An Adult Mouse Model of Dilated Cardiomyopathy Caused by Inducible Cardiac-Specific Bis Deletion

BCL-2 interacting cell death suppressor (BIS) is a multifunctional protein that has been implicated in cancer and myopathy. Various mutations of the BIS gene have been identified as causative of cardiac dysfunction in some dilated cardiomyopathy (DCM) patients. This was recently verified in cardiac-specific knock-out (KO) mice. In this study, we developed tamoxifen-inducible cardiomyocyte-specific BIS-KO (Bis-iCKO) mice to assess the role of BIS in the adult heart using the Cre-loxP strategy. The disruption of the Bis gene led to impaired ventricular function and subsequent heart failure due to DCM, characterized by reduced left ventricular contractility and dilatation that were observed using serial echocardiography and histology. The development of DCM was confirmed by alterations in Z-disk integrity and increased expression of several mRNAs associated with heart failure and remodeling. Furthermore, aggregation of desmin was correlated with loss of small heat shock protein in the Bis-iCKO mice, indicating that BIS plays an essential role in the quality control of cardiac proteins, as has been suggested in constitutive cardiac-specific KO mice. Our cardiac-specific BIS-KO mice may be a useful model for developing therapeutic interventions for DCM, especially late-onset DCM, based on the distinct phenotypes and rapid progressions.

SRSF3 Is a Critical Requirement for Inclusion of Exon 3 of BIS Pre-mRNA

BCL-2 interacting cell death suppressor (BIS), also known as BAG3, is a multifunctional protein. Aberrant expression and mutation of BIS have been implicated in cancers and myopathy. However, there have only been a few studies on the splicing of BIS pre-mRNA. In the present study, through RT-PCR and sequencing in various cell lines and mouse tissues, we identified for the first time the presence of BIS mRNA isomers in which exon 3 or exons 2–3 are skipped. We also demonstrated that the depletion of SRSF3 promoted the skipping of exon 3 of BIS pre-mRNA in endogenous BIS and the GFP-BIS minigene. SRSF3 specifically interacts with the putative binding sites in exon 3, in which deletion promoted the skipping of exon 3 in the GFP-BIS minigene, which was comparable to the effect of SRSF knockdown. Even though acceleration of exon 3 skipping was not observed in response to various stimuli, SRSF3 depletion, accompanied by the production of a truncated BIS protein, inhibited the nuclear translocation of HSF1, which was restored by the wild-type BIS, not by exon 3-depleted BIS. Therefore, our results suggested that the maintenance of SRSF3 levels and subsequent preservation of the intact BIS protein is an important factor in modulating HSF1 localization upon cellular stress.

Identification and Characterization of Suppressor Mutants of spl11-Mediated Cell Death in Rice

Lesion mimic mutants have been used to dissect programmed cell death (PCD) and defense-related pathways in plants. The rice lesion-mimic mutant spl11 exhibits race nonspecific resistance to the bacterial pathogen Xanthomonas oryzae pv. oryzae and the fungal pathogen Magnaporthe oryzae. Spl11 encodes an E3 ubiquitin ligase and is a negative regulator of PCD in rice. To study the regulation of Spl11-mediated PCD, we performed a genetic screen and identified three spl11 cell-death suppressor (sds) mutants. These suppressors were characterized for their resistance to X. oryzae pv. oryzae and M. oryzae and for their expression of defense-related genes. The suppression of the cell-death phenotypes was generally correlated with reduced expression of defense-related genes. When rice was challenged with avirulent isolates of M. oryzae, the disease phenotype was unaffected in the sds mutants, indicating that the suppression might be Spl11-mediated pathway specific and may only be involved in basal defense. In addition, we mapped one of the suppressor mutations to a 140-kb interval on the long arm of rice chromosome 1. Identification and characterization of these sds mutants should facilitate our efforts to elucidate the Spl11-mediated PCD pathway.