Dysregulation of PRMT5 in chronic lymphocytic leukemia promotes progression with high risk of Richter's transformation.

Richter's Transformation (RT) is a poorly understood and fatal progression of chronic lymphocytic leukemia (CLL) manifesting histologically as diffuse large B-cell lymphoma. Protein arginine methyltransferase 5 (PRMT5) is implicated in lymphomagenesis, but its role in CLL or RT progression is unknown. We demonstrate herein that tumors uniformly overexpress PRMT5 in patients with progression to RT. Furthermore, mice with B-specific overexpression of hPRMT5 develop a B-lymphoid expansion with increased risk of death, and Eµ-PRMT5/TCL1 double transgenic mice develop a highly aggressive disease with transformation that histologically resembles RT; where large-scale transcriptional profiling identifies oncogenic pathways mediating PRMT5-driven disease progression. Lastly, we report the development of a SAM-competitive PRMT5 inhibitor, PRT382, with exclusive selectivity and optimal in vitro and in vivo activity compared to available PRMT5 inhibitors. Taken together, the discovery that PRMT5 drives oncogenic pathways promoting RT provides a compelling rationale for clinical investigation of PRMT5 inhibitors such as PRT382 in aggressive CLL/RT cases.

X-linked Dystonia-Parkinsonism patient cells exhibit altered signaling via nuclear factor-kappa B.

X-linked Dystonia-Parkinsonism (XDP) is a progressive neurodegenerative disease involving the loss of medium spiny neurons within the striatum. An XDP-specific haplotype has been identified, consisting of seven sequence variants which cluster around the human TAF1 gene, but a direct relationship between any of these variants and disease pathogenesis has not yet been demonstrated. Because the pathogenic gene lesion remains unclear, it has been difficult to predict cellular pathways which are affected in XDP cells. To address that issue, we assayed expression of defined gene sets in XDP vs. control fibroblasts to identify networks of functionally-related transcripts which may be dysregulated in XDP patient cells. That analysis derived a 51-gene signature distinguishing XDP vs. control fibroblasts which mapped strongly to nuclear factor-kappa B (NFκB), a transcription factor pathway also implicated in the pathogenesis of other neurodegenerative diseases, including Parkinson's (PD) and Huntington's disease (HD). Constitutive and TNFα-evoked NFκB signaling was further evaluated in XDP vs. control fibroblasts based on luciferase reporter activity, DNA binding of NFκB subunits, and endogenous target gene transcription. Compared to control cells, XDP fibroblasts exhibited decreased basal NFκB activity and decreased levels of the active NFκB p50 subunit, but increased target gene expression in response to TNFα. NFκB signaling was further examined in neural stem cells differentiated from XDP and control induced pluripotent stem cell (iPSC) lines, revealing a similar pattern of increased TNFα responses in the patient lines compared to controls. These data indicate that an NFκB signaling phenotype is present in both patient fibroblasts and neural stem cells, suggesting this pathway as a site of dysfunction in XDP.

Decreased N-TAF1 expression in X-linked dystonia-parkinsonism patient-specific neural stem cells.

X-linked dystonia-parkinsonism (XDP) is a hereditary neurodegenerative disorder involving a progressive loss of striatal medium spiny neurons. The mechanisms underlying neurodegeneration are not known, in part because there have been few cellular models available for studying the disease. The XDP haplotype consists of multiple sequence variations in a region of the X chromosome containingTAF1, a large gene with at least 38 exons, and a multiple transcript system (MTS) composed of five unconventional exons. A previous study identified an XDP-specific insertion of a SINE-VNTR-Alu (SVA)-type retrotransposon in intron 32 ofTAF1, as well as a neural-specific TAF1 isoform, N-TAF1, which showed decreased expression in post-mortem XDP brain compared with control tissue. Here, we generated XDP patient and control fibroblasts and induced pluripotent stem cells (iPSCs) in order to further probe cellular defects associated with this disease. As initial validation of the model, we compared expression ofTAF1and MTS transcripts in XDP versus control fibroblasts and iPSC-derived neural stem cells (NSCs). Compared with control cells, XDP fibroblasts exhibited decreased expression ofTAF1transcript fragments derived from exons 32-36, a region spanning the SVA insertion site. N-TAF1, which incorporates an alternative exon (exon 34'), was not expressed in fibroblasts, but was detectable in iPSC-differentiated NSCs at levels that were ∼threefold lower in XDP cells than in controls. These results support the previous findings that N-TAF1 expression is impaired in XDP, but additionally indicate that this aberrant transcription might occur in neural cells at relatively early stages of development that precede neurodegeneration.