Furin sustains tumor-promoting signals in KRAS- and BRAF-mutated colorectal cancer by engaging the TGF-β1-COX-2 axis in a reciprocal regulatory network.

KRAS and BRAF mutations drive colorectal cancer (CRC) progression by sustaining aberrant signaling and promoting therapeutic resistance. Here, we identify TGF-β1-COX-2 axis as a critical regulatory pathway mediated by Furin in CRC harboring KRAS or BRAF mutation. Genetic silencing or pharmacological inhibition of Furin in KRAS-mutant (KPN) and BRAF-mutant (BPN) tumor-derived cells suppressed tumor growth, reduced angiogenesis, and enhanced CD8⁺ T cell infiltration in mouse tumor models. KRAS- and BRAF-mutant organoids with impaired Furin activity exhibited increased sensitivity to 5-FU and irinotecan, whereas only KPN organoids were sensitive to oxaliplatin. Mechanistically, Furin inhibition via shRNA or the Furin inhibitor MI1148 blocked IGF-1 receptor and TGF-β1 precursor maturation and signaling, which was associated with repressed COX-2 expression. Conversely, COX-2 overexpression elevated TGF-β1 levels, which in turn enhanced Furin expression, establishing a feed-forward loop that promoted tumor progression and angiogenesis. Moreover, Furin inhibition largely disrupted the activity of multiple kinases linked to KRAS and BRAF oncogenic signaling. In CRC patient samples, Furin expression positively correlated with KRAS, BRAF, TGF-β1, and COX-2. Collectively, these findings identify Furin as a pivotal regulator of oncogenic signaling in KRAS- and BRAF-mutant CRC, and highlight the therapeutic potential of targeting the Furin-TGF-β1-COX-2 axis.