Deacetyltransferase SirT1 Involved In Apoptosis Mediated By Apoptosis Inducing Factor AIF

Apoptosis-inducing factor (AIF) is a phylogeneticallyconserved flavoprotein. In healthy cells, AIF is confined to inner membrane of mitochondria where it excerts a vital function in redox metabolism, catylatics electron transport between cytochrome C and NAD. Upon cell death insults, AIF is cleaved by calpains from inner memberane of mitochondria to cytosol, then to nucleus with the help of N-terminal nuclear localization signal.In nucleaus, AIF binds DNA directly to provoke chromatinolysis and large-scale DNA fragmentation with CypA and H2AX. AIF mediate caspase-independent cell death that its function is not inhibited by the pan-caspase inhibitor like Z-VAD fmk.Currently, there are a lot of studies on AIF translocating to nucleus mechanism while it is not clear that how AIF mediates chromatin condensation and DNA degradation in nucleus.In our study, we find that SirT1 is a novel binding protein of AIF by mass spectra. SirT1 is an NAD+dependent hitone deacetylase that plays important roles in several signal passways including cell cycle control, aging and apoptosis, neuroprotecion, insulin secretion, metabolism of glucose and lipoid, inflammation, oxidative stress reaction, angiogenesis and so on.In order to study the interaction between AIF and SirT1, we do many researches both in vivo and in vitro. We purified AIF and SirT1 protein through prokaryotic expression system. Then we prove that the binding of AIF and SirT1 is direct.We also finds that AIF is an acetylated protein and it can be deacetylate by SirT1 at site K295.At last, we finds that SirT1 can inhibit apoptosis inducing function of AIF by interrupt the interaction of AIF and CypA other than decrease the DNA binding ability of AIF through gel retardation assay. We provide the basis for interaction between AIF and SirT1 in vivo and the posttranslational modification of AIF.