Michinori Koebis

Alternative splicing of myomesin 1 gene is aberrantly regulated in myotonic dystrophy type 1

Myotonic dystrophy type 1 (DM1) is a multisystemic disease caused by a CTG repeat expansion in the 3′‐UTR of dystrophia myotonica‐protein kinase. Aberrant regulation of alternative splicing is a characteristic feature of DM. Dozens of genes have been found to be abnormally spliced; however, few reported splicing abnormalities explain the phenotypes of DM1 patients. Thus, we hypothesized that other, unknown abnormal splicing events exist. Here, by using exon array, we identified aberrant inclusion of myomesin 1 (MYOM1) exon 17a as a novel splicing abnormality in DM1 muscle. A cellular splicing assay with a MYOM1 minigene revealed that not only MBNL1‐3 but also CELF1 and 2 decreased the inclusion of MYOM1 exon 17a in HEK293T cells. Expression of expanded CUG repeat impeded MBNL1 activity but did not affect CELF1 activity on the splicing of MYOM1 minigene. Our results suggest that the downregulation of MBNL proteins should lead to the abnormal splicing of MYOM1 exon 17a in DM1 muscle.

Ultrasound-enhanced delivery of Morpholino with Bubble liposomes ameliorates the myotonia of myotonic dystrophy model mice

Phosphorodiamidate morpholino oligonucleotide (PMO)-mediated control of the alternative splicing of the chloride channel 1 (CLCN1) gene is a promising treatment for myotonic dystrophy type 1 (DM1) because the abnormal splicing of this gene causes myotonia in patients with DM1. In this study, we optimised a PMO sequence to correct Clcn1 alternative splicing and successfully remedied the myotonic phenotype of a DM1 mouse model, the HSALR mouse. To enhance the efficiency of delivery of PMO into HSALR mouse muscles, Bubble liposomes, which have been used as a gene delivery tool, were applied with ultrasound exposure. Effective delivery of PMO led to increased expression of Clcn1 protein in skeletal muscle and the amelioration of myotonia. Thus, PMO-mediated control of the alternative splicing of the Clcn1 gene must be important target of antisense therapy of DM1.

Regulation of the alternative splicing of sarcoplasmic reticulum Ca2+-ATPase1 (SERCA1) by phorbol 12-myristate 13-acetate (PMA) via a PKC pathway

Myotonic dystrophy type 1 (DM1) is a multi-systemic disease with no established treatment to date. Small, cell-permeable molecules hold the potential to treat DM1. In this study, we investigated the association between protein kinase C (PKC) signaling and splicing of sarcoplasmic reticulum Ca(2+)-ATPase1 (SERCA1). Our aim was to clarify the mechanisms underlying the regulation of alternative splicing, in order to explore new therapeutic strategies for DM1. By assessing the splicing pattern of the endogenous SERCA1 gene in HEK293 cells, we found that treatment with phorbol 12-myristate 13-acetate (PMA) regulated SERCA1 splicing. Interestingly, treatment with PMA for 48 h normalized SERCA1 splicing, while treatment for 1.5h promoted aberrant splicing. These two responses showed dose dependency and were completely abolished by the PKC inhibitor Ro 31-8220. Furthermore, repression of PKCβII and PKCθ by RNAi mimicked prolonged PMA treatment. These results indicate that PKC signaling is involved in the splicing of SERCA1 and provide new evidence for a link between alternative splicing and PKC signaling.

ABLIM1 splicing is abnormal in skeletal muscle of patients with DM1 and regulated by MBNL, CELF and PTBP1

Myotonic dystrophy type 1 (DM1) is an RNA‐mediated disorder characterized by muscle weakness, cardiac defects and multiple symptoms and is caused by expanded CTG repeats within the 3′ untranslated region of the DMPK gene. In this study, we found abnormal splicing of actin‐binding LIM protein 1 (ABLIM1) in skeletal muscles of patients with DM1 and a DM1 mouse model (HSALR). An exon 11 inclusion isoform is expressed in skeletal muscle and heart of non‐DM1 individuals, but not in skeletal muscle of patients with DM1 or other adult human tissues. Moreover, we determined that ABLIM1 splicing is regulated by several splice factors, including MBNL family proteins, CELF1, 2 and 6, and PTBP1, using a cellular splicing assay. MBNL proteins promoted the inclusion of ABLIM1 exon 11, but other proteins and expanded CUG repeats repressed exon 11 of ABLIM1. This result is consistent with the hypothesis that MBNL proteins are trapped by expanded CUG repeats and inactivated in DM1 and that CELF1 is activated in DM1. However, activation of PTBP1 has not been reported in DM1. Our results suggest that the exon 11 inclusion isoform of ABLIM1 may have a muscle‐specific function, and its abnormal splicing could be related to muscle symptoms of DM1.

Hyperactive mTOR induces neuroendocrine differentiation in prostate cancer cell with concurrent up-regulation of IRF1

Neuroendocrine‐differentiated prostate cancer (NEPCa) is refractory to androgen deprivation therapy and shows a poor prognosis. The underlying mechanisms responsible for neuroendocrine differentiation (NED) are yet to be clarified. In this study, we investigated the role of mammalian target of rapamycin (mTOR) in NEPCa.

Splicing of human chloride channel 1

Expression of chloride channel 1 (CLCN1/ClC-1) in skeletal muscle is driven by alternative splicing, a process regulated in part by RNA-binding protein families MBNL and CELF. Aberrant splicing of CLCN1 produces many mRNAs, which were translated into inactive proteins, resulting in myotonia in myotonic dystrophy (DM), a genetic disorder caused by the expansion of a CTG or CCTG repeat. This increase in abnormal splicing variants containing exons 6B, 7A or the insertion of a TAG stop codon just before exon 7 leads to a decrease in expression of the normal splice pattern. The majority of studies examining splicing in CLCN1 have been performed using mouse Clcn1, as have investigations into the activation and suppression of normal splicing variant expression by MBNL1-3 and CELF3–6, respectively. In contrast, examinations of human CLCN1 have been less common due to the greater complexity of splicing patterns. Here, we constructed a minigene containing CLCN1 exons 5–7 and established a novel assay system to quantify the expression of the normal splicing variant of CLCN1 using real-time RT-PCR. Antisense oligonucleotides could promote normal CLCN1 alternative splicing but the effective sequence was different from that of Clcn1. This result differs from previous reports using Clcn1, highlighting the effect of differences in splicing patterns between mice and humans.