The gamma secretase-generated carboxyl-terminal domain of the amyloid precursor protein induces apoptosis via Tip60 in H4 cells

The amyloid precursor protein (APP), a large glycoprotein highly expressed in neurons, is cleaved in its intramembranous domain by gamma secretase to generate amyloid-beta and a free carboxyl-terminal intracellular fragment (APP-CT), which has previously been suggested to interact with the adapter protein Fe65 and the histone acetyltransferase Tip60. An identical gamma secretase activity mediates cleavage of Notch, releasing an intracellular signaling domain that translocates to the nucleus. We examined the effect of an ectopically expressed 58-amino acid APP-CT fragment (APP-C58) on human H4 neuroglioma cells. We demonstrate by confocal microscopy and fluorescence resonance energy transfer analysis that APP-C58 translocates to the nucleus and forms a complex in the nucleus with the Tip60, independent of interactions with Fe65. APP-C58 transfected H4 cells undergo apoptosis within 48-72 h, marked by nuclear blebbing, terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling (TUNEL) staining, and blockade by a caspase inhibitor. When nuclear access of APP-C58 is prevented by fusing with a strong membrane-targeting farnesylation domain, apoptosis is blocked. APP-C58-induced apoptosis was markedly enhanced by co-transfection with wild type Tip60 and decreased by mutant Tip60 lacking histone acetyltransferase activity, suggesting that Tip60 mediates APP-CT-induced cell death. Thus, gamma secretase cleavage of APP may contribute to Alzheimer's disease-related neurodegeneration in two ways: release of amyloid-beta and liberation of a bioactive carboxyl-terminal domain from membrane-bound APP.     

Regulation of FE65 nuclear translocation and function by amyloid beta-protein precursor in osmotically stressed cells

FE65, a neural adaptor protein, interacts with amyloid beta-protein precursor (APP) and is known to regulate amyloid beta generation from APP. FE65 also associates with nuclear proteins; however, its physiological function in the nucleus remains unclear. A fixed population of cytoplasmic FE65 is tethered to membranes by binding APP. This membrane-tethered FE65 is liberated from membranes by APP phosphorylation, which is facilitated by a stress-activated protein kinase in sorbitol-treated cells. Here we show that liberated FE65, which is distinct from "virgin" FE65 in the cytoplasm, translocates into the nucleus and accumulates in the nuclear matrix forming a patched structure. Targeting of FE65 into the nuclear matrix was suppressed by the APP intracellular domain fragment, which is generated by consecutive cleavages of APP. Thus, nuclear translocation of FE65 is under the regulation of APP. In the nucleus, FE65 induced gammaH2AX, which plays an important role in DNA repair as a cellular response by stress-damaged cells. These observations suggest that APP-regulated FE65 plays an important role in the early stress response of cells and that FE65 deregulated from APP induces apoptosis.     

乙酰基转移酶Tip60(KAT5)的功能研究进展

Tip60(KAT5)属于MYST乙酰基转移酶家族,同时它也是进化上非常保守的Nu A4蛋白质复合体的重要成员.过去十几年的研究证实,Tip60一方面可以作为转录调控因子结合核受体(如雄激素受体,AR)或c-MYC、AICD/Fe65、NCo R、E2F等转录因子来激活或抑制下游基因的表达,另一方面,KAT5可以乙酰化一系列蛋白来调控这些蛋白质的活性及稳定性,进而调控DNA损伤修复反应、细胞周期进程、细胞周期检查点的激活、凋亡、代谢及自噬等重要细胞功能.此外,Tip60在肿瘤的发生发展及转移、胚胎发育等过程中也发挥着至关重要的作用.本文将主要对Tip60近几年的研究进展做一个综述.