Dysregulation of the basal RNA polymerase transcription apparatus in cancer

Global kinetic mechanism describing single nucleotide incorporation for RNA polymerase I reveals fast UMP incorporation

RNA polymerase I (Pol I) is responsible for synthesizing ribosomal RNA, which is the rate limiting step in ribosome biogenesis. We have reported wide variability in the magnitude of the rate constants defining the rate limiting step in sequential nucleotide additions catalyzed by Pol I. in this study we sought to determine if base identity impacts the rate limiting step of nucleotide addition catalyzed by Pol I. To this end, we report a transient state kinetic interrogation of AMP, CMP, GMP, and UMP incorporations catalyzed by Pol I. We found that Pol I uses one kinetic mechanism to incorporate all nucleotides. However, we found that UMP incorporation is faster than AMP, CMP, and GMP additions. Further, we found that endonucleolytic removal of a dimer from the 3' end was fastest when the 3' terminal base is a UMP. It has been previously shown that both downstream and upstream template sequence identity impacts the kinetics of nucleotide addition. The results reported here show that the incoming base identity also impacts the magnitude of the observed rate limiting step.

TTF1 control of LncRNA synthesis delineates a tumor suppressor pathway directly regulating the ribosomal RNA genes

The tumor suppressor p14/19ARF regulates ribosomal RNA (rRNA) synthesis by controlling the nucleolar localization of Transcription Termination Factor 1 (TTF1). However, the role played by TTF1 in regulating the rRNA genes and in potentially controlling growth has remained unclear. We now show that TTF1 expression regulates cell growth by determining the cellular complement of ribosomes. Unexpectedly, it achieves this by acting as a "roadblock" to synthesis of the noncoding LncRNA and pRNA that we show are generated from the "Spacer Promoter" duplications present upstream of the 47S pre-rRNA promoter on the mouse and human ribosomal RNA genes. Unexpectedly, the endogenous generation of these noncoding RNAs does not induce CpG methylation or gene silencing. Rather, it acts in cis to suppress 47S preinitiation complex formation and hence de novo pre-rRNA synthesis by a mechanism reminiscent of promoter interference or occlusion. Taken together, our data delineate a pathway from p19ARF to cell growth suppression via the regulation of ribosome biogenesis by noncoding RNAs and validate a key cellular growth law in mammalian cells.

Chromatin damage generated by DNA intercalators leads to degradation of RNA Polymerase II

In cancer therapy, DNA intercalators are mainly known for their capacity to kill cells by inducing DNA damage. Recently, several DNA intercalators have attracted much interest given their ability to inhibit RNA Polymerase I transcription (BMH-21), evict histones (Aclarubicin) or induce chromatin trapping of FACT (Curaxin CBL0137). Interestingly, these DNA intercalators lack the capacity to induce DNA damage while still retaining cytotoxic effects and stabilize p53. Herein, we report that these DNA intercalators impact chromatin biology by interfering with the chromatin stability of RNA polymerases I, II and III. These three compounds have the capacity to induce degradation of RNA polymerase II and they simultaneously enable the trapping of Topoisomerases TOP2A and TOP2B on the chromatin. In addition, BMH-21 also acts as a catalytic inhibitor of Topoisomerase II, resembling Aclarubicin. Moreover, BMH-21 induces chromatin trapping of the histone chaperone FACT and propels accumulation of Z-DNA and histone eviction, similarly to Aclarubicin and CBL0137. These DNA intercalators have a cumulative impact on general transcription machinery by inducing accumulation of topological defects and impacting nuclear chromatin. Therefore, their cytotoxic capabilities may be the result of compounding deleterious effects on chromatin homeostasis.

Clinical significance of PNO1 as a novel biomarker and therapeutic target of hepatocellular carcinoma

The RNA-binding protein PNO1 plays an essential role in ribosome biogenesis. Recent studies have shown that it is involved in tumorigenesis; however, its role in hepatocellular carcinoma (HCC) is not well understood. The purpose of this study was to examine whether PNO1 can be used as a biomarker of HCC and also examine the therapeutic potential of PNO1 knockout for the treatment of HCC. PNO1 expression was upregulated in HCC and associated with poor prognosis. PNO1 expression was positively associated with tumour stage, lymph node metastasis and poor survival. PNO1 expression was significantly higher in HCC compared to that in fibrolamellar carcinoma or normal tissues. Furthermore, HCC tissues with mutant Tp53 expressed higher PNO1 than those with wild-type Tp53. PNO1 knockout suppressed cell viability, colony formation and EMT of HCC cells. Since activation of Notch signalling pathway promotes HCC, we measured the effects of PNO1 knockout on the components of Notch pathway and its targets. PNO1 knockout suppressed Notch signalling by modulating the expression of Notch ligands and their receptors, and downstream targets. PNO1 knockout also inhibited genes involved in surface adhesion, cell cycle, inflammation and chemotaxis. PNO1 knockout also inhibited colony and spheroid formation, cell migration and invasion, and markers of stem cells, pluripotency and EMT in CSCs. Overall, our data suggest that PNO1 can be used as a diagnostic and prognostic biomarker of HCC, and knockout of PNO1 by CRISPR/Cas9 can be beneficial for the management of HCC by targeting CSCs.

Live Cell Imaging and Real-Time Monitoring of Nucleolus Morphology and Mitophagy with a Red Fluorescent and Photostable rRNA-Specific Probe in Human Cancer Cells

rRNAs are prevalent in living organisms. They are produced in nucleolus and mitochondria and play essential cellular functions. In addition to the primary biofunction in protein synthesis, rRNAs have been recognized as the emerging signaling molecule and drug target for studies on nucleolus morphology, mitochondrial autophagy, and tumor cell malignancy. Currently, only a few rRNA-selective probes have been developed, and most of them encounter the drawbacks of low water solubility, poor nuclear membrane permeability, short emission wavelength, low stability against photobleaching, and high cytotoxicity. These unfavorable properties of rRNA probes limit their potential applications. In the present study, we reported a new rRNA-selective and near-infrared fluorescent turn-on probe, 4MPS-TO, capable of tracking rRNA in live human cancer cells. The real-time monitoring performance in nucleolus morphology and mitochondrial autophagy is demonstrated in HeLa cells. The probe shows great application potential for being used as a rRNA-selective, sensitive, and photostable imaging tool in chemical biology study and drug screening.

Therapeutic targeting of CPSF3-dependent transcriptional termination in ovarian cancer

Transcriptional dysregulation is a recurring pathogenic hallmark and an emerging therapeutic vulnerability in ovarian cancer. Here, we demonstrated that ovarian cancer exhibited a unique dependency on the regulatory machinery of transcriptional termination, particularly, cleavage and polyadenylation specificity factor (CPSF) complex. Genetic abrogation of multiple CPSF subunits substantially hampered neoplastic cell viability, and we presented evidence that their indispensable roles converged on the endonuclease CPSF3. Mechanistically, CPSF perturbation resulted in lengthened 3'-untranslated regions, diminished intronic polyadenylation and widespread transcriptional readthrough, and consequently suppressed oncogenic pathways. Furthermore, we reported the development of specific CPSF3 inhibitors building upon the benzoxaborole scaffold, which exerted potent antitumor activity. Notably, CPSF3 blockade effectively exacerbated genomic instability by down-regulating DNA damage repair genes and thus acted in synergy with poly(adenosine 5'-diphosphate-ribose) polymerase inhibition. These findings establish CPSF3-dependent transcriptional termination as an exploitable driving mechanism of ovarian cancer and provide a promising class of boron-containing compounds for targeting transcription-addicted human malignancies.

From signalling pathways to targeted therapies: unravelling glioblastoma's secrets and harnessing two decades of progress

Glioblastoma, a rare, and highly lethal form of brain cancer, poses significant challenges in terms of therapeutic resistance, and poor survival rates for both adult and paediatric patients alike. Despite advancements in brain cancer research driven by a technological revolution, translating our understanding of glioblastoma pathogenesis into improved clinical outcomes remains a critical unmet need. This review emphasises the intricate role of receptor tyrosine kinase signalling pathways, epigenetic mechanisms, and metabolic functions in glioblastoma tumourigenesis and therapeutic resistance. We also discuss the extensive efforts over the past two decades that have explored targeted therapies against these pathways. Emerging therapeutic approaches, such as antibody-toxin conjugates or CAR T cell therapies, offer potential by specifically targeting proteins on the glioblastoma cell surface. Combination strategies incorporating protein-targeted therapy and immune-based therapies demonstrate great promise for future clinical research. Moreover, gaining insights into the role of cell-of-origin in glioblastoma treatment response holds the potential to advance precision medicine approaches. Addressing these challenges is crucial to improving outcomes for glioblastoma patients and moving towards more effective precision therapies.

The RNA polymerase II subunit B (RPB2) functions as a growth regulator in human glioblastoma

Glioblastoma multiforme (GBM) is the most common and aggressive brain tumor with a poor prognosis. The growth of GBM cells depends on the core transcriptional apparatus, thus rendering RNA polymerase (RNA pol) complex as a candidate therapeutic target. The RNA pol II subunit B (POLR2B) gene encodes the second largest subunit of the RNA pol II (RPB2); however, its genomic status and function in GBM remain unclear. Certain GBM data sets in cBioPortal were used for investigating the genomic status and expression of POLR2B in GBM. The function of RPB2 was analyzed following knockdown of POLR2B expression by shRNA in GBM cells. The cell counting kit-8 assay and PI staining were used for cell proliferation and cell cycle analysis. A xenograft mouse model was established to analyze the function of RPB2 in vivo. RNA sequencing was performed to analyze the RPB2-regulated genes. GO and GSEA analyses were applied to investigate the RPB2-regulated gene function and associated pathways. In the present study, the genomic alteration and overexpression of the POLR2B gene was described in glioblastoma. The data indicated that knockdown of POLR2B expression suppressed tumor cell growth of glioblastoma in vitro and in vivo. The analysis further demonstrated the identification of the RPB2-regulated gene sets and highlighted the DNA damage-inducible transcript 4 gene as the downstream target of the POLR2B gene. The present study provides evidence indicating that RPB2 functions as a growth regulator in glioblastoma and could be used as a potential therapeutic target for the treatment of this disease.

Multi-omics analysis and validation of the tumor microenvironment of hepatocellular carcinoma under RNA modification patterns

BACKGROUND

Multiple types of RNA modifications are associated with the prognosis of hepatocellular carcinoma (HCC) patients. However, the overall mediating effect of RNA modifications on the tumor microenvironment (TME) and the prognosis of patients with HCC is unclear.

METHODS

Thoroughly analyze the TME, biological processes, immune infiltration and patient prognosis based on RNA modification patterns and gene patterns. Construct a prognostic model (RNA modification score, RNAM-S) to predict the overall survival (OS) in HCC patients. Analyze the immune status, cancer stem cell (CSC), mutations and drug sensitivity of HCC patients in both the high and low RNAM-S groups. Verify the expression levels of the four characteristic genes of the prognostic RNAM-S using in vitro cell experiments.

RESULTS

Two modification patterns and two gene patterns were identified in this study. Both the high-expression modification pattern and the gene pattern exhibited worse OS. A prognostic RNAM-S model was constructed based on four featured genes (KIF20A, NR1I2, NR2F1 and PLOD2). Cellular experiments suggested significant dysregulation of the expression levels of these four genes. In addition, validation of the RNAM-S model using each data set showed good predictive performance of the model. The two groups of HCC patients (high and low RNAM-S groups) exhibited significant differences in immune status, CSC, mutation and drug sensitivity.

CONCLUSION

The findings of the study demonstrate the clinical value of RNA modifications, which provide new insights into the individualized treatment for patients with HCC.

Dynamic de novo heterochromatin assembly and disassembly at replication forks ensures fork stability

Chromatin is dynamically reorganized when DNA replication forks are challenged. However, the process of epigenetic reorganization and its implication for fork stability is poorly understood. Here we discover a checkpoint-regulated cascade of chromatin signalling that activates the histone methyltransferase EHMT2/G9a to catalyse heterochromatin assembly at stressed replication forks. Using biochemical and single molecule chromatin fibre approaches, we show that G9a together with SUV39h1 induces chromatin compaction by accumulating the repressive modifications, H3K9me1/me2/me3, in the vicinity of stressed replication forks. This closed conformation is also favoured by the G9a-dependent exclusion of the H3K9-demethylase JMJD1A/KDM3A, which facilitates heterochromatin disassembly upon fork restart. Untimely heterochromatin disassembly from stressed forks by KDM3A enables PRIMPOL access, triggering single-stranded DNA gap formation and sensitizing cells towards chemotherapeutic drugs. These findings may help in explaining chemotherapy resistance and poor prognosis observed in patients with cancer displaying elevated levels of G9a/H3K9me3.

Expression of RNA polymerase I catalytic core is influenced by RPA12

RNA Polymerase I (Pol I) has recently been recognized as a cancer therapeutic target. The activity of this enzyme is essential for ribosome biogenesis and is universally activated in cancers. The enzymatic activity of this multi-subunit complex resides in its catalytic core composed of RPA194, RPA135, and RPA12, a subunit with functions in RNA cleavage, transcription initiation and elongation. Here we explore whether RPA12 influences the regulation of RPA194 in human cancer cells. We use a specific small-molecule Pol I inhibitor BMH-21 that inhibits transcription initiation, elongation and ultimately activates the degradation of Pol I catalytic subunit RPA194. We show that silencing RPA12 causes alterations in the expression and localization of Pol I subunits RPA194 and RPA135. Furthermore, we find that despite these alterations not only does the Pol I core complex between RPA194 and RPA135 remain intact upon RPA12 knockdown, but the transcription of Pol I and its engagement with chromatin remain unaffected. The BMH-21-mediated degradation of RPA194 was independent of RPA12 suggesting that RPA12 affects the basal expression, but not the drug-inducible turnover of RPA194. These studies add to knowledge defining regulatory factors for the expression of this Pol I catalytic subunit.

Targeting RNA Polymerase I Transcription Activity in Osteosarcoma: Pre-Clinical Molecular and Animal Treatment Studies

The survival rate of patients with osteosarcoma (OS) has not improved over the last 30 years. Mutations in the genes TP53, RB1 and c-Myc frequently occur in OS and enhance RNA Polymerase I (Pol I) activity, thus supporting uncontrolled cancer cell proliferation. We therefore hypothesised that Pol I inhibition may be an effective therapeutic strategy for this aggressive cancer. The Pol I inhibitor CX-5461 has demonstrated therapeutic efficacy in different cancers in pre-clinical and phase I clinical trials; thus, the effects were determined on ten human OS cell lines. Following characterisation using genome profiling and Western blotting, RNA Pol I activity, cell proliferation and cell cycle progression were evaluated in vitro, and the growth of TP53 wild-type and mutant tumours was measured in a murine allograft model and in two human xenograft OS models. CX-5461 treatment resulted in reduced ribosomal DNA (rDNA) transcription and Growth 2 (G2)-phase cell cycle arrest in all OS cell lines. Additionally, tumour growth in all allograft and xenograft OS models was effectively suppressed without apparent toxicity. Our study demonstrates the efficacy of Pol I inhibition against OS with varying genetic alterations. This study provides pre-clinical evidence to support this novel therapeutic approach in OS.

Transcription by the Three RNA Polymerases under the Control of the TOR Signaling Pathway in Saccharomyces cerevisiae

Ribosomes are the basis for protein production, whose biogenesis is essential for cells to drive growth and proliferation. Ribosome biogenesis is highly regulated in accordance with cellular energy status and stress signals. In eukaryotic cells, response to stress signals and the production of newly-synthesized ribosomes require elements to be transcribed by the three RNA polymerases (RNA pols). Thus, cells need the tight coordination of RNA pols to adjust adequate components production for ribosome biogenesis which depends on environmental cues. This complex coordination probably occurs through a signaling pathway that links nutrient availability with transcription. Several pieces of evidence strongly support that the Target of Rapamycin (TOR) pathway, conserved among eukaryotes, influences the transcription of RNA pols through different mechanisms to ensure proper ribosome components production. This review summarizes the connection between TOR and regulatory elements for the transcription of each RNA pol in the budding yeast Saccharomyces cerevisiae. It also focuses on how TOR regulates transcription depending on external cues. Finally, it discusses the simultaneous coordination of the three RNA pols through common factors regulated by TOR and summarizes the most important similarities and differences between S. cerevisiae and mammals.

SPOC domain proteins in health and disease

Since it was first described >20 yr ago, the SPOC domain (Spen paralog and ortholog C-terminal domain) has been identified in many proteins all across eukaryotic species. SPOC-containing proteins regulate gene expression on various levels ranging from transcription to RNA processing, modification, export, and stability, as well as X-chromosome inactivation. Their manifold roles in controlling transcriptional output implicate them in a plethora of developmental processes, and their misregulation is often associated with cancer. Here, we provide an overview of the biophysical properties of the SPOC domain and its interaction with phosphorylated binding partners, the phylogenetic origin of SPOC domain proteins, the diverse functions of mammalian SPOC proteins and their homologs, the mechanisms by which they regulate differentiation and development, and their roles in cancer.

Tuning between Nuclear Organization and Functionality in Health and Disease

The organization of eukaryotic genome in the nucleus, a double-membraned organelle separated from the cytoplasm, is highly complex and dynamic. The functional architecture of the nucleus is confined by the layers of internal and cytoplasmic elements, including chromatin organization, nuclear envelope associated proteome and transport, nuclear-cytoskeletal contacts, and the mechano-regulatory signaling cascades. The size and morphology of the nucleus could impose a significant impact on nuclear mechanics, chromatin organization, gene expression, cell functionality and disease development. The maintenance of nuclear organization during genetic or physical perturbation is crucial for the viability and lifespan of the cell. Abnormal nuclear envelope morphologies, such as invagination and blebbing, have functional implications in several human disorders, including cancer, accelerated aging, thyroid disorders, and different types of neuro-muscular diseases. Despite the evident interplay between nuclear structure and nuclear function, our knowledge about the underlying molecular mechanisms for regulation of nuclear morphology and cell functionality during health and illness is rather poor. This review highlights the essential nuclear, cellular, and extracellular components that govern the organization of nuclei and functional consequences associated with nuclear morphometric aberrations. Finally, we discuss the recent developments with diagnostic and therapeutic implications targeting nuclear morphology in health and disease.

Ribosome biogenesis factors-from names to functions

The assembly of ribosomal subunits is a highly orchestrated process that involves a huge cohort of accessory factors. Most eukaryotic ribosome biogenesis factors were first identified by genetic screens and proteomic approaches of pre-ribosomal particles in Saccharomyces cerevisiae. Later, research on human ribosome synthesis not only demonstrated that the requirement for many of these factors is conserved in evolution, but also revealed the involvement of additional players, reflecting a more complex assembly pathway in mammalian cells. Yet, it remained a challenge for the field to assign a function to many of the identified factors and to reveal their molecular mode of action. Over the past decade, structural, biochemical, and cellular studies have largely filled this gap in knowledge and led to a detailed understanding of the molecular role that many of the players have during the stepwise process of ribosome maturation. Such detailed knowledge of the function of ribosome biogenesis factors will be key to further understand and better treat diseases linked to disturbed ribosome assembly, including ribosomopathies, as well as different types of cancer.

Nanomedicine as potential cancer therapy via targeting dysregulated transcription factors

Cancer as a disease possess quite complicated pathophysiological implications and is among the prominent causes of morbidity and mortality on global scales. Anti-cancer chemotherapy, surgery, and radiation therapy are some of the present-day conventional treatment options. However, these therapeutic paradigms own several retreats, including lack of specificity, non-targeted toxicological implications, inefficient drug delivery to targeted cells, and emergence of cancer resistance, ultimately causing ineffective cancer management. Owing to the advanced and better biophysical characteristic features and potentiality for the tailoring and customizations and in several fashions, nanotechnology can entirely transubstantiate the cancer identification and its managements. Additionally, nanotechnology also renders several answers to present-day mainstream limitations springing-up in anti-cancer therapeutics. Nanocarriers, owing to their outstanding physicochemical features including but not limited to their particle size, surface morphological features viz. shape etc., have been employed in nanomedicinal platforms for targeting various transcription factors leading to worthy pharmacological outcomes. This transcription targeting activates the wide array of cellular and molecular events like antioxidant enzyme-induction, apoptotic cell death, cell-cycle arrest etc. These outcomes are obtained after the activation or inactivation of several transcription factors and cellular pathways. Further, nanoformulations have been precisely calibrated and functionalized with peculiar targeting groups for improving their efficiency to deliver the drug-payload to specified and targeted cancerous cells and tissues. This review undertakes an extensive, across-the-board and all-inclusive approach consisting of various studies encompassing different types of tailored and customized nanoformulations and nanomaterials designed for targeting the transcription factors implicated in the process of carcinogenesis, tumor-maturation, growth and metastasis. Various transcription factors viz. nuclear factor kappa (NF-κB), signal transducer and activators of transcription (STAT), Cmyc and Twist-related protein 1 (TWIST1) along with several types of nanoparticles targeting these transcription factors have been summarized here. A section has also been dedicated to the different types of nanoparticles targeting the hypoxia inducing factors. Efforts have been made to summarize several other transcription factors implicated in various stages of cancer development, growth, progression and invasion, and their targeting with different kinds of nanomedicinal agents.

Inhibition of ribosome assembly factor PNO1 by CRISPR/Cas9 technique suppresses lung adenocarcinoma and Notch pathway: Clinical application

Growth is crucially controlled by the functional ribosomes available in cells. To meet the enhanced energy demand, cancer cells re-wire and increase their ribosome biogenesis. The RNA-binding protein PNO1, a ribosome assembly factor, plays an essential role in ribosome biogenesis. The purpose of this study was to examine whether PNO1 can be used as a biomarker for lung adenocarcinoma and also examine the molecular mechanisms by which PNO1 knockdown by CRISPR/Cas9 inhibited growth and epithelial-mesenchymal transition (EMT). The expression of PNO1 was significantly higher in lung adenocarcinoma compared to normal lung tissues. PNO1 expression in lung adenocarcinoma patients increased with stage, nodal metastasis, and smoking. Lung adenocarcinoma tissues from males expressed higher PNO1 than those from females. Furthermore, lung adenocarcinoma tissues with mutant Tp53 expressed higher PNO1 than those with wild-type Tp53, suggesting the influence of Tp53 status on PNO1 expression. PNO1 knockdown inhibited cell viability, colony formation, and EMT, and induced apoptosis. Since dysregulated signalling through the Notch receptors promotes lung adenocarcinoma, we measured the effects of PNO1 inhibition on the Notch pathway. PNO1 knockdown inhibited Notch signalling by suppressing the expression of Notch receptors, their ligands, and downstream targets. PNO1 knockdown also suppressed CCND1, p21, PTGS-2, IL-1α, IL-8, and CXCL-8 genes. Overall, our data suggest that PNO1 can be used as a diagnostic biomarker, and also can be an attractive therapeutic target for the treatment of lung adenocarcinoma.

The proteomic landscape shows oncologic relevance in cystitis glandularis

BACKGROUND

The relationship between cystitis glandularis (CG) and bladder malignancy remains unclear.

METHODS

We identified the oncologic significance of CG at the molecular level using liquid chromatography-tandem mass spectrometry-based proteomic analysis of 10 CG, 12 urothelial carcinoma (UC), and nine normal urothelium (NU) specimens. Differentially expressed proteins (DEPs) were identified based on an analysis of variance false discovery rate < 0.05, and their functional enrichment was analyzed using a network model, Gene Set Enrichment Analysis, and Gene Ontology annotation.

RESULTS

We identified 9,890 proteins across all samples and 1,139 DEPs among the three entities. A substantial number of DEPs overlapped in CG/NU, distinct from UC. Interestingly, we found that a subset of DEP clusters (n = 53, 5%) was differentially expressed in NU but similarly between CG and UC. This "UC-like signature" was enriched for reactive oxygen species (ROS) and energy metabolism, growth and DNA repair, transport, motility, epithelial-mesenchymal transition, and cell survival. Using the top 10 shortlisted DEPs, including SOD2, PRKCD, CYCS, and HCLS1, we identified functional elements related to ROS metabolism, development, and transport using network analysis. The abundance of these four molecules in UC/CG than in NU was consistent with the oncologic functions in CG.

CONCLUSIONS

Using a proteomic approach, we identified a predominantly non-neoplastic landscape of CG, which was closer to NU than to UC. We also confirmed a small subset of common DEPs in UC and CG, suggesting that altered ROS metabolism might imply potential cancerous risks in CG.

Regulation of RNA Polymerase I Stability and Function

RNA polymerase I is a highly processive enzyme with fast initiation and elongation rates. The structure of Pol I, with its in-built RNA cleavage ability and incorporation of subunits homologous to transcription factors, enables it to quickly and efficiently synthesize the enormous amount of rRNA required for ribosome biogenesis. Each step of Pol I transcription is carefully controlled. However, cancers have highjacked these control points to switch the enzyme, and its transcription, on permanently. While this provides an exceptional benefit to cancer cells, it also creates a potential cancer therapeutic vulnerability. We review the current research on the regulation of Pol I transcription, and we discuss chemical biology efforts to develop new targeted agents against this process. Lastly, we highlight challenges that have arisen from the introduction of agents with promiscuous mechanisms of action and provide examples of agents with specificity and selectivity against Pol I.

Identification of an E3 ligase that targets the catalytic subunit of RNA Polymerase I upon transcription stress

RNA Polymerase I (Pol I) synthesizes rRNA, which is the first and rate-limiting step in ribosome biogenesis. Factors governing the stability of the polymerase complex are not known. Previous studies characterizing Pol I inhibitor BMH-21 revealed a transcriptional stress-dependent pathway for degradation of the largest subunit of Pol I, RPA194. To identify the E3 ligase(s) involved, we conducted a cell-based RNAi screen for ubiquitin pathway genes. We establish Skp-Cullin-F-box protein complex F-box protein FBXL14 as an E3 ligase for RPA194. We show that FBXL14 binds to RPA194 and mediates RPA194 ubiquitination and degradation in cancer cells treated with BMH-21. Mutation analysis in yeast identified lysines 1150, 1153, and 1156 on Rpa190 relevant for the protein degradation. These results reveal the regulated turnover of Pol I, showing that the stability of the catalytic subunit is controlled by the F-box protein FBXL14 in response to transcription stress.

A transcriptional program associated with cell cycle regulation predominates in the anti-inflammatory effects of CX-5461 in macrophage

CX-5461, a novel selective RNA polymerase I inhibitor, shows potential anti-inflammatory and immunosuppressive activities. However, the molecular mechanisms underlying the inhibitory effects of CX-5461 on macrophage-mediated inflammation remain to be clarified. In the present study, we attempted to identify the systemic biological processes which were modulated by CX-5461 in inflammatory macrophages. Primary peritoneal macrophages were isolated from normal Sprague Dawley rats, and primed with lipopolysaccharide or interferon-γ. Genome-wide RNA sequencing was performed. Gene Ontology and Kyoto Encyclopedia of Genes and Genomes databases were used for gene functional annotations. Enrichment analysis was conducted using the ClusterProfiler package of R software. We found that CX-5461 principally induced a molecular signature related to cell cycle inhibition in primed macrophages, featuring downregulation of genes encoding cell cycle mediators and concomitant upregulation of cell cycle inhibitors. At the same concentration, however, CX-5461 did not induce a systemic anti-inflammatory transcriptional program, although some inflammatory genes such as IL-1β and gp91phox NADPH oxidase were downregulated by CX-5461. Our data further highlighted a central role of p53 in orchestrating the molecular networks that were responsive to CX-5461 treatment. In conclusion, our study suggested that limiting cell proliferation predominated in the inhibitory effects of CX-5461 on macrophage-mediated inflammation.

Pharmacologic Targeting of TFIIH Suppresses KRAS-Mutant Pancreatic Ductal Adenocarcinoma and Synergizes with TRAIL

Pancreatic ductal adenocarcinoma (PDAC) typically presents as metastatic disease at diagnosis and remains refractory to treatment. Next-generation sequencing efforts have described the genomic landscape, classified molecular subtypes, and confirmed frequent alterations in major driver genes, with coexistent alterations in KRAS and TP53 correlating with the highest metastatic burden and poorest outcomes. However, translating this information to guide therapy remains a challenge. By integrating genomic analysis with an arrayed RNAi druggable genome screen and drug profiling of a KRAS/TP53 mutant PDAC cell line derived from a patient-derived xenograft (PDCL), we identified numerous targetable vulnerabilities that reveal both known and novel functional aspects of pancreatic cancer biology. A dependence on the general transcription and DNA repair factor TFIIH complex, particularly the XPB subunit and the CAK complex (CDK7/CyclinH/MAT1), was identified and further validated utilizing a panel of genomically subtyped KRAS mutant PDCLs. TFIIH function was inhibited with a covalent inhibitor of CDK7/12/13 (THZ1), a CDK7/CDK9 kinase inhibitor (SNS-032), and a covalent inhibitor of XPB (triptolide), which led to disruption of the protein stability of the RNA polymerase II subunit RPB1. Loss of RPB1 following TFIIH inhibition led to downregulation of key transcriptional effectors of KRAS-mutant signaling and negative regulators of apoptosis, including MCL1, XIAP, and CFLAR, initiating caspase-8 dependent apoptosis. All three drugs exhibited synergy in combination with a multivalent TRAIL, effectively reinforcing mitochondrial-mediated apoptosis. These findings present a novel combination therapy, with direct translational implications for current clinical trials on metastatic pancreatic cancer patients. Significance: This study utilizes functional genetic and pharmacological profiling of KRAS-mutant pancreatic adenocarcinoma to identify therapeutic strategies and finds that TFIIH inhibition synergizes with TRAIL to induce apoptosis in KRAS-driven pancreatic cancer.

Targeted protein degradation reveals RNA Pol II heterogeneity and functional diversity

RNA polymerase II (RNA Pol II) subunits are thought to be involved in various transcription-associated processes, but it is unclear whether they play different regulatory roles in modulating gene expression. Here, we performed nascent and mature transcript sequencing after the acute degradation of 12 mammalian RNA Pol II subunits and profiled their genomic binding sites and protein interactomes to dissect their molecular functions. We found that RNA Pol II subunits contribute differently to RNA Pol II cellular localization and transcription processes and preferentially regulate RNA processing (such as RNA splicing and 3' end maturation). Genes sensitive to the depletion of different RNA Pol II subunits tend to be involved in diverse biological functions and show different RNA half-lives. Sequences, associated protein factors, and RNA structures are correlated with RNA Pol II subunit-mediated differential gene expression. These findings collectively suggest that the heterogeneity of RNA Pol II and different genes appear to depend on some of the subunits.

EventPointer 3.0: flexible and accurate splicing analysis that includes studying the differential usage of protein-domains

Alternative splicing (AS) plays a key role in cancer: all its hallmarks have been associated with different mechanisms of abnormal AS. The improvement of the human transcriptome annotation and the availability of fast and accurate software to estimate isoform concentrations has boosted the analysis of transcriptome profiling from RNA-seq. The statistical analysis of AS is a challenging problem not yet fully solved. We have included in EventPointer (EP), a Bioconductor package, a novel statistical method that can use the bootstrap of the pseudoaligners. We compared it with other state-of-the-art algorithms to analyze AS. Its performance is outstanding for shallow sequencing conditions. The statistical framework is very flexible since it is based on design and contrast matrices. EP now includes a convenient tool to find the primers to validate the discoveries using PCR. We also added a statistical module to study alteration in protein domain related to AS. Applying it to 9514 patients from TCGA and TARGET in 19 different tumor types resulted in two conclusions: i) aberrant alternative splicing alters the relative presence of Protein domains and, ii) the number of enriched domains is strongly correlated with the age of the patients.

Treacle is Upregulated in Cancer and Correlates With Poor Prognosis

Treacle/TCOF1 is an adaptor protein specifically associated with nucleolar chromatin. In the nucleolus it stimulates ribosome biogenesis, thereby promoting growth and proliferation. A second role of Treacle has emerged as a coordinator of the nucleolar responses to DNA damage, where it facilitates nucleolar DNA repair and cellular survival after genotoxic insults. The involvement of Treacle in multiple fundamental processes such as growth, proliferation, and genome stability, which are tightly linked to cancer, raises the question of Treacle’s role in the development of this disease. On one hand, overexpression of Treacle could stimulate nucleolar transcription and ribosome biogenesis providing a growth advantage in cancer cells. On the other hand, the function of Treacle as a gatekeeper in response to nucleolar DNA damage could favor mutations that would impair its function. In this perspective, we analyze paired Treacle expression data from the Cancer Genome Atlas (TCGA) and correlate expression with patient survival in different cancer types. We also discuss other recently published observations of relevance to the role of Treacle in cancer. In light of these new observations, we propose possible roles of Treacle in carcinogenesis and discuss its potential as a therapeutic target.

Toxicity of 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) in early development: A wide-scope metabolomics assay in zebrafish embryos

The tobacco-specific nitrosamine 4-(Methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) is a carcinogenic and ubiquitous environmental pollutant for which toxic activity has been thoroughly investigated in murine models and human tissues. However, its potential deleterious effects on vertebrate early development are yet poorly understood. In this work, we characterized the impact of NNK exposure during early developmental stages of zebrafish embryos, a known alternative model for mammalian toxicity studies. Embryos exposed to different NNK concentrations were monitored for lethality and for the appearance of malformations during the first five days after fertilization. LC-MS based untargeted metabolomics was subsequently performed for a wide-scope assay of NNK-related metabolic alterations. Our results revealed the presence of not only the parental compound, but also of two known NNK metabolites, 4-Hydroxy-4-(3-pyridyl)-butyric acid (HPBA) and 4-(Methylnitrosamino)-1-(3-pyridyl-N-oxide)-1-butanol (NNAL-N-oxide) in exposed embryos likely resulting from active CYP450-mediated α-hydroxylation and NNK detoxification pathways, respectively. This was paralleled by a disruption in purine and pyrimidine metabolisms and the activation of the base excision repair pathway. Our results confirm NNK as a harmful embryonic agent and demonstrate zebrafish embryos to be a suitable early development model to monitor NNK toxicity.

CDK12 Is Necessary to Promote Epidermal Differentiation Through Transcription Elongation

Proper differentiation of the epidermis is essential to prevent water loss and to protect the body from the outside environment. Perturbations in this process can lead to a variety of skin diseases that impacts 1 in 5 people. While transcription factors that control epidermal differentiation have been well characterized, other aspects of transcription control such as elongation are poorly understood. Here we show that of the two cyclin-dependent kinases (CDK12 and CDK13), that are known to regulate transcription elongation, only CDK12 is necessary for epidermal differentiation. Depletion of CDK12 led to loss of differentiation gene expression and absence of skin barrier formation in regenerated human epidermis. CDK12 binds to genes that code for differentiation promoting transcription factors (GRHL3, KLF4, and OVOL1) and is necessary for their elongation. CDK12 is necessary for elongation by promoting Ser2 phosphorylation on the C-terminal domain of RNA polymerase II and the stabilization of binding of the elongation factor SPT6 to target genes. Our results suggest that control of transcription elongation by CDK12 plays a prominent role in adult cell fate decisions.

Targeting Ribosome Biogenesis in Cancer: Lessons Learned and Way Forward

Simple Summary

Cells need to produce ribosomes to sustain continuous proliferation and expand in numbers, a feature that is even more prominent in uncontrollably proliferating cancer cells. Certain cancer cell types are expected to depend more on ribosome biogenesis based on their genetic background, and this potential vulnerability can be exploited in designing effective, targeted cancer therapies. This review provides information on anti-cancer molecules that target the ribosome biogenesis machinery and indicates avenues for future research.

Abstract

Rapid growth and unrestrained proliferation is a hallmark of many cancers. To accomplish this, cancer cells re-wire and increase their biosynthetic and metabolic activities, including ribosome biogenesis (RiBi), a complex, highly energy-consuming process. Several chemotherapeutic agents used in the clinic impair this process by interfering with the transcription of ribosomal RNA (rRNA) in the nucleolus through the blockade of RNA polymerase I or by limiting the nucleotide building blocks of RNA, thereby ultimately preventing the synthesis of new ribosomes. Perturbations in RiBi activate nucleolar stress response pathways, including those controlled by p53. While compounds such as actinomycin D and oxaliplatin effectively disrupt RiBi, there is an ongoing effort to improve the specificity further and find new potent RiBi-targeting compounds with improved pharmacological characteristics. A few recently identified inhibitors have also become popular as research tools, facilitating our advances in understanding RiBi. Here we provide a comprehensive overview of the various compounds targeting RiBi, their mechanism of action, and potential use in cancer therapy. We discuss screening strategies, drug repurposing, and common problems with compound specificity and mechanisms of action. Finally, emerging paths to discovery and avenues for the development of potential biomarkers predictive of therapeutic outcomes across cancer subtypes are also presented.

Discovery and Evaluation of Novel Angular Fused Pyridoquinazolinonecarboxamides as RNA Polymerase I Inhibitors

RNA polymerase I (Pol I) transcribes ribosomal DNA (rDNA) into the 47S ribosomal RNA (rRNA) precursor. Further processing produces the 28S, 5.8S, and 18S rRNAs that are assembled into mature ribosomes. Many cancers exhibit higher Pol I transcriptional activity, reflecting a need for increased ribosome biogenesis and protein synthesis and making the inhibition of this process an attractive therapeutic strategy. Lead molecule BMH-21 (1) has been established as a Pol I inhibitor by affecting the destruction of RPA194, the Pol I large catalytic subunit. A previous structure-activity relationship (SAR) study uncovered key pharmacophores, but activity was constrained within a tight chemical space. This work details further SAR efforts that have yielded new scaffolds and improved off-target activity while retaining the desired RPA194 degradation potency. Pharmacokinetic profiling was obtained and provides a starting point for further optimization. New compounds present additional opportunities for the development of Pol I inhibitory cancer therapies.

SET and MYND domain-containing protein 2 (SMYD2): A prognostic biomarker associated with immune infiltrates in cervical squamous cell carcinoma and endocervical adenocarcinoma

The histone lysine methyltransferase SET (Suppressor of variegation, Enhancer of Zeste, Trithorax) and MYND (Myeloid-Nervy-DEAF1) domaincontaining protein (SMYD2) plays a role in the tumorigenesis of cervical squamous cell carcinoma and endocervical adenocarcinoma (CESC). However, the prognostic significance of SMYD2 in CESC and the link between SMYD2 and tumor-infiltrating immune cells are unknown. The prognostic value of SMYD2 in CESC was obtained from The Cancer Genome Atlas (TCGA). SMYD2 mRNA and protein were both highly expressed in CESC compared with normal tissues. The high expression of SMYD2 was associated with advanced tumor status and poor prognosis in CESC patients. SMYD2 was an independent prognostic factor for overall survival. In vitro experiments with knockdown of SMYD2 suppressed CESC cell migration and invasion. The online tumor immune estimation resource (TIMER) and Kaplan-Meier analysis results revealed that the infiltration of CD4+ T and CD8+ T cells was related to poor prognosis. In TIMER-based multivariate Cox regression analysis, CD8+ T cells and SMYD2 were demonstrated as independent prognostic factors of CESC. In conclusion, our data suggest that high SMYD2 expression is a predictor of poor prognosis in CESC patients; SMYD2 could serve as a prognostic biomarker and molecular therapeutic target for CESC.

Comprehensive analyses of microRNA and mRNA expression in colorectal serrated lesions and colorectal cancer with a microsatellite instability phenotype

MicroRNA (miRNA) expression is dysregulated in human tumors, thereby contributing to tumorigenesis through altered expression of mRNA. Thus, identification of the relationships between miRNAs and mRNAs is important for evaluating the molecular mechanisms of tumors. In addition, elucidation of the molecular features of serrated lesions is essential in colorectal tumorigenesis. Here, we examined the relationships of miRNA and mRNA expressed in serrated lesions, including 26 sessile serrated lesions (SSLs), 12 traditional serrated adenomas (TSAs), and 11 colorectal cancers (CRCs) with a microsatellite instability (MSI) phenotype using crypt isolation. We divided the samples into the first and second cohorts for validation. Array-based expression analyses were used to evaluate miRNAs and mRNAs with opposite expression patterns in isolated tumor glands. In addition, we validated the relationships of miRNA/mRNA pairs in the second cohort using real-time polymerase chain reaction. We found that the expression of miRNA-5787 was correlated with reciprocal expression of two mRNAs, that is, SRRM2 and POLR2J3, in SSL samples. In TSA samples, two pairs of miRNAs/mRNAs showing opposite expression patterns, that is, miRNA-182-5p/ETF1 and miRNA-200b-3p/MYB, were identified. Ultimately, three pairs of miRNAs/mRNAs with opposite expression patterns, including miRNA-222-3p/SLC26A3, miRNA-6753-3p/FABP1, and miRNA-222-3p/OLFM4, were retained in CRC with an MSI phenotype. Finally, we performed transfection with an miR-222-3p mimic to confirm the expression of SLC26A3 and OLFM4; the results showed that ectopic expression of miR-222-3p moderately suppressed OLFM4 and downregulated SLC26A3 to some extent. Overall, our results provided basic insights into the evaluation of colorectal tumorigenesis of serrated lesions and CRC with an MSI phenotype.

Identification of Prognosis-Related RNA-Binding Proteins to Reveal the Role of RNA-Binding Proteins in the Progression and Prognosis of Colon Cancer

Background

RNA binding proteins (RBPs) are now under discussion as novel promising bio-markers for patients with colon cancer. The purpose of our study is to identify several RBPs related to the progression and prognosis of colon cancer and to further investigate the mechanism of their influence on tumor progression.

Methods

The transcriptome data of colon cancer and clinical characteristics were downloaded from The Cancer Genome Atlas (TCGA) database. Gene ontology (GO), Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis, and Gene Set Enrichment Analysis (GSEA) were performed to elucidate the gene functions and relative pathways. Cox and Lasso regression analyses were used to analyze the effect of immune genes on the prognosis of colon cancer. An immune risk scoring model was constructed based on the statistical correlation between hub immune genes and survival. Meanwhile, multivariate Cox regression analysis was utilized to investigate whether the immune gene risk score model was an independent factor for predicting the prognosis of colon cancer. A nomogram was constructed to comprehensively predict the survival rate of colon cancer. P < 0.05 was considered statistically significant.

Results

The results showed that 473 RBPs exhibited differential expression between normal and colon cancer tissues (P < 0.05). Univariate Cox regression analysis revealed 25 RBPs statistically correlated with colon cancer-related survival risk (P < 0.05). In addition, a 10-RBPs based risk scoring model was constructed through multivariate Cox regression analysis. A K–M curve indicated that high-risk patients were associated with poor outcomes (P < 0.001). A ROC curve indicated that the immune risk score model was reliable in predicting survival risk (5-year overall survival (OS), area under curve (AUC) = 0.782). Our model showed satisfying AUC and survival correlation in the validation dataset (5-year OS, AUC = 0.744). Furthermore, multivariate Cox regression analysis confirmed that the immune risk score model was an independent factor for predicting the prognosis of colon cancer. Finally, we found that 10-RBPs and risk scores were significantly associated with clinical factors and prognosis and were involved in multiple oncogenic pathways.

Conclusion

Collectively, RBPs play an essential role in the progression and prognosis of colon cancer by regulating multiple biological pathways. Furthermore, the RBP risk score was an independent predictive factor of colon cancer, indicating poor survival.

Targeting the Transcriptome Through Globally Acting Components

Transcription is a step in gene expression that defines the identity of cells and its dysregulation is associated with diseases. With advancing technologies revealing molecular underpinnings of the cell with ever-higher precision, our ability to view the transcriptomes may have surpassed our knowledge of the principles behind their organization. The human RNA polymerase II (Pol II) machinery comprises thousands of components that, in conjunction with epigenetic and other mechanisms, drive specialized programs of development, differentiation, and responses to the environment. Parts of these programs are repurposed in oncogenic transformation. Targeting of cancers is commonly done by inhibiting general or broadly acting components of the cellular machinery. The critical unanswered question is how globally acting or general factors exert cell type specific effects on transcription. One solution, which is discussed here, may be among the events that take place at genes during early Pol II transcription elongation. This essay turns the spotlight on the well-known phenomenon of promoter-proximal Pol II pausing as a step that separates signals that establish pausing genome-wide from those that release the paused Pol II into the gene. Concepts generated in this rapidly developing field will enhance our understanding of basic principles behind transcriptome organization and hopefully translate into better therapies at the bedside.

Hypertranscription and replication stress in cancer

Replication stress results from obstacles to replication fork progression, including ongoing transcription, which can cause transcription-replication conflicts. Oncogenic signaling can promote global increases in transcription activity, also termed hypertranscription. Despite the widely accepted importance of oncogene-induced hypertranscription, its study remains neglected compared with other causes of replication stress and genomic instability in cancer. A growing number of recent studies are reporting that oncogenes, such as RAS, and targeted cancer treatments, such as bromodomain and extraterminal motif (BET) bromodomain inhibitors, increase global transcription, leading to R-loop accumulation, transcription-replication conflicts, and the activation of replication stress responses. Here we discuss our mechanistic understanding of hypertranscription-induced replication stress and the resulting cellular responses, in the context of oncogenes and targeted cancer therapies.

Ribosomal proteins and human diseases: molecular mechanisms and targeted therapy

Ribosome biogenesis and protein synthesis are fundamental rate-limiting steps for cell growth and proliferation. The ribosomal proteins (RPs), comprising the structural parts of the ribosome, are essential for ribosome assembly and function. In addition to their canonical ribosomal functions, multiple RPs have extra-ribosomal functions including activation of p53-dependent or p53-independent pathways in response to stress, resulting in cell cycle arrest and apoptosis. Defects in ribosome biogenesis, translation, and the functions of individual RPs, including mutations in RPs have been linked to a diverse range of human congenital disorders termed ribosomopathies. Ribosomopathies are characterized by tissue-specific phenotypic abnormalities and higher cancer risk later in life. Recent discoveries of somatic mutations in RPs in multiple tumor types reinforce the connections between ribosomal defects and cancer. In this article, we review the most recent advances in understanding the molecular consequences of RP mutations and ribosomal defects in ribosomopathies and cancer. We particularly discuss the molecular basis of the transition from hypo- to hyper-proliferation in ribosomopathies with elevated cancer risk, a paradox termed "Dameshek's riddle." Furthermore, we review the current treatments for ribosomopathies and prospective therapies targeting ribosomal defects. We also highlight recent advances in ribosome stress-based cancer therapeutics. Importantly, insights into the mechanisms of resistance to therapies targeting ribosome biogenesis bring new perspectives into the molecular basis of cancer susceptibility in ribosomopathies and new clinical implications for cancer therapy.

Clinical significance of anti-NOR90 antibodies in systemic sclerosis and idiopathic interstitial pneumonia

OBJECTIVE

Anti-NOR90 antibodies are usually found in patients with systemic sclerosis (SSc); however, their clinical relevance remains obscure. We developed an enzyme-linked immunosorbent assay (ELISA) for measuring them to investigate the clinical features of patients with anti-NOR90 antibodies.

METHODS

Serum samples from 1,252 patients with various conditions from Nagoya University Hospital and 244 patients with idiopathic interstitial pneumonia (IIP) from Tosei General Hospital were included. Anti-NOR90 antibodies were assayed by an ELISA using the recombinant protein produced by in vitro transcription/translation.

RESULTS

Five (0.4%) patients in the Nagoya University Hospital cohort had anti-NOR90 antibodies. One patient with diffuse cutaneous SSc, 3 with limited cutaneous SSc, and 1 with Raynaud's disease were positive for anti-NOR90 antibodies. Anti-NOR90 antibodies were found more frequently in patients with systemic scleroderma-spectrum disorders (SSDs) than without SSDs (5/316 vs. 0/936, P<0.00101) and were found more frequently in patients with SSc than without SSc (4/249 vs. 0/528, P<0.0104) in the systemic autoimmune rheumatic diseases cohort. Three of the 4 anti-NOR90-positive SSc patients had interstitial lung disease (ILD), and 2 of those 4 had cancer. Three (1.2%) patients in the Tosei General Hospital cohort had anti-NOR90 antibodies. All 3 of the anti-NOR90-positive IIP patients had gastrointestinal tract involvement, and 2 of those 3 had cancer or skin lesions observed in SSc.

CONCLUSIONS

Although anti-NOR90 antibodies are rarely found in clinics, our ELISA is useful for their detection. Further studies are needed to confirm the association of anti-NOR90 antibodies with ILD and cancer in SSc and IIP patients.

Identification of Nucleolin as a Novel AEG-1-Interacting Protein in Breast Cancer via Interactome Profiling

Breast cancer is one of the most common malignant diseases worldwide. Astrocyte elevated gene-1 (AEG-1) is upregulated in breast cancer and regulates breast cancer cell proliferation and invasion. However, the molecular mechanisms by which AEG-1 promotes breast cancer have yet to be fully elucidated. In order to delineate the function of AEG-1 in breast cancer development, we mapped the AEG-1 interactome via affinity purification followed by LC-MS/MS. We identified nucleolin (NCL) as a novel AEG-1 interacting protein, and co-immunoprecipitation experiments validated the interaction between AEG-1 and NCL in breast cancer cells. The silencing of NCL markedly reduced not only migration/invasion, but also the proliferation induced by the ectopic expression of AEG-1. Further, we found that the ectopic expression of AEG-1 induced the tyrosine phosphorylation of c-Met, and NCL knockdown markedly reduced this AEG-1 mediated phosphorylation. Taken together, our report identifies NCL as a novel mediator of the oncogenic function of AEG-1, and suggests that c-Met could be associated with the oncogenic function of the AEG-1-NCL complex in the context of breast cancer.

The Ribosomal Gene Loci-The Power behind the Throne

Nucleoli form around actively transcribed ribosomal RNA (rRNA) genes (rDNA), and the morphology and location of nucleolus-associated genomic domains (NADs) are linked to the RNA Polymerase I (Pol I) transcription status. The number of rDNA repeats (and the proportion of actively transcribed rRNA genes) is variable between cell types, individuals and disease state. Substantial changes in nucleolar morphology and size accompanied by concomitant changes in the Pol I transcription rate have long been documented during normal cell cycle progression, development and malignant transformation. This demonstrates how dynamic the nucleolar structure can be. Here, we will discuss how the structure of the rDNA loci, the nucleolus and the rate of Pol I transcription are important for dynamic regulation of global gene expression and genome stability, e.g., through the modulation of long-range genomic interactions with the suppressive NAD environment. These observations support an emerging paradigm whereby the rDNA repeats and the nucleolus play a key regulatory role in cellular homeostasis during normal development as well as disease, independent of their role in determining ribosome capacity and cellular growth rates.

Cell surface nucleolin as active bait for nanomedicine in cancer therapy: a promising option

Conventional chemotherapy used against cancer is mostly limited due to their non-targeted nature, affecting normal tissue and causing undesirable toxic effects to the affected tissue. With the aim of improving these treatments both therapeutically and in terms of their safety, numerous studies are currently being carried out using nanoparticles (NPs) as a vector combining tumor targeting and carrying therapeutic tools. In this context, it appears that nucleolin, a molecule over-expressed on the surface of tumor cells, is an interesting therapeutic target. Several ligands, antagonists of nucleolin of various origins, such as AS1411, the F3 peptide and the multivalent pseudopeptide N6L have been developed and studied as therapeutic tools against cancer. Over the last ten years or so, numerous studies have been published demonstrating that these antagonists can be used as tumor targeting agents with NPs from various origins. Focusing on nucleolin ligands, the aim of this article is to review the literature recently published or under experimentation in our research team to evaluate the efficacy and future development of these tools as anti-tumor agents.

RAF-MEK-ERK pathway in cancer evolution and treatment

The RAF-MEK-ERK signaling cascade is a well-characterized MAPK pathway involved in cell proliferation and survival. The three-layered MAPK signaling cascade is initiated upon RTK and RAS activation. Three RAF isoforms ARAF, BRAF and CRAF, and their downstream MEK1/2 and ERK1/2 kinases constitute a coherently orchestrated signaling module that directs a range of physiological functions. Genetic alterations in this pathway are among the most prevalent in human cancers, which consist of numerous hot-spot mutations such as BRAF^V600E. Oncogenic mutations in this pathway often override otherwise tightly regulated checkpoints to open the door for uncontrolled cell growth and neoplasia. The crosstalk between the RAF-MEK-ERK axis and other signaling pathways further extends the proliferative potential of this pathway in human cancers. In this review, we summarize the molecular architecture and physiological functions of the RAF-MEK-ERK pathway with emphasis on its dysregulations in human cancers, as well as the efforts made to target the RAF-MEK-ERK module using small molecule inhibitors.

MYC function and regulation in flies: how Drosophila has enlightened MYC cancer biology

Progress in our understanding of the complex signaling events driving human cancer would have been unimaginably slow without discoveries from Drosophila genetic studies. Significantly, many of the signaling pathways now synonymous with cancer biology were first identified as a result of elegant screens for genes fundamental to metazoan development. Indeed the name given to many core cancer-signaling cascades tells of their history as developmental patterning regulators in flies—e.g. Wingless (Wnt), Notch and Hippo. Moreover, astonishing insight has been gained into these complex signaling networks, and many other classic oncogenic signaling networks (e.g. EGFR/RAS/RAF/ERK, InR/PI3K/AKT/TOR), using sophisticated fly genetics. Of course if we are to understand how these signaling pathways drive cancer, we must determine the downstream program(s) of gene expression activated to promote the cell and tissue over growth fundamental to cancer. Here we discuss one commonality between each of these pathways: they are all implicated as upstream activators of the highly conserved MYC oncogene and transcription factor. MYC can drive all aspects of cell growth and cell cycle progression during animal development. MYC is estimated to be dysregulated in over 50% of all cancers, underscoring the importance of elucidating the signals activating MYC. We also discuss the FUBP1/FIR/FUSE system, which acts as a ‘cruise control’ on the MYC promoter to control RNA Polymerase II pausing and, therefore, MYC transcription in response to the developmental signaling environment. Importantly, the striking conservation between humans and flies within these major axes of MYC regulation has made Drosophila an extremely valuable model organism for cancer research. We therefore discuss how Drosophila studies have helped determine the validity of signaling pathways regulating MYC in vivo using sophisticated genetics, and continue to provide novel insight into cancer biology.

Cullin-5 neddylation-mediated NOXA degradation is enhanced by PRDX1 oligomers in colorectal cancer

NOXA, a BH3-only proapoptotic protein involved in regulating cell death decisions, is highly expressed but short-lived in colorectal cancer (CRC). Neddylated cullin-5 (CUL5)-mediated ubiquitination and degradation of NOXA is crucial to prevent its overaccumulation and maintain an appropriate action time. However, how this process is manipulated by CRC cells commonly exposed to oxidative stress remain unknown. The peroxiredoxin PRDX1, a conceivable antioxidant overexpressed in CRC tissues, has been shown to inhibit apoptosis and TRAF6 ubiquitin-ligase activity. In this study, we found that PRDX1 inhibits CRC cell apoptosis by downregulating NOXA. Mechanistically, PRDX1 promotes NOXA ubiquitination and degradation, which completely depend on CUL5 neddylation. Further studies have demonstrated that PRDX1 oligomers bind with both the Nedd8-conjugating enzyme UBE2F and CUL5 and that this tricomplex is critical for CUL5 neddylation, since silencing PRDX1 or inhibiting PRDX1 oligomerization greatly dampens CUL5 neddylation and NOXA degradation. An increase in reactive oxygen species (ROS) is not only a hallmark of cancer cells but also the leading driving force for PRDX1 oligomerization. As shown in our study, although ROS play a role in upregulating NOXA mRNA transcription, ROS scavenging in CRC cells by N-acetyl-L-cysteine (NAC) can significantly reduce CUL5 neddylation and extend the NOXA protein half-life. Therefore, in CRC, PRDX1 plays a key role in maintaining intracellular homeostasis under conditions of high metabolic activity by reinforcing UBE2F-CUL5-mediated degradation of NOXA, which is also evidenced in the resistance of CRC cells to etoposide treatment. Based on these findings, targeting PRDX1 could be an effective strategy to overcome the resistance of CRC to DNA damage-inducing chemotherapeutics.

Therapeutic efficacy of the novel selective RNA polymerase I inhibitor CX-5461 on pulmonary arterial hypertension and associated vascular remodelling

Background and Purpose

CX‐5461 is a novel selective RNA polymerase I (Pol I) inhibitor. Previously, we found that CX‐5461 could inhibit pathological arterial remodelling caused by angioplasty and transplantation. In the present study, we explored the pharmacological effects of CX‐5461 on experimental pulmonary arterial hypertension (PAH) and PAH‐associated vascular remodelling.

Experimental Approach

PAH was induced in Sprague–Dawley rats by monocrotaline or Sugen/hypoxia.

Key Results

We demonstrated that CX‐5461 was well tolerated for in vivo treatments. CX‐5461 prevented the development of pulmonary arterial remodelling, perivascular inflammation, pulmonary hypertension, and improved survival. More importantly, CX‐5461 partly reversed established pulmonary hypertension. In vitro, CX‐5461 induced cell cycle arrest in human pulmonary arterial smooth muscle cells. The beneficial effects of CX‐5461 in vivo and in vitro were associated with increased activation (phosphorylation) of p53.

Conclusion and Implications

Our results suggest that pharmacological inhibition of Pol I may be a novel therapeutic strategy to treat otherwise drug‐resistant PAH.

Recent progress in development of cyclin-dependent kinase 7 inhibitors for cancer therapy

Introduction: Cyclin-dependent kinase 7 (CDK7) is a part of the CDK-activating kinase family (CAK) which has a key role in the cell cycle and transcriptional regulation. Several lines of evidence suggest that CDK7 is a promising therapeutic target for cancer. CDK7 selective inhibitors such as SY-5609 and CT7001 are in clinical development. Areas covered: We explore the biology of CDK7 and its role in cancer and follow this with an evaluation of the preclinical and clinical progress of CDK7 inhibitors, and their potential in the clinic. We searched PubMed and ClinicalTrials to identify relevant data from the database inception to 14 October 2020. Expert opinion: CDK7 inhibitors are next generation therapeutics for cancer. However, there are still challenges which include selectively, side effects, and drug resistance. Nevertheless, with ongoing clinical development of these inhibitors and greater analysis of their target, CDK7 inhibitors will become a promising approach for treatment of cancer in the near future.

Ribosomal RNA 2'O-methylation as a novel layer of inter-tumour heterogeneity in breast cancer

Recent epitranscriptomics studies unravelled that ribosomal RNA (rRNA) 2′O-methylation is an additional layer of gene expression regulation highlighting the ribosome as a novel actor of translation control. However, this major finding lies on evidences coming mainly, if not exclusively, from cellular models. Using the innovative next-generation RiboMeth-seq technology, we established the first rRNA 2′O-methylation landscape in 195 primary human breast tumours. We uncovered the existence of compulsory/stable sites, which show limited inter-patient variability in their 2′O-methylation level, which map on functionally important sites of the human ribosome structure and which are surrounded by variable sites found from the second nucleotide layers. Our data demonstrate that some positions within the rRNA molecules can tolerate absence of 2′O-methylation in tumoral and healthy tissues. We also reveal that rRNA 2′O-methylation exhibits intra- and inter-patient variability in breast tumours. Its level is indeed differentially associated with breast cancer subtype and tumour grade. Altogether, our rRNA 2′O-methylation profiling of a large-scale human sample collection provides the first compelling evidence that ribosome variability occurs in humans and suggests that rRNA 2′O-methylation might represent a relevant element of tumour biology useful in clinic. This novel variability at molecular level offers an additional layer to capture the cancer heterogeneity and associates with specific features of tumour biology thus offering a novel targetable molecular signature in cancer.

Discovery of AZD4573, a Potent and Selective Inhibitor of CDK9 That Enables Short Duration of Target Engagement for the Treatment of Hematological Malignancies

A CDK9 inhibitor having short target engagement would enable a reduction of Mcl-1 activity, resulting in apoptosis in cancer cells dependent on Mcl-1 for survival. We report the optimization of a series of amidopyridines (from compound 2), focusing on properties suitable for achieving short target engagement after intravenous administration. By increasing potency and human metabolic clearance, we identified compound 24, a potent and selective CDK9 inhibitor with suitable predicted human pharmacokinetic properties to deliver transient inhibition of CDK9. Furthermore, the solubility of 24 was considered adequate to allow i.v. formulation at the anticipated effective dose. Short-term treatment with compound 24 led to a rapid dose- and time-dependent decrease of pSer2-RNAP2 and Mcl-1, resulting in cell apoptosis in multiple hematological cancer cell lines. Intermittent dosing of compound 24 demonstrated efficacy in xenograft models derived from multiple hematological tumors. Compound 24 is currently in clinical trials for the treatment of hematological malignancies.

In silico pathway analysis based on chromosomal instability in breast cancer patients

BACKGROUND

Complex genomic changes that arise in tumors are a consequence of chromosomal instability. In tumor cells genomic aberrations disrupt core signaling pathways involving various genes, thus delineating of signaling pathways can help understand the pathogenesis of cancer. The bioinformatics tools can further help in identifying networks of interactions between the genes to get a greater biological context of all genes affected by chromosomal instability.

METHODS

Karyotypic analyses was done in 150 clinically confirmed breast cancer patients and 150 age and gender matched healthy controls after 72 h Peripheral lymphocyte culturing and GTG-banding. Reactome database from Cytoscape software version 3.7.1 was used to perform in-silico analysis (functional interaction and gene enrichment).

RESULTS

Frequency of chromosomal aberrations (structural and numerical) was found to be significantly higher in patients as compared to controls. The genes harbored by chromosomal regions showing increased aberration frequency in patients were further analyzed in-silico. Pathway analysis on a set of genes that were not linked together revealed that genes HDAC3, NCOA1, NLRC4, COL1A1, RARA, WWTR1, and BRCA1 were enriched in the RNA Polymerase II Transcription pathway which is involved in recruitment, initiation, elongation and dissociation during transcription.

CONCLUSION

The current study employs the information inferred from chromosomal instability analysis in a non-target tissue for determining the genes and the pathways associated with breast cancer. These results can be further extrapolated by performing either mutation analysis in the genes/pathways deduced or expression analysis which can pinpoint the relevant functional impact of chromosomal instability.

Nucleolar stress induces a senescence-like phenotype in smooth muscle cells and promotes development of vascular degeneration

Senescence of smooth muscle cells (SMCs) has a crucial role in the pathogenesis of abdominal aortic aneurysm (AAA), a disease of vascular degeneration. Perturbation of cellular ribosomal DNA (rDNA) transcription triggers nucleolar stress response. Previously we demonstrated that induction of nucleolar stress in SMCs elicited cell cycle arrest via the ataxia-telangiectasia mutated (ATM)/ATM- and Rad3-related (ATR)-p53 axis. However, the specific roles of nucleolar stress in vascular degeneration remain unexplored. In the present study, we demonstrated for the first time that in both human and animal AAA tissues, there were non-coordinated changes in the expression of RNA polymerase I machinery components, including a downregulation of transcription initiation factor-IA (TIF-IA). Genetic deletion of TIF-IA in SMCs in mice (smTIF-IA^-/-) caused spontaneous aneurysm-like lesions in the aorta. In vitro, induction of nucleolar stress triggered a non-canonical DNA damage response, leading to p53 phosphorylation and a senescence-like phenotype in SMCs. In human AAA tissues, there was increased nucleolar stress in medial cells, accompanied by localized DNA damage response within the nucleolar compartment. Our data suggest that perturbed rDNA transcription and induction of nucleolar stress contribute to the pathogenesis of AAA. Moreover, smTIF-IA^-/- mice may be a novel animal model for studying spontaneous AAA-like vascular degenerations.