TCR signal strength and proliferation affect Runx2 expression and histone modifications in CD8+ T cells

Abstract

Abstract Runx family transcription factors are crucial for the establishment of genetic programs during important cell differentiation stages. Although the roles of Runx1 and Runx3 in T cells have been extensively studied, the role of Runx2 has not fully been explored. T cell specific Runx2 deletion leads to a cell intrinsic defect in the longevity of the CD8+ memory population and decreased expression of memory markers like TCF1 and Eomes. As histone modifiers are known Runx2 binding partners, we propose that Runx2 may bind CD8+ memory associated gene promotors, allowing for the maintenance of chromatin as memory cells undergo homeostatic proliferation. To further explore the function of Runx2 in T cells, we utilize a Runx2 fl/fl CD4-Cre model of T cell specific Runx2 deletion. We use an in vitroCD8+ T cell stimulation assay in which we co-culture DC2.4 (a mouse dendritic cell line) cells loaded with ovalbumin peptide variants (N4, T4, and V4) with OT-1 CD8+ T cells for 72 hours to observe the effects of Runx2 expression changes. Additionally, we utilize chromatin analyses in this system to examine histone modifications associated with Runx2 activity. In accordance with previous data, Runx2 expression is inversely correlated with TCR signal strength, as cells stimulated with low dose/affinity peptides upregulate higher levels of Runx2. Additionally, cell proliferation dye labeling reveals that Runx2 expression increases as cells divide during stimulation and continues to increase as activated CD8+ T cells are rested post-stimulation. Preliminary data also suggest that histone modifications associated with poised chromatin vary with Runx2 expression, indicating that Runx2 may play a role in chromatin modifications in CD8+ memory T cells.