KRAS Suppression-Induced Degradation of MYC Is Antagonized by a MEK5-ERK5 Compensatory Mechanism

Area of Science:

• Oncology
• Molecular Biology
• Cancer Signaling

Background:

• Pancreatic ductal adenocarcinoma (PDAC) often exhibits stable MYC protein, even with ERK1/2 inhibitor treatment.
• The precise signaling pathways regulating MYC stability in KRAS-mutant PDAC remain incompletely understood.

Purpose of the Study:

• To elucidate the ERK1/2-independent mechanisms governing MYC protein stability in pancreatic ductal adenocarcinoma.
• To identify novel therapeutic targets by understanding how mutant KRAS regulates MYC.

Main Methods:

• Utilized high-throughput screening for MYC protein degradation.
• Conducted kinome-wide proteomics to identify signaling networks.
• Investigated signaling pathways including PI3K-AKT-GSK3β and E3 ligase FBWX7.
• Analyzed the role of epidermal growth factor receptor (EGFR) and SRC in MYC regulation.

Main Results:

• Mutant KRAS drives MYC protein stability through both ERK1/2-dependent and -independent pathways.
• MYC degradation was found to be independent of PI3K-AKT-GSK3β signaling and the FBWX7 E3 ligase.
• An ERK1/2 inhibition-induced feedforward loop involving EGFR and SRC was identified, activating ERK5.
• ERK5 activation led to MYC phosphorylation at S62, preventing its degradation.
• Concurrent inhibition of ERK1/2 and ERK5 synergistically reduced MYC levels and suppressed PDAC growth.

Conclusions:

• A novel ERK1/2-independent mechanism maintains MYC stability in PDAC, involving an EGFR-SRC-ERK5 axis.
• Targeting both ERK1/2 and ERK5 simultaneously presents a promising therapeutic strategy for pancreatic ductal adenocarcinoma.
• Understanding these complex signaling networks is crucial for developing effective PDAC treatments.