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Hsin Chien, Christine Iris Alston, Richard D Dix; Knockdown of suppressor of cytokine signaling (SOCS)1 or SOCS3 gene expression during human cytomegalovirus (HCMV) infection results in altered expression of SOCS inducers and cell-type-dependent SOCS expression. Invest. Ophthalmol. Vis. Sci. 2014;55(13):2821.
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© ARVO (1962-2015); The Authors (2016-present)
SOCS family proteins regulate immune responses to pathogen invasion by dampening cytokine expression and favoring pathogenesis and disease development. SOCS1 inhibits antiviral interferon (IFN-α/β) signaling, whereas SOCS3 regulates signaling by the proinflammatory interleukin-6 (IL-6) cytokine family. We have shown previously that SOCS1 and SOCS3 mRNAs and proteins are robustly upregulated within MCMV-infected eyes of mice with retinitis during retrovirus-induced immunodeficiency (MAIDS). To extend these findings to AIDS-related HCMV retinitis, we performed in vitro experiments to determine the effect of knockdown of SOCS1 or SOCS3 gene expression on IFN-α/β and IL-6 mRNA production during productive (lytic) HCMV infection.
Monolayers of human retinal pigment epithelial (ARPE-19) cells and human lung fibroblast (MRC-5) cells were transfected with SOCS1 or SOCS3 siRNAs (200 nM), inoculated 24 hr later with HCMV (Towne) (moi = 5) or maintenance medium (control), harvested at 30 min to 48 hr postinfection (pi), and compared by quantitative RT-PCR assay for SOCS1, SOCS3, IFN-α, IFN-β, and IL-6 mRNA production.
When compared with mock-infected cells, knockdown of SOCS3 in HCMV-infected ARPE-19 cells resulted in stimulation of SOCS1 mRNA production at 24 to 48 hr pi, and, conversely, knockdown of SOCS1 resulted in stimulation of SOCS3 mRNA production at 30 min pi. Knockdown of either SOCS1 or SOCS3 also induced significant production of IFN-α, IFN-β, and IL-6 mRNAs in HCMV-infected ARPE-19 cells. In contrast, knockdown of SOCS3 or SOCS1 in HCMV-infected MRC-5 cells failed to stimulate SOCS1 or SOCS3 mRNA production, respectively, as seen in HCMV-infected ARPE-19 cells. Whereas knockdown of either SOCS3 or SOCS1 resulted in IL-6 mRNA induction at 24 to 48 hr pi, SOCS3 knockdown induced IFN-α mRNA production at 6 hr pi and SOCS1 knockdown induced IFN-β production at 6 to 24 hr pi.
HCMV infection of both ARPE-19 and MRC-5 cells resulted in induction of IFN-α, IFN-β, and IL-6 mRNAs following knockdown of SOCS1 or SOCS3 gene expression. HCMV-infected ARPE-19 cells, but not HCMV-infected MRC-5 cells, showed SOCS1 expression after SOCS3 knockdown and vice-versa, a finding that suggests that SOCS expression is cell-type-dependent during HCMV infection.
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