PMLIV is the only PML isoform able to boost IFN-β synthesis through IRF3 activation.

<p>(A) Quantification of IFN-β mRNA in infected cells expressing different PML isoforms. U373MG-EV cells or cells stably expressing PMLI, PMLII, PMLIII, PMLIV, PMLV, PMLVI or PMLVIIb were infected with VSV at an MOI of 0.2 for 12 h. Total RNA was extracted and mRNA encoding IFN-β and GAPDH quantified by RT-qPCR. Mean values and standard deviations of two independent experiments are shown. (B) IRF-3 phosphorylation in VSV-infected or poly(I:C)-transfected cells expressing PMLIV. U373MG-EV or U373MG-PMLIV cells were left untreated (-), infected with VSV at an MOI of 1 for 3 or 6 h or transfected with poly(I:C). Cell extracts were analyzed by Western blotting using antibodies directed against PML, P-IRF3, IRF3 or Actin. (C) Effect of IRF3 knockdown on VSV inhibition and IFN-β induction. U373MG-EV and U373MG-PMLIV cells, prepared in duplicate, were transfected with scramble (Sc) or IRF3-specific siRNA. Two days later, cells were infected with VSV at an MOI of 1 for 8 h. Total RNA was extracted in one series and mRNA encoding IFN-βand GAPDH was quantified by RT-qPCR (left panel). Means and standard deviations of three independent experiments are shown. The second series was used for the determination by Western blot of IRF3 and VSV protein expression (right panel).