Recurrent MLK4 Loss-of-Function Mutations Suppress JNK Signaling to Promote Colon Tumorigenesis

Area of Science:

• Molecular biology
• Cancer research
• Signal transduction

Background:

• Mixed-lineage kinase 4 (MLK4) is a kinase regulating JNK, p38, and ERK pathways.
• MLK4 mutations are frequent in colorectal cancer, but their role is unclear.

Purpose of the Study:

• To investigate the functional impact of MLK4 mutations in colon cancer.
• To determine if MLK4 is required for maintaining cancer phenotypes.

Main Methods:

• Biochemical analysis of MLK4 mutations, including structural elucidation of its catalytic domain.
• Reconstitution of MLK4 signaling in colon cancer cells with inactivating mutations.
• Assessment of cell viability, proliferation, colony formation, and tumor growth in vivo.
• Analysis of downstream JNK pathway targets.

Main Results:

• Most MLK4 mutations are loss-of-function and can have dominant-negative effects.
• Restoring MLK4 activity reduced colon cancer cell viability, proliferation, and tumor growth.
• Restored MLK4 function selectively activated the JNK pathway and its targets (cJUN, ATF3, CDKN1A, CDKN2B).

Conclusions:

• MLK4 is a novel tumor-suppressing kinase in colon cancer.
• Frequent loss-of-function MLK4 mutations contribute to colon tumorigenesis by reducing JNK signaling and promoting proliferation.