GLI3-dependent repression of DR4 mediates hedgehog antagonism of TRAIL-induced apoptosis

Area of Science:

• Oncology
• Molecular Biology
• Cancer Signaling Pathways

Background:

• Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) triggers apoptosis in cancer cells via death receptors DR4 and DR5.
• Many malignant cells exhibit resistance to TRAIL-induced apoptosis through incompletely understood mechanisms.

Purpose of the Study:

• To investigate the role of the Hedgehog (Hh)-GLI pathway in TRAIL resistance using cholangiocarcinoma as a model.
• To elucidate the molecular mechanisms by which the Hh-GLI pathway regulates TRAIL sensitivity.

Main Methods:

• Pharmacological and genetic blockade of the Hh pathway.
• Analysis of DR4 and other death effector protein expression.
• Luciferase assays, chromatin immunoprecipitation, and expression assays to study promoter activity.
• Small interfering RNA (siRNA)-mediated knockdown of GLI transcription factors (GLI1, GLI2, GLI3).

Main Results:

• Hedgehog (Hh) pathway blockade sensitizes TRAIL-resistant cholangiocarcinoma cells to TRAIL.
• Restored TRAIL sensitivity is associated with increased DR4 expression, while other death effector proteins remain unchanged.
• The transcription factor GLI3 binds to the DR4 promoter, and Hh signaling requires GLI3 repression activity to downregulate DR4.
• Knockdown of GLI3, but not GLI1 or GLI2, restores DR4 expression and TRAIL sensitivity.

Conclusions:

• The oncogenic Hh-GLI pathway, specifically through GLI3, confers TRAIL resistance by suppressing DR4 expression in cancer cells.
• These findings reveal a novel regulatory mechanism for TRAIL signaling and suggest therapeutic strategies targeting the Hh-GLI pathway for TRAIL-resistant cancers.