Cellular senescence induced by RUNX1 and its fusion oncoprotein derivatives as a barrier to leukaemogenesis

Anderson, Gail (2017) Cellular senescence induced by RUNX1 and its fusion oncoprotein derivatives as a barrier to leukaemogenesis. PhD thesis, University of Glasgow.

Abstract

This thesis explores the ability of RUNX1 and its fusion oncoprotein derivatives to induce senescence-like growth arrest (SLGA) in primary cell cultures. While this phenomenon resembles replicative senescence seen in normal diploid human fibroblasts after extensive passage, it does not involve telomere attrition. From previous studies in the host laboratory it can also be distinguished from Ras oncogene-induced senescence (OIS) as it does not appear to depend on a DNA damage response secondary to hyper-proliferation.
Despite these differences, this study supports the hypothesis that RUNX SLGA is an anti-cancer fail-safe which protects cells against oncogenic transformation. In favour of the fail-safe model, two out of the three RUNX1 fusion oncoproteins examined fail to induce SLGA in a well characterised human fibroblast cell system (Hs68). In the case of TEL-RUNX1 (TR), a fusion which is associated with around 25% of childhood B-cell acute lymphoblastic leukaemias, loss of SLGA activity is due to N—terminal fusion to TEL. SLGA activity is regained by deletion of the HLH dimerisation domain in TEL or by introduction of a single amino acid mutation (K99R). The other major RUNX1 fusion oncoprotein, RUNX1-ETO (RE) which is commonly observed in M2 subtype acute myeloid leukaemia (AML), induces a potent SLGA. However, the RE phenotype differs from that of RUNX1, as RE strongly induces reactive oxygen species (ROS) and a pronounced senescence-associated secretory phenotype (SASP). In human AML, RE is co-expressed with a truncated variant generated by alternative splicing (RE9a), which has been shown to be much more potently leukaemogenic in animal models. This study demonstrates that RE9a also fails to induce SLGA and induces a markedly attenuated SASP. RE is generated by fusion of the N-terminal moiety of RUNX1 to the ETO C-terminus that encompasses a series of repressive nervy homology regions (NHRs), three of which are missing from RE9a. The effect of deleting or mutating NHRs from RE was also examined and show that loss of both NHR3 and NHR4 is necessary for complete ablation of RE SLGA. It was also demonstrated that aspects of RUNX1-induced SLGA are dissociable as, for example, the RUNX1P2 isoform induces profound growth arrest but only a minimal SASP.

This study supports the hypothesis that RUNX1-induced SLGA must be overcome to allow oncogenic transformation, either by intrinsic inactivation (TR, RE9a) or by co-operating mutations (RUNX1, RE). Notably, loss of sensitivity to RUNX1-induced SLGA appears to correlate with mutational loss of p16INK4A, and it was shown that growth of the human leukaemia cell line REH is stimulated rather than repressed by the TR K99R mutant. The possibility that the RE-induced SASP has pro-oncogenic effects through effects on cell survival or on bystander cells is also discussed.

• Item Type: Thesis (PhD)
• Qualification Level: Doctoral
• Keywords: Senescence, Leukaemia, Cancer, RUNX1, RUNX1-ETO, RUNX1-ETO9a, TEL-RUNX1, AML, ALL, Fusion protein, oncogene, oncogenesis, tumour suppressor, SASP, ROS.
• Subjects: Q Science > QR Microbiology > QR355 Virology
• Colleges/Schools: College of Medical Veterinary and Life Sciences > School of Infection & Immunity > Centre for Virus Research
• Supervisor's Name: Kilbey, Dr. Anna and James, Professor Neil
• Date of Award: 2017
• Depositing User: Dr Gail Anderson
• Unique ID: glathesis:2017-7878
• Copyright: Copyright of this thesis is held by the author.
• Date Deposited: 07 Feb 2017 16:28
• Last Modified: 01 Aug 2022 08:41
• URI: https://theses.gla.ac.uk/id/eprint/7878