Abstract LT03: C/EBPα Acts as an RNA Binding Protein Essential for, and Promotes End-Stage Macrophage Differentiation

Abstract

Abstract The transcription factor C/EBPα is a well characterized DNA binding protein with essential functions in controlling and regulating myeloid differentiation and lipid metabolism. Herein, we describe C/EBPα’s separate and distinct RNA binding characteristics. Using Chromatin RNA Immunoprecipitation, we identified that C/EBPα interacts primarily with RNA introns in both HL-60 and THP-1 cells, with a preference for a palindromic GC-rich binding motif. Structural prediction in conjunction with RNA electrophoretic mobility shift assays show that C/EBPα interacts with RNA through two previously undescribed domains located towards the proteins N terminus. These domains are distinct from C/EBPα’s DNA binding b-ZIP domain which is instead located on the proteins C terminus. Mouse bone marrow transplantation and in vitro cytokine assays reveal that C/EBPα RNA binding appears to be essential for macrophage maturation but not neutrophil differentiation. To better understand these phenotypic differences, we expanded our observations into the transcriptomic space by utilizing single-cell CITE-Seq. In line with biochemical data, notable mature cell populations were absent when the C/EBPα’s RNA binding domains are excluded from the protein. Intriguingly, differential gene expression revealed strong, selective upregulation of Lipoprotein Lipase (Lpl) in monocyte, but not neutrophil populations. It has been previously reported that dysregulation of Lpl affects bone marrow monocyte progenitor differentiation and results in dysregulated cellular mobilization from the bone marrow, a phenotype that is commonly seen in cancers such as AML. The increased abundance of monocyte and neutrophil populations in the C/EBPα RNA deletion samples is therefore suggestive that C/EBPα RNA binding is critical in regulating terminal differentiation and mobilization circuits which may become dysregulated or perturbed in diseases such as AML. On-going analyses are investigating the RNA velocity trajectory of captured cell populations in an attempt to better understand at which stage C/EBPα RNA binding becomes essential for terminal maturation and differentiation of select cell populations. Taken together though, we demonstrate that C/EBPα is also an RNA binding protein with unique functions distinct from its DNA binding activity that is essential for monocyte maturation, differentiation and mobilization. Citation Format: Mahmoud A. Bassal, Yanzhou Zhang, Yanjing V. Liu, Virginia Camacho, Simone Ummarino, Robert S. Welner, Daniel G Tenen. C/EBPα Acts as an RNA Binding Protein Essential for, and Promotes End-Stage Macrophage Differentiation [abstract]. In: Proceedings of Frontiers in Cancer Science; 2023 Nov 6-8; Singapore. Philadelphia (PA): AACR; Cancer Res 2024;84(8_Suppl):Abstract nr LT03.