Cholesterol metabolism in t(4;11) leukemia

Abstract

Chromosomal translocations involving the KMT2A gene (KMT2Ar leukemia) occur in nearly 5% to 10% of acute leukemia cases and are associated with an aggressive disease course and poor prognosis. The AFF1 gene is the most common translocation partner of the KMT2A gene, causing t(4;11) leukemia. It is well known that cancer cells undergo metabolic reprogramming, including changes in cholesterol homeostasis, which contribute to increased proliferation and survival. Thus, dysregulated cholesterol metabolism not only promotes tumorigenesis and chemotherapy resistance, but also represents an emerging new hallmark of cancer. Research on leukemia suggests that leukemia cells have an abnormal cholesterol metabolism characterized by increased cholesterol synthesis, lipid uptake, and potential effects of oxysterols. Statins, which inhibit 3-hydroxy-3-methylglutaryl-CoA reductase (HMGCR), the rate-limiting enzyme in cholesterol homeostasis, may have anti-leukemic properties by interfering with the cellular cholesterol pathway. Preclinical and early clinical studies have investigated the potential of statins as an adjuvant therapy option for leukemia patients. However, the results are controversial and require a deeper understanding of cholesterol metabolism in subgroups of leukemia patients who may benefit from such therapy. This study was dedicated to the comprehensive investigation of cholesterol homeostasis in t(4;11) leukemia cells, including the regulatory activities of two transcription factors, sterol regulatory element-binding protein 2 (SREBP2) and retinoid-related orphan receptor gamma (RORγ). In addition, the effect of inhibition of the cholesterol signaling cascade on cellular cholesterol metabolism and t(4;11) tumor growth was examined. The aim was to understand the basis of these signaling pathways in order to identify potential therapeutic targets for the treatment of leukemia patients harboring a KMT2A-AFF1 chromosomal translocation. The results of this work revealed a significant overexpression of SREBP2 in t(4;11) leukemia cells, indicating a dysregulated cholesterol homeostasis. By specifically inhibiting RORγ, a dose-dependent reduction in leukemia cell growth was observed, along with the induction of cell cycle changes and apoptosis. RNA sequencing (RNA-Seq) analysis revealed a significant change in the transcriptome of t(4;11) leukemia cells after RORγ inhibition. This included downregulation of SREBP2-dependent key genes involved in cholesterol synthesis and import, as well as modulation of genes associated with intrinsic, mitochondrial involvement in apoptosis. This suggests that RORγ has a regulatory effect on SREBP2. When t(4;11) cells were treated with a combination of the RORγ inhibitor and cytarabine, additive effects were observed. Furthermore, when atorvastatin was added, a strong anti-leukemia synergism was observed by circumventing the statin-induced feedback. These findings provide insights into the molecular basis of cholesterol metabolism in t(4;11) leukemia cells and suggest that targeted inhibition of these pathways may be a promising therapeutic approach for the treatment of t(4;11) leukemia patients.