Small Molecule RBI2 Disrupts Ribosome Biogenesis through Pre-rRNA Depletion

Cancer cells are especially sensitive to perturbations in ribosome biogenesis as they rely on finely tuned protein homeostasis to facilitate their rapid growth and proliferation. While ribosome synthesis and cancer have a well-established relationship, ribosome biogenesis has only recently drawn interest as a cancer therapeutic target. In this study, we exploited the relationship between ribosome biogenesis and cancer cell proliferation by using a potent ribosome biogenesis inhibitor, RBI2 (Ribosome Biogenesis Inhibitor 2), to perturb cancer cell growth and viability. We demonstrate herein that RBI2 significantly decreases cell viability in malignant melanoma cells and breast cancer cell lines. Treatment with RBI2 dramatically and rapidly decreased ribosomal RNA (rRNA) synthesis, without affecting the occupancy of RNA polymerase I (Pol I) on the ribosomal DNA template. Next-generation RNA sequencing (RNA-seq) revealed that RBI2 and previously described ribosome biogenesis inhibitor CX-5461 induce distinct changes in the transcriptome. An investigation of the content of the pre-rRNAs through RT-qPCR revealed an increase in the polyadenylation of cellular rRNA after treatment with RBI2, constituting a known pathway by which rRNA degradation occurs. Northern blotting revealed that RBI2 does not appear to impair or alter rRNA processing. Collectively, these data suggest that RBI2 inhibits rRNA synthesis differently from other previously described ribosome biogenesis inhibitors, potentially acting through a novel pathway that upregulates the turnover of premature rRNAs.

Metagenomics of Parkinson's disease implicates the gut microbiome in multiple disease mechanisms

Parkinson's disease (PD) may start in the gut and spread to the brain. To investigate the role of gut microbiome, we conducted a large-scale study, at high taxonomic resolution, using uniform standardized methods from start to end. We enrolled 490 PD and 234 control individuals, conducted deep shotgun sequencing of fecal DNA, followed by metagenome-wide association studies requiring significance by two methods (ANCOM-BC and MaAsLin2) to declare disease association, network analysis to identify polymicrobial clusters, and functional profiling. Here we show that over 30% of species, genes and pathways tested have altered abundances in PD, depicting a widespread dysbiosis. PD-associated species form polymicrobial clusters that grow or shrink together, and some compete. PD microbiome is disease permissive, evidenced by overabundance of pathogens and immunogenic components, dysregulated neuroactive signaling, preponderance of molecules that induce alpha-synuclein pathology, and over-production of toxicants; with the reduction in anti-inflammatory and neuroprotective factors limiting the capacity to recover. We validate, in human PD, findings that were observed in experimental models; reconcile and resolve human PD microbiome literature; and provide a broad foundation with a wealth of concrete testable hypotheses to discern the role of the gut microbiome in PD.