Cytoplasmic p21 Mediates 5-Fluorouracil Resistance by Inhibiting Pro-Apoptotic Chk2

Area of Science:

• Oncology
• Molecular Biology
• Cancer Research

Background:

• The oncogenic role of cytoplasmic p21 in cancer aggressiveness and treatment failure is recognized, but its precise molecular mechanisms are not fully understood.
• Understanding how cancer cells develop resistance to chemotherapy is crucial for improving patient outcomes.

Purpose of the Study:

• To elucidate the molecular mechanisms by which cytoplasmic p21 contributes to 5-Fluorouracil (5FU) resistance in colorectal cancer.
• To identify p21 as a potential prognostic marker and therapeutic target for 5FU-based chemotherapy.

Main Methods:

• Investigated cytoplasmic p21 levels in 5FU-resistant colorectal cancer cells (in vitro and in vivo CAM model).
• Utilized kinase array analysis to identify p-Chk2 as a key target of cytoplasmic p21.
• Employed co-immunoprecipitation, immunofluorescence, and proximity ligation assays to study p21/p-Chk2 complex formation.
• Applied in silico computer modeling to predict the mechanism of nuclear export.

Main Results:

• Cytoplasmic p21 levels were elevated in 5FU-resistant colorectal cancer cells.
• Cytoplasmic p21 directly interacts with and sequesters p-Chk2, preventing its nuclear localization and pro-apoptotic functions.
• p21^T145D transfection reduced p-Chk2-mediated activation of E2F1 and apoptosis.
• In silico modeling suggested that p21 binding inhibits p-Chk2 nuclear import.

Conclusions:

• Cytoplasmic p21 confers 5FU resistance by exporting p-Chk2 from the nucleus, thereby protecting tumor cells from apoptosis.
• This study reveals a novel mechanism for oncogenic p21 in regulating chemotherapy resistance.
• Cytoplasmic p21 may serve as a valuable prognostic marker and therapeutic target in colorectal cancer.