Goebel Wiebke, Obermeyer Natalie, Bleicher Nadja, Kratzmeier Martin, Eibl Hans-Jörg, Doenecke Detlef, Albig Werner
Institute for Biochemistry and Molecular Cell Biology, University of Göttingen, Humboldtallee 23, D-37073 Göttingen, Germany.
Biol Chem. 2007 Feb;388(2):197-206. doi: 10.1515/BC.2007.022.
Changes in chromatin structure, histone phosphorylation and cleavage of DNA into nucleosome-size fragments are characteristic features of apoptosis. Since H1 histones bind to the site of DNA cleavage between nucleosomal cores, the question arises as to whether the state of H1 phosphorylation influences the rate of internucleosomal cleavage. Here, we tested the relation between DNA fragmentation and H1 phosphorylation both in cultured cells and in vitro. In Jurkat cells, hyperosmotic mannitol concentration resulted in apoptosis, including nucleosomal fragmentation, whereas apoptosis induction by increased NaCl concentration was not accompanied by DNA fragmentation. However, both treatments induced dephosphorylation of H1 histones. In contrast, treatment of Raji cells with alkylphosphocholine led to induction of apoptosis with internucleosomal fragmentation, albeit without notable histone H1 dephosphorylation. These results demonstrate that dephosphorylation of H1 histones is neither a prerequisite for nor a consequence of internucleosomal cleavage. Moreover, we observed with an in vitro assay that the known enhancing effect of H1 histones on the activity of the apoptosis-induced endonuclease DFF40 is independent of the subtype or the phosphorylation state of the linker histone.
染色质结构的改变、组蛋白磷酸化以及DNA裂解为核小体大小的片段是细胞凋亡的特征性表现。由于H1组蛋白结合在核小体核心之间的DNA裂解位点，因此出现了H1磷酸化状态是否会影响核小体间裂解速率的问题。在此，我们在培养细胞和体外环境中测试了DNA片段化与H1磷酸化之间的关系。在Jurkat细胞中，高渗甘露醇浓度导致细胞凋亡，包括核小体片段化，而增加NaCl浓度诱导的细胞凋亡并未伴随DNA片段化。然而，两种处理均诱导了H1组蛋白的去磷酸化。相比之下，用烷基磷胆碱处理Raji细胞导致细胞凋亡并伴有核小体间片段化，尽管没有明显的组蛋白H1去磷酸化。这些结果表明，H1组蛋白的去磷酸化既不是核小体间裂解的先决条件，也不是其结果。此外，我们通过体外试验观察到，H1组蛋白对凋亡诱导内切酶DFF40活性的已知增强作用与连接组蛋白的亚型或磷酸化状态无关。
