Antisense oligonucleotide-mediated MDM4 exon 6 skipping impairs tumor growth

Ribosomal RNA transcription governs splicing through ribosomal protein RPL22

Ribosome biosynthesis is a cancer vulnerability executed by targeting RNA polymerase I (Pol I) transcription. We developed advanced, specific Pol I inhibitors to identify drivers of this sensitivity. By integrating multi-omics features and drug sensitivity data from a large cancer cell panel, we discovered that RPL22 frameshift mutation conferred Pol I inhibitor sensitivity in microsatellite instable cancers. Mechanistically, RPL22 directly interacts with 28S rRNA and mRNA splice junctions, functioning as a splicing regulator. RPL22 deficiency, intensified by 28S rRNA sequestration, promoted the splicing of its paralog RPL22L1 and p53 negative regulator MDM4. Chemical and genetic inhibition of rRNA synthesis broadly remodeled mRNA splicing controlling hundreds of targets. Strikingly, RPL22-dependent alternative splicing was reversed by Pol I inhibition revealing a ribotoxic stress-initiated tumor suppressive pathway. We identify a mechanism that robustly connects rRNA synthesis activity to splicing and reveals their coordination by ribosomal protein RPL22.

SPLASH2 provides ultra-efficient, scalable, and unsupervised discovery on raw sequencing reads

SPLASH is an unsupervised, reference-free, and unifying algorithm that discovers regulated sequence variation through statistical analysis of k-mer composition, subsuming many application-specific methods. Here, we introduce SPLASH2, a fast, scalable implementation of SPLASH based on an efficient k-mer counting approach. SPLASH2 enables rapid analysis of massive datasets from a wide range of sequencing technologies and biological contexts, delivering unparalleled scale and speed. The SPLASH2 algorithm unveils new biology (without tuning) in single-cell RNA-sequencing data from human muscle cells, as well as bulk RNA-seq from the entire Cancer Cell Line Encyclopedia (CCLE), including substantial unannotated alternative splicing in cancer transcriptome. The same untuned SPLASH2 algorithm recovers the BCR-ABL gene fusion, and detects circRNA sensitively and specifically, underscoring SPLASH2's unmatched precision and scalability across diverse RNA-seq detection tasks.

RPL22 is a tumor suppressor in MSI-high cancers and a key splicing regulator of MDM4

Microsatellite instability high (MSI-H) tumors are malignant tumors that, despite harboring a high mutational burden, often have intact TP53. One of the most frequent mutations in MSI-H tumors is a frameshift mutation in RPL22, a ribosomal protein. Here, we identified RPL22 as a modulator of MDM4 splicing through an alternative splicing switch in exon 6. RPL22 loss increases MDM4 exon 6 inclusion, cell proliferation, and augments resistance to the MDM inhibitor Nutlin-3a. RPL22 represses expression of its paralog, RPL22L1, by mediating the splicing of a cryptic exon corresponding to a truncated transcript. Therefore, damaging mutations in RPL22 drive oncogenic MDM4 induction and reveal a common splicing circuit in MSI-H tumors that may inform therapeutic targeting of the MDM4-p53 axis and oncogenic RPL22L1 induction.

MitoTracer facilitates the identification of informative mitochondrial mutations for precise lineage reconstruction

Mitochondrial (MT) mutations serve as natural genetic markers for inferring clonal relationships using single cell sequencing data. However, the fundamental challenge of MT mutation-based lineage tracing is automated identification of informative MT mutations. Here, we introduced an open-source computational algorithm called "MitoTracer", which accurately identified clonally informative MT mutations and inferred evolutionary lineage from scRNA-seq or scATAC-seq samples. We benchmarked MitoTracer using the ground-truth experimental lineage sequencing data and demonstrated its superior performance over the existing methods measured by high sensitivity and specificity. MitoTracer is compatible with multiple single cell sequencing platforms. Its application to a cancer evolution dataset revealed the genes related to primary BRAF-inhibitor resistance from scRNA-seq data of BRAF-mutated cancer cells. Overall, our work provided a valuable tool for capturing real informative MT mutations and tracing the lineages among cells.

Teaser

MitoTracer enables automatically and accurately discover informative mitochondrial mutations for lineage tracing.

Alternative splicing regulation of cell-cycle genes by SPF45/SR140/CHERP complex controls cell proliferation

The regulation of pre-mRNA processing has important consequences for cell division and the control of cancer cell proliferation, but the underlying molecular mechanisms remain poorly understood. We report that three splicing factors, SPF45, SR140, and CHERP, form a tight physical and functionally coherent complex that regulates a variety of alternative splicing events, frequently by repressing short exons flanked by suboptimal 3' splice sites. These comprise alternative exons embedded in genes with important functions in cell-cycle progression, including the G2/M key regulator FOXM1 and the spindle regulator SPDL1. Knockdown of either of the three factors leads to G2/M arrest and to enhanced apoptosis in HeLa cells. Promoting the changes in FOXM1 or SPDL1 splicing induced by SPF45/SR140/CHERP knockdown partially recapitulates the effects on cell growth, arguing that the complex orchestrates a program of alternative splicing necessary for efficient cell proliferation.