Pentamidine reverses the splicing defects associated with myotonic dystrophy

Myotonic dystrophy (DM) is a genetic disorder caused by the expression (as RNA) of expanded CTG or CCTG repeats. The alternative splicing factor MBNL1 is sequestered to the expanded RNA repeats, resulting in missplicing of a subset of pre-mRNAs linked to symptoms found in DM patients. Current data suggest that if MBNL1 is released from sequestration, disease symptoms may be alleviated. We identified the small molecules pentamidine and neomycin B as compounds that disrupt MBNL1 binding to CUG repeats in vitro. We show in cell culture that pentamidine was able to reverse the missplicing of 2 pre-mRNAs affected in DM, whereas neomycin B had no effect. Pentamidine also significantly reduced the formation of ribonuclear foci in tissue culture cells, releasing MBNL1 from the foci in the treated cells. Furthermore, pentamidine partially rescued splicing defects of 2 pre-mRNAs in mice expressing expanded CUG repeats

Npr2, Yeast Homolog of the Human Tumor Suppressor NPRL2, Is a Target of Grr1 Required for Adaptation to Growth on Diverse Nitrogen Sources ▿

Npr2, a putative “nitrogen permease regulator” and homolog of the human tumor suppressor NPRL2, was found to interact with Grr1, the F-box component of the SCFGrr1 (Skp1–cullin–F-box protein complex containing Grr1) E3 ubiquitin ligase, by mass spectrometry-based multidimensional protein identification technology. Npr2 has two PEST sequences and has been previously identified among ubiquitinated proteins. Like other Grr1 targets, Npr2 is a phosphoprotein. Phosphorylated Npr2 accumulates in grr1Δ mutants, and Npr2 is stabilized in cells with inactivated proteasomes. Phosphorylation and instability depend upon the type I casein kinases (CK1) Yck1 and Yck2. Overexpression of Npr2 is detrimental to cells and is lethal in grr1Δ mutants. Npr2 is required for robust growth in defined medium containing ammonium or urea as a nitrogen source but not for growth on rich medium. npr2Δ mutants also fail to efficiently complete meiosis. Together, these data indicate that Npr2 is a phosphorylation-dependent target of the SCFGrr1 E3 ubiquitin ligase that plays a role in cell growth on some nitrogen sources