Norwood Laura E, Moss Timothy J, Margaryan Naira V, Cook Sara L, Wright Lindsay, Seftor Elisabeth A, Hendrix Mary J C, Kirschmann Dawn A, Wallrath Lori L
Department of Biochemistry, University of Iowa, Iowa City, Iowa 52242, USA.
J Biol Chem. 2006 Jul 7;281(27):18668-76. doi: 10.1074/jbc.M512454200. Epub 2006 Apr 28.
The development and progression of cancer is controlled by gene expression, often regulated through chromatin packaging. Heterochromatin protein 1(Hsalpha) (HP1(Hsalpha)), one of three human HP1 family members, participates in heterochromatin formation and gene regulation. HP1(Hsalpha) possesses an amino-terminal chromodomain, which binds methylated lysine 9 of histone H3 (meK9 H3), and a carboxyl-terminal chromoshadow domain (CSD) that is required for dimerization and interaction with partner proteins. HP1(Hsalpha) is down-regulated in invasive metastatic breast cancer cells compared with poorly invasive nonmetastatic breast cancer cells. Expression of EGFP-HP1(Hsalpha) in highly invasive MDA-MB-231 cells causes a reduction in in vitro invasion, without affecting cell growth. Conversely, knock-down of HP1(Hsalpha) levels in the poorly invasive breast cancer cell line MCF-7 increased invasion, without affecting cell growth. To determine whether functions of the CSD were required for the regulation of invasion, mutant forms of HP1(Hsalpha) were expressed in MDA-MB-231 cells. A W174A mutation that disrupts interactions between HP1(Hsalpha) and PXVXL-containing partner proteins reduced invasion similar to that of the wild type protein. In contrast, an I165E mutation that disrupts dimerization of HP1(Hsalpha) did not decrease invasion. No gross changes in localization and abundance of HP1(Hsbeta), HP1(Hsgamma), and meK9 H3 were observed upon expression of wild type and mutant forms of HP1(Hsalpha) in MDA-MB-231 cells. Taken together, these data demonstrate that modulation of HP1(Hsalpha) alters the invasive potential of breast cancer cells through mechanisms requiring HP1 dimerization, but not interactions with PXVXL-containing proteins.
癌症的发展和进程由基因表达控制，而基因表达通常通过染色质包装来调节。异染色质蛋白1（Hsα）（HP1（Hsα））是人类HP1家族的三个成员之一，参与异染色质的形成和基因调控。HP1（Hsα）具有一个氨基末端的色域，可与组蛋白H3的甲基化赖氨酸9（meK9 H3）结合，以及一个羧基末端的染色体阴影结构域（CSD），该结构域是二聚化和与伴侣蛋白相互作用所必需的。与低侵袭性的非转移性乳腺癌细胞相比，HP1（Hsα）在侵袭性转移性乳腺癌细胞中表达下调。在高侵袭性的MDA-MB-231细胞中表达EGFP-HP1（Hsα）会导致体外侵袭能力降低，而不影响细胞生长。相反，在低侵袭性乳腺癌细胞系MCF-7中敲低HP1（Hsα）水平会增加侵袭能力，而不影响细胞生长。为了确定CSD的功能是否是调节侵袭所必需的，在MDA-MB-231细胞中表达了HP1（Hsα）的突变形式。破坏HP1（Hsα）与含PXVXL的伴侣蛋白之间相互作用的W174A突变降低了侵袭能力，与野生型蛋白相似。相比之下，破坏HP1（Hsα）二聚化的I165E突变并没有降低侵袭能力。在MDA-MB-231细胞中表达野生型和突变型HP1（Hsα）后，未观察到HP1（Hsβ）、HP1（Hsγ）和meK9 H3的定位和丰度有明显变化。综上所述，这些数据表明，HP1（Hsα）的调节通过需要HP1二聚化但不需要与含PXVXL的蛋白相互作用的机制改变了乳腺癌细胞的侵袭潜能。
