Critical Role of STAT5 Transcription Factor Tetramerization for Cytokine Responses and Normal Immune Function (RNA)

Cytokine-activated STAT proteins dimerize and bind to high-affinity motifs, and N-terminal domain-mediated oligomerization of dimers allows tetramer formation and binding to low-affinity tandem motifs, but the functions of dimers versus tetramers are unknown. We generated Stat5a and Stat5b double knock-in (DKI) N-domain mutant mice that form dimers but not tetramers, identified cytokine-regulated genes whose expression required STAT5 tetramers, and defined consensus motifs for dimers versus tetramers. Whereas Stat5- deficient mice exhibited perinatal lethality, DKI mice were viable, indicating that STAT5 dimers were sufficient for survival. Nevertheless, STAT5 DKI mice had fewer CD4+CD25+ T cells, NK cells, and CD8+ T cells, with impaired cytokine-induced proliferation and homeostatic proliferation of CD8+ T cells. DKI CD8+ T cell proliferation following viral infection was diminished and DKI Treg cells did not efficiently control colitis. Thus, tetramerization of STAT5 is dispensable for survival but is critical for cytokine responses and normal immune function. T cells were extracted from spleen of wt and STAT5 double knocked in mice, and treated with IL-2. The cells were collected from 0h (without treatment), 2h, 6h and 17h, and chipped on Affy mouse 430 2.0 arrays.