The transcription factor RUNX2 regulates a critical step in the extravasation of human, pathogenic type 17 CD4+ T cells

Authors

• A Bhasym
• SP Singh
• N Singh
• F Parween
• PJ Gardina
• FO Carrasquero
• TE Markowitz
• JM Farber

Abstract

The pathogenic subset of Th17/type 17 CD4+ T cells produce IFNg and GM-CSF and is implicated in inflammatory disease. We have found that human CCR6+CCR2+CD4+ T cells are highly enriched in pathogenic type 17 cells. Pathogenic activity requires migration into inflamed tissue, and these cells are efficient at diapedesis across activated endothelial cells (ECs) in vessel-like flow assays, where we have shown that CCR6 mediates adhesion to ECs and CCR2 mediates the subsequent step of transendothelial migration. Our project’s goal has been to identify transcription factors (TFs) and their target genes that form the regulatory networks controlling these cells’ extravasation. We focused on identifying regulators of CCR2 using bulk and single cell RNA-seq and ATAC-seq of CCR6+CCR2+ vs. CCR6-CCR2- cells. Among the candidate TFs we identified was RUNX2, one of a family of three RUNX proteins that has been best studied in osteoblast differentiation. We found that knocking down RUNX2 in CCR6+CCR2+ cells diminished expression of CCR2, and ChIP experiments showed RUNX2 binding to a region predicted to regulate CCR2. Surprisingly, knockdown of RUNX2 did not affect the CCR2-mediated step of transendothelial migration, but instead decreased the number of CCR6+CCR2+ cells undergoing the prior step of EC adhesion. To understand this RUNX2 activity, we are undertaking genome-wide analyses of RUNX2 binding sites and RUNX2-regulated gene expression in the CCR6+CCR2+ cells. Together, our studies suggest that RUNX2 supports a critical step in the extravasation of human, pathogenic T cells and should reveal fundamental molecular mechanisms controlling their entry into inflamed tissues.

Scientific Focus Area: Immunology

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