INDUCTION OF LATE ACTIVATION EVENTS BY IG-BETA SIGNALING SUBUNIT OF B-CELL RECEPTOR IN JURKAT T-CELL WITHOUT TYROSINE PHOSPHORYLATION

T-lymphocyte activation consists of multiple intracellular signaling e vents, eventually leading to cellular proliferation by the control of cytokine gene expression and the acquisition of diverse effector funct ion. To investigate the functional specificity of ITAM (Immunoreceptor Tyrosine-based Activation Motif), chimeric molecules CD8-zeta, CD8-Ig alpha, CD8-Ig beta, which contain the extracellular and transmembrane domains of the human CD8 alpha molecule and the cytoplasmic tail of T -cell receptor (TcR) zeta chain, Ig alpha or Ig beta subunit of B-cell receptor, respectively, were stably expressed in a Jurkat cell line. Upon stimulation with anti-CD8 mAb OKT8, CD8-zeta and CD8-Ig alpha chi meric proteins induced tyrosine phosphorylation of various cytoplasmic substrates as seen in TcR stimulation, They were also capable of stim ulating IL-2 gene expression in a NF-AT dependent manner and inducing CD69 expression on the surface, However, stimulation of CD8-Ig beta ca n induce activation of CD69 surface expression and IL-2 gene expressio n equivalent to the level by CD8-Ig alpha and CD8-zeta without inducti on of the tyrosine phosphorylation of intracellular signaling molecule s. These results suggested that some of signaling chains containing IT AM may utilize a signal pathway without substrate tyrosine phosphoryla tion during T-cell activation leading to the IL-2 secretion.