MECHANISTIC STUDIES OF TRANSFORMING GROWTH-FACTOR-BETA INHIBITION OF IL-2-DEPENDENT ACTIVATION OF CD3- LARGE ANTIGRANULOCYTES LYMPHOCYTE FUNCTIONS - REGULATION OF IL-2R-BETA (P75) SIGNAL TRANSDUCTION

CD3- large granular lymphocyte (LGL) express constitutive levels of functional IL-2R-beta. TGF-beta inhibited several IL-2R-beta-mediated events in LGL, including IL-2-induced NK and lymphokine-activating factor activities, IFN-gamma gene expression and secretion, and IL-2R-alpha expression. TGF-beta inhibited these IL-2-induced LGL functions in a dose-dependent and reversible manner. By contrast, TGF-beta had little effect on LGL IL-2R-beta expression and TGF-beta receptors were not induced by IL-2. Studies were performed to examine binding and internalization of radiolabeled IL-2. These experiments demonstrated that the rapid binding and internalization of [I-125]IL-2 was not altered in CD3-LGL pretreated with TGF-beta. These internalization studies indicated that the TGF-beta inhibition represented postreceptor-binding events in NK cells. Further studies were initiated to examine signaling events in CD3-LGL. When IL-2-induced tyrosine phosphorylation events were examined, significant inhibition was seen of selected phosphoproteins in TGF-beta-pretreated cells. In addition, the ability of TGF-beta to also inhibit IL-2 induction of LGL IL-2R-alpha and IFN-gamma mRNA expression was consistent with the hypothesis that posttranscriptional mechanisms were unlikely to be affected by TGF-beta. Collectively, these data indicated that TGF-beta inhibited IL-2-induced CD3- LGL functions and suggested that TGF-beta inhibition occurs either at the level of specific tyrosine phosphorylation and/or IL-2-induced transcriptional control factors.