MGA Deletion Promotes Richter’s Transformation by Regulating Mitochondrial Oxidative Phosphorylation

This article mainly focuses on the transformation of chronic lymphocytic leukemia (CLL) into aggressive lymphoma, known as Richter’s Transformation (RT), exploring the function and molecular mechanism of MGA (MAX Gene Associated). MGA is a functional MYC inhibitor, with a mutation rate of 3% in CLL, increasing to 36% in RT. Given the frequent occurrence of MGA mutations in RT, but its specific role and mechanism in the transformation of CLL to RT remain unclear, this study established MGA gene knockout mice to explore its role in RT.

Academic Background and Research Objectives

RT is the progression of CLL to aggressive lymphoma, mainly transforming into diffuse large B-cell lymphoma (DLBCL), with a very poor prognosis. Even with the current application of medium to high-intensity chemo-immunotherapy, the median survival of RT patients is less than one year, and after targeted therapy, the survival is shortened to about 4 months. This highlights the importance and urgency of understanding the biological characteristics of RT and designing better treatment methods. Despite the large amount of large-scale sequencing data for CLL, research on RT has faced major obstacles due to the ambiguity of RT diagnostic criteria, scarcity of samples, and similarities between RT and aggressive CLL. Therefore, using mouse models to study the transformation of CLL to RT is expected to make breakthroughs in understanding and treating RT.

Article Source and Background

This paper was written by authors including Prajish Iyer, Bo Zhang, and others from institutions such as City of Hope National Comprehensive Cancer Center and Technical University of Munich, published in the journal “Science Translational Medicine” on July 31, 2024.

Research Details

a) Research Process

1. Establishing RT mouse model: Using CRISPR-Cas9 to knockout MGA in CLL model mice carrying sf3b1 and mdr mutations to generate RT mouse model.

   • Gene knockout and cell transplantation: Obtained donor mice by crossing CLL mice (cd19cre/+ mdrfl/+ sf3b1 k700efl/+) with Cas9 conditional expression mice. Extracted hematopoietic stem cells (lsk cells) from donor mice, gene-edited, and transplanted into sub-lethally irradiated Cd45.1 recipient mice.
   • Disease monitoring: Monitored CLL occurrence in transplanted mice through flow cytometry of peripheral blood, observing for 6 to 24 months.

2. RNA sequencing and functional analysis: Performed RNA sequencing, material waiting, and functional analysis on RT mice, discovering nme1 as a target of MGA.

   • Gene expression analysis: RNA-seq revealed upregulation of numerous genes related to MYC pathway and oxidative phosphorylation (Oxphos).

3. Experiments and data analysis: Validated discovered phenotypic features, including upregulation of nme1 and MYC, using various experimental techniques (such as immunoblotting, immunohistochemistry, cell proliferation assays, etc.).

   • Cell and animal experiments: Conducted oxidative phosphorylation assays, cell growth curves, and survival rate experiments after knocking out MGA in human cell lines.
   • Oxidative phosphorylation and mitochondrial analysis: Detected the expression and function of complexes on the MITOCH proton transfer chain in MGA KO cells.

b) Main Research Findings

1. MGA knockout guides rapid transformation of CLL to RT: After MGA knockout, CLL rapidly transformed to RT, accompanied by abnormal mitochondrial performance and enhanced oxidative phosphorylation.

   • Transformation module: Spleen cells (mainly B220+CD5+) isolated from initial donor mice, when transplanted into new recipient mice (CD45.1), rapidly expanded and showed RT characteristics.

2. Molecular mechanism exploration: RNA sequencing revealed significant upregulation of MYC and nme1 pathways in RT cells after MGA knockout, suggesting MGA regulates RT transformation through the MYC-nme1 axis.

   • MYC and nme1 upregulation: Immunoblotting verified the upregulation of MYC and nme1 in RT and CLL cells, which was also validated in human samples.

3. Therapeutic target research: Dual pathway inhibition of MYC and electron transfer chain complex II significantly prolonged the survival of RT mice.

   • CDK9 and TTFA treatment: In RT mice, the effects of AZ5576 (CDK9 inhibitor) and TTFA (complex II inhibitor) were analyzed, finding that combination therapy significantly increased the survival of RT mice.

c) Conclusions and Value

This study firstly revealed the key regulatory mechanism of MGA in the transformation of CLL to RT, where MGA regulates mitochondrial oxidative phosphorylation through the MYC-nme1 axis, driving disease progression. This process provides us with new therapeutic targets, and inhibiting MYC and mitochondrial complex II can significantly improve the treatment effect of RT. This offers new hope for patients and has important guiding significance for future clinical treatment of RT.

d) Research Highlights

1. Discovery of MGA-MYC-nme1 axis: First clarified that MGA regulates mitochondrial function through MYC and nme1, driving the transformation of CLL to RT.
2. Dual-target therapy: Dual-target therapy showed significant efficacy, providing new ideas for future RT treatment strategies.
3. Construction of mouse model: Systematically explored the role of MGA in RT through mouse models, validating the similarity between mouse models and human disease.

e) Other Values

This study not only deeply explored the key molecular mechanisms in the transformation of CLL to RT but also provided new therapeutic targets, while also offering methods for establishing mouse models for more RT transformation research. This achievement is not only scientifically significant but also provides potential treatment options for clinical applications.

Through the above systematic research, the authors pointed out the key position of MGA in the RT transformation process, revealed new molecular mechanisms, and proposed effective targeted treatment plans. These findings bring new directions and hope for future in-depth research and clinical treatment.