Evolutionary history of TOPIIA topoisomerases in animals

TOPIIA topoisomerases are required for the regulation of DNA topology by DNA cleavage and re-ligation and are important targets of antibiotic and anticancer agents. Humans possess two TOPIIA paralogue genes (TOP2A and TOP2B) with high sequence and structural similarity but distinct cellular functions. Despite their functional and clinical relevance, the evolutionary history of TOPIIA is still poorly understood. Here we show that TOPIIA is highly conserved and could be used to resolve deep phylogenies within Metazoa. We also found that TOPIIA paralogues from jawed and jawless vertebrates had different origins related with tetraploidization events. After duplication, TOP2B evolved under a stronger purifying selection than TOP2A, perhaps promoted by the more specialized role of TOP2B in postmitotic cells. We also detected genetic signatures of positive selection in the highly variable C-terminal domain (CTD), possibly associated with adaptation to cellular interactions. By comparing TOPIIA from modern and archaic humans, we found two amino acid substitutions in the TOP2A CTD, suggesting that TOP2A may have contributed to the evolution of present-day humans, as also suggested by other cell cycle-related genes. Finally, we identified six residues conferring resistance to chemotherapy differing between TOP2A and TOP2B. The six residues can be targets for the development of TOP2A-specific inhibitors that would avoid the side effects caused by inhibiting TOP2B. Altogether, our findings clarify the origin, diversification and selection pressures governing the evolution of animal TOPIIA.

TOPIIA拓扑异构酶对于通过DNA切割与重新连接调节DNA拓扑结构至关重要，且是抗生素和抗癌药物的重要靶点。人类拥有两个TOPIIA同源基因（TOP2A和TOP2B），它们在序列和结构上高度相似，但具有不同的细胞功能。尽管其在功能与临床上的相关性显著，但TOPIIA的进化历程仍鲜为人知。本研究揭示，TOPIIA在脊索动物中高度保守，可用于解析深层次的系统发育关系。我们还发现，具有颌部和无颌脊椎动物的TOPIIA同源基因起源不同，与四倍化事件相关。在复制后，TOP2B相对于TOP2A经历了更强的净化选择，这或许与TOP2B在分细胞后细胞中更为专业化的角色有关。此外，我们在高度可变的C端结构域（CTD）中检测到正选择的遗传标志，这可能与细胞间相互作用的适应相关。通过比较现代和古人类的TOPIIA，我们在TOP2A的CTD中发现了两个氨基酸替换，这表明TOP2A可能对现代人类的进化做出了贡献，如其他细胞周期相关基因所暗示。最终，我们确定了六个在不同TOP2A和TOP2B中赋予化疗耐药性的氨基酸残基。这六个残基可成为开发TOP2A特异性抑制剂的靶点，从而避免抑制TOP2B所带来的副作用。总之，我们的研究阐明了动物TOPIIA的起源、多样化和支配其进化的选择压力。