Exploring TERT Expression and Regulation in Tumorigenesis: Lessons from ALV

TERT;ALV;chicken;cancer;provirus;integration;Biology

Lam, GaryCunningham, Kyle W. ;

Johns Hopkins University

关键词: TERT;    ALV;    chicken;    cancer;    provirus;    integration;    Biology;   

Others  :  https://jscholarship.library.jhu.edu/bitstream/handle/1774.2/59195/LAM-DISSERTATION-2018.pdf?sequence=1&isAllowed=y

瑞士|英语

来源: JOHNS HOPKINS DSpace Repository

【 摘 要 】

Avian leukosis virus (ALV) is a simple retrovirus that infects chickens and causes cancer.Chickens exposed to ALV typically develop B-cell lymphomas within a few months after hatching.ALV-induced tumors have been shown to develop by insertional mutagenesis mediated by proviral integration.ALV proviral integration into the chicken genome disrupts the normal expression of neighboring host genes, commonly by promoter insertion and/or enhancer activation.Previous studies have identified several common proviral integration sites near genes that are now known to drive tumorigenesis.Notable genes include MYC, MYB, mir-155, and, more importantly, TERT.Unique clonal integrations in the TERT promoter suggest that they are early events in ALV-induced B-cell lymphomas.In this thesis, I report the results of overexpressing TERT in early chicken embryos coinfected with ALV in new in vivo experiments.Although no definite conclusion could be made about TERT overexpression and tumor progression, two tumors in one chicken were identified to retain the recombinant virus used to overexpress TERT.High-throughput sequencing analysis of integration sites in one tumor implicated genes previously described.In contrast, the other tumor implicated an AT-rich interacting transcriptional coactivator, ARIDB5, as the top potential cooperating gene in TERT overexpressing cells.In addition, we observed an unexpected prevalence of hemangiomas in our chickens infected with ALV-A, which is more commonly associated with ALV-J.Integration site analysis of multiple hemangiomas implicate an exclusive subset of genes that include FRK, PLAG1, and GLIS3.In human cancers, the association between TERT promoter methylation and TERT expression is an area of active investigation.The relationship between the two factors has proven to be complex and controversial.Proviral integration adds another layer of complexity.Investigation of clonal TERT promoter integrations by bisulfite sequencing showed that ALV integration is associated with a decrease in methylation of the flanking genomic DNA, suggesting that ALV may contribute to TERT expression by inhibiting methylation at the TERT promoter.Lastly, we surveyed an extensive subset of human hematological malignancies for the prevalence of previously reported TERT promoter mutations by conventional Sanger sequencing.TERT promoter mutations have been recently identified as a highly conserved and ubiquitous somatic change in various cancers where TERT expression has been directly induced.We observed a lack of TERT promoter mutations in the human samples tested, suggesting that TERT promoter mutations are not a prevalent mechanism of TERT activation in hematological malignancies.