Jason S. Rawlings, PhD, Furman University
PROJECT TITLE: Mechanisms of chromatin decondensation in lymphocytes
Control of T cell proliferation is essential to proper immune function; lack of proper control can lead to pathologies such as autoimmunity, immunodeficiency, and cancer. STAT5 is a transcription factor that is absolutely essential for peripheral T cell proliferation. Following TCR engagement, activated T cells produce IL-2 which induces proliferation via STAT5. Naïve T cells, for which TCR engagement has not occurred, are refractory to IL-2 stimulation, remaining quiescent during an immune response. This ensures a clonal expansion of antigen specific T cells. Recently, we demonstrated that IL-2 induces STAT5 activation and nuclear localization in naïve T cells; however, STAT5 cannot engage DNA due to the condensed nature of chromatin in these cells. This condensation is not due to global modification of histones as previously thought, but to a higher-order chromatin condensation that is dependent on the activity of the condensin II complex. In this proposal we will determine the signaling pathway(s) downstream of the TCR that are responsible for chromatin decondensation during T cell activation. We will also determine if chromatin condensation is a conserved mechanism to regulate proliferation in other lymphocyte populations. These studies will provide important insight into the epigenetic control of lymphocyte proliferation and function.
This project has identified the role that PKC signaling plays in controlling the decondensation of chromatin during an immune response. Specifically, we determined that a calcium-dependent PKC is required for proper chromatin decondensation during activation. Furthermore, this PKC acts through p44/42 MAPK to make αβ T lymphocytes competent to respond to growth factors during an immune response. Furthermore, we were able to show that NF-κB as well as p38 MAPK are not involved in the decondensation event or in the ability of cells to acquire competence to respond to IL-2.
We also investigated whether other lymphocyte populations decondense chromatin as a function of activation, with the goal of determining if chromatin decondensation is a conserved mechanism to control lymphocyte proliferation. We determined that B lymphocytes also decondense chromatin when activated, and that this decondensation is also dependent on intracellular calcium, suggesting that αβ T cells and B cells share a conserved mechanism to control chromatin decondensation. Finally, we assessed chromatin in γδ T cells and found that naïve γδ T cells possess a more decondensed chromatin compared to αβ T cells, which may explain why γδ T cells can respond to pathogens faster than αβ T cells.
Furthermore, we were able to demonstrate that αβ T cells are not the only lymphocytes that decondense their chromatin during activation.
SC INBRE Developmental Research Project Program funds were used to purchase the supplies and reagents; covered animal costs; supported conference travel for the PI and the students involved.
The data generated from this project provides insight on the molecular mechanisms that regulate the proliferation of lymphocytes. This will help us understand not only how the immune system functions normally, but will provide insight into pathologies caused by abnormal immune proliferation, such as autoimmunity and cancer.
March 16, 2018