O-GlcNAcylation of GLI transcription factors in hyperglycemic conditions augments Hedgehog activity

Area of Science:

• Biochemistry
• Molecular Biology
• Cancer Biology

Background:

• Protein O-linked β-N-acetylglucosamine (O-GlcNAc) modification influences cellular processes.
• Elevated glucose is linked to cancer progression and drug resistance.
• The Hedgehog signaling pathway plays a role in cancer development.

Purpose of the Study:

• To investigate the role of O-GlcNAcylation in regulating the Hedgehog/GLI pathway under elevated glucose conditions.
• To determine the impact of O-GlcNAc modification on cancer drug resistance proteins.
• To explore the interplay between glucose metabolism and the Hedgehog pathway in cancer.

Main Methods:

• Analysis of drug resistance protein expression (ABCB1, ABCG2, ERCC1, XRCC1) under elevated glucose.
• Assessment of O-GlcNAcylation status of GLI1 and GLI2 transcription factors.
• Inhibition and activation of O-GlcNAcase and O-GlcNAc transferase.
• Investigation of pyruvate kinase M2 (PKM2) influence on GLI activity.
• Gene silencing of PKM2.

Main Results:

• Elevated glucose increased expression of drug resistance proteins regulated by the Hedgehog pathway.
• GLI1 and GLI2 transcription factors undergo O-GlcNAcylation, enhancing their activity under high glucose.
• Inhibition of O-GlcNAcase boosted GLI activity, while O-GlcNAc transferase inhibition decreased it.
• PKM2, in its less active state under high glucose, directly enhanced GLI activity.
• PKM2 knockdown significantly reduced GLI activity and drug resistance protein expression.

Conclusions:

• Elevated glucose promotes chemoresistance by upregulating the Hedgehog/GLI pathway via O-GlcNAcylation.
• PKM2 plays a crucial role in mediating the effect of glucose on GLI activity.
• Targeting O-GlcNAcylation of GLI transcription factors presents a potential therapeutic strategy for breast cancer and drug resistance.