FAM46B is a prokaryotic-like cytoplasmic poly(A) polymerase essential in human embryonic stem cells

Nucleic Acids Res. 2020 Mar 18;48(5):2733-2748. doi: 10.1093/nar/gkaa049.

Jia-Li Hu ¹ ², He Liang ³, Hong Zhang ¹, Ming-Zhu Yang ⁴, Wei Sun ⁵ ⁶, Peng Zhang ³, Li Luo ¹, Jian-Xiong Feng ¹, Huajun Bai ³, Fang Liu ⁴, Tianpeng Zhang ⁷, Jin-Yu Yang ¹, Qingsong Gao ⁶, Yongkang Long ⁵, Xiao-Yan Ma ¹, Yang Chen ¹, Qian Zhong ¹, Bing Yu ¹, Shuang Liao ¹, Yongbo Wang ⁸, Yong Zhao ⁷, Mu-Sheng Zeng ¹, Nan Cao ⁴, Jichang Wang ⁴, Wei Chen ⁵, Huang-Tian Yang ³, Song Gao ¹ ⁹

Affiliations

1 State Key Laboratory of Oncology in South China, Collaborative Innovation Center for Cancer Medicine, Sun Yat-sen University Cancer Center, Guangzhou 510060, China.
2 Department of Oncology, The Second Affiliated Hospital of Nanchang University, Nanchang, Jiangxi 330006, P.R. China.
3 CAS Key Laboratory of Tissue Microenvironment and Tumor, Laboratory of Molecular Cardiology, Shanghai Institute of Nutrition and Health, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai 200031, China.
4 MOE Key Laboratory for Stem Cells and Tissue Engineering, Department of Histology and Embryology, Zhongshan School of Medicine, Sun Yat-sen University, Guangzhou 510080, China.
5 Department of Biology, Southern University of Science and Technology, Shenzhen 518055, P.R. China.
6 Laboratory for Functional Genomics and Systems Biology, The Berlin Institute for Medical Systems Biology, 13092 Berlin, Germany.
7 MOE Key Laboratory of Gene Function and Regulation, State Key Laboratory for Biocontrol, School of Life Sciences, Sun Yat-sen University, Guangzhou 510006, China.
8 Department of Cellular and Genetic Medicine, School of Basic Medical Sciences, Fudan University, Shanghai 200032, China.
9 Guangzhou Regenerative Medicine and Health Guangdong Laboratory, Guangzhou 510530, China.

PMID: 32009146 DOI: 10.1093/nar/gkaa049

Abstract

Family with sequence similarity (FAM46) proteins are newly identified metazoan-specific poly(A) polymerases (PAPs). Although predicted as Gld-2-like eukaryotic non-canonical PAPs, the detailed architecture of FAM46 proteins is still unclear. Exact biological functions for most of FAM46 proteins also remain largely unknown. Here, we report the first crystal structure of a FAM46 protein, FAM46B. FAM46B is composed of a prominently larger N-terminal catalytic domain as compared to known eukaryotic PAPs, and a C-terminal helical domain. FAM46B resembles prokaryotic PAP/CCA-adding Enzymes in overall folding as well as certain inter-domain connections, which distinguishes FAM46B from other eukaryotic non-canonical PAPs. Biochemical analysis reveals that FAM46B is an active PAP, and prefers adenosine-rich substrate RNAs. FAM46B is uniquely and highly expressed in human pre-implantation embryos and pluripotent stem cells, but sharply down-regulated following differentiation. FAM46B is localized to both cell nucleus and cytosol, and is indispensable for the viability of human embryonic stem cells. Knock-out of FAM46B is lethal. Knock-down of FAM46B induces Apoptosis and restricts protein synthesis. The identification of the bacterial-like FAM46B, as a pluripotent stem cell-specific PAP involved in the maintenance of translational efficiency, provides important clues for further functional studies of this PAP in the early embryonic development of high eukaryotes.

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