cells from regional lymph nodes had the potential to differentiate into IFN gamma- and IL17-producing cells. Treatment with an anti-Gr-1 antibody diminished the Raf-induced cutaneous inflammation and partially reversed the epidermal hyperplasia and hyperkeratosis.

Activation of the Raf signaling pathway is involved in the epidermal hyperplasia and the neutrophil-dominant cutaneous inflammatory reactions which are characteristics of psoriasis.