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Alternative Splicing and Regulation of Innate Immune Mediators in Normal and Malignant Hematopoiesis

Smith, Molly
http://orcid.org/0000-0002-2913-6847
http://rave.ohiolink.edu/etdc/view?acc_num=ucin1563527303459942

Abstract Details

2019, PhD, University of Cincinnati, Medicine: Cancer and Cell Biology.
The innate immune system is a complex network that recognizes and responds to foreign particles. Innate immune signaling is fundamentally involved in inflammation and increasing evidence implicates chronic innate and inflammatory signaling as a risk factor in cancer and hematologic malignancies. Recent studies have implicated the dysregulation of innate immune signaling in the pathogenesis of Myelodysplastic Syndrome (MDS) and Acute Myeloid Leukemia (AML). However, the precise genetic alterations that cause innate immune signaling activation in hematologic malignancies are not fully defined. Hematologic malignancies have a particularly high frequency of mutations in RNA splicing factors. How these mutations contribute to disease is not fully understood. A global analysis of exon usage in AML samples revealed a subset of genes is regulated exclusively at the isoform level in leukemia, resulting in anticorrelated expression of individual RNA isoforms. Many of these genes regulated by RNA isoform changes are associated with inflammatory and immune pathways. IRAK4 was the most significant immune pathway gene that undergoes isoform switching. Increased expression of the long isoform of IRAK4 (IRAK4-L), which includes exon 4, was found in MDS and AML cell lines and primary patient samples and results in maximal activation of NF-kB. Elevated IRAK4-L isoform expression is associated with poor prognosis in MDS and AML and is significantly associated with mutations in splicing factor U2AF1. Further, U2AF1 directly regulates the splicing of IRAK4 to increase the expression of IRAK4-L. Inhibition of IRAK4 abrogates leukemic growth in vitro and in vivo and is more efficacious in AML cells with U2AF1 mutations and/or higher expression of the IRAK4-L isoform. Thus, mutations in U2AF1 splicing factor induce expression of therapeutically targetable "active" IRAK4 isoforms and provide the first genetic link to activation of chronic innate immune signaling in MDS and AML. The consequences of loss of another inflammatory signaling molecule, A20, in hematopoiesis was determined. Despite the evidence of A20’s involvement in immune signaling pathways and chronic innate immune signaling in hematologic malignancies, limited research has been done to explore the function of A20 in hematopoiesis. We generated a mouse lacking A20 in the hematopoietic system to investigate the cellular requirement of A20 in hematopoietic stem cell (HSC) function. While complete ablation of A20 expression was incompatible with normal HSC function, mice with deletion of one A20 allele had cytopenias of the peripheral blood in myeloid lineages. Transplantation of A20-deficient bone marrow increased the number of HSCs in recipient mice; however, the HSCs were functionally impaired and less competitive than their wild-type counterparts. Given that the phenotype in heterozygous mice is subtle compared to knockout mice, we posit that HSCs are sensitive to the dosage of A20. Therefore, in contrast to complete A20 loss, modest reduction of A20 expands the HSC pool and is likely an important molecular event affecting HSC function. Taken together, our results suggest A20 insufficiency negatively affects hematopoiesis by reducing stem cell function. In summary, our findings report that IRAK4 and A20 are important innate immune signaling mediators and their dysregulation is implicated in malignant hematopoiesis.
Daniel Starczynowski, Ph.D. (Committee Chair)
Jose Cancelas-Perez, M.D. (Committee Member)
Matthew Flick, Ph.D. (Committee Member)
Kakajan Komurov, Ph.D. (Committee Member)
Nathan Salomonis, M.D. (Committee Member)
190 p.
Oncology
Alternative RNA splicing; innate immune signaling; Myelodysplastic Syndromes; hematopoiesis; hematopoietic stem cells; Acute Myeloid Leukemia

Recommended Citations

Citations

  • Smith, M. (2019). Alternative Splicing and Regulation of Innate Immune Mediators in Normal and Malignant Hematopoiesis [Doctoral dissertation, University of Cincinnati]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1563527303459942

    APA Style (7th edition)

  • Smith, Molly. Alternative Splicing and Regulation of Innate Immune Mediators in Normal and Malignant Hematopoiesis. 2019. University of Cincinnati, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=ucin1563527303459942.

    MLA Style (8th edition)

  • Smith, Molly. "Alternative Splicing and Regulation of Innate Immune Mediators in Normal and Malignant Hematopoiesis." Doctoral dissertation, University of Cincinnati, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1563527303459942

    Chicago Manual of Style (17th edition)

ucin1563527303459942
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© 2019, all rights reserved.
This open access ETD is published by University of Cincinnati and OhioLINK.
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