N-Terminal deleted isoforms of E3 ligase RNF220 are ubiquitously expressed and required for mouse muscle differentiation.

ABSTRACT: Four isoform peptides of the novel E3 ligase ring finger protein 220 (RNF220) have been identified in humans. However, all of the previous studies have predominantly focused on isoform 1 (the full-length form), which consists of 566 amino acids. Here, we show that a shorter isoform, which is 308 amino acids lacking most of the N-terminus (human isoform 4; mouse isoform 3; ΔN-RNF220), is the predominant and ubiquitously expressed variant that warrants functional investigation. Both isoform 1 and ΔN-RNF220 are expressed in the brain; however, ΔN-RNF220 is the major isoform expressed in all other tissues in mice. Consistently, H3K4me3 ChIP-seq data from ENCODE reveal that the transcription start site for ΔN-RNF220 demonstrates broader and stronger activity across human tissues than that of isoform 1. ΔN-RNF220 produces 2 peptides (4a and 4b) through alternative translation initiation, with isoform 4b displaying distinct subcellular localization, subnuclear structures and interaction with a nuclear protein WDR5. Notably, during embryonic stem cell differentiation into neural stem cells, isoform 1 expression increases, whereas ΔN-RNF220 expression decreases. In murine myoblasts, ΔN-RNF220 is the sole expressed isoform and is required for MyoD and myogenin expression, as well as for muscle differentiation. Our findings highlight ΔN-RNF220 as the ubiquitously and highly expressed variant, likely playing a fundamental role across tissues while exhibiting functional differences from isoform 1. These results emphasize the critical importance of ΔN-RNF220 in future studies investigating the biological functions of RNF220.

SUBMITTER: Choi S 

PROVIDER: S-EPMC12296455 | biostudies-literature | 2025 Sep

REPOSITORIES: biostudies-literature