P56LCK PLAYS A KEY ROLE IN TRANSDUCING APOPTOTIC SIGNALS IN T-CELLS

The CD4 receptor synergizes with the T-cell antigen receptor (TCR) in helper T-cell activation, However CD4 crosslinking in the absence of s imultaneous TCR engagement leaves the cells primed to activation depen dent apoptosis, To assess the role of the CD4 associated protein tyros ine kinase p56lck in CD4 priming to apoptosis we have constructed Jurk at T-cell lines stably transfected with a constitutively active form o f p56lck, These cells were constitutively primed to undergo apoptosis upon TCR crosslinking with specific antibodies, In addition the Jurkat JCaM1 line, which is defective for p56lck expression, was resistant t o TCR induced apoptosis, These data indicate that p56lck is required f or T-cell apoptosis and that CD4 priming of T-cells for antigen depend ent apoptosis is due to inappropriate or partial activation of the p56 lck signal transduction pathway.