Disruption of the nuclear localization signal in RBM20 is causative in dilated cardiomyopathy

Human patients carrying genetic mutations in RNA binding motif 20 (RBM20) develop a clinically aggressive dilated cardiomyopathy (DCM). Genetic mutation knockin (KI) animal models imply that altered function of the arginine-serine-rich (RS) domain is crucial for severe DCM. To test this hypothesis, we generated an RS domain deletion mouse model (Rbm20 & UDelta;RS). We showed that Rbm20 & UDelta;RS mice manifested DCM with mis-splicing of RBM20 target transcripts. We found that RBM20 was mis-localized to the sarcoplasm in Rbm20 & UDelta;RS mouse hearts and formed RBM20 granules similar to those detected in mutation KI animals. In contrast, mice lacking the RNA recognition motif showed similar mis-splicing of major RBM20 target genes but did not develop DCM or exhibit RBM20 granule formation. Using in vitro studies with immunocytochemical staining, we demonstrated that only DCM-associated mutations in the RS domain facilitated RBM20 nucleocytoplasmic transport and promoted granule assembly. Further, we defined the core nuclear localization signal (NLS) within the RS domain of RBM20. Mutation analysis of phosphorylation sites in the RS domain suggested that this modification may be dispensable for RBM20 nucleocytoplasmic transport. Collectively, our findings revealed that disruption of RS domain-mediated nuclear localization is crucial for severe DCM caused by NLS mutations.

Automated summary

Human patients with genetic mutations in RBM20 develop severe dilated cardiomyopathy (DCM). A mouse model with RS domain deletion (Rbm20 & UDelta;RS) showed DCM and mis-splicing of RBM20 target transcripts, indicating the importance of RS domain function for severe DCM. Further studies revealed that DCM-associated mutations in the RS domain facilitate RBM20 nucleocytoplasmic transport and granule assembly, while mutations in the RNA recognition motif do not cause DCM or RBM20 granule formation.