Epigenetic Regulation of Bmi1 by Ubiquitination and Proteasomal Degradation Inhibit Bcl-2 in Acute Myeloid Leukemia

Abstract

Bmi1 is associated with advanced prognosis of acute myeloid leukemia (AML), and polyethylenimine (PEI)-stabilized Bmi1 siRNA-entrapped human serum albumin (HSA) nanocarriers (PEI@HSANCs) were used to protect siRNA from degradation and also to control epigenetic regulation-based AML therapy. The nanoform increased the transfection efficiency of Bmi1 siRNA through caveolae-mediated endocytosis and enhanced Bax translocation into the mitochondria. It enhanced the caspase 3-mediated apoptosis through the Bax activation and Bcl-2 inhibition. The molecular analysis reveals the downregulation of polycomb proteins, Bmi1 and EzH2, along with inhibition of H3K27me3 and H2AK119ub1. The signaling cascade revealed downregulation of Bmi1 through ubiquitin-mediated degradation and is reversed by a proteasome inhibitor. Further mechanistic studies established a crucial role of transcription factor, C-Myb and Bmi1, as its direct targets for maintenance and progression of AML. Chromatin immunoprecipitation (ChIP) assay confirmed Bmi1 as a direct target of C-Myb as it binds to promoter sequence of Bmi1 between −235 to +43 and −111 to +43. The in vivo studies performed in the AML xenograft model evidence a decrease in the population of leukemic stem cells marker (CD45+) and an increase in the myeloid differentiating marker expression (CD11b+) in the bone marrow after the Bmi1 siRNA nanoconjugated therapy. Activation of apoptotic pathways and withdrawal of epigenetic repression through a ubiquitin proteasomal pathway potentiating a novel antileukemic therapy were established.

Optical Imaging of Epigenetic Modifications in Cancer: A Systematic Review

“…This ICG-tagged stable nanosized complex not only allowed the visualization of the expression of EZH2 in the engrafted tumor in a leukemia mouse model but also could inhibit tumor growth by targeting EZH2. Some other studies have also confirmed the feasibility of epigenetic regulation-based strategies for precision treatment of cancer (Dev et al 2021;Kushwaha et al 2020;Sardoiwala et al 2020).…”

Development and application of nanomaterials, nanotechnology and nanomedicine for treating hematological malignancies

“…The drug uses PEI and has as nanocarriers and encapsulates si-Bmi1 for Bmi1 gene. In animal experiments, this nanomedicine substantially prolonged the survival of diseased mice [ 235 ]. Similarly, Chandran et al .…”

Human Serum Albumin Based Nanodrug Delivery Systems: Recent Advances and Future Perspective

“…Some studies have shown that the polycomb protein Bmi1 is overexpressed in AML and plays a role in disease development through its downstream targets [ 74 ], making it a potential epigenetic target. Kushwaha et al proposed a delivery strategy using HSA nanoparticles as carriers (nanocarriers, NCs) for Bmi1 siRNA, which was stabilized by polyethylenimine (PEI) [ 61 ]. This innovative approach, known as PEI@HSANCs, aimed to enhance the effectiveness of Bmi1 siRNA delivery.…”

“… Schematic representation of the construction of HSA NPs-PEI@EZH2 siRNA and the possible mechanism of AML therapy. Reproduced with permission from the work of Kushwaha et al (2020) [ 61 ]. …”