Network analysis of differential Ras isoform mutation effects on intestinal epithelial responses to TNF-α

Area of Science:

• Cellular biology
• Systems biology
• Molecular signaling

Background:

• Tumor necrosis factor alpha (TNF-α) is a key inflammatory cytokine.
• Mitogen-activated protein kinase (MAPK) pathways, particularly the extracellular signal-regulated kinase (Erk) pathway, integrate environmental cues to modulate TNF-α responses.
• Ras isoforms (K-Ras, N-Ras) play critical roles in cellular signaling, but their specific contributions to TNF-α-induced phenotypes in vivo are not fully understood.

Purpose of the Study:

• To investigate how variations in Erk pathway flux, modulated by different Ras mutations, affect TNF-α-elicited phenotypes in the mouse intestinal epithelium.
• To elucidate the distinct signaling network states and downstream effects of K-Ras and N-Ras in response to TNF-α exposure.

Main Methods:

• Exposure of mice with K-Ras activation, N-Ras activation, or N-Ras ablation to TNF-α.
• Observation of phenotypic and signaling changes in the intestinal epithelium.
• Application of a systems biology approach and constrained Fuzzy Logic (cFL) modeling to analyze signaling network states.

Main Results:

• Hyperactivation of Mek1 (an Erk kinase) was observed in both K-Ras-activated and N-Ras-null mice, but led to different phenotypes.
• N-Ras null intestine showed hypersensitivity to TNF-α-induced cell death, while K-Ras mutant intestine did not.
• Systems biology modeling revealed distinct signaling contexts: N-Ras ablation predicted a pro-death state, while K-Ras activation did not.
• cFL modeling demonstrated that N-Ras and K-Ras have different downstream signaling distributions and dynamics, with N-Ras effects being more transient and PI3K-Akt-biased, and K-Ras effects being more sustained and broadly activating.

Conclusions:

• Ras isoform-specific signaling contexts are critical determinants of TNF-α-induced cellular phenotypes.
• N-Ras and K-Ras exhibit distinct downstream signaling kinetics and pathway activation profiles.
• Modeling approaches are essential for understanding complex in vivo biological mechanisms, such as the differential roles of Ras isoforms in intestinal epithelial responses.