Deregulated Expression of Circular RNAs in Acute Myeloid Leukemia

Circular RNAs (circRNAs) are dynamically regulated during differentiation and show cell-type specific expression, which is altered in cancer and can have a direct impact on various hallmarks of cancer. In accordance, we hypothesized that circRNA expression is deregulated in acute myeloid leukemia (AML), and that circRNA candidates might contribute to the pathogenesis of the disease. To identify leukemia-specific and differentiation-independent changes in circRNA expression, we determined the whole circular RNAome of 61 AML patients and 16 healthy hematopoietic stem and progenitor cell (HSPC) samples using ribosomal RNA-depleted RNA sequencing. We found hundreds of circRNAs that were differentially expressed between AML and healthy HSPCs. Gene set analysis found that many of these circRNAs were transcribed from genes implicated in leukemia biology. We discovered a circRNA derived from the T cell transcription factor gene BCL11B, circBCL11B, which was exclusively expressed in AML patients and associated with a T cell-like gene expression signature. We were able to validate this finding in an independent cohort of 332 AML patients, and knockdown of circBCL11B had a negative effect on leukemic cell proliferation, thereby suggesting circBCL11B as a novel functionally relevant candidate in AML pathogenesis. In summary, our study enables comprehensive insights into circRNA expression changes upon leukemic transformation, and provides valuable information on the biology of leukemic cells and potential novel pathway dependencies relevant for AML therapy. Ribosomal RNA-depleted RNAseq of 61 AML patient samples (including NPM1mut, t(8;21), inv(16), U2AF1mut, SF3B1mut, SRSF2mut) and 16 healthy samples of mobilized CD34+ HSPCs