THE LONG NON-CODING FOXP3 REGULATES CELL IDENTITY AND FUNCTION OF T REGULATORY LYMPHOCYTES STABILIZING THE KEY TRANSCRITPTION FACTOR FOXP3

Abstract The human immune system is a suitable context to study plasticity in response to environmental stimuli. Differentiation of Naïve cells into specialized subsets guarantees the proper immune system function. These cellular subsets were once considered as terminally differentiated, but recent findings, showed that they display a high degree of plasticity, whose underlying molecular mechanisms are still poorly understood. In this context, CD4+ T regulatory lymphocytes (Treg) are the principal actors in the regulation of immune responses and maintenance of immunological self-tolerance thanks to their peculiar suppressive function. Treg cells dysfunction is associated to autoimmune pathologies, inflammatory diseases and cancer. Their inherent plasticity could be exploited as a promising therapeutic opportunity to modulate their differentiation and function in the context of several immune-mediated diseases. A better characterization of the molecular mechanism underlying plasticity is thus compelling. Long non-coding RNAs (lncRNAs) has been identified as novel players in the modulation of cell plasticity and in the maintenance of cell identity. These features, along with their cellular specificity, brought lncRNAs to the fore as novel and promising therapeutic targets. In this study, we demonstrate that the expression of lncFOXP3, a CD4+ T regulatory specific lncRNAs located upstream of FOXP3 gene, is crucial for the maintenance of Treg phenotype and proper function. Expression of lncFOXP3 correlates with FoxP3, the master transcription factor of Treg cells, but the two transcripts are not co-regulated. Functional experiments revealed that lncFOXP3 down-regulation reduces FoxP3 protein levels and, moreover, impacts on Treg suppressive activity. Finally, the analysis of lncFOXP3 protein interactors highlighted the association with Ubiquitin-specific-processing protease 7 (USP7), indicating its putative role in the maintenance of FoxP3 protein stability. Our results suggest a direct involvement of lncRNAs in the maintenance of Treg cell proper function. Therefore, modulation of lncRNAs could potentially be exploited to either enhance or quench Treg cell suppressive function in the treatment of autoimmune diseases, cancer or immunodeficiencies.