Aberrant activation of RPB1 is critical for cell overgrowth in acute myeloid leukemia.

Acute myeloid leukemia (AML) is a group of highly aggressive malignancies with a 5-year overall survival of less than 40%. Cell overgrowth with defective apoptosis is a hallmark of AML, but little is known about how it occurs. Here, we show that aberrant activation of the largest subunit of RNA polymerase II (RPB1) encoded by POLR2A gene is critically involved in this hallmark. We retrospectively analyzed the expression profiles of POLR2A and RPB1 in a panel of AML cell lines, primary AML patients and peripheral blood samples. Meanwhile, correlation analysis was used to explore the correlation between the expression of RPB1 with tumor burden and overall survival time in untreated AML samples. RNA-Seq approach was performed to identify the differentially expressed genes between RPB1 silencing AML cells with control cells after knocking out RPB1. Furthermore, orthotopic AML models were established with RPB1 silencing and control cells to investigate the effects of RPB1 protein level on leukemia cell growth. In most AML patients, RPB1 was aberrantly activated and closely associated with poor prognosis, but not in normal hematopoietic cells. Global transcriptomic analysis revealed that POLR2A knockout strongly impaired growth of AML cells by selectively depleting a substantial set of AML-related oncogenic and anti-apoptosis genes such as MYC, RUNX2, MEIS1, CDC25A and BCL-2. Silencing RPB1 by genetic technology led to a potent regression of human refractory AML in mouse models. These findings reveal that dysregulated RPB1 is a central oncogenic hub that drives overgrowth by hijacking an array of oncogenic and anti-apoptosis factors. Targeting RPB1 is a potential therapeutic for treating AML.