La-related protein 4B maintains murine MLL-AF9 leukemia stem cell self-renewal by regulating cell cycle progression.

Our recent study identified a nonsense mutation of La-related protein 4B (LARP4B) from whole genome sequencing of a 3-year-old female monozygotic twin pair discordant for MLL-associated acute myeloid leukemia (AML). To study the role of LARP4B in AML, we established a LARP4B-knockdown MLL-AF9 AML mouse model. Using this mouse model, we found that LARP4B knockdown significantly decreased leukemia cells in the peripheral blood, spleen, and bone marrow and prolonged the survival of AML recipient mice. Additional studies showed that LARP4B knockdown reduced leukemia stem cells (LSCs) and impaired the self-renew capacity of LSCs. Cell cycle analysis revealed that LARP4B knockdown arrested more LSCs in the G0 phase. The transcription of the cell cycle inhibitors p16, p19, and p21 and of the lineage-specific transcription factor CCAAT-enhancer-binding protein α was increased in the LARP4B-knockdown LSCs. Thus, our results demonstrate that LARP4B plays an important role in the maintenance of LSCs and suggest that LARP4B may regulate the cell cycle of LSCs via suppressing the expression of the cell cycle inhibitors p16, p19, and p21 and the myeloid specific transcription factor CCAAT-enhancer-binding protein α.