CONSEQUENCES OF BRCA1 EPIGENETIC SILENCING ON HOMOLOGOUS RECOMBINATION AND DISEASE PROGRESSION IN MYELOID NEOPLASMS

Epigenetics;Homologous Recombination;Myeloid Neoplasms;PARP inhibition;Cell Biology

Poh, WeijieEshleman, James R. ;

Johns Hopkins University

关键词: Epigenetics;    Homologous Recombination;    Myeloid Neoplasms;    PARP inhibition;    Cell Biology;   

Others  :  https://jscholarship.library.jhu.edu/bitstream/handle/1774.2/40206/POH-DISSERTATION-2015.pdf?sequence=1&isAllowed=y

瑞士|英语

来源: JOHNS HOPKINS DSpace Repository

【 摘 要 】

Myeloid malignancies are hematological disorders encompassing chronic myeloid neoplasms to acute leukemias. In recent years, insight from genome-wide discovery studies has improved our understanding and ability to predict prognosis and treatment outcome. Despite these advances, there remains considerable clinical heterogeneity within current classification systems as these diseases often present with diverse and overlapping pathological features. At the same time, there has been limited success in translating these findings into effective therapeutics to improve overall survival. Increasingly, it is recognized that these complex and dynamic molecular changes converge into a small number of biological pathways. Therefore, a pathway-driven approach identifying commonly perturbed processes could yield greater success in developing broadly applicable therapeutics. One promising candidate is the homologous recombination (HR) pathway responsible for repairing double-stranded breaks, since most myeloid neoplasms are characterized by gross chromosomal instability. To objectively assess HR repair in fresh mononuclear cells from myeloid malignancy patients, we developed an ex vivo, short-term assay that determines HR repair based on nuclear RAD51 foci induction after DNA damage. Using this technique, we observed HR defects in 9 of 21 myeloid malignancy samples. Since there is little evidence for mutational alterations in HR genes, we screened HR gene promoters and observed BRCA1 promoter methylation in a significant subpopulation (22/96 samples) that strongly associates with disrupted HR repair. To our knowledge, this is the first report linking BRCA1 methylation to HR defects in patient samples. Next, we validated the patient samples findings by silencing BRCA1 expression in AML cells that recapitulated the HR defects. We treated AML cells with poly(ADP-ribose) polymerase (PARP) inhibitors and observed increased sensitivity with BRCA1 repression, providing a mechanistic justification for previous studies highlighting toxicities with PARP inhibitors in myeloid malignancies. The high prevalence of BRCA1 silencing led us to consider additional roles in driving myeloid disease, as it is known to repress microRNA-155 (miR-155) that is frequently elevated in myeloid malignancies. By correlating gene expression in the patient samples, we found an inverse correlation between BRCA1 and miR-155 levels. miR-155 is frequently elevated in myeloid malignancies and its targets include key regulators of inflammation (SHIP1) and myeloid differentiation (PU.1). Our results here show that BRCA1 loss due to promoter methylation not only contributes to HR defects, but also contributes to disease progression via miR-155 upregulation.