CCNA2 dually encodes a microprotein that regulates mitochondrial function and cell cycle via PMPCA-PMPCB complex

The mitochondrial processing peptidase PMPCA-PMPCB complex is responsible for cleaving the mitochondrial targeting sequence of preproteins, thereby sustaining mitochondrial proteome integrity and functionality. However, it is currently unclear how this complex is regulated in cells. Here, we show that the human CCNA2 gene dually encodes an unannotated microprotein MMOP (Microprotein modulator of PMPCA-PMPCB complex), which mainly localizes to the mitochondria and is cell-cycle regulated with a global high expression during G2/M phase. Loss of MMOP alters mitochondrial morphology and impairs mitochondrial function, leading to decreased ATP production. Loss of MMOP also prolongs the M phase and delays cell proliferation. Mechanistically, MMOP interacts with PMPCA-PMPCB complex, and loss of MMOP alters mitochondrial proteome, leading to an overall decrease in mitochondrial protein levels. Together, these results demonstrate that MMOP acts as a modulator of PMPCA-PMPCB complex, regulating mitochondrial proteome and function. In addition, the CCNA2 transcript encodes two sequence-independent proteins that co-regulate cell cycle through different molecular mechanisms, broadening our understanding of multicistronic human gene functions.

线粒体加工肽酶PMPCA-PMPCB复合物负责切割前体蛋白的线粒体靶向序列，进而维持线粒体蛋白质组的完整性与功能活性。然而，目前学界尚未明确该复合物在细胞内的调控方式。本研究结果显示，人类CCNA2基因可双重编码一种未注释的微蛋白MMOP（PMPCA-PMPCB复合物微蛋白调节因子，Microprotein modulator of PMPCA-PMPCB complex），该蛋白主要定位于线粒体，且受细胞周期调控，在G2/M期呈现全局高表达水平。MMOP缺失会改变线粒体形态并损伤线粒体功能，导致ATP生成量下降；同时还会延长M期并延缓细胞增殖。机制研究表明，MMOP可与PMPCA-PMPCB复合物发生相互作用；MMOP缺失会改变线粒体蛋白质组特征，造成线粒体蛋白整体水平下降。综上，上述结果证实MMOP可作为PMPCA-PMPCB复合物的调节因子，调控线粒体蛋白质组与功能活性。此外，CCNA2转录本可编码两种序列非依赖型蛋白，二者通过不同分子机制共同调控细胞周期，这一发现拓展了我们对多顺反子人类基因功能的认知。