Joselin Alvin P, Schulze-Osthoff Klaus, Schwerk Christian
Institute of Molecular Medicine, the University of Düsseldorf, 40225 Düsseldorf, Germany.
J Biol Chem. 2006 May 5;281(18):12475-84. doi: 10.1074/jbc.M509859200. Epub 2006 Mar 14.
Chromatin condensation and oligonucleosomal DNA fragmentation are the nuclear hallmarks of apoptosis. A proteolytic fragment of the apoptotic chromatin condensation inducer in the nucleus (Acinus), which is generated by caspase cleavage, has been implicated in mediating apoptotic chromatin condensation prior to DNA fragmentation. Acinus is also involved in mRNA splicing and a component of the apoptosis and splicing-associated protein (ASAP) complex. To study the role of Acinus for apoptotic nuclear alterations, we generated stable cell lines in which Acinus isoforms were knocked down by inducible and reversible RNA interference. We show that Acinus is not required for nuclear localization and interaction of the other ASAP subunits SAP18 and RNPS1; however, knockdown of Acinus leads to a reduction in cell growth. Most strikingly, down-regulation of Acinus did not inhibit apoptotic chromatin condensation either in intact cells or in a cell-free system. In contrast, although apoptosis proceeds rapidly, analysis of nuclear DNA from apoptotic Acinus knockdown cells shows inhibition of oligonucleosomal DNA fragmentation. Our results therefore suggest that Acinus is not involved in DNA condensation but rather point to a contribution of Acinus in internucleosomal DNA cleavage during programmed cell death.
染色质凝聚和寡核小体DNA片段化是细胞凋亡的核标志。细胞核内凋亡染色质凝聚诱导因子（Acinus）的一个蛋白水解片段由半胱天冬酶切割产生，该片段被认为在DNA片段化之前介导凋亡染色质凝聚。Acinus还参与mRNA剪接，是凋亡与剪接相关蛋白（ASAP）复合物的一个组成部分。为了研究Acinus在凋亡核改变中的作用，我们构建了稳定细胞系，通过诱导性和可逆性RNA干扰敲低Acinus异构体。我们发现，Acinus对于其他ASAP亚基SAP18和RNPS1的核定位及相互作用并非必需；然而，敲低Acinus会导致细胞生长减缓。最显著的是，在完整细胞或无细胞体系中，Acinus的下调均未抑制凋亡染色质凝聚。相反，尽管凋亡迅速发生，但对凋亡Acinus敲低细胞的核DNA分析显示寡核小体DNA片段化受到抑制。因此，我们的结果表明Acinus不参与DNA凝聚，而是提示Acinus在程序性细胞死亡过程中的核小体间DNA切割中发挥作用。
