Pathobiology and Treatment of the UBTF E210K Neuroregression Syndrome

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Recurrent de novo dominant mutations in UBTF (NM_014233.3:c.628G>A, p.Glu210Lys) were recently associated with a distinct neurological disorder dubbed the UBTF E210K neuroregression syndrome. UBTF exists as two major isoforms, UBTF1 and UBTF2. UBTF1 regulates ribosomal RNA (rRNA) transcription by RNA polymerase 1 (Pol I), whereas UBTF2 regulates mRNA transcription by RNA polymerase 2 (Pol II). UBTF c.628G>A results in the same amino acid change in both UBTF1 and UBTF2 (E210K). Disease onset is at 2.5 to 3 yrs and characterized by slow progression of global motor, cognitive and behavioral dysfunction. UBTF E210K modified binding to the rDNA promoter that affects formation of the preinitiation complex by the Pol1-specific TBP-complex SL1. Since both UBTF1 and UBTF2 contribute to DNA accessibility and genomic stability, the increased binding affinity of the UBTF E210K mutant to DNA could alter the interchange with histone chromatin that occurs when genes are switched off, potentially leaving the underlying DNA poorly protected. UBTF E210K fibroblasts show increased expression of pre-rRNA and 18S rRNA, nucleolar abnormalities, markedly increased numbers of DNA double-strand breaks (DSBs), defective cell-cycle progression, and apoptosis. Ubtf-/- is early embryonic lethal in mice and transgenic expression of mutant human UBTF E210K in Drosophila neurons is also lethal. There are no known disease-modifying treatments for this disorder. Furthermore, we have not yet (i) clarified the relationships among increase expression of rRNA, DNA DSBs and cell-cycle abnormalities identified in patient fibroblasts, (ii) determined the mechanistic connections between nucleolar dysfunction and non-nucleolar DNA damage, or (iii) fully characterized a UBTF E210K mammalian model system. Our overall goals are to understand the mechanisms by which UBTF E210K causes progressive cellular dysfunction and develop a treatment for this devastating disorder. We hypothesize that Ubtf+/E210K mice will exhibit progressive motor and cognitive deficits, nucleolar abnormalities and apoptotic neuronal loss in association with accumulated DNA damage. Next, we will determine the effects of UBTF E210K on rRNA transcription, RNA processing, and RNA Pol I transcription elongation. Integrated analysis of ChIP-Seq and RNA-Seq will be used to determine the effects of UBTF E210K on chromatin structure and genome-wide gene expression. We will quantify the effects of UBTF E210K on rDNA, non-rDNA, and nucleolar structure. Psoralen cross-linking will be used to determine the ratio of active to inactive genes. ChIP-Seq mapping of γH2A.X will be used to map sites of DNA damage at the genome-wide level. Finally, we will test pre-clinical treatment of UBTF E210K cellular and animal models with orally-bioavailable and central nervous system penetrant Pol I inhibitors.