The role of G-quadruplexes in myeloid dendritic cells

Abstract

DNA can fold into different secondary structures such as G-quadruplexes (G4s). G4s are highly stable and can form in specific guanine-rich regions within DNA and RNA both in vitro and in vivo. Due to their conserved localization within the genome, G4s are suggested to affect different cellular processes, such as DNA replication, gene expression and genome stability. Their formation is cell type specific and dynamically regulated by G4-interacting proteins, cell stages and exogenous stimuli. G4 structures have already been investigated in several cell types, including stem cells and cancer cells, but little is known about G4s in immune cells such as dendritic cells (DCs). DCs are antigen-presenting cells, that link the innate and adaptive immunity by inducing an antigen-specific immune response. Here, we characterise the molecular effects of G4 stabilisation on dendritic cell (DC) phenotype and function using the G4 ligand pyridostatin (PDS). Stabilisation of G4s in bone marrow-derived dendritic cells (BMDCs) induced DC activation and maturation as indicated by elevated levels of co-stimulatory molecules CD40, CD80 and CD86, MHC molecules. G4 stabilisation in DCs also stimulate DC migration, in line with enhanced expression of the chemokine receptor CCR7. Furthermore, coculture experiments revealed that activation of DCs by PDS is enough to trigger the ability of T cell activation, indicated by the upregulation of the specific T cell markers CD69 and CD25 and respective cytokine secretion. Using a B16Ova melanoma model, we show that intratumoral injection of PDS leads to enhanced DC activation within the tumor as well. To further characterise the molecular mechanisms of how G4 formation leads to these cellular changes, we identified proteins that interact with G4s in DCs. Strikingly, among those were STAT3 and STAT1. In subsequent work, we confirmed this interaction and even demonstrated that it binds to a G4 of PD-L1.<br /> With this study, we could show that G4 stabilisation in DCs can be used to affect gene expression of specific genes, leading to enhanced DC activation and functionality.