Table 1.

Fold change in IFN antiviral EC₅₀ values for shUSP18 stable cell lines

Cell line	% USP18 expression (95% confidence limit)a	HCVcc assay		HCV replicon		EMCV assay
		FC in IFN antiviral potency (95% confidence limit)b	P value	FC in IFN antiviral potency (95% confidence limit)b	P value	FC in IFN antiviral potency (95% confidence limit)b	P value
Control	70.4 (63–77)	1.1 (0.5–2.1)	0.90	0.7 (0.4–1.3)	0.29	0.7 (0.3–1.4)	0.26
shUSP18a	13.9 (11–17)	2.9 (1.4–5.7)	0.003	2.9 (1.5–5.7)	0.002	2.6 (1.3–5.1)	0.0076
shUSP18b	49.4 (37–62)	1.4 (0.7–3.0)	0.37	0.7 (0.3–1.5)	0.33	0.7 (0.4–1.4)	0.32
shUSP18c	10.9 (8–14)	1.1 (0.6–2.2)	0.73	1.4 (0.8–2.6)	0.25	0.9 (0.5–1.8)	0.77
shUSP18d	16.5 (10–23)	1 (0.5–2.1)	1.00	2.9 (1.5–5.6)	0.002	0.4 (0.2–0.8)	0.013

^aThe USP18 mRNA levels were assayed by using RT-PCR, and values were corrected for actin expression by adjusting the USP18 arbitrary copy number in each well by the relative amount of actin present. The corrected values were then normalized to the nontransfected cell control to give the percent expression (percent USP18). Values from Huh7.5 cells (n = 2), Huh7 cells (n = 1), and HeLa cells (n = 4) were averaged, and the 95% confidence limits are given in parentheses.

^bThe fold change (FC) is the difference in EC₅₀s between the nontargeting shRNA control stable cells and USP18 shRNA stable cell line (note that the control FC values were calculated relative to nontransfected cells). The FC values and probabilities were calculated by generating control test pairwise comparisons The shUSP18 IFN EC₅₀s were analyzed on the logarithmic scale by using a linear mixed model, comparing the nontargeting shRNA control stable cells and USP18 shRNA stable test cell lines within each assay type and accounting for experimental variation. The comparisons were summarized with FC values, 95% confidence limits (in parentheses), and P values.