Ikeda Mitsunobu, Hirabayashi Susumu, Fujiwara Naoyuki, Mori Hiroki, Kawata Akira, Iida Junko, Bao Yijun, Sato Yuji, Iida Tadatsune, Sugimura Haruhiko, Hata Yutaka
Department of Medical Biochemistry, Graduate School of Medicine, Rm D602, 1-5-45 Yushima, Bunkyo-ku, Tokyo 113-8519, Japan.
Exp Cell Res. 2007 Apr 15;313(7):1484-95. doi: 10.1016/j.yexcr.2007.02.013. Epub 2007 Feb 23.
The Ras-association domain family (RASSF) comprises six members (RASSF1-6) that each harbors a RalGDS/AF-6 (RA) and Sav/RASSF/Hippo (SARAH) domain. The RASSF proteins are known as putative tumor suppressors but RASSF6 has not yet been studied. We have here characterized human RASSF6. Although RASSF6 has RA domain, it does not bind Ki-Ras, Ha-Ras, N-Ras, M-Ras, or TC21 under the condition that Nore1 (RASSF5) binds these Ras proteins. The message of RASSF6 is detected by RT-PCR in several cell lines including HeLa, MCF-7, U373, A549, and HepG2 cells, but the protein expression is low. The enhanced expression of RASSF6 causes apoptosis in HeLa cells. RASSF6 activates Bax and induces cytochrome C release. Caspase-3 activation is also induced, but the caspase inhibitor, Z-VAD-FMK, does not block RASSF6-mediated apoptosis. Apoptosis-inducing factor and endonuclease G are released from the mitochondria upon expression of RASSF6 and their releases are not blocked by Z-VAD-FMK. The knock down of RASSF6 partially blocks tumor necrosis factor-alpha-induced cell death in HeLa cells. These findings indicate that RASSF6 is implicated in apoptosis in HeLa cells and that it triggers both caspase-dependent and caspase-independent pathways.
Ras 关联结构域家族（RASSF）由六个成员（RASSF1 - 6）组成，每个成员都含有一个 RalGDS/AF - 6（RA）结构域和一个 Sav/RASSF/Hippo（SARAH）结构域。RASSF 蛋白被认为是潜在的肿瘤抑制因子，但 RASSF6 尚未得到研究。我们在此对人类 RASSF6 进行了表征。尽管 RASSF6 具有 RA 结构域，但在 Nore1（RASSF5）能结合这些 Ras 蛋白的条件下，它不与 Ki - Ras、Ha - Ras、N - Ras、M - Ras 或 TC21 结合。通过 RT - PCR 在包括 HeLa、MCF - 7、U373、A549 和 HepG2 细胞在内的多种细胞系中检测到了 RASSF6 的信使，但蛋白表达水平较低。RASSF6 的过表达会导致 HeLa 细胞凋亡。RASSF6 激活 Bax 并诱导细胞色素 C 释放。同时也诱导了半胱天冬酶 - 3 的激活，但半胱天冬酶抑制剂 Z - VAD - FMK 并不能阻断 RASSF6 介导的凋亡。在 RASSF6 表达时，凋亡诱导因子和核酸内切酶 G 从线粒体释放，且它们的释放不受 Z - VAD - FMK 的阻断。敲低 RASSF6 可部分阻断肿瘤坏死因子 -α 诱导的 HeLa 细胞死亡。这些发现表明 RASSF6 参与了 HeLa 细胞的凋亡，并且它触发了半胱天冬酶依赖性和半胱天冬酶非依赖性途径。
