| Summary: | RNA binding motif 20 (RBM20) is a key regulator of pre-mRNA splicing of titin and other genes that are associated with cardiac diseases. Hormones, like insulin, triiodothyronine (T3), and angiotensin II (Ang II), can regulate gene-splicing through RBM20, but the detailed mechanism remains unclear. This study was aimed at investigating the signaling mechanism by which hormones regulate pre-mRNA splicing through RBM20. We first examined the role of RBM20 in Z-, I-, and M-band titin splicing at different ages in wild type (WT) and <i>RBM20</i> knockout (KO) rats using RT-PCR; we found that RBM20 is the predominant regulator of I-band titin splicing at all ages. Then we treated rats with propylthiouracil (PTU), T3, streptozotocin (STZ), and Ang II and evaluated the impact of these hormones on the splicing of titin, LIM domain binding 3 (<i>Ldb3</i>), calcium/calmodulin-dependent protein kinase II gamma (<i>Camk2g</i>), and triadin (<i>Trdn</i>). We determined the activation of mitogen-activated protein kinase (MAPK) signaling in primary cardiomyocytes treated with insulin, T3, and Ang II using western blotting; MAPK signaling was activated and <i>RBM20</i> expression increased after treatment. Two downstream transcriptional factors c-jun and ETS Transcription Factor (ELK1) can bind the promoter of <i>RBM20</i>. A dual-luciferase activity assay revealed that Ang II, but not insulin and T3, can trigger ELK1 and thus promote transcription of <i>RBM20</i>. This study revealed that Ang II can trigger ELK1 through activation of MAPK signaling by enhancing <i>RBM20</i> expression which regulates pre-mRNA splicing. Our study provides a potential therapeutic target for the treatment of cardiac diseases in RBM20-mediated pre-mRNA splicing.
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