Interferon alpha activates the tyrosine kinase Lyn in haemopoietic cells.

We investigated whether the src-family tyrosine kinase Lyn is involved in the generation of interferon alpha (IFN alpha) signals in haemopoietic cells. In vitro kinase assays using IFN alpha-sensitive cells of B-cell origin demonstrated the presence of IFN alpha-dependent kinase activity in anti-Lyn immunoprecipitates. Further studies demonstrated that Lyn associates via its src homology 2 (SH2) domain with the Janus family tyrosine kinase Tyk-2. This interaction was IFN alpha-dependent and involved direct binding of the SH2 domain of Lyn to the IFN alpha-activated form of Tyk-2. Thus, during binding of IFN alpha to its receptor in malignant haemopoietic cells, Lyn is engaged in an IFN alpha-signalling pathway, probably downstream of Tyk-2.