BRG1 Regulates Adult B-Cell Acute Lymphoblastic Leukemia Proliferation and Apoptosis By Interacting with c-MYC and Activating PI3K/AKT Pathway

Background and objective：Adult B-cell acute lymphoblastic leukemia（B-ALL）has historically had a dismal prognosis, with limited treatment options and cure rates less than 40%. Only 25% of patients older than 50 years old were alive 5 years after diagnosis, highlighting the need for further improvements in treatment for older adult patients (≥40 years). Recently years, genome profiling revealed that cancer cells frequently depend on chromatin regulatory activities to maintain a malignant phenotype and proliferation. Brahma-related gene 1（BRG1）, a core catalytic ATPase subunits of the SWI/SNF chromatin remodelling complex, has been reported to support oncogenic transcriptional program and sustain leukaemogenic transformation in leukemia. However, the specific role and mechanisms of BRG1 in B-ALL development and progression remains largely unknown. Therefore, elucidating the underlying maintenance mechanisms is essential to develop novel effective treatment strategies.

Methods：For clinical sample, we analyzed the mRNA expression level of BRG1 in newly diagnosed B-ALL patients(n=576) and healthy donors(n=74) in the GSE13159 subset from GEO database. Then, quantitative reverse transcription-PCR (RT-PCR) and Western blot were used to detect the expression of BRG1 in 38 newly diagnosed B-ALL patients and 25 healthy donors in our department. For further exploring the effects of BRG1 on B-ALL , lentiviral transfection were used to knock down BRG1 in SUP-B15 and Nalm-6 cells and overexpress BRG1 in RS4:11 cell, and CCK-8, Edu, clone formation assay, cell cycle, apoptosis, IF, RT-PCR and Western Blot were used to detect the effects. In addition, TMT proteomics was used to analyze the differential proteins between sh-ctrl and sh-BRG1 of Nalm-6 cell. Western Bolt was used to detect the changes of key proteins in related pathways.

Results: Our investigation of SMARCA4 revealed that BRG1 is over-expressed in the 576 newly diagnosed B-ALL patients from GSE13159 dataset, as well as in 38 of our department. Downregulated BRG1 inhibited growth and increased the apoptosis of ALL, while ectopic expression of BRG1 showed the opposite effects. Mechanistically, TMT proteomics analysis and vitro experiments further revealed that BRG1 exerted these functions through its interaction with c-MYC and regulated the expression of CDK4/6, BCL-2 and BCL-xl.

Conclusion: Our study demonstrates that BRG1 upregulation is closely associated with proliferation and anti-apoptosis in adult B-ALL.