Iap Family Proteins Livin In The Mechanism Of Apoptosis

Apoptosis, also known as programmed cell death (PCD), is a gene controlled active cell suicide process that is important for the maintenance of balance of organisms. Livin (also called ML-IAP or KIAP) , a member of the inhibitor of apoptosis protein (IAP) family encodes a protein containing a single baculoviral IAP repeat (BIR) domain and a COOH-terminal RING finger domain. It has been reported that Livin directly interacts with caspase-3, -7 in vitro and caspase-9 in vivo via its BIR domain and is negatively regulated by Smac/DIABLO. Livin is a poor caspases inhibitor, the detailed mechanism underlying its anti-apoptotic function needs to be clarified and characterized. So we do the underlying research and get some conclusions.In this report, we provided, for the first time, the evidence that Livin can act as an E3 ubiquitin ligase for targeting the degradation of Smac/DIABLO. Both BIR domain and RING finger domain of Livin are indispensable for this degradation of Smac/DIABLO in vivo and in vitro.We also demonstrated that Livin is an unstable protein with a half-life of less than 4 hours in living cells. Degradation of Livin can be blocked by proteasome inhibitor MG132 or ALLN, suggesting that Livin is a target for ubiquitin-proteasome degradation.Furthermore, we found that RING domain of Livin promotes its auto-ubiquitination, whereas BIR domain displays degradation-inhibitory activity.We constructed several BIR point mutants of Cys124, Trp134, His144 to form C124A, W134A and H144A and RING deletion mutant. Mutation in the Livin BIR domain greatly enhances its instability and nullifies its binding to Smac/DIABLO, resulting in a reduced anti-apoptosis inhibition, while RING deletion mutant can still interact with Smac/DIABLO. Livin BIR mutant may...