Publications by authors named "Ka Wai Leong"

Circular RNAs (circRNAs) are produced by head-to-tail back-splicing which is mainly facilitated by base-pairing of reverse complementary matches (RCMs) in circRNA flanking introns. Adenosine deaminases acting on RNA (ADARs) are known to bind double-stranded RNAs for adenosine to inosine (A-to-I) RNA editing. Here we characterize ADARs as potent regulators of circular transcriptome by identifying over a thousand of circRNAs regulated by ADARs in a bidirectional manner through and beyond their editing function.

View Article and Find Full Text PDF

Assaying for large numbers of low-frequency mutations requires sequencing at extremely high depth and accuracy. Increasing sequencing depth aids the detection of low-frequency mutations yet limits the number of loci that can be simultaneously probed. Here we report a method for the accurate tracking of thousands of distinct mutations that requires substantially fewer reads per locus than conventional hybrid-capture duplex sequencing.

View Article and Find Full Text PDF

The use of next-generation sequencing (NGS) to profile genomic variation of individual cancer species is revolutionizing the practice of clinical oncology. In liquid biopsy of cancer, sequencing of circulating-free DNA (cfDNA) is gradually applied to all stages of cancer diagnosis and treatment, serving as complement or replacement of tissue biopsies. However, analysis of cfDNA obtained from blood draws still faces technical obstacles due in part to an excess of wild-type DNA originating from normal tissues and hematopoietic cells.

View Article and Find Full Text PDF

Detection of low-level DNA mutations can reveal recurrent, hotspot genetic changes of clinical relevance to cancer, prenatal diagnostics, organ transplantation or infectious diseases. However, the high excess of wild-type (WT) alleles, which are concurrently present, often hinders identification of salient genetic changes. Here, we introduce UV-mediated cross-linking minor allele enrichment (UVME), a novel approach that incorporates ultraviolet irradiation (∼365 nm UV) DNA cross-linking either before or during PCR amplification.

View Article and Find Full Text PDF

Multiple noncoding natural antisense transcripts (ncNAT) are known to modulate key biological events such as cell growth or differentiation. However, the actual impact of ncNATs on cancer progression remains largely unknown. In this study, we identified a complete list of differentially expressed ncNATs in hepatocellular carcinoma.

View Article and Find Full Text PDF

Microsatellite instability (MSI), a phenotype displayed as deletions/insertions of repetitive genomic sequences, has drawn great attention due to its application in cancer including diagnosis, prognosis and immunotherapy response prediction. Several methods have been developed for the detection of MSI, facilitating the MSI classification of cancer patients. In view of recent interest in minimally-invasive detection of MSI via liquid biopsy samples, which requires methods with high sensitivity to identify small fractions of altered DNA in the presence of large amount of wild type copies, sensitive MSI detection approaches are emerging.

View Article and Find Full Text PDF

Sensitive detection of microsatellite instability (MSI) in tissue or liquid biopsies using next generation sequencing (NGS) has growing prognostic and predictive applications in cancer. However, the complexities of NGS make it cumbersome as compared to established multiplex-PCR detection of MSI. We present a new approach to detect MSI using inter-Alu-PCR followed by targeted NGS, that combines the practical advantages of multiplexed-PCR with the breadth of information provided by NGS.

View Article and Find Full Text PDF
Article Synopsis
  • RNA editing can alter RNA sequences and is linked to cancer, particularly a type called hepatocellular carcinoma (HCC), where the COPA protein plays a significant role.
  • * In a study with 125 HCC patients, researchers used CRISPR to examine how changes in COPA's RNA sequence affect its function and stability, showing that edited COPA can shift from promoting tumors to suppressing them.
  • * The findings suggest that decreased RNA editing of COPA leads to tumor growth by destabilizing the protein and activating cancer-promoting pathways, highlighting the importance of RNA editing in cancer development.
View Article and Find Full Text PDF

Purpose: Existing cell-free DNA (cfDNA) methods lack the sensitivity needed for detecting minimal residual disease (MRD) following therapy. We developed a test for tracking hundreds of patient-specific mutations to detect MRD with a 1,000-fold lower error rate than conventional sequencing.

Experimental Design: We compared the sensitivity of our approach to digital droplet PCR (ddPCR) in a dilution series, then retrospectively identified two cohorts of patients who had undergone prospective plasma sampling and clinical data collection: 16 patients with ER+/HER2- metastatic breast cancer (MBC) sampled within 6 months following metastatic diagnosis and 142 patients with stage 0 to III breast cancer who received curative-intent treatment with most sampled at surgery and 1 year postoperative.

View Article and Find Full Text PDF
Article Synopsis
  • - RNA editing and splicing are crucial processes that enhance the diversity of human transcripts, with ADAR1 being a key player linking the two, especially in relation to diseases like cancer.
  • - The research identifies around a hundred key splicing events influenced by ADAR1 and ADAR2, demonstrating their ability to regulate exon selection in various ways.
  • - The study reveals specific mechanisms by which ADAR proteins interact with double-stranded RNA to affect splicing, and these changes in splicing have direct implications for tumor development, rather than being side effects of RNA editing.
View Article and Find Full Text PDF

DNA target enrichment via hybridization capture is a commonly adopted approach which remains expensive due in-part to using biotinylated-probe panels. Here we provide a novel isothermal amplification reaction to amplify rapidly existing probe panels without knowledge of the sequences involved, thereby decreasing a major portion of the overall sample preparation cost. The reaction employs two thermostable enzymes, BST-polymerase and duplex-specific nuclease DSN.

View Article and Find Full Text PDF

Background: Although interest in droplet-digital PCR technology (ddPCR) for cell-free circulating DNA (cfDNA) analysis is burgeoning, the technology is compromised by subsampling errors and the few clinical targets that can be analyzed from limited input DNA. The paucity of starting material acts as a "glass ceiling" in liquid biopsies because, irrespective how analytically sensitive ddPCR techniques are, detection limits cannot be improved past DNA input limitations.

Methods: We applied denaturation-enhanced ddPCR (dddPCR) using fragmented genomic DNA (gDNA) with defined mutations.

View Article and Find Full Text PDF

Detection of microsatellite-instability in colonoscopy-obtained polyps, as well as in plasma-circulating DNA, is frequently confounded by sensitivity issues due to co-existing excessive amounts of wild-type DNA. While also an issue for point mutations, this is particularly problematic for microsatellite changes, due to the high false-positive artifacts generated by polymerase slippage (stutter-bands). Here, we describe a nuclease-based approach, NaME-PrO, that uses overlapping oligonucleotides to eliminate unaltered micro-satellites at the genomic DNA level, prior to PCR.

View Article and Find Full Text PDF

PIN1 is a peptidyl-prolyl isomerase that catalyzes the / isomerization of peptide bonds between proline and phosphorylated serine/threonine residues. By changing the conformation of its protein substrates, PIN1 increases the activities of key proteins that promote cell cycle progression and oncogenesis. Moreover, it has been shown that PIN1 stabilizes and increases the level of the cyclin-dependent kinase (CDK) inhibitor p27, which inhibits cell cycle progression by binding cyclin A- and cyclin E-CDK2.

View Article and Find Full Text PDF

PIN1 is a peptidyl-prolyl cis/trans isomerase (PPIase) that regulates multiple signaling pathways to control cell fate and is found to be over-expressed in cancers, including hepatocellular carcinoma (HCC). However, the regulation of PIN1 in HCC remains poorly defined. Micro-RNAs (miRNAs) have been reported to play a pivotal role in oncogenesis by targeting the 3'-untranslated region (UTR) of mRNAs encoded by oncogenes and tumour suppressor genes, thereby suppressing the levels of both oncoproteins and tumour suppressors.

View Article and Find Full Text PDF

PIN1 is a peptidyl-prolyl isomerase that binds and catalyses isomerization of the specific motif comprising a phosphorylated serine or threonine residue preceding a proline (pSer/Thr-Pro) in proteins. PIN1 can therefore induce conformational and functional changes of its interacting proteins that are regulated by proline-directed serine/threonine phosphorylation. Through this phosphorylation-dependent prolyl isomerization, PIN1 fine-tunes the functions of key phosphoproteins (.

View Article and Find Full Text PDF

Activity in dorsal attention (DAN) and frontoparietal (FPN) functional brain networks is linked to allocation of attention to external stimuli, and activity in the default-mode network (DMN) is linked to allocation of attention to internal representations. Tasks requiring attention to external stimuli shift activity to the DAN/FPN and away from the DMN, and optimal task performance depends on balancing DAN/FPN against DMN activity. The current functional magnetic resonance imaging (fMRI) study assessed the balance of DAN/FPN and DMN activity in 13 schizophrenia patients and 13 healthy controls while they were engaged in a task switching Stroop paradigm which demanded internally directed attention to task instructions.

View Article and Find Full Text PDF

Objective: Medically unexplained somatic complaints are highly prevalent, and lead to significant impairment and disability. The number of effective treatment modalities for somatic symptom and related disorders (SSDs) or somatoform disorders (SDs) remains limited. To date, there is no formal indication for electroconvulsive therapy (ECT) in SSD or SD.

View Article and Find Full Text PDF

The roles of human serum IgA, in contrast to that of mucosal IgA, are relatively unexplored. Previous studies have shown that IgA mediates either pro- or anti-inflammatory effects in innate immune cells. Serum IgA has been shown to interact with many proteins and glycoproteins of which the functions and mechanisms are not fully characterized.

View Article and Find Full Text PDF

Objective: Mindfulness practices are associated with changes in different cortical regions, including the dorsolateral prefrontal cortices (DLPFCs). Our study sought to examine how an index course of repetitive transcranial magnetic stimulation (rTMS) over the DLPFC improved components of mindfulness as assessed by Baer's Five Facet Mindfulness Questionnaire (FFMQ) and the Experience Questionnaire (EQ).

Method: Our preliminary study is a retrospective chart review of 32 patients who had undergone an index course of rTMS for major depressive episode between 2009 and 2012.

View Article and Find Full Text PDF

Background: Protein Kinase C (PKC) is a serine/threonine kinase that involved in controlling of many cellular processes such as cell proliferation and differentiation. We have observed previously that TPA (12-O-tetradecanoylphorbol 13-acetate) induces cell cycle arrest in G0/G1 phase in human hepatoma HepG2 cells. However, is there any miRNA involved in PKCalpha mediated cell growth arrest is still unknown.

View Article and Find Full Text PDF