Multiple immune-cell types can infiltrate tumors and promote progression and metastasis through different mechanisms, including immunosuppression. How distinct genetic alterations in tumors affect the composition of the immune landscape is currently unclear. Here, we characterized the immune-cell composition of prostate cancers driven by the loss of the critical tumor suppressor gene Pten, either alone or in combination with the loss of Trp53, Zbtb7a or Pml. We observed a striking quantitative and qualitative heterogeneity that was directly dependent on the specific genetic events in the tumor and ranged from 'cold', noninflamed tumors to massively infiltrated landscapes-results with important therapeutic implications. Further, we showed these qualitative differences in transcriptomic analysis of human prostate cancer samples. These data suggest that patient stratification on the basis of integrated genotypic-immunophenotypic analyses may be necessary for successful clinical trials and tailored precision immunological therapies..

The transcriptional network acting downstream of LIF, WNT and MAPK-ERK to stabilize mouse embryonic stem cells (ESCs) in their naive state has been extensively characterized. However, the upstream factors regulating these three signaling pathways remain largely uncharted. PR-domain-containing proteins (PRDMs) are zinc-finger sequence-specific chromatin factors that have essential roles in embryonic development and cell fate decisions. Here we characterize the transcriptional regulator PRDM15, which acts independently of PRDM14 to regulate the naive state of mouse ESCs. Mechanistically, PRDM15 modulates WNT and MAPK-ERK signaling by directly promoting the expression of Rspo1 (R-spondin1) and Spry1 (Sprouty1). Consistent with these findings, CRISPR-Cas9-mediated disruption of PRDM15-binding sites in the Rspo1 and Spry1 promoters recapitulates PRDM15 depletion, both in terms of local chromatin organization and the transcriptional modulation of these genes. Collectively, our findings uncover an essential role for PRDM15 as a chromatin factor that modulates the transcription of upstream regulators of WNT and MAPK-ERK signaling to safeguard naive pluripotency..

Circular RNAs (circRNAs) are a novel class of RNA whose physiological function has yet to be investigated. A recent publication in Science provides the first evidence of the biological relevance of a circRNA in an in vivo model and unveils an unexpected twist on their crosstalk with miRNAs..

MDM4 is a promising target for cancer therapy, as it is undetectable in most normal adult tissues but often upregulated in cancer cells to dampen p53 tumor-suppressor function. The mechanisms that underlie MDM4 upregulation in cancer cells are largely unknown. Here, we have shown that this key oncogenic event mainly depends on a specific alternative splicing switch. We determined that while a nonsense-mediated, decay-targeted isoform of MDM4 (MDM4-S) is produced in normal adult tissues as a result of exon 6 skipping, enhanced exon 6 inclusion leads to expression of full-length MDM4 in a large number of human cancers. Although this alternative splicing event is likely regulated by multiple splicing factors, we identified the SRSF3 oncoprotein as a key enhancer of exon 6 inclusion. In multiple human melanoma cell lines and in melanoma patient-derived xenograft (PDX) mouse models, antisense oligonucleotide-mediated (ASO-mediated) skipping of exon 6 decreased MDM4 abundance, inhibited melanoma growth, and enhanced sensitivity to MAPK-targeting therapeutics. Additionally, ASO-based MDM4 targeting reduced diffuse large B cell lymphoma PDX growth. As full-length MDM4 is enhanced in multiple human tumors, our data indicate that this strategy is applicable to a wide range of tumor types. We conclude that enhanced MDM4 exon 6 inclusion is a common oncogenic event and has potential as a clinically compatible therapeutic target..

Chromosomal translocations encode oncogenic fusion proteins that have been proven to be causally involved in tumorigenesis. Our understanding of whether such genomic alterations also affect non-coding RNAs is limited, and their impact on circular RNAs (circRNAs) has not been explored. Here, we show that well-established cancer-associated chromosomal translocations give rise to fusion circRNAs (f-circRNA) that are produced from transcribed exons of distinct genes affected by the translocations. F-circRNAs contribute to cellular transformation, promote cell viability and resistance upon therapy, and have tumor-promoting properties in in vivo models. Our work expands the current knowledge regarding molecular mechanisms involved in cancer onset and progression, with potential diagnostic and therapeutic implications..

Deregulated expression of the MYC transcription factor occurs in most human cancers and correlates with high proliferation, reprogrammed cellular metabolism and poor prognosis. Overexpressed MYC binds to virtually all active promoters within a cell, although with different binding affinities, and modulates the expression of distinct subsets of genes. However, the critical effectors of MYC in tumorigenesis remain largely unknown. Here we show that during lymphomagenesis in Eµ-myc transgenic mice, MYC directly upregulates the transcription of the core small nuclear ribonucleoprotein particle assembly genes, including Prmt5, an arginine methyltransferase that methylates Sm proteins. This coordinated regulatory effect is critical for the core biogenesis of small nuclear ribonucleoprotein particles, effective pre-messenger-RNA splicing, cell survival and proliferation. Our results demonstrate that MYC maintains the splicing fidelity of exons with a weak 5' donor site. Additionally, we identify pre-messenger-RNAs that are particularly sensitive to the perturbation of the MYC-PRMT5 axis, resulting in either intron retention (for example, Dvl1) or exon skipping (for example, Atr, Ep400). Using antisense oligonucleotides, we demonstrate the contribution of these splicing defects to the anti-proliferative/apoptotic phenotype observed in PRMT5-depleted Eµ-myc B cells. We conclude that, in addition to its well-documented oncogenic functions in transcription and translation, MYC also safeguards proper pre-messenger-RNA splicing as an essential step in lymphomagenesis..

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Although much is known about the molecular players in insulin signaling, there is scant information about transcriptional regulation of its key components. We now find that NUCKS is a transcriptional regulator of the insulin signaling components, including the insulin receptor (IR). Knockdown of NUCKS leads to impaired insulin signaling in endocrine cells. NUCKS knockout mice exhibit decreased insulin signaling and increased body weight/fat mass along with impaired glucose tolerance and reduced insulin sensitivity, all of which are further exacerbated by a high-fat diet (HFD). Genome-wide ChIP-seq identifies metabolism and insulin signaling as NUCKS targets. Importantly, NUCKS is downregulated in individuals with a high body mass index and in HFD-fed mice, and conversely, its levels increase upon starvation. Altogether, NUCKS is a physiological regulator of energy homeostasis and glucose metabolism that works by regulating chromatin accessibility and RNA polymerase II recruitment to the promoters of IR and other insulin pathway modulators..

The tight control of gene expression at the level of both transcription and post-transcriptional RNA processing is essential for mammalian development. We here investigate the role of protein arginine methyltransferase 5 (PRMT5), a putative splicing regulator and transcriptional cofactor, in mammalian development. We demonstrate that selective deletion of PRMT5 in neural stem/progenitor cells (NPCs) leads to postnatal death in mice. At the molecular level, the absence of PRMT5 results in reduced methylation of Sm proteins, aberrant constitutive splicing, and the alternative splicing of specific mRNAs with weak 5' donor sites. Intriguingly, the products of these mRNAs are, among others, several proteins regulating cell cycle progression. We identify Mdm4 as one of these key mRNAs that senses the defects in the spliceosomal machinery and transduces the signal to activate the p53 response, providing a mechanistic explanation of the phenotype observed in vivo. Our data demonstrate that PRMT5 is a master regulator of splicing in mammals and uncover a new role for the Mdm4 pre-mRNA, which could be exploited for anti-cancer therapy..

Adipose tissue is the largest compartment in the mammalian body for storing energy as fat, providing an important reservoir of fuel for maintaining whole body energy homeostasis. Herein, we identify the transcriptional cofactor hairless (HR) to be required for white adipogenesis. Moreover, forced expression of HR in non-adipogenic precursor cells induces adipogenic gene expression and enhances adipocyte formation under permissive conditions. HR exerts its proadipogenic effects by regulating the expression of PPARγ, one of the central adipogenic transcription factors. In conclusion, our data provide a new mechanism required for white adipogenesis..

The asymmetric dimethylation of histone H3 arginine 2 (H3R2me2a) acts as a repressive mark that antagonizes trimethylation of H3 lysine 4. Here we report that H3R2 is also symmetrically dimethylated (H3R2me2s) by PRMT5 and PRMT7 and present in euchromatic regions. Profiling of H3-tail interactors by SILAC MS revealed that H3R2me2s excludes binding of RBBP7, a central component of co-repressor complexes Sin3a, NURD and PRC2. Conversely H3R2me2s enhances binding of WDR5, a common component of the coactivator complexes MLL, SET1A, SET1B, NLS1 and ATAC. The interaction of histone H3 with WDR5 distinguishes H3R2me2s from H3R2me2a, which impedes the recruitment of WDR5 to chromatin. The crystallographic structure of WDR5 and the H3R2me2s peptide elucidates the molecular determinants of this high affinity interaction. Our findings identify H3R2me2s as a previously unknown mark that keeps genes poised in euchromatin for transcriptional activation upon cell-cycle withdrawal and differentiation in human cells..

p21 is a potent cyclin-dependent kinase inhibitor that plays a role in promoting G1 cell cycle arrest and cellular senescence. Consistent with this role, p21 is a downstream target of several tumour suppressors and oncogenes, and it is downregulated in the majority of tumours, including breast cancer. Here, we report that protein arginine methyltransferase 6 (PRMT6), a type I PRMT known to act as a transcriptional cofactor, directly represses the p21 promoter. PRMT6 knock-down (KD) results in a p21 derepression in breast cancer cells, which is p53-independent, and leads to cell cycle arrest, cellular senescence and reduced growth in soft agar assays and in severe combined immunodeficiency (SCID) mice for all the cancer lines examined. We finally show that bypassing the p21-mediated arrest rescues PRMT6 KD cells from senescence, and it restores their ability to grow on soft agar. We conclude that PRMT6 acts as an oncogene in breast cancer cells, promoting growth and preventing senescence, making it an attractive target for cancer therapy..

Post-translational modifications (PTMs) are commonly used to modify protein function. Modifications such as phosphorylation, acetylation and methylation can influence the conformation of the modified protein and its interaction with other proteins or DNA. In the case of histones, PTMs on specific residues can influence chromatin structure and function by modifying the biochemical properties of key amino acids. Histone methylation events, especially on arginine- and lysine-residues, are among the best-characterized PTMs, and many of these modifications have been linked to downstream effects. The addition of a methyl group to either residue results in a slight increase in hydrophobicity, in the loss of a potential hydrogen-bond donor site and, in the alteration of the protein interaction surface. Thus far, a number of protein domains have been demonstrated to directly bind to methylated lysine residues. However, the biochemical mechanisms linking histone arginine methylation to downstream biological outputs remain poorly characterized. This review will focus on the role of histone arginine methylation in transcriptional regulation and on the crosstalk between arginine methylation and other PTMs. We will discuss the mechanisms by which differentially methylated arginines on histones modulate transcriptional outcomes and contribute to the complexity of the 'histone code'..