Laboratory of Gene Expression, Medical Research Institute, Tokyo Medical and Dental University (TMDU), Bunkyo-ku, Tokyo, 113-8510, Japan.
Graduate School of Biomedical Science, Tokyo Medical and Dental University (TMDU), Bunkyo-ku, Tokyo, 113-8510, Japan.
Sci Rep. 2018 Jun 12;8(1):8970. doi: 10.1038/s41598-018-26624-w.
RBM20 is a major regulator of heart-specific alternative pre-mRNA splicing of TTN encoding a giant sarcomeric protein titin. Mutation in RBM20 is linked to autosomal-dominant familial dilated cardiomyopathy (DCM), yet most of the RBM20 missense mutations in familial and sporadic cases were mapped to an RSRSP stretch in an arginine/serine-rich region of which function remains unknown. In the present study, we identified an R634W missense mutation within the stretch and a G1031X nonsense mutation in cohorts of DCM patients. We demonstrate that the two serine residues in the RSRSP stretch are constitutively phosphorylated and mutations in the stretch disturb nuclear localization of RBM20. Rbm20 knock-in mouse mimicking an S635A mutation reported in a familial case showed a remarkable effect on titin isoform expression like in a patient carrying the mutation. These results revealed the function of the RSRSP stretch as a critical part of a nuclear localization signal and offer the Rbm20 mouse as a good model for in vivo study.
RBM20 是心肌特异性 TTN 编码的巨大肌节蛋白 titin 可变剪接的主要调节因子。RBM20 的突变与常染色体显性家族性扩张型心肌病（DCM）有关，但家族性和散发性病例中的大多数 RBM20 错义突变都映射到富含精氨酸/丝氨酸的区域中的 RSRSP 延伸，其功能仍不清楚。在本研究中，我们在 DCM 患者队列中鉴定了延伸区内的 R634W 错义突变和 G1031X 无义突变。我们证明，RSRSP 延伸区内的两个丝氨酸残基被持续磷酸化，延伸区内的突变会干扰 RBM20 的核定位。模拟家族性病例中报道的 S635A 突变的 Rbm20 敲入小鼠表现出与携带该突变的患者相似的 titin 异构体表达的显著影响。这些结果揭示了 RSRSP 延伸作为核定位信号关键部分的功能，并为体内研究提供了 Rbm20 小鼠这一良好模型。
