CHARACTERIZATION OF CYTOKINE DIFFERENTIAL INDUCTION OF STAT COMPLEXESIN PRIMARY HUMAN T-CELL AND NK-CELL

Cytokines IL-2, IL-4, IL-6, IL-7, IL-12, and IL-15 are hey regulators of human peripheral blood T and NK cell activation and differentiation but the precise mechanisms that give rise to their differential activ ities within these cells are not clear. Recent studies reveal that a f amily of transcription factors, signal transducers and activators of t ranscription (STATs) directly mediate many cytokine signals. We analyz ed the activation of STATs in primary human T and NK cells by a variet y of specific cytokines. We demonstrate that IL-12 induces STAT4 only in freshly isolated primary NK cells, hut not in primary T cells, cons istent with the lack of the IL-12 receptor in resting T cells. hi cont rast, IL-4 induces different C epsilon GAS DNA-protein binding complex es in both T and NIC cells. Moreover, IL-4 costimulation T,idl IL-2 or IL-12 does not alter their own preferential GAS-like DNA binding patt erns when C epsilon-, Fc gamma RI-, and SIE GAS motif containing oligo nucleotide probes are compared, suggesting that induction of GAS-like DNA-protein binding complexes by IL-2, IL-4, and IL-12 is highly selec tive and represents one important factor in determining specific gene activation. In addition, IL-6 and IL-2 synergistically induce homo- an d heterodimerized STAT1 alpha and STAT3 in both NK and T cells, consis tent with their reported synergism in modulating perforin gene express ion. We further demonstrated that IL-2, -7, and. -15 induce multiple S TAT proteins, including STAT5a, STAT5b, STAT1 alpha, STAT3, and anothe r unidentified Fc gamma RI GAS DNA-binding protein. Finally, we observ ed that activated STAT5a and STAT5b proteins form distinct Fc gamma RI GAS binding patterns in T and NK cells, suggesting that they might ha re different roles in gene regulation. Our data provide evidence that the differential responses in gene expression and cell activation seen in primary Nh and T cells on direct stimulation with different cytoki nes may be a direct result of distinct activation of STAT transcriptio n factors.