Mitochondrial Dysfunction in Human Leukemic Stem/Progenitor Cells upon Loss of RAC2

Area of Science:

• Hematology
• Molecular Biology
• Cell Biology

Background:

• Leukemic stem cells (LSCs) are maintained by bone marrow niches, conferring treatment resistance.
• Microenvironmental signals often converge on RAC GTPases, but their downstream effectors in leukemia are poorly understood.

Purpose of the Study:

• To investigate the role of RAC GTPases, specifically RAC1 and RAC2, in the function and maintenance of BCR-ABL-transduced hematopoietic stem/progenitor cells (HSPCs).

Main Methods:

• Depletion of RAC1 and RAC2 in BCR-ABL-transduced HSPCs.
• Assessment of proliferation, progenitor frequency, cobblestone formation, and replating capacity.
• Cell cycle analysis and apoptosis assays.
• Mitochondrial membrane potential measurements and electron microscopy.
• Proteome analysis and co-immunoprecipitation to identify RAC2 interacting proteins.

Main Results:

• RAC2 depletion, but not RAC1, significantly reduced proliferation, self-renewal, and progenitor frequency of BCR-ABL HSPCs.
• RAC2 downregulation led to decreased cell cycle activity, increased apoptosis, and reduced mitochondrial membrane potential with ultrastructural malformations.
• Proteome analysis identified RAC2 interacting proteins, including mitochondrial transport proteins SAM50 and Metaxin 1.
• SAM50 downregulation also impaired BCR-ABL cell proliferation and mitochondrial function.

Conclusions:

• RAC2 plays a critical role in maintaining the self-renewal and proliferation of BCR-ABL-expressing leukemic stem cells.
• RAC2 is essential for mitochondrial integrity and function in these cells.
• Targeting RAC2 or its interacting mitochondrial proteins may represent a novel therapeutic strategy for chronic myeloid leukemia.