Mutations in CIC and IDH1 cooperatively regulate 2-hydroxyglutarate levels and cell clonogenicity.

Area of Science:

• Oncology
• Molecular Biology
• Genetics

Background:

• Oligodendrogliomas (ODGs) frequently feature 1p/19q chromosome co-deletions and isocitrate dehydrogenase (IDH) mutations.
• Somatic mutations in the Capicua Transcriptional Repressor (CIC) gene are observed in approximately 70% of ODGs with 1p/19q co-deletions.

Purpose of the Study:

• To investigate the functional roles of wild-type and mutant Capicua Transcriptional Repressor (CIC) proteins.
• To establish and utilize cell models for studying oligodendroglioma pathogenesis, particularly in the context of 1p/19q co-deleted and IDH-mutated tumors.

Main Methods:

• Creation of HEK293 and HOG stable cell lines with ectopic co-expression of CIC and IDH1.
• Assessment of cellular clonogenicity, 2-Hydroxyglutarate (2HG) levels, and phosphorylated ATP-citrate Lyase (ACLY) activity.
• Analysis of CIC protein localization (nuclear CIC-L vs. cytoplasmic CIC-S).

Main Results:

• Co-expression of mutant IDH1-R132H with mutant CIC-S (R201W or R1515H) resulted in additively reduced cellular clonogenicity compared to non-mutant lines.
• Mutant CIC-R1515H expression elevated cellular 2-Hydroxyglutarate (2HG) levels in an IDH1-R132H background.
• Reduced levels of phosphorylated ATP-citrate Lyase (ACLY) were observed in cells expressing mutant CIC-S proteins, suggesting a role in cytosolic citrate metabolism and reduced clonogenicity.

Conclusions:

• Mutant CIC and IDH1 exhibit cooperative effects that reduce oligodendroglioma cell clonogenicity.
• Altered cytosolic citrate metabolism, indicated by reduced ACLY phosphorylation, may contribute to the reduced clonogenicity observed in CIC-mutant cells.
• Findings are supported by similar reductions in ACLY/phospho-ACLY in patient-derived CIC-mutant, 1p/19q co-deleted oligodendroglioma samples.