Caspase 3 activation is controlled by a sequence located in the N-terminus of its large subunit

Area of Science:

• Molecular Biology
• Cell Biology
• Biochemistry

Background:

• Doxorubicin resistance is a significant challenge in cancer therapy.
• Apoptosis, or programmed cell death, is a critical cellular process often dysregulated in cancer.
• Multidrug resistance proteins (mrp) are transmembrane transporters involved in drug efflux.

Purpose of the Study:

• To investigate the mechanisms underlying delayed apoptosis in doxorubicin-resistant cells (HL60/ADR).
• To identify molecular defects responsible for impaired apoptotic signaling downstream of mrp.
• To elucidate the role of caspase 3 (C3) activation in doxorubicin resistance.

Main Methods:

• Cell culture of doxorubicin-resistant (HL60/ADR) and sensitive cell lines.
• In vitro biochemical assays to assess caspase activation.
• Gene sequencing to identify mutations in caspase 3.
• Transfection studies using modified caspase 3 constructs.

Main Results:

• Doxorubicin-resistant HL60/ADR cells exhibit delayed apoptosis induction and completion.
• These cells show impaired activation of procaspase 3 (pC3), the key executioner caspase.
• Point mutations were identified in the N-terminal region (amino acids 31-37) of caspase 3 in HL60/ADR cells, creating a C3 N-terminal modified (C3-NTM) form.
• The C3-NTM form demonstrated partial activity when expressed in cells with low endogenous pC3.
• Deletion of amino acids 31-37 in wild-type C3 resulted in a similar phenotype.

Conclusions:

• A specific sequence (amino acids 31-37) in the N-terminal region of caspase 3 is crucial for its proper activation during apoptosis.
• Mutations in this sequence contribute to doxorubicin resistance by hindering the apoptotic program.
• The findings provide insights into novel mechanisms of chemoresistance and potential therapeutic targets.