Department of Molecular Biophysics & Biochemistry, Yale University School of Medicine, New Haven, Connecticut, United States of America.
Yale Center for Molecular Discovery, Yale University, West Haven, Connecticut, United States of America.
PLoS Biol. 2024 Jul 8;22(7):e3002718. doi: 10.1371/journal.pbio.3002718. eCollection 2024 Jul.
Cancer initiates as a consequence of genomic mutations and its subsequent progression relies in part on increased production of ribosomes to maintain high levels of protein synthesis for unchecked cell growth. Recently, cytidine deaminases have been uncovered as sources of mutagenesis in cancer. In an attempt to form a connection between these 2 cancer driving processes, we interrogated the cytidine deaminase family of proteins for potential roles in human ribosome biogenesis. We identified and validated APOBEC3A and APOBEC4 as novel ribosome biogenesis factors through our laboratory's established screening platform for the discovery of regulators of nucleolar function in MCF10A cells. Through siRNA depletion experiments, we highlight APOBEC3A's requirement in making ribosomes and specific role within the processing and maturation steps that form the large subunit 5.8S and 28S ribosomal (r)RNAs. We demonstrate that a subset of APOBEC3A resides within the nucleolus and associates with critical ribosome biogenesis factors. Mechanistic insight was revealed by transient overexpression of both wild-type and a catalytically dead mutated APOBEC3A, which both increase cell growth and protein synthesis. Through an innovative nuclear RNA sequencing methodology, we identify only modest predicted APOBEC3A C-to-U target sites on the pre-rRNA and pre-mRNAs. Our work reveals a potential direct role for APOBEC3A in ribosome biogenesis likely independent of its editing function. More broadly, we found an additional function of APOBEC3A in cancer pathology through its function in ribosome biogenesis, expanding its relevance as a target for cancer therapeutics.
癌症是由于基因组突变引发的，其后续进展部分依赖于核糖体产量的增加，以维持不受控制的细胞生长所需的高水平蛋白质合成。最近，胞嘧啶脱氨酶已被发现是癌症诱变的来源。为了在这两个致癌过程之间建立联系，我们研究了胞嘧啶脱氨酶家族蛋白在人类核糖体生物发生中的潜在作用。我们通过实验室建立的 MCF10A 细胞核仁功能调节剂发现筛选平台，鉴定并验证了 APOBEC3A 和 APOBEC4 是新的核糖体生物发生因子。通过 siRNA 耗尽实验，我们强调了 APOBEC3A 在制造核糖体中的作用以及在形成大核糖体亚基 5.8S 和 28S rRNA 的加工和成熟步骤中的特定作用。我们证明了一部分 APOBEC3A 存在于核仁内，并与关键的核糖体生物发生因子相关联。通过瞬时过表达野生型和催化失活突变型 APOBEC3A，揭示了机制上的见解，这两种蛋白都增加了细胞生长和蛋白质合成。通过一种创新的核 RNA 测序方法，我们仅在 pre-rRNA 和 pre-mRNAs 上鉴定到预测的 APOBEC3A C-to-U 靶位数量适中。我们的工作揭示了 APOBEC3A 在核糖体生物发生中的潜在直接作用，可能与其编辑功能无关。更广泛地说，我们通过其在核糖体生物发生中的功能发现了 APOBEC3A 在癌症发病机制中的另一个功能，扩大了其作为癌症治疗靶点的相关性。
