Department of Human Genetics, University of Michigan, Ann Arbor, MI 48109, USA.
Department of Genomic Medicine, GENYO, Centre for Genomics and Oncological Research, Pfizer-University of Granada-Andalusian Regional Government, PTS Granada 18016, Spain.
Nucleic Acids Res. 2024 Jul 22;52(13):7761-7779. doi: 10.1093/nar/gkae448.
Alu elements are non-autonomous Short INterspersed Elements (SINEs) derived from the 7SL RNA gene that are present at over one million copies in human genomic DNA. Alu mobilizes by a mechanism known as retrotransposition, which requires the Long INterspersed Element-1 (LINE-1) ORF2-encoded protein (ORF2p). Here, we demonstrate that HeLa strains differ in their capacity to support Alu retrotransposition. Human Alu elements retrotranspose efficiently in HeLa-HA and HeLa-CCL2 (Alu-permissive) strains, but not in HeLa-JVM or HeLa-H1 (Alu-nonpermissive) strains. A similar pattern of retrotransposition was observed for other 7SL RNA-derived SINEs and tRNA-derived SINEs. In contrast, mammalian LINE-1s, a zebrafish LINE, a human SINE-VNTR-Alu (SVA) element, and an L1 ORF1-containing mRNA can retrotranspose in all four HeLa strains. Using an in vitro reverse transcriptase-based assay, we show that Alu RNAs associate with ORF2p and are converted into cDNAs in both Alu-permissive and Alu-nonpermissive HeLa strains, suggesting that 7SL- and tRNA-derived SINEs use strategies to 'hijack' L1 ORF2p that are distinct from those used by SVA elements and ORF1-containing mRNAs. These data further suggest ORF2p associates with the Alu RNA poly(A) tract in both Alu-permissive and Alu-nonpermissive HeLa strains, but that Alu retrotransposition is blocked after this critical step in Alu-nonpermissive HeLa strains.
Alu 元件是非自主的短散布元件 (SINEs),源自 7SL RNA 基因,在人类基因组 DNA 中存在超过一百万份拷贝。Alu 通过一种称为逆转录转座的机制移动,该机制需要长散布元件-1 (LINE-1) ORF2 编码的蛋白 (ORF2p)。在这里,我们证明 HeLa 株系在支持 Alu 逆转录转座的能力上有所不同。人类 Alu 元件在 HeLa-HA 和 HeLa-CCL2(Alu 允许)株系中有效地逆转录转座,但在 HeLa-JVM 或 HeLa-H1(Alu 不允许)株系中不行。其他 7SL RNA 衍生的 SINEs 和 tRNA 衍生的 SINEs 的逆转录转座也呈现出类似的模式。相比之下,哺乳动物 LINE-1s、一种斑马鱼 LINE、一种人类 SINE-VNTR-Alu (SVA) 元件和一种含有 L1 ORF1 的 mRNA 可以在所有四种 HeLa 株系中逆转录转座。使用基于体外逆转录酶的测定,我们表明 Alu RNA 与 ORF2p 结合,并在 Alu 允许和 Alu 不允许的 HeLa 株系中转化为 cDNA,这表明 7SL 和 tRNA 衍生的 SINEs 使用与 SVA 元件和含有 ORF1 的 mRNA 不同的策略来“劫持”L1 ORF2p。这些数据进一步表明,ORF2p 与 Alu 允许和 Alu 不允许的 HeLa 株系中的 Alu RNA 聚 (A) 区结合,但 Alu 逆转录转座在 Alu 不允许的 HeLa 株系中这一关键步骤之后被阻断。