Dynamic analysis of STAT6 signalling in living cells.

Functional activity of N- and C-terminal fluorescent fusion proteins between STAT6 and EGFP was demonstrated through IL-4-dependent transcriptional activation and nuclear translocation. The N-terminal (EGFP-STAT6) fusion protein appeared to be more active than the C-terminal fusion. In HEK-293 cells both fusion proteins formed fluorescent nuclear foci following IL-4 stimulation, but in HeLa cells nuclear accumulation was homogeneous. Stimulation of the NF-kappaB pathway through TNFalpha treatment, or expression of p65-EGFP fusion protein, repressed both basal STAT6-dependent transcriptional activity and the extent of activation in response to IL-4. This indicates a novel mechanism of inhibition of STAT6 signalling by NF-kappaB activation.