Non-Coding RNAs in Ovarian Cancer

Ovarian cancer (OC) is the most lethal form of gynaecological cancer, with high- grade serous ovarian carcinoma (HGSOC) being the most common and the deadliest subtype. Non-coding RNAs are a recently discovered species of RNAs that do not code for proteins, yet play a crucial role in both normal physiology and disease. The overall goal of this thesis was to apply the power of non-coding RNAs to OC with the following aims: (1) to identify novel small non-coding RNAs present in serum that could separate patients with HGSOC from healthy women as well as predict their surgical outcome, (2) to assess the role of long non-coding RNAs (lncRNAs) in promoting cisplatin resistance in cell line models of OC, and (3) to study the effects of mutant-p53 on mRNAs and lncRNAs using a small compound known as APR-246 as well as investigating the drug’s mechanisms of action. Firstly, the lethality of OC could partially be attributed to the lack of specific symptoms, leading this disease to be termed the ‘silent killer’, as well as low inci- dence rate of 9.4 cases per 100,000 individuals, both requiring a highly accurate test for population screening that remains an ongoing challenge. Measuring the levels of small non-coding RNAs, known as microRNAs, in serum, experiments described in this thesis aimed to identify novel microRNAs that could separate pa- tients with HGSOC from healthy women as well as predict their surgical outcome, one of the most important factors influencing overall patient survival. Because serum microRNAs can be affected by pre-analytical factors such as haemolysis, the sensitivity of four methodologies to detect low levels of haemolysis was first determined. This work is published in Plos One. The work described in this thesis identified a novel serum microRNA, miR-375, that could improve the accuracy of CA-125, a routinely used biomarker in diagnosing OC, in separating patients with HGSOC from healthy women. Next, serum microRNA miR-34a-5p was found to predict the surgical outcome of patients with HGSOC. In fact, miR-34a-5p was found to be superior to CA-125 for this purpose. Although the standard therapy for treating OC consists of surgical removal of the tumour followed by chemotherapy containing platinum/taxane agents, this regimen may be too aggressive for a sub- set of patients who might benefit from neoadjuvant chemotherapy, i.e. chemother- apy followed by the surgery. A pre-operative expectation of the the surgical out- come could help surgeons decide on optimal timing for surgery. Both miR-375 and miR-34a-5p were also unaffected by haemolysis. Secondly, although OC is initially sensitive to chemotherapy, most patients develop resistance within two years, resulting in recurrent disease that is difficult to treat. To identify novel lncRNAs that could promote drug resistance, expression of ninety lncRNAs was profiled in cell line models of cisplatin resistance. Five lncRNAs were found to have the potential to promote cisplatin resistance in vitro, and lncRNA Urothelial Cancer Associated 1 (UCA1) was selected for further investigations. Despite its role in promoting cisplatin resistance in bladder cancer, UCA1 was not found to promote cisplatin resistance in cell line models of OC. Lastly, the tumour suppressor TP53 plays a central role in the biology of cancer and it is almost universally mutated in HGSOC. Recent evidence suggests that p53, the protein encoded by TP53, can significantly influence the expression of both small and long non-coding RNAs. Experiments described in this thesis aimed to investigate the effect of mutant-p53 on protein-coding and non-coding RNAs by using a small compound known as APR-246 which has been reported to restore wild-type p53 activities in multiple cancers by stabilising the structure of mutant- p53. Despite currently undergoing a phase Ib/II clinical trial for potential treatment of recurrent HGSOC, the ability of APR-246 to restore wild-type p53 activities in HGSOC has not been tested. A global transcriptomic analysis conducted in this thesis discovered that p53-responsive mRNAs and lncRNAs were not robustly induced following APR-246 treatment in two cell line models of HGSOC, but indicated that APR-246 could function by inducing high levels of reactive oxidative species (ROS). Overall, data presented in this thesis demonstrated the utility of small non- coding RNAs in identifying patients with HGSOC from healthy women as well as predicting their surgical outcome. This thesis also implicated that lncRNAs, in general, could have a role in promoting cisplatin resistance in OC as well as suggested that APR-246 could, based on evidence obtained from the expression of p53-responsive mRNAs and lncRNAs, act independently of mutant-p53. Together, this research raises novel ways for clinical management of patients with HGSOC and addresses the challenge of drug resistance using non-coding RNAs, as well as questions the assumed mechanisms of action of the ‘p53-activating’ drug APR- 246

The intricate interplay between epigenetic events, alternative splicing and noncoding RNA deregulation in colorectal cancer

Colorectal cancer (CRC) results from a transformation of colonic epithelial cells into adenocarcinoma cells due to genetic and epigenetic instabilities, alongside remodelling of the surrounding stromal tumour microenvironment. Epithelial-specific epigenetic variations escorting this process include chromatin remodelling, histone modifications and aberrant DNA methylation, which influence gene expression, alternative splicing and function of non-coding RNA. In this review, we first highlight epigenetic modulators, modifiers and mediators in CRC, then we elaborate on causes and consequences of epigenetic alterations in CRC pathogenesis alongside an appraisal of the complex feedback mechanisms realized through alternative splicing and non-coding RNA regulation. An emphasis in our review is put on how this intricate network of epigenetic and post-transcriptional gene regulation evolves during the initiation, progression and metastasis formation in CRC

The Fusion of CLEC12A and MIR223HG Arises from a trans-Splicing Event in Normal and Transformed Human Cells

Chimeric RNAs are often associated with chromosomal rearrangements in cancer. In addition, they are also widely detected in normal tissues, contributing to transcriptomic complexity. Despite their prevalence, little is known about the characteristics and functions of chimeric RNAs. Here, we examine the genetic structure and biological roles of CLEC12A-MIR223HG, a novel chimeric transcript produced by the fusion of the cell surface receptor CLEC12A and the miRNA-223 host gene (MIR223HG), first identified in chronic myeloid leukemia (CML) patients. Surprisingly, we observed that CLEC12A-MIR223HG is not just expressed in CML, but also in a variety of normal tissues and cell lines. CLEC12A-MIR223HG expression is elevated in pro-monocytic cells resistant to chemotherapy and during monocyte-to-macrophage differentiation. We observed that CLEC12A-MIR223HG is a product of trans-splicing rather than a chromosomal rearrangement and that transcriptional activation of CLEC12A with the CRISPR/Cas9 Synergistic Activation Mediator (SAM) system increases CLEC12A-MIR223HG expression. CLEC12A-MIR223HG translates into a chimeric protein, which largely resembles CLEC12A but harbours an altered C-type lectin domain altering key disulphide bonds. These alterations result in differences in post-translational modifications, cellular localization, and protein–protein interactions. Taken together, our observations support a possible involvement of CLEC12A-MIR223HG in the regulation of CLEC12A function. Our workflow also serves as a template to study other uncharacterized chimeric RNAs

The Fusion of CLEC12A and MIR223HG Arises from a trans-Splicing Event in Normal and Transformed Human Cells

Chimeric RNAs are often associated with chromosomal rearrangements in cancer. In addition, they are also widely detected in normal tissues, contributing to transcriptomic complexity. Despite their prevalence, little is known about the characteristics and functions of chimeric RNAs. Here, we examine the genetic structure and biological roles of CLEC12A-MIR223HG, a novel chimeric transcript produced by the fusion of the cell surface receptor CLEC12A and the miRNA-223 host gene (MIR223HG), first identified in chronic myeloid leukemia (CML) patients. Surprisingly, we observed that CLEC12A-MIR223HG is not just expressed in CML, but also in a variety of normal tissues and cell lines. CLEC12A-MIR223HG expression is elevated in pro-monocytic cells resistant to chemotherapy and during monocyte-to-macrophage differentiation. We observed that CLEC12A-MIR223HG is a product of trans-splicing rather than a chromosomal rearrangement and that transcriptional activation of CLEC12A with the CRISPR/Cas9 Synergistic Activation Mediator (SAM) system increases CLEC12A-MIR223HG expression. CLEC12A-MIR223HG translates into a chimeric protein, which largely resembles CLEC12A but harbours an altered C-type lectin domain altering key disulphide bonds. These alterations result in differences in post-translational modifications, cellular localization, and protein–protein interactions. Taken together, our observations support a possible involvement of CLEC12A-MIR223HG in the regulation of CLEC12A function. Our workflow also serves as a template to study other uncharacterized chimeric RNAs

Widespread Aberrant Alternative Splicing despite Molecular Remission in Chronic Myeloid Leukaemia Patients

Vast transcriptomics and epigenomics changes are characteristic of human cancers, including leukaemia. At remission, we assume that these changes normalise so that omics-profiles resemble those of healthy individuals. However, an in-depth transcriptomic and epigenomic analysis of cancer remission has not been undertaken. A striking exemplar of targeted remission induction occurs in chronic myeloid leukaemia (CML) following tyrosine kinase inhibitor (TKI) therapy. Using RNA sequencing and whole-genome bisulfite sequencing, we profiled samples from chronic-phase CML patients at diagnosis and remission and compared these to healthy donors. Remarkably, our analyses revealed that abnormal splicing distinguishes remission samples from normal controls. This phenomenon is independent of the TKI drug used and in striking contrast to the normalisation of gene expression and DNA methylation patterns. Most remarkable are the high intron retention (IR) levels that even exceed those observed in the diagnosis samples. Increased IR affects cell cycle regulators at diagnosis and splicing regulators at remission. We show that aberrant splicing in CML is associated with reduced expression of specific splicing factors, histone modifications and reduced DNA methylation. Our results provide novel insights into the changing transcriptomic and epigenomic landscapes of CML patients during remission. The conceptually unanticipated observation of widespread aberrant alternative splicing after remission induction warrants further exploration. These results have broad implications for studying CML relapse and treating minimal residual disease

Redefining the Expression and Function of the Inhibitor of Differentiation 1 in Mammary Gland Development

The accumulation of poorly differentiated cells is a hallmark of breast neoplasia and progression. Thus an understanding of the factors controlling mammary differentiation is critical to a proper understanding of breast tumourigenesis. The Inhibitor of Differentiation 1 (Id1) protein has well documented roles in the control of mammary epithelial differentiation and proliferation in vitro and breast cancer progression in vivo. However, it has not been determined whether Id1 expression is sufficient for the inhibition of mammary epithelial differentiation or the promotion of neoplastic transformation in vivo. We now show that Id1 is not commonly expressed by the luminal mammary epithelia, as previously reported. Generation and analysis of a transgenic mouse model of Id1 overexpression in the mammary gland reveals that Id1 is insufficient for neoplastic progression in virgin animals or to prevent terminal differentiation of the luminal epithelia during pregnancy and lactation. Together, these data demonstrate that there is no luminal cell-autonomous role for Id1 in mammary epithelial cell fate determination, ductal morphogenesis and terminal differentiation

Sensitivities of four methods to detect hemolysis.

<p><b>(A)</b> A hemolysis series was prepared by diluting 100% hemolyzed sample with unhemolyzed serum (0%), and the sensitivity of each method determined by its ability to detect hemolysis (indicated by arrows). <b>(B—E)</b> Detection of hemolysis using four methods. For visual inspection, samples were scored from 0 (unhemolyzed sample) to 5 (100% hemolysis). Averages of technical replicates are shown where appropriate. ‘Unhem’ denotes unhemolyzed serum. Absorbance measures (D) and miR ratios (E) are noted on the graphs.</p

Comparison of Methodologies to Detect Low Levels of Hemolysis in Serum for Accurate Assessment of Serum microRNAs

<div><p>microRNAs have emerged as powerful regulators of many biological processes, and their expression in many cancer tissues has been shown to correlate with clinical parameters such as cancer type and prognosis. Present in a variety of biological fluids, microRNAs have been described as a ‘gold mine’ of potential noninvasive biomarkers. Release of microRNA content of blood cells upon hemolysis dramatically alters the microRNA profile in blood, potentially affecting levels of a significant number of proposed biomarker microRNAs and, consequently, accuracy of serum or plasma-based tests. Several methods to detect low levels of hemolysis have been proposed; however, a direct comparison assessing their sensitivities is currently lacking. In this study, we evaluated the sensitivities of four methods to detect hemolysis in serum (listed in the order of sensitivity): measurement of hemoglobin using a Coulter® AcT diff™ Analyzer, visual inspection, the absorbance of hemoglobin measured by spectrophotometry at 414 nm and the ratio of red blood cell-enriched miR-451a to the reference microRNA miR-23a-3p. The miR ratio detected hemolysis down to approximately 0.001%, whereas the Coulter® AcT diff™ Analyzer was unable to detect hemolysis lower than 1%. The spectrophotometric method could detect down to 0.004% hemolysis, and correlated with the miR ratio. Analysis of hemolysis in a cohort of 86 serum samples from cancer patients and healthy controls showed that 31 of 86 (36%) were predicted by the miR ratio to be hemolyzed, whereas only 8 of these samples (9%) showed visible pink discoloration. Using receiver operator characteristic (ROC) analyses, we identified absorbance cutoffs of 0.072 and 0.3 that could identify samples with low and high levels of hemolysis, respectively. Overall, this study will assist researchers in the selection of appropriate methodologies to test for hemolysis in serum samples prior to quantifying expression of microRNAs.</p></div

Hemolysis-sensitive high and low abundant microRNAs are significantly altered between categories defined by the miR ratio.

<p><b>(A)</b> Levels of hemolysis-sensitive highly abundant serum microRNA miR−16−5p was found to be significantly altered across low, moderate and severely hemolyzed serum samples defined by miR ratios <b>(B)</b> Levels of a hemolysis-sensitive low abundant microRNA miR−15b−3p were also different across all miR ratio categories. <b>(C)</b> miR−23a−3p was present at a similar level amongst three categories, supporting its use as a reference microRNA in determining the miR ratio. * <i>P</i> <0.05, ** <i>P</i> < 0.001 and *** <i>P</i> < 0.0001.</p