Comparison of IL-13- and IL-4-induced signaling in EBV-immortalized human B cells

Interleukin 4 (IL-4) and Interleukin 13 (IL-13) have been shown to have numerous similar effects on human B cells; however, the mechanism of signal transduction is not known. We have examined IL-4- and IL-13-induced signal transduction in Epstein-Barr virus (EBV)-immortalized B cells. We demonstrate that Janus kinase 3 (JAK3) and Tyk2 but not JAK1 and JAK2 tyrosine kinases were constitutively phosphorylated in three EBV B cell lines. The phosphorylation level of Tyk2 was augmented at a low level in response to IL-13 and IL-4 in two of three cell lines; however, IL-13 did not induce or augment phosphorylation of the other JAK kinases. On the other hand, IL-4 further augmented phosphorylation of JAK3 and induced the phosphorylation of JAK1 kinases. IL-4 receptor p140 protein was also constitutively phosphorylated in two of three EBV B cell lines examined and both IL-4 and IL-13 further augmented its phosphorylation. Insulin receptor substrate (IRS)-1 or IRS-2 proteins were not constitutively phosphorylated nor did IL-13 and IL-4 induce phosphorylation of these proteins. In contrast to JAKs, IL-4-specific signal transducer and activator of transcription (STAT6) was not constitutively phosphorylated or activated in these cell lines, but both IL-4 and IL-13 induced their phosphorylation and activation. These findings suggest that in EBV-immortalized B cells JAK3 and Tyk2 proteins were constitutively phosphorylated but STAT6 protein was not constitutively phosphorylated. In addition, despite major similarities in biological effects between IL-4 and IL-13, phosphorylation patterns of JAK kinases in response to IL-13 in EBV-immortalized B cells appear to be different from those of IL-4.