Novel intestinal splice variants of RNA-binding protein CUGBP2: isoform-specific effects on mitotic catastrophe

Area of Science:

• Molecular Biology
• Cell Biology
• Genetics

Background:

• CUG triplet repeat-binding protein 2 (CUGBP2) is an RNA-binding protein involved in mRNA translation and apoptosis.
• Alternative splicing generates different CUGBP2 isoforms with potentially distinct functions.
• Understanding CUGBP2 variant function is crucial for comprehending cellular regulation and disease.

Purpose of the Study:

• To identify and characterize novel splice variants of CUGBP2.
• To investigate the differential functions of CUGBP2 variants, particularly concerning apoptosis and cell cycle regulation.
• To elucidate the role of CUGBP2 variants in intestinal epithelial cells and their response to genotoxic stress.

Main Methods:

• Identification of CUGBP2 splice variants in human intestinal cells and mouse gastrointestinal tract.
• Analysis of variant expression levels under normal and gamma-irradiated conditions.
• Assessment of mRNA translation inhibition, cellular localization, proliferation, apoptosis, and cell cycle progression assays.
• Western blot analysis to determine protein levels and phosphorylation status of key apoptosis and cell cycle regulators.

Main Results:

• Two novel CUGBP2 splice variants (variants 2 and 3) with additional N-terminal residues were identified.
• Variant 2 is predominant in normal intestine, while variant 1 is overexpressed post-irradiation; variants 2 and 3 are cytoplasmic, variant 1 is nuclear.
• Only variant 1 inhibits cyclooxygenase-2 (COX-2) mRNA translation and induces G(2)/M cell cycle arrest, apoptosis, and mitotic catastrophe.
• Variant 1 activates caspases-3 and -9, increases p53 and Bax, decreases Bcl2, and affects mitotic regulators like Chk1/2, Cdc2, and cyclin B1.

Conclusions:

• The novel CUGBP2 variants (2 and 3) possess distinct cellular localization and functional properties compared to variant 1.
• CUGBP2 variant 1 induces apoptosis during mitosis, potentially through mitotic catastrophe, a process influenced by prostaglandin E2.
• Differential expression and function of CUGBP2 variants highlight their complex roles in intestinal cell biology and response to DNA damage.