Identification and validation of Ikaros (IKZF1) as a cancer driver gene for Marek’s disease virus-induced lymphomas

Authors: STEEP, ALEC - Michigan State University; Hildebrandt, Evin; XU, HONGEN - Technical University Of Munich; Hearn, Cari; FRISHMAN, DMITRIJ - Technical University Of Munich; NIIKURA, MASAHIRO - Simon Fraser University; Dunn, John; Kim, Taejoong; Conrad, Steven; MUIR, WILLIAM - Purdue University; Cheng, Hans

Submitted to: Microorganisms
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/25/2022
Publication Date: 2/9/2022
Citation: Steep, A., Hildebrandt, E.C., Xu, H., Hearn, C.J., Frishman, D., Niikura, M., Dunn, J.R., Kim, T.N., Conrad, S.J., Muir, W.M., Cheng, H.H. 2022. Identification and validation of Ikaros (IKZF1) as a cancer driver gene for Marek’s disease virus-induced lymphomas. Microorganisms. 10(2):401. https://doi.org/10.3390/microorganisms10020401.
DOI: https://doi.org/10.3390/microorganisms10020401

Interpretive Summary: Marek's disease virus (MDV) is the causative agent for Marek's disease (MD), which is characterized by T cell lymphomas in chickens. A complete understanding how this viral pathogen induces tumors in chickens is needed in order to achieve better and more sustainable control. In this submission, we identified and validated the first MD cancer driver gene. Specifically, a high frequency of MD tumors contained a somatic mutation in the IKZF1 gene, which encodes Ikaros, the master regulator of lymphocyte development. This result confirms our hypothesis that MDV infection is not sufficient and requires additional somatic mutations in key genes. Using this knowledge, breeders can better select for more MD genetically resistant birds, which will result in improvement in animal welfare and reduced costs to poultry producers and consumers.

Technical Abstract: Marek’s disease virus (MDV) is the causative agent for Marek’s disease (MD), which is characterized by T-cell lymphomas in chickens. While the viral Meq oncogene is necessary for transformation, it is insufficient, as not every bird infected with virulent MDV goes on to develop a gross tumor. Thus, we postulated that the chicken genome contains cancer driver genes; i.e., ones with somatic mutations that promote tumors, as is the case for most human cancers. To test this hypothesis, MD tumors and matching control tissues were sequenced. Using a custom bioinformatics pipeline, 9 of the 22 tumors analyzed contained one or more somatic mutation in Ikaros (IKFZ1), a transcription factor that acts as the master regulator of lymphocyte development. The mutations found were in key Zn-finger DNA-binding domains that also commonly occur in human cancers such as B-cell acute lymphoblastic leukemia (B-ALL). To validate that IKFZ1 was a cancer driver gene, recombinant MDVs that expressed either wild-type or a mutated Ikaros allele were used to infect chickens. As predicted, birds infected with MDV expressing the mutant Ikaros allele had high tumor incidences (~90%), while there were only a few minute tumors (~12%) produced in birds infected with the virus expressing wild-type Ikaros. Thus, in addition to Meq, key somatic mutations in Ikaros or other potential cancer driver genes in the chicken genome are necessary for MDV to induce lymphomas.