PI3Kα Translocation Mediates Nuclear PtdIns(3,4,5)P₃ Effector Signaling in Colorectal Cancer

Area of Science:

• Cell Biology
• Molecular Oncology
• Cancer Signaling

Background:

• The canonical PI3Kα signaling pathway primarily involves phosphatidylinositol-3,4,5-trisphosphate (PtdIns(3,4,5)P3) generation at the plasma membrane or endosomes.
• Colorectal cancer (CRC) progression is linked to dysregulated signaling pathways, but the precise localization and function of PI3Kα within cancer cells remain incompletely understood.

Purpose of the Study:

• To investigate the subcellular localization of PI3Kα in CRC cells and identify its nuclear targets.
• To elucidate the functional role of nuclear PI3Kα signaling in CRC, particularly concerning RNA metabolism.
• To correlate nuclear PI3Kα expression with clinical parameters in CRC patients.

Main Methods:

• Analysis of PI3Kα distribution in CRC cell lines, revealing both plasma membrane and nuclear localization.
• Utilizing importin β-dependent pathway for nuclear translocation.
• Employing PtdIns(3,4,5)P3 affinity capture mass spectrometry to identify nuclear PtdIns(3,4,5)P3-binding proteins (interactome).
• Performing splicing reporter assays and SC-35 foci staining to assess pre-mRNA splicing modulation.
• Examining nuclear p110α staining in patient tumor samples.

Main Results:

• CRC cell lines display diverse PI3Kα localization, including significant nuclear presence.
• Identified 867 potential nuclear PtdIns(3,4,5)P3 effector proteins, many with noncanonical PtdIns(3,4,5)P3-binding domains.
• The nuclear PtdIns(3,4,5)P3 interactome is enriched in proteins involved in RNA metabolism.
• Nuclear PI3Kα signaling, stimulated by epidermal growth factor, modulates pre-mRNA splicing.
• Nuclear p110α expression in tumors correlates with lower T stage and mucinous histology.

Conclusions:

• PI3Kα nuclear translocation is a key mechanism in CRC, establishing nuclear PtdIns(3,4,5)P3 effector signaling.
• Nuclear PI3Kα signaling plays a significant role in regulating RNA metabolism and pre-mRNA splicing in CRC.
• Nuclear PI3Kα localization serves as a potential prognostic biomarker in colorectal cancer.