Imperial College London


Faculty of MedicineDepartment of Surgery & Cancer

Advanced Research Fellow



+44 (0)20 7594 2821claire.fletcher07 CV




ICTEM buildingHammersmith Campus





Publication Type

15 results found

Fletcher C, Taylor M, Bevan C, 2023, PLK1 regulates microRNA biogenesis through Drosha phosphorylation, International Journal of Molecular Sciences, Vol: 24, ISSN: 1422-0067

Polo-Like Kinase 1 (PLK1), a key mediator of cell-cycle progression, is associated with poor prognosis and is a therapeutic target in a number of malignancies. Putative phosphorylation sites for PLK1 have been identified on Drosha, the main catalytic component of the microprocessor responsible for miR biogenesis. Several kinases, including GSK3β, p70 S6 kinase, ABL, PAK5, p38 MAPK, CSNK1A1 and ANKRD52-PPP6C, have been shown to phosphorylate components of the miR biogenesis machinery, altering their activity and/or localisation, and therefore the biogenesis of distinct miR subsets. We hypothesised that PLK1 regulates miR biogenesis through Drosha phosphorylation. In vitro kinase assays confirmed PLK1 phosphorylation of Drosha at S300 and/or S302. PLK1 inhibition reduced serine-phosphorylated levels of Drosha and its RNA-dependent association with DGCR8. In contrast, a “phospho-mimic” Drosha mutant showed increased association with DGCR8. PLK1 phosphorylation of Drosha alters Drosha Microprocessor complex subcellular localisation, since PLK1 inhibition increased cytosolic protein levels of both DGCR8 and Drosha, whilst nuclear levels were decreased. Importantly, the above effects are independent of PLK1’s cell cycle-regulatory role, since altered Drosha:DGCR8 localisation upon PLK1 inhibition occurred prior to significant accumulation of cells in M-phase, and PLK1-regulated miRs were not increased in M-phase-arrested cells. Small RNA sequencing and qPCR validation were used to assess downstream consequences of PLK1 activity on miR biogenesis, identifying a set of ten miRs (miR-1248, miR-1306-5p, miR-2277-5p, miR-29c-5p, miR-93-3p, miR-152-3p, miR-509-3-5p, miR-511-5p, miR-891a-5p and miR-892a) whose expression levels were statistically significantly downregulated by two pharmacological PLK1 kinase domain inhibitors, RO-5203280 and GSK461364. Opposingly, increased levels of these miRs were observed upon transfection of wild-type or constitutively

Journal article

Fletcher C, Zamarbide Losada J, Sulpice E, Combe S, Serrano de Almeida G, Leach D, Choo J, Protopapa P, Hamilton M, McGuire S, Gidrol X, Bevan Cet al., 2023, Apoptosis-modulatory miR-361-3p as a novel treatment target in endocrine-responsive and endocrine-resistant breast cancer, Journal of Endocrinology, Vol: 256, Pages: 1-20, ISSN: 0022-0795

Breast cancer (BC) is the most diagnosed cancer in women worldwide. In estrogen receptor (ER)-positive disease, anti-estrogens and aromatase inhibitors (AI) improve patient survival; however, many patients develop resistance. Dysregulation of apoptosis is a common resistance mechanism; thus, agents that can reinstate the activity of apoptotic pathways represent promising therapeutics for advanced drug-resistant disease. Emerging targets in this scenario include microRNAs (miRs). To identify miRs modulating apoptosis in drug-responsive and -resistant BC, a high-throughput miR inhibitor screen was performed, followed by high-content screening microscopy for apoptotic markers. Validation demonstrated that miR-361-3p inhibitor significantly increases early apoptosis and reduces proliferation of drug-responsive (MCF7), plus AI-/antiestrogen-resistant derivatives (LTED, TamR, FulvR), and ER- cells (MDA-MB-231). Importantly, proliferation-inhibitory effects were observed in vivo in a xenograft model, indicating the potential clinical application of miR-361-3p inhibition. RNA-seq of tumour xenografts identified FANCA as a direct miR-361-3p target, and validation suggested miR-361-3p inhibitor effects might be mediated in part through FANCA modulation. Moreover, miR-361-3p inhibition resulted in p53-mediated G1 cell cycle arrest through activation of p21 and reduced BC invasion. Analysis of publicly available datasets showed miR-361-3p expression is significantly higher in primary breast tumours vspaired normal tissue and is associated with decreased overall survival. In addition, miR-361-3p inhibitor treatment of BC patient explants decreased levels of miR-361-3p and proliferation marker, Ki67. Finally, miR-361-3p inhibitor showed synergistic effects on BC growth when combined with PARP inhibitor, Olaparib. Together, these studies identify miR-361-3p inhibitor as a potential new treatment for drug-responsive and -resistant advanced BC.

Journal article

Fletcher C, Deng L, Orafidiya F, Yuan W, Lorentzen M, Cyran O, Varela Carver A, Constantin T, Dobbs F, Figueiredo I, Gurel B, Parkes E, Bogdan D, Pereira R, Zhao S, Neeb A, Issa F, Hester J, Kudo H, Liu Y, Philippou Y, Bristow R, Knudsen K, Bryant R, Feng F, Reed S, Mills I, de Bono J, Bevan Cet al., 2022, A non-coding RNA balancing act: miR-346-induced DNA damage is limited by the long non-coding RNA NORAD in prostate cancer, Molecular Cancer, Vol: 21, ISSN: 1476-4598

Background: miR‑346 was identified as an activator of Androgen Receptor (AR) signalling that associates with DNA damage response (DDR)‑linked transcripts in prostate cancer (PC). We sought to delineate the impact of miR‑346 on DNA damage, and its potential as a therapeutic agent.Methods: RNA‑IP, RNA‑seq, RNA‑ISH, DNA fibre assays, in vivo xenograft studies and bioinformatics approaches were used alongside a novel method for amplification‑free, single nucleotide‑resolution genome‑wide mapping of DNA breaks (INDUCE‑seq).Results: miR‑346 induces rapid and extensive DNA damage in PC cells ‑ the first report of microRNA‑induced DNA damage. Mechanistically, this is achieved through transcriptional hyperactivation, R‑loop formation and replication stress, leading to checkpoint activation and cell cycle arrest. miR‑346 also interacts with genome‑protective lncRNA NORAD to disrupt its interaction with PUM2, leading to PUM2 stabilisation and its increased turnover of DNA damage response (DDR) transcripts. Confirming clinical relevance, NORAD expression and activity strongly correlate with poorPC clinical outcomes and increased DDR in biopsy RNA‑seq studies. In contrast, miR‑346 is associated with improved PC survival.INDUCE‑seq reveals that miR‑346‑induced DSBs occur preferentially at binding sites of the most highly‑transcriptionally active transcription factors in PC cells, including c‑Myc, FOXA1, HOXB13, NKX3.1, and importantly, AR, resulting in target transcript downregulation. Further, RNA‑seq reveals widespread miR‑346 and shNORAD dysregulation of DNAdamage, replication and cell cycle processes.NORAD drives target‑directed miR decay (TDMD) of miR‑346 as a novel genome protection mechanism: NORAD silencing increases mature miR‑346 levels by several thousand‑fold, and WT but not TDMD‑mutant NORAD rescues miR‑346‑induced DNA damage. Importantly, miR‑346 sensitises PC cells to DNA‑damaging drugs including PARP inhibitor and chemotherapy, and induces tumour regression as a m

Journal article

Orafidiya F, Deng L, Bevan C, Fletcher Cet al., 2022, Crosstalk between long non coding RNAs, microRNAs and DNA damage repair in prostate cancer: new therapeutic opportunities?, Cancers, Vol: 14, ISSN: 2072-6694

It is increasingly appreciated that transcripts derived from non-coding parts of the human genome, such as long non-coding RNAs (lncRNAs) and microRNAs (miRNAs), are key regulators of biological processes both in normal physiology and disease. Their dysregulation during tumourigenesis has attracted significant interest in their exploitation as novel cancer therapeutics. Prostate cancer (PCa), as one of the most diagnosed malignancies and a leading cause of cancer-related death in men, continues to pose a major public health problem. In particular, survival of men with metastatic disease is very poor. Defects in DNA damage response (DDR) pathways culminate in genomic instability in PCa, which is associated with aggressive disease and poor patient outcome. Treatment options for metastatic PCa remain limited. Thus, researchers are increasingly targeting ncRNAs and DDR pathways to develop new biomarkers and therapeutics for PCa. Increasing evidence points to a widespread and biologically-relevant regulatory network of interactions between lncRNAs and miRNAs, with implications for major biological and pathological processes. This review summarises the current state of knowledge surrounding the roles of the lncRNA:miRNA interactions in PCa DDR, and their emerging potential as predictive and diagnostic biomarkers. We also discuss their therapeutic promise for the clinical management of PCa.

Journal article

Fletcher C, Deng L, Orafidiya F, Yuan W, Figueiredo I, Gurel B, Leach D, Issa F, Neeb A, Bogdan D, Dobbs F, Philippou Y, Murphy EA, Zhao SG, Hester J, Bryant RJ, Reed SH, Knudsen KE, Mills IG, de Bono J, Bevan CLet al., 2021, Long non-coding RNA NORAD interaction with miR-346 impacts DNA damage response and anti-tumor immunity in prostate cancer., Annual Meeting of the American-Association-for-Cancer-Research (AACR), Publisher: AMER ASSOC CANCER RESEARCH, ISSN: 0008-5472

Conference paper

Eringyte I, Zamarbide Losada JN, Powell SM, Bevan CL, Fletcher CEet al., 2020, Coordinated AR and microRNA regulation in prostate cancer, Asian Journal of Urology, Vol: 7, Pages: 233-250, ISSN: 2214-3882

The androgen receptor (AR) remains a key driver of prostate cancer (PCa) progression, even in the advanced castrate-resistant stage, where testicular androgens are absent. It is therefore of critical importance to understand the molecular mechanisms governing its activity and regulation during prostate tumourigenesis. MicroRNAs (miRs) are small ∼22 nt non-coding RNAs that regulate target gene, often through association with 3' untranslated regions (3'UTRs) of transcripts. They display dysregulation during cancer progression, can function as oncogenes or tumour suppressors, and are increasingly recognised as targets or regulators of hormonal action. Thus, understanding factors which modulate miRs synthesis is essential. There is increasing evidence for complex and dynamic bi-directional cross-talk between the multi-step miR biogenesis cascade and the AR signalling axis in PCa. This review summarises the wealth of mechanisms by which miRs are regulated by AR, and conversely, how miRs impact AR's transcriptional activity, including that of AR splice variants. In addition, we assess the implications of the convergence of these pathways on the clinical employment of miRs as PCa biomarkers and therapeutic targets.

Journal article

Fletcher CE, 2019, The Role of Splicing Regulators in the Emergence of Treatment-induced Neuroendocrine Prostate Cancer: The Next Generation of Drug Targets?, EUROPEAN UROLOGY, Vol: 76, Pages: 167-169, ISSN: 0302-2838

Journal article

Fletcher C, Sulpice E, Combe S, Shibakawa A, Leach D, Hamilton MP, Chrysostomou SL, Sharp A, Welti J, Yuan W, Dart D, Knight E, Ning J, Francis JC, Kounatidou EE, Gaughan L, Swain A, Lupold SE, De Bono JS, McGuire SE, Gidrol X, Bevan Cet al., 2019, Androgen receptor-modulatory microRNAs provide insight into therapy resistance and therapeutic targets in advanced prostate cancer, Oncogene, Vol: 38, Pages: 5700-5724, ISSN: 0950-9232

Androgen receptor (AR) signalling is a key prostate cancer (PC) driver, even inadvanced ‘castrate-resistant’ disease (CRPC). To systematically identify microRNAs (miRs) modulating AR activity in lethal disease, hormone-responsive and -resistant PC cells expressing a luciferase-based AR reporter were transfected with a miR inhibitor library; 78 inhibitors significantly altered AR activity. Upon validation, miR-346, miR-361-3p and miR-197 inhibitors dramatically reduced AR transcriptional activity, mRNA and protein levels, increased apoptosis, reduced proliferation, repressed EMT, inhibited PC migration and invasion, demonstrating additive effects with AR inhibition. Corresponding miRs increased AR activity through a novel and anti-dogmatic mechanism of direct association with AR 6.9kb 3’UTR and transcript stabilisation. In addition, miR-346 and miR-361-3p modulation altered levels of constitutively-active AR variants, and inhibited variant-driven PC cell proliferation, so may contribute to persistent AR signalling in CRPC in the absence of circulating androgens. Pathway analysis of AGO-PAR-CLIP-identified miR targets revealed roles in DNA replication and repair, cell cycle, signal transduction and immune function. Silencing these targets, including tumour suppressors ARHGDIA and TAGLN2, phenocopied miR effects, demonstrating physiological relevance. MiR-346 additionally upregulated the oncogene, YWHAZ, which correlated with grade, biochemical relapse and metastasis in patients. These AR-modulatory miRs and targets correlated with AR activity in patient biopsies, and were elevated in response to long-term enzalutamide treatment of patient-derived CRPC xenografts. In summary, we identified miRs that modulate AR activity in PC and CRPC, via novel mechanisms, and may represent novel PC the

Journal article

Fletcher CE, 2017, AR-v7 liquid biopsy for treatment stratification in prostate cancer: how close are we?, Current Opinion in Urology, ISSN: 0963-0643

Journal article

Fletcher CE, Godfrey JD, Shibakawa A, Bushell M, Bevan CLet al., 2017, A novel role for GSK3β as a modulator of Drosha microprocessor activity and MicroRNA biogenesis, Nucleic Acid Research, Vol: 45, Pages: 2809-2828, ISSN: 2159-3345

Regulation of microRNA (miR) biogenesis is complex and stringently controlled. Here, we identify the kinase GSK3ß as a important modulator of miR biogenesis at Microprocessor level. Repression of GSK3ß activity reduces Drosha activity towards pri-miRs, leading to accumulation of unprocessed pri-miRs and reduction of mature pri-miRs without altering levels or cellular locations of miR biogenesis proteins...

Journal article

Fletcher CE, Bevan CL, Sita-Lumsden A, Shibakawa Aet al., 2015, Circulating Nucleic Acids as Prostate Cancer Biomarkers, Epigenetic Biomarkers and Diagnostics, Editors: Garcia-Giménez, Publisher: Elsevier

Book chapter

Fletcher CE, Dart DA, Bevan CL, 2014, Interplay between steroid signalling and microRNAs: implications for hormone-dependent cancers, Endocrine-Related Cancer, Vol: 21, Pages: R409-R429, ISSN: 1479-6821

Hormones are key drivers of cancer development. To date, interest has largely been focussed on the classical model of hormonal gene regulation, but there is increasing evidence for a role of hormone signalling pathways in post-translational regulation of gene expression. In particular, a complex and dynamic network of bi-directional interactions with microRNAs (miRs) at all stages of biogenesis and during target gene repression is emerging. miRs, which act mainly by negatively regulating gene expression through association with 3′-UTRs of mRNA species, are increasingly understood to be important in development, normal physiology and pathogenesis. Given recent demonstrations of altered miR profiles in a diverse range of cancers, their ability to function as oncogenes or tumour suppressors, and hormonal regulation of miRs, understanding mechanisms by which miRs are generated and regulated is vitally important. miRs are transcribed by RNA polymerase II and then processed in the nucleus by the Drosha-containing Microprocessor complex and in the cytoplasm by Dicer, before mature miRs are incorporated into the RNA-induced silencing complex. It is increasingly evident that multiple cellular signalling pathways converge upon the miR biogenesis cascade, adding further layers of regulatory complexity to modulate miR maturation. This review summarises recent advances in identification of novel components and regulators of the Microprocessor and Dicer complexes, with particular emphasis on the role of hormone signalling pathways in regulating their activity. Understanding hormone regulation of miR production and how this is perturbed in cancer are critical for the development of miR-based therapeutics and biomarkers.

Journal article

Sita-Lumsden A, Fletcher CE, Dart DA, Brooke GN, Waxman J, Bevan CLet al., 2013, Circulating nucleic acids as biomarkers of prostate cancer, BIOMARKERS IN MEDICINE, Vol: 7, Pages: 867-877, ISSN: 1752-0363

Journal article

Frampton AE, Fletcher CE, Gall TMH, Castellano L, Bevan CL, Stebbing J, Krell Jet al., 2013, Circulating peripheral blood mononuclear cells exhibit altered miRNA expression patterns in pancreatic cancer, EXPERT REVIEW OF MOLECULAR DIAGNOSTICS, Vol: 13, Pages: 425-430, ISSN: 1473-7159

Journal article

Fletcher CE, Dart DA, Sita-Lumsden A, Cheng H, Rennie PS, Bevan CLet al., 2012, Androgen-regulated processing of the oncomir MiR-27a, which targets Prohibitin in prostate cancer, HUMAN MOLECULAR GENETICS, Vol: 21, Pages: 3112-3127, ISSN: 0964-6906

Journal article

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