IL-2 Family Cytokines and Receptors-- Mechanisms of Regulation & Action

National Heart, Lung, And Blood Institute

Investigators

Linked publications, trials & patents

Abstract

The IL-2 receptor and related cytokine/cytokine receptor systems are being studied to understand the T cell immune response in normal and disease. After T-cell activation, the magnitude and duration of the response is controlled by the amount of IL-2 produced, levels of IL-2 receptors, and the time course of their induction. IL-2Ra expression is highly expressed by cells infected with HTLV-I, the cause of adult T cell leukemia (ATL). There are 3 chains of the receptor: IL-2Ra, IL-2Rb, and gc, with IL-2Ra and IL-2Rb regulated at the level of transcription. gc is shared by the IL-4, IL-7, IL-9, IL-15, and IL-21 receptors and is mutated in XSCID. We study the signals induced by these cytokines, particularly STAT proteins and the mechanisms by which they regulate target genes. Given our prior data that Stat5a or Stat5b transgenic mice develop tumors, consistent with STAT5 being implicated in malignant transformation and elevated in a range of human tumors, this has relevance for both normal and pathological states. Moreover, humans and mice with altered STAT protein expression or activation have a range of immunological defects. T helper cell differentiation is critical for normal immune responses, with Th1 differentiation important for host defense to viruses and other intracellular pathogens, Th2 differentiation vital in allergic disorders/helminths, and Th17 differentiation vital in inflammatory disorders. We previously showed that IL-2 is important for Th2 differentiation and that IL-2 induces IL-4 receptor expression in a STAT5-dependent manner and controls priming for Th2 differentiation. Moreover, using genome-wide chromatin immunoprecipitation coupled to DNA sequencing (ChIP-Seq), we previously found regulation of Th2 differentiation via STAT5A and STAT5B and extended these findings to show that IL-2 via STAT5 induces IL-12Rb2, which is critical for Th1 differentiation and that IL-2 via STAT5 also regulates T-bet. we also had elucidated mechanism by which IL-2 inhibits Th17 differentiation. We also reported a critical role of IL-2 in Th9 differentiation, with IL2 inducing STAT5 binding to the Il9 promoter and IL-2 and IL-21 having opposing actions in Th9 differentiation based on induction of BCL6 by IL-21 but repression by IL-2. With Dr. K. Christopher Garcia (Stanford), we previously studied novel IL-2 variant partial agonists that function as "receptor signaling clamps. We previously showed that one variant, H9-RETR, prolonged survival in a model of graft-versus-host disease and blocked spontaneous proliferation of smoldering ATL cells. This receptor-clamping approach might be a general mechanism-based strategy. IL-2 REH was reported as a partial agonist that specifically expanded Treg rather than CD8 T cells, with benefit in DSS colitis, and we studied another partial agonist that promoted a TCSM phenotype of CD8 T cells, with enhanced efficacy in adoptive transfer treatment of B16 melanoma and in a second generated CAR T antitumor model. In the latter, we had discovered by STAT5 is a promoter of T cell exhaustion, with attenuated STAT5 activation resulting in a TSCM phenotype and elucidated underlying mechanisms. In the past year, we have pursued studies of other IL-2 partial agonists and IL-21 mimics. IL-21 has broad actions on T- and B-cells, and we previously reported that it also induces apoptosis of conventional dendritic cells. ChIP-Seq analysis had revealed genome-wide binding competition between GM-CSF-induced STAT5 and IL-21-induced STAT3, and we previously elucidated roles for STAT1 vs. STAT3 in IL-21 signaling inT cells. Previously, we also showed that IL-21 regulates expression of the Prdm1 gene that encodes BLIMP1 via a response element that depends on STAT3 and IRF4 and subsequently discovered that in contrast to its known ability to cooperate with PU.1 in B cells to act via Ets-IRF composite elements (EICEs), IRF4 cooperates with BATF/JUN family proteins to act via novel AP1-IRF composite elements (AICEs) in T cells, as well as in B cells. In other studies, we previously studied the biological roles of Egr1 and Egr2 and elucidated some non-immunological roles for Egr1, demonstrating that this transcription factor has a genetic-background dependent effect on eyelid development-- being required for such development on the BALB/c background but not on the C57BL/6 background. In collaborative studies, we have advanced studies of Egr family proteins and this year a collaborative study was published on the role of EGR family proteins in the homing and pathogenicity of Th17 cells in the CNS and we have also collaborated with Jim Salzer related to roles of EGR proteins in the CNS. Previously, we studied the biological significance of STAT5 tetramerization in vivo by generating mice expressing mutant forms of STAT5A and STAT5B that could form dimers but not tetramers and previously reported modeling of the 3-dimensional structure of the tetramer, and we also previously reported the basis for defective NK cell development in the double knockin mice, demonstrating a critical role for STAT5 tetramers for the survival of NK cells. In the current year, we now have extended our studies of STAT5 tetramers and reported their role related to the regulation of monocyte differentiation. We also previously globally characterized super-enhancers regulated by IL-2-activated STAT5 and IL-21-activated STAT3 and their relationship to highly inducible genes and had found that the Il2ra gene contains the most highly ranked STAT5-dependent super enhancer. Using CRISPR-Cas9 technology, we previously functionally dissected the elements of this super-enhancer, providing key new insights into the molecular regulation of the Il2ra in particular and super-enhancers more generally, and in the current year, we have significantly extended these studies, clarifying the differential importance of different super-enhancer elements in different cell types. Moreover, this year we contributed to studies of IL-4 mimetics in the distinctive activation of type 1 IL-4 receptors, with RNA-seq indicating similar effects of neo-4 to those of IL-4 and IL-13 on monocytes. We also have reported in a collaborative study an efficient new approach, ChIATAC, for the multiomics mapping of 3D epigenomes and reported a new user-friendly R Shiny application for RNA-sequencing analysis and biomarker discovery. Overall, these studies enhance our understanding of mechanisms by which gc family cytokines regulate gene expression and biological processes and are relevant to normal and pathological immune cell function, including in disease states, with potential therapeutic implications.