Human C-myc Research Articles

Grainyhead-like 2 Deficiency and Kidney Cyst Growth in a Mouse Model.

The transcription factor Grainyhead-like 2 (GRHL2) plays a crucial role in maintaining the epithelial barrier properties of the renal collecting duct and is essential for osmoregulation. We noticed a reduction in GRHL2 expression in cysts derived from the collecting ducts in kidneys affected by Autosomal Dominant Polycystic Kidney Disease (ADPKD). However, the specific role of GRHL2 in cystic kidney disease remains unknown. The functional role of the transcription factor Grhl2 in the context of cystic kidney disease was examined through analysis of its expression pattern in patient samples with ADPKD and generating a transgenic cystic kidney disease (TCKD) mouse model by overexpressing the human proto-oncogene c-MYC in kidney collecting ducts. Next, TCKD mice bred with collecting duct-specific Grhl2 knockout mice (Grhl2KO). The resulting TCKD-Grhl2KO mice and their littermates were examined by various types of histological and biochemical assays and gene profiling analysis via RNA-seq. A comprehensive examination of kidney samples from patients with ADPKD revealed GRHL2 downregulation in collecting duct-derived cyst epithelia. Comparative analysis of TCKD and TCKD-Grhl2KO mice exhibited that the collecting duct-specific deletion of Grhl2 resulted in markedly aggravated cyst growth, worsened kidney dysfunction, and shortened life span. Furthermore, transcriptomic analyses indicated sequential downregulation of kidney epithelial cyst development regulators (Frem2, Muc1, Cdkn2c, Pkd2, and Tsc1) during cyst progression in kidneys of TCKD-Grhl2KO mice which included presumed direct Grhl2 target genes. These results suggest GRHL2 as a potential progression modifier, especially for cysts originating from collecting ducts.

Therapeutic interventions on human breast cancer xenografts promote systemic dissemination of oncogenes.

Metastatic dissemination following successful treatment of the primary tumour remains a common cause of death. There is mounting evidence that therapeutic interventions themselves may promote development of metastatic disease. We earlier reported that cell-free chromatin particles (cfChPs) released from dying cancer cells are potentially oncogenic. Based on this observation we hypothesized that therapeutic interventions may lead to the release of cfChPs from therapy induced dying cancer cells which could be carried via the blood stream to distant organs to transform healthy cells into new cancers that would masquerade as metastasis. To test this hypothesis, we generated xenografts of MDA-MB-231 human breast cancer cells in severe combined immune-deficient mice, and using immuno-fluorescence and FISH analysis looked for cfChPs in their brain cells. We detected multiple human DNA signals representing cfChPs in nuclei of brain cells of mice which co-localized with eight human onco-proteins. No intact MDA-MB-231 cells were detected. The number of co-localizing human DNA and human c-Myc signals increased dramatically following treatment with chemotherapy, localized radiotherapy or surgery, which could be prevented by concurrent treatment with three different cfChPs deactivating agents. These results suggest that therapeutic interventions lead to the release cfChPs from therapy induced dying cancer cells carrying oncogenes and are transported via the blood stream to brain cells to potentially transform them to generate new cancers that would appear as metastases. cfChPs induced metastatic spread of cancer is preventable by concurrent treatment with agents that deactivate cfChPs.

Targeted upregulation of dMyc restricts JNK-mediated degeneration of dopaminergic neurons in the paraquat-induced Parkinson’s disease model of Drosophila

Parkinson’s disease is the second most common neurodegenerative disease characterized by the loss of dopaminergic neurons in the brain. Parkinson’s disease has both familial and sporadic cases of origin governed differentially by genetic and/or environmental factors. Different epidemiological studies have proposed an association between the pathogenesis of cancer and Parkinson’s disease; however, a precise correlation between these two illnesses could not be established yet. In this study, we examined the disease-modifying property of dmyc (a Drosophila homolog of human cmyc proto-oncogene) in the paraquat-induced sporadic Parkinson’s disease model of Drosophila. We report for the first time that targeted upregulation of dMyc significantly restricts paraquat-mediated neurotoxicity. We observed that paraquat feeding reduces the cellular level of dMyc. We further noted that targeted upregulation of dMyc in paraquat-exposed flies mitigates degeneration of dopaminergic neurons by reinstating the aberrantly activated JNK pathway, and this in turn improves the motor performance and survival rate of the flies. Our study provides the first evidence that improved cellular level of dMyc could efficiently minimize the neurotoxic effects of paraquat, which could be beneficial in designing novel therapeutic strategies against Parkinson’s disease.

Clinicopathologic and Molecular Characterization of Anorectal Neuroendocrine Carcinomas Reveals Human Papillomavirus, p53, and c-Myc as Alternative Mechanisms of Carcinogenesis

Poorly differentiated neuroendocrine carcinomas (NECs) are rare malignant neoplasms with aggressive behavior. The diagnosis remains challenging due to ever-changing terminologies and morphologic overlaps with other disease entities. Herein, we seek to better define anorectal NECs by high-risk human papillomavirus (HPV) status and molecular profiling. Fourteen cases, including 3 men and 11 women with a median age of 63 years, were included. High-risk HPV RNA in situ hybridization was diffusely positive (+) in 7 cases, focal rarely positive (+/−) in 2 cases, and completely negative (−) in 5 cases. By morphology, all HPV(−) NECs were large-cell type, 3 mixed with a tubular adenoma/dysplasia or invasive adenocarcinoma. HPV-related (+ or +/−) NECs were mostly small-cell type, 3 mixed with squamous dysplasia and/or squamous cell carcinoma. Immunohistochemically, all NECs were positive for at least 2 neuroendocrine markers. The HPV(−) NECs were also positive for CDX2, whereas all HPV-related NECs were negative or only focally positive for CDX2, p40, and p63. Overexpression of p53 was found in 3 HPV(−) and 2 HPV(+/−) NECs but not in any HPV(+) NECs. Molecular analysis revealed MYC gene amplification in 4 cases: 2 HPV(−), 1 HPV(+/−), and 1 HPV(+). This was confirmed by fluorescence in situ hybridization in all but 1 HPV(−) NEC, which showed polysomy 8 but no true MYC amplification. Interestingly, only 2 of the 4 MYC amplification–bearing cases, both p53 normal/wild-type, expressed c-Myc protein by immunohistochemistry. The other 2 cases, both p53 overexpressed, did not show c-Myc expression despite true MYC amplification. Our study demonstrates that anorectal NECs arise in HPV-dependent or -independent pathways, with heterogeneous expression of other lineage markers and different molecular signatures. Expressions of p53 and c-Myc proteins appear to be mutually exclusive regardless of HPV status, likely mediating alternative mechanisms of NEC carcinogenesis.

Abstract A27: Cellular barcoding of the leukemic niche reveals an apelin-mediated clonal expansion of niche endothelial and mesenchymal stromal cell clones

Abstract Hematopoietic stem and progenitor cells (HSPCs) reside in niches that provide regulatory signals for their function. Perturbations such as acute leukemia induce cellular and molecular insults to the niche to support disease progression. Mutation of the MYC oncogene family is a frequent event leading to leukemogenesis. We developed a new zebrafish model of acute erythroid leukemia (AEL) by overexpression of human CMYC under the blood specific promotor draculin (drl). Analyses of drl:CMYC marrows demonstrated a significant expansion of progenitors and a decrease of erythroid, lymphoid and myeloid mature cells (fc=4.8, -4.5, -3.3, -6.5; p<0.000001). RNA-Sequencing of drl:CMYC marrows revealed an upregulation of the erythroid master regulator gata1a (fc=1.4, p=0.01) and fetal hemoglobins hbbe1.1/2 (fc=4.7, 2.9; p=0.0004). Primary and secondary transplantation of drl:CMYC marrows resulted in engraftment and disease propagation (7/7; 17/18). We used the cellular barcoding GESTALT technique to uniquely barcode single cells using CRISPR-CAS9 during embryonic development. We induced a round of barcoding at the one-cell stage and another one at 28 hours post-fertilization, the time of HSC birth. We injected these GESTALT embryos with drl:CMYC to induce AEL, barcode HSPCs and their niche to perform clone tracing. The number of HSPC clones was decreased by half compared to controls (p=0.008) indicative of a clonal expansion of the disease. We performed barcode and single-cell transcriptome profiling of flk1:GFP+ niche endothelial cells and found a significant decrease in the number of endothelial cells clones (fc= -3.5, p<0.05) paired with the identification of a novel AEL venous endothelial population upregulating 99 genes (fc>1; p<0.05) suggestive of angiogenesis likely supporting leukemogenesis. We sorted cxcl12a:dsRed+ niche stromal cells and found that AEL marrows have significantly less stromal clones (fc= -2.1, p<0.01) that are selectively amplified (>20% of the stromal compartment). We hypothesized that AEL expands a subset of stromal cells to promote disease progression and scRNA-Seq of 3,263 cxcl12a:dsRed+ stromal cells revealed an increased fraction of lepr+ mesenchymal stromal cells (MSCs, 66 vs 24% in controls). We hypothesized that AEL progenitors secrete a signal that can specifically remodel the marrow niche and we mined our scRNA-Sequencing data for a candidate ligand significantly upregulated in AEL cells compared to control HSPCs (fc>1; p<0.05) and paired receptors expressed on more than 20% of AEL associated endothelial and/or stromal cells. We identified the peptide hormone apelin expressed by the leukemia and tested if apelin alone could remodel the normal marrow niche endothelial and stromal cells by overexpressing apelin under the drl promotor. Adult marrow analyses revealed a decrease in the absolute number of stromal cells per marrow (fc= -2.2, p<0.001). Together our data support a model in which leukemia induces a clonal expansion of HSPC niche clones via apelin signaling to promote disease progression. Citation Format: Chloé S Baron, Serine Avagyan, Song Yang, Aaron McKenna, Leonard Zon. Cellular barcoding of the leukemic niche reveals an apelin-mediated clonal expansion of niche endothelial and mesenchymal stromal cell clones [abstract]. In: Proceedings of the AACR Special Conference: Acute Myeloid Leukemia and Myelodysplastic Syndrome; 2023 Jan 23-25; Austin, TX. Philadelphia (PA): AACR; Blood Cancer Discov 2023;4(3_Suppl):Abstract nr A27.

High Intrinsic Oncogenic Potential in the Myc-Box-Deficient Hydra Myc3 Protein.

The proto-oncogene myc has been intensively studied primarily in vertebrate cell culture systems. Myc transcription factors control fundamental cellular processes such as cell proliferation, cell cycle control and stem cell maintenance. Myc interacts with the Max protein and Myc/Max heterodimers regulate thousands of target genes. The genome of the freshwater polyp Hydra encodes four myc genes (myc1-4). Previous structural and biochemical characterization showed that the Hydra Myc1 and Myc2 proteins share high similarities with vertebrate c-Myc, and their expression patterns suggested a function in adult stem cell maintenance. In contrast, an additional Hydra Myc protein termed Myc3 is highly divergent, lacking the common N-terminal domain and all conserved Myc-boxes. Single cell transcriptome analysis revealed that the myc3 gene is expressed in a distinct population of interstitial precursor cells committed to nerve- and gland-cell differentiation, where the Myc3 protein may counteract the stemness actions of Myc1 and Myc2 and thereby allow the implementation of a differentiation program. In vitro DNA binding studies showed that Myc3 dimerizes with Hydra Max, and this dimer efficiently binds to DNA containing the canonical Myc consensus motif (E-box). In vivo cell transformation assays in avian fibroblast cultures further revealed an unexpected high potential for oncogenic transformation in the conserved Myc3 C-terminus, as compared to Hydra Myc2 or Myc1. Structure modeling of the Myc3 protein predicted conserved amino acid residues in its bHLH-LZ domain engaged in Myc3/Max dimerization. Mutating these amino acid residues in the human c-Myc (MYC) sequence resulted in a significant decrease in its cell transformation potential. We discuss our findings in the context of oncogenic transformation and cell differentiation, both relevant for human cancer, where Myc represents a major driver.

G-Quadruplex Binding of an NIR Emitting Osmium Polypyridyl Probe Revealed by Solution NMR and Time-Resolved Infrared Studies.

G-quadruplexes are emerging targets in cancer research and understanding how diagnostic probes bind to DNA G-quadruplexes in solution is critical to the development of new molecular tools. In this study the binding of an enantiopure NIR emitting [Os(TAP)2 (dppz)]2+ complex to different G-quadruplex structures formed by human telomer (hTel) and cMYC sequences in solution is reported. The combination of NMR and time-resolved infrared spectroscopic techniques reveals the sensitivity of the emission response to subtle changes in the binding environment of the complex. Similar behaviour is also observed for the related complex [Os(TAP)2 (dppp2)]2+ upon quadruplex binding.

The anticancer peptide LL-III binds with nanomolar affinity to human telomeric and cMyc G-quadruplexes.

LL-III is a natural anticancer peptide able to cross the membrane of cancer cells and to localize in the nucleolus, but its intracellular target is unknown. Here, we show that LL-III is able to bind with nM affinity to specific G-quadruplex structures known to be relevant anticancer targets.

Novel Planar Pt(II) Cyclometallated Cytotoxic Complexes with G-Quadruplex Stabilisation and Luminescent Properties.

Herein is described the development of a series of novel quadruplex DNA (QDNA)-stabilising cyclometallated square–planar metal complexes (CMCs). Melting experiments using quadruplex DNA (QDNA) demonstrated that interactions with the complexes increased the melting temperature by up to 19 °C. This QDNA stabilisation was determined in two of the major G-quadruplex structures formed in the human c-MYC promoter gene (c-MYC) and a human telomeric repeat sequence (H-Telo). The CMCs were found to stabilise H-telo more strongly than c-MYC, and the CMCs with the highest cytotoxic effect had a low–moderate correlation between H-telo binding capacity and cytotoxicity (R2 values up to 10 times those of c-MYC). The melting experiments further revealed that the stabilisation effect was altered depending on whether the CMC was introduced before or after the formation of QDNA. All CMCs’ GI50 values were comparable or better than cisplatin in human cancer cell lines HT29, U87, MCF-7, H460, A431, Du145, BE2-C, SJ-G2, MIA, and ADDP. Complexes 6, 7, and 9 were significantly more cytotoxic than cisplatin in all cell lines tested and had good to moderate selectivity indices, 1.7–4.5 in MCF10A/MCF-7. The emission quantum yields were determined to be relatively high (up to 0.064), and emission occurred outside cellular autofluorescence, meaning CMC fluorescence is ideal for in vitro analyses.

Abstract 1728: Single cell RNA-seq analysis reveals a role of pro-inflammatory tumor-associated macrophages in driving prostate cancer progression

Abstract Genomic amplification and increased expression of C-MYC are found in high-grade intraepithelial neoplasm (HGPIN) and primary prostate adenocarcinoma. What role C-MYC plays in the initiation and progression of prostate cancer remains unclear. A genetically engineered mouse model with a high level of human C-MYC protein expression under a probasin promoter (Hi-Myc model) was developed that captures prostate cancer progression from hyperplasia at 6-week-old, to HGPIN at 3-6 month-old, and ultimately to invasive adenocarcinoma at 8-month-old. Applying single-cell RNA sequencing (scRNA-seq) technology, we have carefully studied the temporal transcriptional change in MYC-expressing tumor-initiating cells and the tumor-infiltrating immune cells to understand the cell-intrinsic and -extrinsic mechanisms by which C-MYC promotes the transition from HGPIN to invasive prostate cancer. We have identified a particular type of luminal cells, Prom1+ L1 cells, as the likely tumor initiating cells in the Hi-Myc model. The MYC-expressing L1 tumor initiating cells were more abundant and cycling more often in the invasive cancer at 8-month-old, compared to the pre-invasive stage. Interestingly, significant infiltration of novel M1-like tumor-associated macrophages (TAMs) correlated with the histologic tumor progression from HGPIN to invasive cancer. Targeting TAMs with anti-CSF1R antibody delayed prostate cancer progression and invasion, which appears to be independent of CD8 T-cells. Mechanistically, TAMs expressed a high level of IL-1b, which stimulated Hi-Myc prostate cell proliferation in an organoid co-culture system. More importantly, depleting IL-1b with a neutralizing antibody slowed prostate cancer progression in Hi-Myc mice. Lastly, we found that increased macrophage gene expression was associated with higher Gleason scores and worse disease-free survival in a TCGA clinical patient cohort. In summary, we have identified a molecular mechanism involving pro-inflammatory TAMs and IL-1b in driving early prostate cancer progression in a MYC-driven prostate cancer model, opening a potential therapeutic avenue to target TAMs and pro-inflammatory cytokine in preventing early prostate cancer progression. Citation Format: Jimmy L. Zhao, Joseph Chan, Max Land, Perianne Smith, Anuradha Gopalan, Michael Haffner, Dana Pe'er, Charles Sawyers. Single cell RNA-seq analysis reveals a role of pro-inflammatory tumor-associated macrophages in driving prostate cancer progression [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 1728.

Transgenic mice encoding modern imaging probes: Properties and applications.

SUMMARYModern biology is increasingly reliant on optical technologies, including visualization and longitudinal monitoring of cellular processes. The major limitation here is the availability of animal models to track the molecules and cells in their natural environment in vivo. Owing to the integrity of the studied tissue and the high stability of transgene expression throughout life, transgenic mice encoding fluorescent proteins and biosensors represent unique tools for in vivo studies in norm and pathology. We review the strategies for targeting probe expression in specific tissues, cell subtypes, or cellular compartments. We describe the application of transgenic mice expressing fluorescent proteins for tracking protein expression patterns, apoptotic events, tissue differentiation and regeneration, neurogenesis, tumorigenesis, and cell fate mapping. We overview the possibilities of functional imaging of secondary messengers, neurotransmitters, and ion fluxes. Finally, we provide the rationale and perspectives for the use of transgenic imaging probes in translational research and drug discovery.

Yamanaka Factors in the Budding Tunicate Botryllus schlosseri Show a Shared Spatio-Temporal Expression Pattern in Chordates.

In vertebrates, the four transcription factors Sox2, c-Myc, Pou5f1 and Klf4 are involved in the differentiation of several tissues during vertebrate embryogenesis; moreover, they are normally co-expressed in embryonic stem cells and play roles in pluripotency, self-renewal, and maintenance of the undifferentiated state in adult cells. The in vitro forced co-expression of these factors, named Yamanaka factors (YFs), induces pluripotency in human or mouse fibroblasts. Botryllus schlosseri is a colonial tunicate undergoing continuous stem cell-mediated asexual development, providing a valuable model system for the study of pluripotency in the closest living relatives of vertebrates. In this study, we identified B. schlosseri orthologs of human Sox2 and c-Myc genes, as well as the closest homologs of the vertebrate-specific Pou5f1 gene, through an in-depth evolutionary analysis of the YF gene families in tunicates and other deuterostomes. Then, we studied the expression of these genes during the asexual cycle of B. schlosseri using in situ hybridization in order to investigate their possible involvement in tissue differentiation and in pluripotency maintenance. Our results show a shared spatio-temporal expression pattern consistent with the reported functions of these genes in invertebrate and vertebrate embryogenesis. Moreover, Myc, SoxB1 and Pou3 were expressed in candidate stem cells residing in their niches, while Pou2 was found expressed exclusively in the immature previtellogenic oocytes, both in gonads and circulating in the colonial vascular system. Our data suggest that Myc, SoxB1 and Pou3 may be individually involved in the differentiation of the same territories seen in other chordates, and that, together, they may play a role in stemness even in this colonial ascidian.

Rational design of small-molecules to recognize G-quadruplexes of c-MYC promoter and telomere and the evaluation of their in vivo antitumor activity against breast cancer.

DNA G4-structures from human c-MYC promoter and telomere are considered as important drug targets; however, the developing of small-molecule-based fluorescent binding ligands that are highly selective in targeting these G4-structures over other types of nucleic acids is challenging. We herein report a new approach of designing small molecules based on a non-selective thiazole orange scaffold to provide two-directional and multi-site interactions with flanking residues and loops of the G4-motif for better selectivity. The ligands are designed to establish multi-site interactions in the G4-binding pocket. This structural feature may render the molecules higher selectivity toward c-MYC G4s than other structures. The ligand–G4 interaction studied with 1H NMR may suggest a stacking interaction with the terminal G-tetrad. Moreover, the intracellular co-localization study with BG4 and cellular competition experiments with BRACO-19 may suggest that the binding targets of the ligands in cells are most probably G4-structures. Furthermore, the ligands that either preferentially bind to c-MYC promoter or telomeric G4s are able to downregulate markedly the c-MYC and hTERT gene expression in MCF-7 cells, and induce senescence and DNA damage to cancer cells. The in vivo antitumor activity of the ligands in MCF-7 tumor-bearing mice is also demonstrated.

Significant structural change in human c-Myc promoter G-quadruplex upon peptide binding in potassium.

We selected the G-quadruplex motif located in the nuclease-hypersensitive elements (NHE) III1 region of the c-Myc promoter and for the first time performed its interaction studies with a designed peptide (QW10). Our CD results showed that the peptide bound to the c-Myc G-quadruplex and induced a significant blue shift in the positive peak of 20 nm in KCl alone or with 40wt% PEG200 or 20wt% PEG8000 in comparison to NaCl. Our Native Gel results confirmed that peptide binding destabilized the duplex and stabilized the unimolecular G-quadruplex and not binding to i-motif. UV thermal results confirmed destabilization of bimolecular structure and stabilization of unimolecular G-quadruplex. QW10 showed preferential binding towards c-MYC promoter G4 with binding constant (Kb) values of the order of 0.05 ± 0.2 μM, 0.12 ± 0.1 μM and 0.05 ± 0.3 μM for complexes in K+ alone or 40wt% PEG 200 or 20wt% PEG 8000 respectively. QW10 showed preferential cytotoxicity with IC50 values of 11.10 μM and 6.44 μM after 72 and 96 hours' incubation on Human Breast Carcinoma MDA-MB 231 cells and was found to be non-toxic with Human Embryonic Kidney (HEK-1) cells. Interestingly, we observed reduction of c-Myc gene expression by 2.5 fold due to QW10 binding and stabilizing c-MYC G4. Our study for the first time provides an expanded overview of significant structural change in human c-Myc promoter G-quadruplex upon peptide binding in potassium.

Exogenous LIN28 Is Required for the Maintenance of Self-Renewal and Pluripotency in Presumptive Porcine-Induced Pluripotent Stem Cells

Porcine species have been used in preclinical transplantation models for assessing the efficiency and safety of transplants before their application in human trials. Porcine-induced pluripotent stem cells (piPSCs) are traditionally established using four transcription factors (4TF): OCT4, SOX2, KLF4, and C-MYC. However, the inefficiencies in the reprogramming of piPSCs and the maintenance of their self-renewal and pluripotency remain challenges to be resolved. LIN28 was demonstrated to play a vital role in the induction of pluripotency in humans. To investigate whether this factor is similarly required by piPSCs, the effects of adding LIN28 to the 4TF induction method (5F approach) on the efficiency of piPSC reprogramming and maintenance of self-renewal and pluripotency were examined. Using a retroviral vector, porcine fetal fibroblasts were transfected with human OCT4, SOX2, KLF4, and C-MYC with or without LIN28. The colony morphology and chromosomal stability of these piPSC lines were examined and their pluripotency properties were characterized by investigating both their expression of pluripotency-associated genes and proteins and in vitro and in vivo differentiation capabilities. Alkaline phosphatase assay revealed the reprogramming efficiencies to be 0.33 and 0.17% for the 4TF and 5TF approaches, respectively, but the maintenance of self-renewal and pluripotency until passage 40 was 6.67 and 100%, respectively. Most of the 4TF-piPSC colonies were flat in shape, showed weak positivity for alkaline phosphatase, and expressed a significantly high level of SSEA-4 protein, except for one cell line (VSMUi001-A) whose properties were similar to those of the 5TF-piPSCs; that is, tightly packed and dome-like in shape, markedly positive for alkaline phosphatase, and expressing endogenous pluripotency genes (pOCT4, pSOX2, pNANOG, and pLIN28), significantly high levels of pluripotent proteins (OCT4, SOX2, NANOG, LIN28, and SSEA-1), and a significantly low level of SSEA-4 protein. VSMUi001-A and all 5F-piPSC lines formed embryoid bodies, underwent spontaneous cardiogenic differentiation with cardiac beating, expressed cardiomyocyte markers, and developed teratomas. In conclusion, in addition to the 4TF, LIN28 is required for the effective induction of piPSCs and the maintenance of their long-term self-renewal and pluripotency toward the development of all germ layers. These piPSCs have the potential applicability for veterinary science.

Correction to: Conformer Analysis of a Biological G-Quadruplex Element in the Human c-MYC Promoter by Native Polyacrylamide Gel Electrophoresis

Correction to: Conformer Analysis of a Biological G-Quadruplex Element in the Human c-MYC Promoter by Native Polyacrylamide Gel Electrophoresis

Investigation of the Interaction of Human Origin Recognition Complex Subunit 1 with G-Quadruplex DNAs of Human c-myc Promoter and Telomere Regions.

Origin recognition complex (ORC) binds to replication origins in eukaryotic DNAs and plays an important role in replication. Although yeast ORC is known to sequence-specifically bind to a replication origin, how human ORC recognizes a replication origin remains unknown. Previous genome-wide studies revealed that guanine (G)-rich sequences, potentially forming G-quadruplex (G4) structures, are present in most replication origins in human cells. We previously suggested that the region comprising residues 413–511 of human ORC subunit 1, hORC1413–511, binds preferentially to G-rich DNAs, which form a G4 structure in the absence of hORC1413–511. Here, we investigated the interaction of hORC1413-511 with various G-rich DNAs derived from human c-myc promoter and telomere regions. Fluorescence anisotropy revealed that hORC1413–511 binds preferentially to DNAs that have G4 structures over ones having double-stranded structures. Importantly, circular dichroism (CD) and nuclear magnetic resonance (NMR) showed that those G-rich DNAs retain the G4 structures even after binding with hORC1413–511. NMR chemical shift perturbation analyses revealed that the external G-tetrad planes of the G4 structures are the primary binding sites for hORC1413–511. The present study suggests that human ORC1 may recognize replication origins through the G4 structure.

Establishment of a human iPSC line XMDYYYi001-A from a patient with Becker muscular dystrophy harboring duplications of exons 2-19 in dystrophin gene

Becker muscular dystrophy (BMD) is an X-linked recessive muscular disorder caused by mutations in the dystrophin. We generated a human iPSC line from peripheral blood mononuclear cells (PBMCs) of a patient with duplications of exons 2-19 in the dystrophin. The PBMCs were reprogrammed using the episomal reprogramming plasmids contained a combination of expressions of human OCT4, SOX2, NANOG, LIN28, C-MYC, KLF4 and SV40LT. We conducted the tests on the iPSCs including Karyotype analysis, expressed pluripotency markers and teratoma forming three germ layers. The iPSC line is a useful cell model to further research on genetic treatment or new therapeutic drugs.

Shaggy functions downstream of dMyc and their concurrent downregulation confers additive rescue against tau toxicity in Drosophila.

Neurodegenerative tauopathies such as Alzheimer's and Parkinson's diseases are characterized by hyperphosphorylation of tau protein and their subsequent aggregation in the forms of paired helical filaments and/or neurofibrillary tangles in specific areas of the brain. Despite several attempts, it remains a challenge to develop reliable biomarkers or effective drugs against tauopathies. It is increasingly evident now that due to the involvement of multiple cellular cascades affected by the pathogenic tau molecules, a single genetic modifier or a molecule is unlikely to be efficient enough to provide an inclusive rescue. Hence, multitargets based combinatorial approach(s) have been suggested to provide an efficient rescue against tauopathies. We have reported earlier that targeted downregulation of dmyc (a Drosophila homolog of human cmyc proto-oncogene) restricts tau etiology by limiting tau hyperphosphorylation and heterochromatin loss. Although, dmyc generates a significant rescue; however, it is not proficient enough to provide a complete alleviation against tauopathies. Here, we report that tissue-specific concurrent downregulation of dmyc and gsk3β conveys a near-complete rescue against tau toxicity in Drosophila. We noted that combinatorial downregulation of dmyc and gsk3β reduces tau hyperphosphorylation, restricts the formation of neurofibrillary tangles, and restores heterochromatin loss to the physiological level. Our subsequent investigations revealed that dmyc regulates gsk3β via protein phosphatase 2A (dPP2A) in a dose-dependent manner to regulate tau pathogenesis. We propose that dmyc and gsk3β candidates can be utilized in a synergistic manner for the development of an efficient combinatorial therapeutic approach against the devastating human tauopathies.

Ordered structure induced in human c-Myc PEST region upon forming a disulphide bonded dimer

PEST rich protein sequences are intrinsically disordered and serve as degradation hotspots in eukaryotic cells. The structure of PEST degrons in proteins and their mechanism of action remain poorly understood. Deregulation or overexpression of human transcription factor c-Myc causes cancer. The PEST region in c-Myc is implicated for its rapid degradation. Here, we investigate how the structure of 77-residue PEST fragment of c-Myc and its mutant (M1, Trp inserted) are affected by the formation of a covalent dimer. DLS and size exclusion data indicated a ~ 30% increase in Stokes radius upon the formation of the dimer. CD showed an increase in helix and strand content with dimer formation in both Wt and mutant. However, counterintuitively, Trp fluorescence anisotropy decay was marginally faster in the dimer compared to monomer. This anomaly was traced to Trp-Trp Forster resonance energy homotransfer in M1 dimer, suggesting close interaction between two chains in the dimer. Our data suggest that indole rings in the PEST M1 dimer are no further than 24 A apart. These results may hold the key to higher stability of c-Myc in tumours and the poorly understood physiological role of c-Myc oligomer in cells.