Loss of SRSF3 in Cardiomyocytes Leads to Decapping of Contraction-Related mRNAs and Severe Systolic Dysfunction

Abstract

Rationale: RBPs (RNA binding proteins) play critical roles in the cell by regulating mRNA transport, splicing, editing, and stability. The RBP SRSF3 (serine/arginine-rich splicing factor 3) is essential for blastocyst formation and for proper liver development and function. However, its role in the heart has not been explored. Objective: To investigate the role of SRSF3 in cardiac function. Methods and Results: Cardiac SRSF3 expression was high at mid gestation and decreased during late embryonic development. Mice lacking SRSF3 in the embryonic heart showed impaired cardiomyocyte proliferation and died in utero. In the adult heart, SRSF3 expression was reduced after myocardial infarction, suggesting a possible role in cardiac homeostasis. To determine the role of this RBP in the adult heart, we used an inducible, cardiomyocyte-specific SRSF3 knockout mouse model. After SRSF3 depletion in cardiomyocytes, mice developed severe systolic dysfunction that resulted in death within 8 days. RNA-Seq analysis revealed downregulation of mRNAs encoding sarcomeric and calcium handling proteins. Cardiomyocyte-specific SRSF3 knockout mice also showed evidence of alternative splicing of mTOR (mammalian target of rapamycin) mRNA, generating a shorter protein isoform lacking catalytic activity. This was associated with decreased phosphorylation of 4E-BP1 (eIF4E-binding protein 1), a protein that binds to eIF4E (eukaryotic translation initiation factor 4E) and prevents mRNA decapping. Consequently, we found increased decapping of mRNAs encoding proteins involved in cardiac contraction. Decapping was partially reversed by mTOR activation. Conclusions: We show that cardiomyocyte-specific loss of SRSF3 expression results in decapping of critical mRNAs involved in cardiac contraction. The molecular mechanism underlying this effect likely involves the generation of a short mTOR isoform by alternative splicing, resulting in reduced 4E-BP1 phosphorylation. The identification of mRNA decapping as a mechanism of systolic heart failure may open the way to the development of urgently needed therapeutic tools.

Poison Exon Splicing Regulates a Coordinated Network of SR Protein Expression during Differentiation and Tumorigenesis

“…PEs regulate SF levels across multiple cell differentiation models, suggesting a post-transcriptional regulatory program that decreases SR protein levels as the tissue differentiates. Our findings also implicate PE splicing in controlling changes in SR protein levels described previously during heart or brain development (Grellscheid et al, 2011;Ortiz-Sá nchez et al, 2019;Roberts et al, 2014;Storbeck et al, 2014). Although we are unable to detect SRSF9-PE splicing in iPSCs, the low levels of PE-containing transcript limit our ability to detect differences in its inclusion and mask its role in cell differentiation.…”

“…In all models, most PEs exhibit low inclusion in iPSCs and are more included during differentiation ( Figures 1B-1F, S1A, and S1B). For example, SRSF3-PE inclusion increases in human cardiomyocytes ( Figures 1C and 1D), a pattern that follows the decrease in SRSF3 coding mRNA in embryonic mouse heart development (Ortiz-Sá nchez et al, 2019). TRA2b, critical for brain development (Grellscheid et al, 2011;Roberts et al, 2014;Storbeck et al, 2014), exhibits increased PE inclusion in mature neurons ( Figures 1E and 1F).…”

“…Therefore, changes in SR protein levels can affect a wide network of downstream targets and AS events. SR proteins are critical for normal development, and defects in SR proteins have been implicated causatively in several pathologies, including cardiac and liver dysfunction, brain abnormalities, diabetes, lupus, and cancer (Dichmann et al, 2015;Ding et al, 2004;Grellscheid et al, 2011;Kaminska et al, 2016;Kumar et al, 2019;Lu et al, 2014;Neugebauer et al, 2000;Ortiz-Sá nchez et al, 2019;Ratnadiwakara et al, 2018;Roberts et al, 2014;Sen et al, 2013;Storbeck et al, 2014;Urbanski et al, 2018;Xu et al, 2005). Solid tumors often exhibit altered levels of SR proteins that subsequently promote formation of RNA isoforms involved in tumor biology (Urbanski et al, 2018).…”

Establishment and validation of an RNA binding protein-associated prognostic model for ovarian cancer

“…Because of the omnidirectional and multifunctional regulation of mRNA by RBP, even small changes can cause significant physiological and pathological effects. Previous studies have indicated that cancer, neurodegenerative diseases, and cardiovascular diseases have been proven to be associated with RBP abnormalities [ 2 , 31 , 42 ]. Cell proliferation, differentiation, apoptosis, and other physiological processes are precisely regulated at the post-transcriptional level, which is involved in the development of tumors [ 24 ].…”

Emerging Roles of SRSF3 as a Therapeutic Target for Cancer

“…SRSF3 plays a critical role in the regulation of RNA splicing and many other cellular functions. Aberrant SRSF3 function can be identified in several human diseases, including Alzheimer's disease ( 7 ), systolic heart failure ( 8 ), ocular hypertension ( 9 ), virus infection ( 10 – 12 ), and tumor ( 13 ). In this review, we summarize current research on the function and expression regulation of SRSF3 and the misregulation and biological implications of SRSF3 in cancer, as well as its therapeutic potential.…”