The course of etoposide-induced apoptosis in Jurkat cells lacking p53 and Bax

Area of Science:

• Cell Biology
• Molecular Biology
• Biochemistry

Background:

• Jurkat T-lymphocytes, lacking p53 and Bax but expressing p73 and Bid, are susceptible to etoposide-induced cell death.
• Etoposide (ETO) is a chemotherapeutic agent known to induce DNA damage.

Purpose of the Study:

• To elucidate the molecular mechanisms by which etoposide induces cell death in Jurkat T-lymphocytes.
• To investigate the roles of p73, Bid, and mitochondrial pathways in etoposide-mediated apoptosis.

Main Methods:

• Utilized Jurkat T-lymphocytes treated with etoposide.
• Assessed protein phosphorylation (c-abl, p73) and translocation (Bid) using Western blotting and subcellular fractionation.
• Investigated mitochondrial permeability transition (MPT) using electron microscopy and cyclosporin A inhibition.
• Evaluated cytochrome c release and cell viability.
• Employed overexpression of Bcl-2 and inhibition of caspases (ZVAD-FMK) to dissect the apoptotic pathway.

Main Results:

• Etoposide treatment led to c-abl phosphorylation and increased p-p73 levels.
• Full-length Bid translocated to mitochondria, inducing MPT and cytochrome c release, inhibited by cyclosporin A.
• Bcl-2 overexpression blocked Bid translocation, cytochrome c release, and cell death.
• Pan-caspase inhibition prevented cell killing but not initial cytochrome c release.
• tBid accumulated later, with associated Bid degradation.

Conclusions:

• A novel sequence links DNA damage to Bid translocation via c-abl and p73 activation.
• Bid translocation initiates MPT, leading to cytochrome c release, caspase activation, and subsequent cell death.
• This pathway highlights a critical role for Bid and mitochondrial events in etoposide-induced apoptosis in these cells.