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BaxΔ2 promotes apoptosis through caspase-8 activation in microsatellite-unstable colon cancer
Honghong Zhang1, Yuting Lin1, Adriana Mañas1
1Department of Biological and Chemical Sciences;
Unlabelled:
Loss of apoptotic Bax due to microsatellite mutation contributes to tumor development and chemoresistance. Recently, a Bax microsatellite mutation was uncovered in combination with a specific alternative splicing event that could generate a unique Bax isoform (BaxΔ2) in otherwise Bax-negative cells. Like the prototype Baxα, BaxΔ2 is a potent proapoptotic molecule. However, the proapoptotic mechanism and therapeutic implication of BaxΔ2 remain elusive. Here, the isolation and analysis of isogenic subcell lines are described that represent different Bax microsatellite statuses from colorectal cancer. Colon cancer cells harboring Bax microsatellite G7/G7 alleles are capable of producing low levels of endogenous BaxΔ2 transcripts and proteins. Interestingly, BaxΔ2-positive cells are selectively sensitive to a subgroup of chemotherapeutics compared with BaxΔ2-negative cells. Unlike other Bax isoforms, BaxΔ2 recruits caspase-8 into the proximity for activation, and the latter, in turn, activates caspase-3 and apoptosis independent of the mitochondrial pathway. These data suggest that the expression of BaxΔ2 may provide alternative apoptotic and chemotherapeutic advantages for Bax-negative tumors.
Implications:
"Bax-negative" colorectal tumors expressing a Bax isoform are sensitive to selective chemotherapeutics.
Insights
A novel Bax isoform (BaxΔ2) found in colorectal cancer cells can trigger apoptosis independently of mitochondria. BaxΔ2-positive tumors show sensitivity to specific chemotherapeutics, offering new treatment avenues.
Area of Science:
- Molecular Biology
- Cancer Research
- Apoptosis
Background:
- Loss of the proapoptotic protein Bax, often due to microsatellite mutations, is linked to tumor development and chemoresistance.
- A specific Bax mutation and alternative splicing can generate a unique Bax isoform, BaxΔ2, in Bax-negative cells.
Purpose of the Study:
- To investigate the proapoptotic mechanism and therapeutic implications of the BaxΔ2 isoform.
- To analyze isogenic colorectal cancer cell lines with varying Bax microsatellite statuses.
Main Methods:
- Isolation and analysis of isogenic colorectal cancer subcell lines.
- Assessment of BaxΔ2 transcript and protein levels.
- Evaluation of chemotherapeutic sensitivity in BaxΔ2-positive versus BaxΔ2-negative cells.
- Investigation of the apoptotic pathway activated by BaxΔ2.
Main Results:
- Colon cancer cells with Bax microsatellite G7/G7 alleles produce detectable BaxΔ2.
- BaxΔ2-positive cells exhibit selective sensitivity to certain chemotherapeutics.
- BaxΔ2 activates caspase-8, which then triggers caspase-3 and apoptosis, bypassing the mitochondrial pathway.
Conclusions:
- The BaxΔ2 isoform represents a distinct apoptotic pathway.
- Expression of BaxΔ2 may offer therapeutic advantages for Bax-negative colorectal tumors.
- "Bax-negative" colorectal tumors expressing BaxΔ2 are sensitive to selective chemotherapeutics.