Muscle-Specific Mis-Splicing and Heart Disease Exemplified by RBM20

Abstract

Alternative splicing is an essential post-transcriptional process to generate multiple functional RNAs or proteins from a single transcript. Progress in RNA biology has led to a better understanding of muscle-specific RNA splicing in heart disease. The recent discovery of the muscle-specific splicing factor RNA-binding motif 20 (RBM20) not only provided great insights into the general alternative splicing mechanism but also demonstrated molecular mechanism of how this splicing factor is associated with dilated cardiomyopathy. Here, we review our current knowledge of muscle-specific splicing factors and heart disease, with an emphasis on RBM20 and its targets, RBM20-dependent alternative splicing mechanism, RBM20 disease origin in induced Pluripotent Stem Cells (iPSCs), and RBM20 mutations in dilated cardiomyopathy. In the end, we will discuss the multifunctional role of RBM20 and manipulation of RBM20 as a potential therapeutic target for heart disease.

Keywords: RNA-binding motif 20; alternative splicing; heart disease; muscle-specific splicing factor; titin.

Figure 1

The schematic diagram of RNA-binding motif 20 (RBM20) with mutation sites. (a) RBM20 structure and known mutation sites. (b) Homologous protein structure modeled with SWISS-MODEL (Q5T481, Homo sapiens) [13]. Modeled region: AA 510-597, which contains RRM domain; QMEAN = −1.56 (QMENS value indicates the degree of nativeness of the structure features and whether the model is of similar quality to experimental structures; Scores of −4.0 or below indicates very low quality); (c) The local quality plot. For each residue of the model in Figure 1b (on the x-axis), y-axis shows the expected similarity of the model to the experimental structure. The residue showing a score below 0.6 are expected to be low quality. AA: amino acid; Pro-rich: proline-rich region; ZnF: zinc finger; RRM: RNA recognition motif; RS: arginine/serine-rich domain; Glu-rich: glutamic acid-rich region; V535I: valine (V) to isoleucine (I) change at AA position 535.

Figure 2

RBM20-dependent titin isoform expression. (a) Schematic representation of titin isoform expression in wild type (WT), Rbm20 heterozygous and Rbm20 homozygous rat heart analyzed by vertical agarose gel electrophoresis; N2BA-G, N2BA and N2B are different titin isoforms resulting from alternative splicing regulated by RBM20; T2 is a proteolytic fragment of titin; Grey box indicates low expression, Black box indicates high expression; (b) RBM20 mutations in humans and deficiency in rats lead to dilated cardiomyopathy (DCM).

Figure 3

RBM20-dependant titin alternative splicing pathways. RBM20 regulates titin alternative splicing in the middle immunoglobulin (Ig) and PEVK (Proline (P), Glutamate (E), Valine (V), Lysine (K)) domain in the heart, however, the splicing events in PEVK region are not shown due to its complexity; without RBM20 in lower panel, most spliced exons indicated in the upper panel are spliced. Arrows represent exon spliced, while lines indicate consecutive exons (modified from [47]).