The zinc finger protein A20 interacts with a novel anti-apoptotic protein which is cleaved by specific caspases

A20 is a Cys(2)/Cys(2) zinc finger protein which is induced by a variety of inflammatory stimuli and which has been characterized as an inhibitor of c ell death by a yet unknown mechanism. In order to clarify its molecular mec hanism of action, we used the yeast two-hybrid system to screen for protein s that interact with A20. A cDNA fragment was isolated which encoded a port ion of a novel protein (TXBP151), which was recently found to be a human T- cell leukemia virus type-I (HTLV-I) Tax-binding protein. The full-length 23 86bp TXBP151 mRNA encodes a protein of 86kDa, Like A20, overexpression of T XBP151 could inhibit apoptosis induced by tumour necrosis factor (TNF) in N IH3T3 cells, Moreover, transfection of antisense TXBP151 partially abolishe d the anti-apoptotic effect of A20, Furthermore, apoptosis induced by TNF o r CD95 (Fas/ APO-1) was associated with proteolysis of TXBP151. This degrad ation could be inhibited by the broad-spectrum caspase inhibitor zVAD-fmk o r by expression of the cowpox virus-derived inhibitor CrmA, suggesting that TXBP151 is a novel substrate for caspase family members. TXBP151 was indee d found to be specifically cleaved in vitro by members of the caspase-3-lik e subfamily, viz, caspase-3, caspase-6 and caspase-7, Thus TXBP151 appears to be a novel A20-binding protein which might mediate the anti-apoptotic ac tivity of A20, and which can be processed by specific caspases.