At the molecular level, SOCS1 binds ZD1839 price to JAK2 through its kinase inhibitory region (KIR), and impedes the IFN-γ receptor (IFN-γR) phosphorylation as well as STAT1 recruitment and activation [10, 11]. In light of this knowledge, epidermal SOCS1 can be considered as a promising target for the modulation of the inflammatory processes occurring in type 1- and Th17-mediated skin disorders. Indeed, SOCS1 manipulation by synthetic peptides mimicking
SOCS1 full-length KIR domain has been formerly performed to inhibit immune responses in some pathological contexts involving cytokine-dependent reactions. For instance, SOCS1 analogs were found to reduce JAK2/STAT1 activation in IFN-γ-activated macrophages, and to prevent inflammatory selleckchem processes in mouse models of allergic encephalomyelitis [12, 13]. Recently, through binding assay screening to JAK2 of a focused simplified combinatorial library, we identified new SOCS1 mimetic peptides, in particular the PS-5 peptide, which differed from
KIR in amino acid sequence and length, as some KIR residues were shortened or substituted to enhance its uptake by keratinocytes or binding to JAK2, respectively . In this study, we tested the ability of the PS-5 SOCS1 mimetic peptide to suppress the inflammatory responses in IFN-γ-activated epidermal keratinocytes by using in vitro and ex vivo experimental approaches. In particular, we evaluated the effects of PS-5 on cultured human keratinocytes and on epidermis of whole-skin explants following IFN-γ exposure, in terms of expression of proinflammatory genes, and capability to sustain inflammatory responses. We found that PS-5 efficiently suppressed the IFN-γ molecular signaling in keratinocytes, for instance the JAK2-STAT1-IRF-1 cascade,
as well as the downstream expression of STAT1-IRF-1-dependent genes. As a direct consequence of the inhibition of such proinflammatory Protein tyrosine phosphatase gene expression, PS-5-treated keratinocytes could no longer retain and induce migration of T lymphocytes in response to IFN-γ. In addition, human skin explants treated with PS-5 did not show the inflammatory signature typically induced by IFN-γ. IFN-γ activates a number of molecular pathways initiated by IFN-γRα phosphorylation, which culminate in the activation of transcription factors, mainly STAT1 and IRF1, and in the expression of IFN-γ-dependent genes [15, 16]. It is known that SOCS1 inhibitory effect on IFN-γ occurs mainly at the IFN-γR complex, which cannot be phosphorylated by JAK2 and, thus, cannot recruit STAT1. Therefore, we started analyzing the capability of the SOCS1 mimetic peptide PS-5 to inhibit the proximal events of the IFN-γ molecular cascade in IFN-γ-activated keratinocytes. In all experiments, PS-5 effects were compared with those obtained with the entire KIR domain of SOCS1 protein (KIR peptide) .