Inomata Mika, Tagawa Hiroyuki, Guo Yong-Mei, Kameoka Yoshihiro, Takahashi Naoto, Sawada Kenichi
Department of Internal Medicine III, Akita University School of Medicine, Akita, Japan.
Blood. 2009 Jan 8;113(2):396-402. doi: 10.1182/blood-2008-07-163907. Epub 2008 Oct 21.
Aberrant overexpression of the miR-17-92 polycistron is strongly associated with B-cell lymphomagenesis. Recent studies have shown that miR-17-92 down-regulates the proapoptotic protein Bim, leading to overexpression of Bcl2, which likely plays a key role in lymphomagenesis. However, the fact that Jeko-1 cells derived from mantle cell lymphoma exhibit both homozygous deletion of BIM and overexpression of miR-17-92 suggests other targets are also involved in B-cell lymphomagenesis. To identify essential target(s) of miR-17-92 in lymphomagenesis, we first transfected miR-17-92 into 2 genetically distinct B-cell lymphoma cell lines: Raji, which overexpress c-Myc, and SUDHL4, which overexpress Bcl2. Raji transfected with miR-17-19b-1 exhibited down-regulated expression of Bim and a slight up-regulation in Bcl2 expression. On the other hand, SUDHL4 transfectants showed aggressive cell growth reflecting facilitated cell cycle progression at the G(1) to S transition and decreased expression of CDKN1A mRNA and p21 protein (CDKN1A/p21) that was independent of p53 expression. Conversely, transfection of antisense oligonucleotides against miR-17 and miR-20a into Jeko-1 led to up-regulation of CDKN1A/p21, resulting in decreased cell growth with G(1) to S arrest. Thus, CDKN1A/p21 appears to be an essential target of miR-17-92 during B-cell lymphomagenesis, which suggests the miR-17-92 polycistron has distinct targets in different B-cell lymphoma subtypes.
miR-17-92多顺反子的异常过表达与B细胞淋巴瘤的发生密切相关。最近的研究表明，miR-17-92下调促凋亡蛋白Bim，导致Bcl2过表达，这可能在淋巴瘤发生中起关键作用。然而，源自套细胞淋巴瘤的Jeko-1细胞同时表现出BIM的纯合缺失和miR-17-92的过表达，这表明其他靶点也参与了B细胞淋巴瘤的发生。为了确定miR-17-92在淋巴瘤发生中的关键靶点，我们首先将miR-17-92转染到两种基因不同的B细胞淋巴瘤细胞系中：过表达c-Myc的Raji细胞和过表达Bcl2的SUDHL4细胞。用miR-17-19b-1转染的Raji细胞表现出Bim表达下调和Bcl2表达略有上调。另一方面，SUDHL4转染细胞显示出侵袭性细胞生长，反映出在G(1)到S期过渡时细胞周期进程加快，以及CDKN1A mRNA和p21蛋白（CDKN1A/p21）表达降低，且这与p53表达无关。相反，将针对miR-17和miR-20a的反义寡核苷酸转染到Jeko-1细胞中导致CDKN1A/p21上调，从而导致细胞生长减少并伴有G(1)到S期停滞。因此，CDKN1A/p21似乎是B细胞淋巴瘤发生过程中miR-17-92的关键靶点，这表明miR-17-92多顺反子在不同的B细胞淋巴瘤亚型中有不同的靶点。
