Differential responses of normal human melanocytes to intra- and extracellular dsRNA.

ABSTRACT

Viral factor has been implicated in the etiopathogenesis of vitiligo. To elucidate the effects of viral double-stranded RNA (dsRNA) on melanocytes and to explore the underlying mechanisms, primary cultured normal human melanocytes were treated with synthetic viral dsRNA analog poly(IC). The results demonstrated that poly(IC)-triggered apoptosis when transfected into melanocytes, while extracellular poly(IC) did not have that effect. Intracellular poly(IC)-induced melanocyte death was decreased by RIG-I or MDA5 siRNA, but not by TLR3 siRNA. Both intracellular and extracellular poly(IC) induced the expression of IFNB, TNF, IL6, and IL8. However, extracellular poly(IC) demonstrated a much weaker induction capacity of cytokine genes than intracellular poly(IC). Further analysis revealed that phosphorylation of TBK1, IRF3, IRF7, and TAK1 was differentially induced by intra- or extracellular poly(IC). NFκB inhibitor Bay 11-7082 decreased the induction of all the cytokines by poly(IC), suggesting the ubiquitous role of NFκB in the process. Poly(IC) treatment also induced the phosphorylation of p38 and JNK in melanocytes. Both JNK and p38 inhibitors showed suppression on the cytokine induction by intra- or extracellular poly(IC). However, only the JNK inhibitor decreased the intracellular poly(IC)-induced melanocyte death. Taken together, this study provides the possible mechanism of viral factor in the pathogenesis of vitiligo.