Rac1 is a member of the Rho family of
small GTPases that control cells proliferation, differentiation, migration, and
inflammation. Rac1 is crucial in
tumorigenesis and development. Keratin17 and CD11b+Gr1+ cells are considered to regulate skin inflmmation. Here we discuss the regulation of Rac1 on skin
tumor formation and its relationship. In samples from human skin
squamous cell carcinoma (SCC), Rac1 activity was higher in
cancer tissues than in normal skin and activity correlated with
keratin 17 overexpression. In a DMBA/TPA-induced mouse skin
tumor model, inhibition of Rac1 activity and depletion of CD11b+Gr1+ cells resulted in significant
tumor formation. TPA induced recruitment of CD11b+Gr1+ cells into dermis; however, Rac1 inhibitor abolished this recruitment. In vitro, Rac1 induced
interferon (IFN) and interlukin (
IL6) production in keratinocytes, repression of
keratin 17 inhibited IFN and
IL6 production induced by Rac1. Moreover, both inhibition of Rac1 activity and repression of
keratin 17 restricted proliferation and induction of differentiation in keratinocytes. Coculture of CD11b+Gr1+ cells with keratinocytes activated Wnt pathway in keratinocytes, resulting in enhanced Rac1 activity, overexpression of
keratin 17, and hyperproliferation of keratinocytes. Our results suggested that hyperactive Rac1 recruited and interacted with CD11b+Gr1+ cells, inducing
keratin 17-regulated
inflammation and promoting skin
tumor formation.