P723: LOSS OF THE NK MOTIF AND ANKYRIN REPEAT DOMAIN 1 (KANK1) LEADS TO LYMPHOID COMPARTMENT DYSREGUATION IN MICE

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Background: We identified a novel germline loss of heterozygosity (LOH) mutation encompassing the NK Motif And AnKyrin Repeat Domain 1 (KANK1) gene in a young Myelodysplastic syndrome (MDS) patient and his healthy father, with no additional MDS-related mutations or chromosomal abnormalities. Clinical investigation suggested development of MDS following severe infection, likely triggered by an autoimmune mechanism. KANK1 protein plays a role in the control of cytoskeleton formation by regulating actin polymerization. A t(5;9) translocation resulting in a fusion of the platelet-derived growth factor receptor beta gene (PDGFRB) and KANK1 was detected in a patient with myeloid neoplasm (MN) characterized with severe thrombocythemia. The protein is thought to have a tumour suppressor function, as its expression is downregulated or missing in several tumor tissues, while over-expressing the protein was reported to inhibit the proliferation of tumor cells in solid cancer models. In addition, defects in cytoskeletal proteins are reported to contribute to immunological dysfunction and disruption of normal immune processes. Aims: To investigate the role of KANK1 in the regulation of normal hematopoiesis and the development of myeloid disorders. Methods: We generated a new genetically modified KANK1 (Kank1-/-) knockout mouse model and analysed the phenotypic and developmental changes in hematopoiesis in young and aged mice. Results: We confirmed the loss of Kank1 mRNA and protein expression by q-PCR and targeted protein mass-spectrometry respectively. The mice are viable and fertile, and reproduced according to mendelian ratio. Over the two years observation period, Kank1-/- mice did not exhibit any signs of disease, and their peripheral blood parameters remained within the normal range. Flow cytometry analysis of bone marrow (BM) cells from 17-20 weeks kank1-/- old mice showed minor increase in CD3+ T-cell population, while the expression of the double positive B220/CD19 B-cells population was reduced in Kank1-/- compared to Kank1+/+. Comprehensive flow cytometry analysis of spleen and thymus cells from young (n=8 each, 6-7 weeks old) and aged (n=8, 68-71 weeks old) Kank1-/- mice showed further dysregulation of the lymphoid compartment when compared to Kank1+/+. In young mice, a slight decrease of Treg cells is noticed in the spleen, coupled with a slight decrease of activated CD4 in the peripheral blood. In the spleen of aged Kank1-/- mice, the proportions of macrophages and Treg cells were decreased, while the central memory CD4+ T-cells were increased. Total protein analysis from BM cells of Kank1-/- (n=3) compared to Kank1+/+ mice (n=3) showed a significant reduction (FC >0.5, adj.p. <0.05) in proteins associated with cytoskeleton formation such as Myosin1 (MYH1), Tropomysin-1 (TDM1) and Annexin (ANXA2), and extracellular matrix components such as Collagena(CO1A1) and Matrix metalloproteinase9 (MMP9). We also detected a significant increase in expression of the DNA licensing factor minichromosome maintenance complex component 7 (MCM7), and the mitochondrial membrane associated transporter ATP binding Cassette Subfamily B Member 10 (ABCBA). Summary/Conclusion: Dysregulation of the immune system has been widely recognized to play a role in the development of MDS. Based on our results, we propose a role for KANK1 in regulating the development of immune cells in the mouse through it invovlement in cytoskeleton regulation. In vivo infectious challenge experiments using our model will futher elucidate the importance of KANK1 in the development of MDS.