Hubmann Rainer, Hilgarth Martin, Löwenstern Tamara, Lienhard Andrea, Sima Filip, Reisinger Manuel, Hobel-Kleisch Claudia, Porpaczy Edit, Haferlach Torsten, Hoermann Gregor, Laccone Franco, Jungbauer Christof, Valent Peter, Staber Philipp B, Shehata Medhat, Jäger Ulrich
Department of Internal Medicine I, Division of Hematology & Hemostaseology, Medical University of Vienna, 1090 Vienna, Austria.
Comprehensive Cancer Center Vienna, Medical University of Vienna, 1090 Vienna, Austria.
Int J Mol Sci. 2024 Nov 22;25(23):12581. doi: 10.3390/ijms252312581.
Constitutively active NOTCH2 signaling is a hallmark in chronic lymphocytic leukemia (CLL). The precise underlying defect remains obscure. Here we show that the mRNA sequence coding for the NOTCH2 negative regulatory region (NRR) is consistently deleted in CLL cells. The most common deletion is associated with two intronic single nucleotide variations (SNVs) which either create (CTTT, G>A for rs2453058) or destroy (CTCT, A>G for rs5025718) a putative splicing branch point sequence (BPS). Phylogenetic analysis demonstrates that rs2453058 is part of an ancient gene variant () which is associated with type 2 diabetes mellitus (T2DM) and is two times more frequent in Europeans than in East Asians, resembling the differences in CLL incidence. In contrast, rs5025718 belongs to a recent variant () that dominates the world outside Africa. Nanopore sequencing indicates that somatic reciprocal crossing over between rs2453058 () and rs5025718 () leads to recombined alleles with altered BPS patterns in CLL cases. This would explain the loss of the NRR domain by aberrant pre-mRNA splicing and consequently the NOTCH2 gain-of-function phenotype. Together, our findings suggest that somatic recombination of inherited variants might be relevant to CLL etiology and may at least partly explain its geographical clustering.
组成型激活的NOTCH2信号传导是慢性淋巴细胞白血病（CLL）的一个标志。确切的潜在缺陷仍不清楚。在此我们表明，编码NOTCH2负调控区（NRR）的mRNA序列在CLL细胞中持续缺失。最常见的缺失与两个内含子单核苷酸变异（SNV）相关，这两个变异要么产生（CTTT，rs2453058的G>A）要么破坏（CTCT，rs5025718的A>G）一个假定的剪接分支点序列（BPS）。系统发育分析表明，rs2453058是一个古老基因变异的一部分，该变异与2型糖尿病（T2DM）相关，在欧洲人中的出现频率是东亚人的两倍，这与CLL发病率的差异相似。相比之下，rs5025718属于一个近期变异，在非洲以外的地区占主导地位。纳米孔测序表明，在CLL病例中，rs2453058和rs5025718之间的体细胞相互交叉导致了具有改变的BPS模式的重组等位基因。这将解释异常前体mRNA剪接导致的NRR结构域缺失，进而解释NOTCH2功能获得性表型。总之，我们的研究结果表明，遗传变异的体细胞重组可能与CLL病因相关，并且可能至少部分解释其地理聚集现象。
