Transcriptional control of HP1a by the RNA binding proteins RBMX/L1 maintain chromatin state in myeloid leukemia
RNA binding proteins (RBPs) are key arbiters of post-transcriptional regulation that have been found to be dysregulated in hematological malignancies. Here, we identify the RBP RBMX and its retrogene RBMXL1 to be required for murine and human myeloid leukemogenesis. RBMX/L1 are overexpressed in acute myeloid leukemia (AML) primary patients compared to healthy individuals, and RBMX/L1 loss delayed leukemia development. Complex chromosomal karyotyping analysis and assay for transposase-accessible chromatin sequencing demonstrated that RBMX/L1 loss led to significant changes in chromatin accessibility and compaction. We found that RBMX/L1 directly binds to mRNAs and affects transcription of multiple loci, including the heterochromatin protein 1 alpha (HP1a) mRNA. Using single molecule resolution RNA fluorescence in situ hybridization, we uncovered that RBMX/L1 controls the nascent transcription of the HP1a locus. Forced HP1a expression rescued the RBMX/L1 depletion effects on cell growth and apoptosis. Overall, we determine that RBMX/L1 control leukemia cell survival by regulating chromatin state through its downstream target HP1a. These findings illuminate a novel mechanism for RBPs directly promoting transcription and suggest RBMX/L1 as well as HP1a as potential novel therapeutic targets in myeloid malignancies. Overall design: 21 human cell line samples,with RBMX/L1 KD and controls