5 versus Estrogen antagonist 38.5% in lane 5 versus lane 11 to 78.7 versus 21.3% in lane 6 versus lane 12). The densitometry data obtained from multiple blots confirmed the concomitant cytosolic accumulation of p48 and pY-STAT6 accompanied with a nuclear decrease in p48 prominent by 4 h post-IFN-α stimulation (Fig. 4B). Furthermore, co-immunoprecipitation experiments demonstrated that pY-STAT6 strongly interacts with IFN-α-induced pY-STAT2 as well as with p48 in the cytoplasm (Fig. 5A), which is also evident by 4 h after IFN-α treatment. On the other hand, neither STAT1 nor importin-α which is known to mediate

the nuclear translocation of STATs 35, interacted with pY-STAT6 (Fig. S3). By confocal analysis, the concomitant cytoplasmic accumulation of pY-STAT6 (green) and p48 (red), or that of STAT2 (green) and p48 (red) was also confirmed upon 4 h pretreatment of IFN-α followed by IL-4 stimulation (Fig. 5B). Together these data suggest that pY-STAT6 is likely to complex with IFN-α-induced pY-STAT2

and p48, and is retained in the cytosol. The concomitant cytosolic retention of pY-STAT6 by pY-STAT2:p48, and the subsequent decrease in pY-STAT6 nuclear translocation may be responsible for the inhibitory effect of IFN-α on the IL-4-activated CD23 gene expression in B cells (Fig. 1C). The above data indicate that IFN-α and IL-4 treatment induced a concurrent cytoplasmic accumulation and complex FK506 chemical structure formation of the IFN-α-induced pY-STAT2:p48 and the IL-4-induced pY-STAT6 in Ramos B cells. As much as the resulting retention of pY-STAT6 by pY-STAT2:p48 in the cytoplasm may lead to the suppression

of IL-4 signaling into Methamphetamine the nucleus, the retention of pY-STAT2:p48 by pY-STAT6 would have a similar role in the inhibition of nuclear localization of ISGF3 induced by IFN-α. In fact, IL-4 is shown to exert an antagonistic action on IFN-α signaling in certain cell systems 17. As an IFN-α target gene counter-regulated by IL-4 in B lymphoma cells, IRF7 was examined. As a member of IRFs involved in IFN-α response, IRF7 has been reported to be induced via IFN-α-activated ISGF3 in lymphomas and DC, and to play a role in the induction of EBV-transformed lymphoma and the activation of type I IFN genes 17, 36, 37. The quantitative RT-PCR analysis of IRF7 mRNA in Ramos B cells has revealed that IFN-α treatment induced IRF7 at a significant level by 4 to 8 h, and IL-4 reduced IFN-α-induced IRF7 mRNA levels in a time-dependent manner (Fig. 6). The result together with the data from Figs 3–5 raises a possibility that the inhibition of IL-4 on the IFN-α-induced IRF7 gene expression (Fig. 6) is probably interceded by the complex formation and cytoplasmic retention of the pY-STAT6:pY-STAT2:p48.