Induction of SOCS-1 in HSV-1-Infected Murine Keratinocytes: A Mechanism of Inhibition of Interferon Gamma

by Frey, Kenneth Gene

Epidermal cells such as keratinocytes are the major site of Herpes Simplex Virus Type 1 (HSV-1) replication in active primary or recurring herpes infection. In this study, a murine keratinocyte cell line (HEL-30) was shown to be refractory to IFN? induction of an antiviral state to HSV-1 infection, while IFN? did induce an antiviral state in a murine fibroblast cell line (L929). Particularly, IFN-gamma and its peptide mimetic protected fibrobasts from viral-induced cytopathic effect while the keratinocytes were destroyed by the infection. Suppressor of cytokine synthesis-1 (SOCS-1) a negative regulator of IFN?, was hypothesized to be responsible for the refractiveness of HEL-30 cells to IFN? treatment. In contrast to negligible expression in the fibroblasts, HSV-1 caused the keratinocytes to express 4-fold higher levels of SOCS-1 mRNA. SOCS-1 protein was also elevated in HSV-1-infected HEL-30 cells. In agreement with these observations, activation of STAT-1?, a key protein involved in IFN? signaling, was inhibited in HSV-1-infected HEL-30 cells while not affected in L929 cells. Additionally, HSV-1-infected HEL-30 cells showed increased activity at the SOCS-1 promoter in a luciferase assay. Keratinocytes were responsive to the antiviral action of IFN-gamma and protected from lysis by pretreatment with either a peptide antagonist of SOCS-1or SOCS-1 small interfering RNA. An interferon-sensitive mutant of HSV-1 (dl1403) was sensitive to IFN? treatment in HEL-30 cells. HSV-1 dl1403 also induced only moderate activity at the SOCS-1 promoter as compared to wild-type virus. These results suggest a role for regulation of SOCS-1 in treatment of HSV-1-induced cytopathology. Further, the actions of the SOCS-1 peptide antagonist have implications for regulation of immune responses in a number of diseases from cancer to auto-immune disorders.