ABSTRACT
The T cell antigen receptor (TcR) in combination with costimulatory signals triggered by accessory molecules present on the surface of the antigen-presenting cells (APC) regulates the activation and growth of T lymphocytes. Calyculin A and Okadaic acid is known to be an inhibitor of serine/threonine phosphatase and RK-682 specifically blocks functions of tyrosine phosphatase. To investigate roles of these inhibitors in TcR-mediated signaling cascade, chimeric molecule CD8-5 which contains the extracellular and transmembrane domains of the human CD8a molecule and the cytoplasmic tail of TcR 5 chain were stably expressed in Jurkat cell line. CD8-5 chimeric protein induced tyrosine phosphorylation of various cytoplasmic substrates and IL-2 gene expression in a NFAT dependent manner by stimulation with anti-CD8 mAb OKT8 as seen in TcR stimulation. When CD8-5 transfectants were preincubated with Okadaic acid, Calyculin or RK682, they differentially affected tyrosine phosphorylation of signaling mediators including CD8-5 molecule. When Jurkat Tag cell line was used where SV40 T antigen is stably expressed and the expression of p-galactosidase is driven by the multiple NFAT binding sites plus minimal IL-2 promoter, these phosphatase inhibitors -RK682, Calyculin A, Okadaic acid- effectively inhibited IL-2 gene expression at the concentration of 1.2832 x 10 ' M, 3.9924 x 10 M, 7.2707 x 10 M respectively. These results suggested that Okadaic acid, Calyculin or RK682 modulate TcR-proximal as well as TcR-distal signaling events during T cell activation.