FLIP overexpression inhibits death receptor-induced apoptosis in malignant mesothelial cells

Area of Science:

• Oncology
• Cell Biology
• Molecular Biology

Background:

• Tumors develop resistance to receptor-induced cell death, a critical process for eliminating abnormal cells.
• Mesothelial cells, including malignant (MM) and normal (NM) counterparts, express death receptors like Fas and TRAIL receptors (DR4/DR5).

Purpose of the Study:

• To investigate the mechanisms of resistance to death receptor-mediated apoptosis in malignant mesothelial cells.
• To determine the role of caspase-8 activation and FLIP expression in MM cell apoptosis resistance.

Main Methods:

• Assessed expression of Fas, DR4, and DR5 receptors in MM and NM cells.
• Evaluated caspase-8 (FLICE) activation in response to death receptor and non-receptor stimuli.
• Quantified FLICE-Inhibitory Protein (FLIP) expression in MM and NM cells.
• Utilized FLIP siRNA to knockdown FLIP expression in MM cell lines.
• Administered caspase-8 inhibitor (z-IETD-fmk) to assess its effect on apoptosis.

Main Results:

• Malignant mesothelial cells exhibit resistance to Fas and TRAIL-induced apoptosis, unlike normal mesothelial cells, despite comparable receptor expression.
• Caspase-8 (FLICE) activation is impaired upon death receptor triggering in MM cells but functional with non-receptor stimuli.
• Constitutive and elevated expression of FLICE-Inhibitory Protein (FLIP) was observed in MM cell lines and primary MM cells.
• Knockdown of FLIP in MM cells restored sensitivity to Fas and DR4/DR5-mediated apoptosis.

Conclusions:

• Malignant mesothelial cells acquire intrinsic resistance to death receptor-induced apoptosis.
• Upregulation of the anti-apoptotic protein c-FLIP is a key mechanism driving this resistance in MM cells.