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BH3-only proteins Noxa, Bmf, and Bim are necessary for arsenic trioxide-induced cell death in myeloma
Alejo A Morales1, Delia Gutman, Kelvin P Lee
1Microbiology and Immunology and The Sylvester Comprehensive Cancer Center, University of Miami, Miller School of Medicine, FL, USA.
Abstract:
The use of arsenic trioxide (ATO) to treat multiple myeloma (MM) is supported by preclinical studies as well as several phase 2 studies, but the precise mechanism(s) of action of ATO has not been completely elucidated. We used gene expression profiling to determine the regulation of apoptosis-related genes by ATO in 4 MM cell lines and then focused on Bcl-2 family genes. ATO induced up-regulation of 3 proapoptotic BH3-only proteins (Noxa, Bmf, and Puma) and down-regulation of 2 antiapoptotic proteins Mcl-1 and Bcl-X(L). Coimmunoprecipitation demonstrated that Noxa and Puma bind Mcl-1 to release Bak and Bim within 6 hours of ATO addition. Bak and Bim are also released from Bcl-X(L). Silencing of Bmf, Noxa, and Bim significantly protected cells from ATO-induced apoptosis, while Puma silencing had no effect. Consistent with a role for Noxa inhibition of Mcl-1, the Bad-mimetic ABT-737 synergized with ATO in the killing of 2 MM lines. Finally, Noxa expression was enhanced by GSH depletion and inhibited by increasing GSH levels in the cells. Understanding the pattern of BH3-only protein response should aid in the rational design of arsenic-containing regimens.
Insights
Arsenic trioxide (ATO) triggers apoptosis in multiple myeloma cells by upregulating proapoptotic proteins like Noxa and Puma, while downregulating Mcl-1 and Bcl-X(L). This mechanism provides insights for developing novel arsenic-based cancer therapies.
Area of Science:
- Oncology
- Molecular Biology
- Cancer Therapeutics
Background:
- Arsenic trioxide (ATO) shows promise for treating multiple myeloma (MM), but its exact mechanisms of action require further elucidation.
- Understanding ATO's molecular targets is crucial for optimizing its therapeutic efficacy in MM treatment.
Purpose of the Study:
- To investigate the precise molecular mechanisms by which ATO induces apoptosis in multiple myeloma cells.
- To identify the specific apoptosis-related genes, particularly Bcl-2 family members, regulated by ATO.
Main Methods:
- Gene expression profiling was employed to analyze ATO's effects on apoptosis-related genes in four MM cell lines.
- Coimmunoprecipitation assays were used to study protein interactions between ATO-regulated proteins.
- Gene silencing techniques were utilized to assess the functional roles of specific proteins in ATO-induced apoptosis.
Main Results:
- ATO up-regulated proapoptotic BH3-only proteins (Noxa, Bmf, Puma) and down-regulated antiapoptotic proteins (Mcl-1, Bcl-X(L)).
- Noxa and Puma were found to bind Mcl-1, releasing Bak and Bim, thereby promoting apoptosis.
- Silencing of Bmf, Noxa, and Bim conferred significant protection against ATO-induced apoptosis, while Puma silencing had no effect.
Conclusions:
- ATO-induced apoptosis in multiple myeloma is mediated by the modulation of Bcl-2 family proteins, with Noxa playing a key role in Mcl-1 inhibition.
- The findings suggest that targeting the BH3-only protein response can aid in the rational design of arsenic-containing therapeutic regimens for MM.
