Speckled Protein (SP)140, an immune-specific chromatin reader, contains a CARD and chromatin-interacting domains that dictate subnuclear localization and macrophage identity

Abstract

Abstract Chromatin regulators that “read” histone post-translational modifications are desirable therapeutic targets in inflammation and cancer. The Speckled Protein (SP) family of chromatin “readers” consists of SP100, SP110, SP140 and SP140L and share high homology with autoimmune regulator (AIRE). SPs possess a caspase activation and recruitment domain (CARD) and multiple chromatin “reader” domains (Plant Homeodomain (PHD), Bromodomain, and SAND). SP140 is preferentially expressed in immune cells and loss-of-function single nucleotide polymorphisms (SNPs) within SP140 significantly associate with immune disorders, such as Crohn’s disease (CD), multiple sclerosis (MS), and chronic lymphocytic leukemia (CLL). We have previously shown that SP140 is a critical orchestrator of macrophage identity and function by occupying and repressing silenced lineage-inappropriate genes. We also demonstrated that PBMCs from patients carrying SP140 SNPs lose SP140 expression and are hypo-responsive to TLR stimulation. How SP140 functions to interact with or maintain heterochromatin for cell identity and function, what SP140 protein domains drive activity, and how disease variants alter SP140 function remain to be determined. Here we show that human SP140 localizes to promyelocytic leukemia (PML) nuclear bodies, sites of transcriptional repression, and we delineate the SP140 protein domains required for this. Furthermore, we determined the impact of SP140 disease-associated SNPs on PML localization and macrophage identity and functional responses. Collectively, our work provides functional characterization of this important chromatin protein and how SP140 disease variants contribute to immunological disease.