Pabpc4, a cytoplasmic poly(A)-binding protein isoform, is an RNA-processing protein. It plays a vital role in enhancing translation and mRNA stability, thus promoting gene expression. It is involved in various biological processes such as erythroid differentiation and metabolic stress response, and is associated with pathways like selective autophagy, which is important for host-defense against virus invasion [1,3,4]. Genetic models like gene knockout could potentially be used to further study its functions.

In terms of its antiviral function, Pabpc4 can be regulated by transcription factor SP1 and broadly inhibits the replication of coronaviruses from four genera of the Coronaviridae family. It targets the nucleocapsid (N) protein of these coronaviruses, recruits the E3 ubiquitin ligase MARCH8/MARCHF8 for ubiquitination of the N protein. The ubiquitinated N protein is then recognized by the cargo receptor NDP52/CALCOCO2 and delivered to autolysosomes for degradation, impairing viral proliferation [1]. In addition, Pabpc4 knockdown experiments in 3T3-L1 pre-adipocytes suggest its role in regulating differentiation and energy metabolism in these cells [2]. Silencing of Pabpc4 in C2C12 and MEF cells induces an oxidative phenotype, through increasing the ubiquitination and degradation of NCoR1, leading to the derepression of PPAR-regulated genes, and enhancing lipid metabolism [3].

In conclusion, Pabpc4 is essential for gene expression regulation, and its functions extend to antiviral defense, adipocyte differentiation, and metabolic stress response. Research using knockout models could further clarify its roles, especially in relation to coronavirus-related diseases, type 2 diabetes, and metabolic diseases [1-3].