Fig. 5

Furin-dependent activity of TARC–PE38 and increase in furin expression by HTLV-1 infection. a To test whether the effect of TARC–PE38 is dependent on furin expression, S1T cells were incubated with 500 ng/ml TARC–PE38 only (closed triangles), 500 ng/ml TARC–PE38 and a furin inhibitor (open squares), or the furin inhibitor only (closed circles) for 4 days. The numbers of live cells were counted daily to assess cell viability. The data are presented as means ± SD (×10⁵/ml). b Furin mRNA expression levels were measured with quantitative RT–PCR in HTLV-1-infected S1T, TL-Om1, HUT-102, and MT-2 cells and uninfected Jurkat cells. The data are presented as the expression level determined in each cell line relative to that in Jurkat cells. c The frequencies of tdTomato-positive cells in parental uninfected JET35 cells and HTLV-1-infected JEX22 cells before and 16 h after stimulation with PMA/ionomycin were analyzed with flow cytometry (upper panels) and the expression levels of furin were measured with quantitative RT–PCR (lower panel). The frequency in stimulated JEX22 cells is presented as a percentage (%) and the expression level determined in each cell line is relative to that in Jurkat cells. As for the stimulated JEX22 cells, only tdTomato-positive HTLV-1-producing cells were isolated and used for the assays. d PBMCs obtained from 29 HTLV-1-infected individuals were used to examine the relationship between furin expression and PVLs. The furin mRNA expression levels and PVLs in these PBMCs were determined with quantitative RT–PCR and quantitative PCR, respectively. Each furin mRNA expression level is presented as the level determined in each sample relative to that in Jurkat cells. PVLs determined in the samples are presented as copies/100 cells. The correlation between the two parameters was then investigated statistically (R = 0.689, p < 0.0001)