C/EBPβ in bone marrow stromal cell-mediated drug resistance of multiple myeloma

PROJECT SUMMARY – C/EBPβ in bone marrow stromal cell-mediated drug resistance of multiple myeloma Epigenetic regulation plays a critical role in numerous biological processes. The overarching goal of my laboratory is to understand epigenetic mechanisms of drug resistance of hematological cancers promoted by the bone marrow (BM) microenvironment. This proposal will investigate the transcriptional-regulatory role of a leucine-zipper transcription factor (TF) called CCAAT/enhancer-binding protein beta (C/EBPβ) in promoting de novo drug resistance of Multiple Myeloma (MM) in the context of the BM microenvironment. MM is a disease caused by malignant plasma B cells mainly residing in the BM. It is incurable largely because of the emergence of drug resistance. One important contribution to drug resistance stems from the protective effect of the BM microenvironment, which includes growth promoting soluble factors and physical interaction with cellular components such as stromal cells, osteoblasts, and matrices. The emergence of de novo drug resistance occurs in a short timeframe and is reversible, suggesting epigenetic mechanisms may be an important driver. However, the mechanisms of chromatin regulators contributing to de novo drug resistance of MM in the BM microenvironment remain largely unexplored. Our work predicted C/EBPβ as a key transcription regulator of target genes of signaling pathways activated by the BM stromal cells. The BM stromal cells induced a genome- wide reprogramming in gene expression (transcriptome) and chromatin accessibility (regulome) of MM cells, mainly driven by soluble factors. Integrative analysis with ENCODE genomic binding data indicated C/EBPβ as a major contributor to the BM stromal cell-induced transformation of transcriptome and regulome. Our preliminary results defined C/EBPβ as a promising subject to understand epigenetic mechanisms for the emergence of de novo drug resistance in MM. We hypothesize that C/EBPβ modulates chromatin accessibility for transcriptional regulation, and through which contributes to soluble factor-mediated drug resistance in MM cells. We will test this hypothesis from two directions. In AIM 1, we will first validate the growth-promoting role of C/EBPβ using CRISPR KO of CEBPB in MM cell lines combined with engraftment model in immunodeficient NSG mice. Then we will define soluble factor-induced signature genes regulated by C/EBPβ through an integrative analysis of genome-wide profiles of gene expression and accessible chromatin. In AIM 2, we will examine the impact of C/EBPβ loss on soluble factor-mediated drug resistance to IMiDs and define the underlying genome-wide transcription signatures linked to the resistance and regulated by C/EBPβ. Results from this proposal will establish whether targeting the C/EBPβ pathway is a rational method for the development of novel therapeutic strategies to suppress de novo drug resistance as promoted by the BM microenvironment for MM cells.