Colorectal cancer (CRC) is the second leading cause of malignant-associated death in the USA with inflammation as a key driving force for its development, growth, and progression. p38?, a member of p38 mitogen-activated protein kinases (p38 MAPK?? ?? ?, and ?), is oncogenic, pro-inflammatory, and overexpressed in clinical CRC but the role of epithelial p38? in CRC tumorigenesis has not been tested. ?- catenin, a critical cofactor of Wnt transcription, is aberrantly activated in 90% of CRC. And yet, ?-catenin is undruggable and there is thus an urgent need to identify druggable ?-catenin activators for therapeutic intervention. Here we propose that p38? MAPK in intestinal epithelial cells (IEC) drives CRC tumorigenesis by stimulating oncogenic ?-catenin phosphorylation. This hypothesis is based on our preliminary studies showing that: 1) inflammation coordinately stimulates p38? and ?-catenin phosphorylation in CRC cells; 2) p38? directly phosphorylates ?-catenin at S605, which increases ?-catenin stability, the ?-catenin-TCF4 interaction, Wnt transcription and CRC growth; 3) inflammation activates p38?, but not p38?, in intestinal tissues of mice, and IEC-specific p38? knockout (KO) reduces pro-inflammatory cytokine expression and attenuates colitis severity; 4) IEC p38? KO inhibits colon tumorigenesis and p-?-catenin/S605/Wnt signaling in the azoxymethane (AOM)/dextran sodium sulfate (DSS) mouse model of colitis-associated cancer (CAC); 5) the p38? pharmacological inhibitor pirfenidone (PFD) suppresses ?-catenin/cytokine expression and colon tumorigenesis in wild-type (WT) mice, but not in p38? KO mice, and further collaborates with the ?-catenin-TCF4 interaction antagonist LF3 and chemotherapeutic drug 5FU to inhibit CRC growth, and 6) p38? is upregulated in clinical CAC specimens and in intestinal tissues of Apcmin and interleukin-10 knockout (IL-10-/-) mice. These results together indicate that IEC p38? is required for tumorigenesis of both CAC and sporadic CRC by stimulating oncogenic ?-catenin phosphorylation. Using genetic and pharmacological approaches, we will test this hypothesis by determining (1) if p38?- induced ?-catenin/S605 phosphorylation stimulates ?-catenin nuclear translocation, ?-catenin-TCF4 interaction, Wnt transcription and CRC growth; (2) if IEC-specific p38? KO blocks tumorigenesis in IL- 10-/- and Apcmin mice and if p38? is essential for the ?-catenin/TCF4/Wnt signaling to promote malignant progression in CRC pathogenesis; and (3) if the p38? pharmacological inhibitor pirfenidone (PFD) blocks CRC tumorigenesis and increases the growth-inhibitory activity of LF3 and 5FU by disrupting the p38?/?-catenin/TCF4/Wnt pathway. Upon completion, these studies will demonstrate if epithelial p38? promotes CRC tumorigenesis by stimulating oncogenic ?-catenin/S605 phosphorylation and Wnt transcription. Demonstrating the effectiveness of PFD in inhibiting Wnt signaling and CRC tumorigenesis by targeting intestinal epithelial p38? will reveal that drugging p38? has a great potential for colon cancer targeted therapy.
The proposed research is relevant to public health as inflammation has long been considered to play a causative role in colon cancer development and druggable targets involved, however, remain largely unknown. This application will test the hypothesis that p38? MAPK activation converts inflammation responses to colon tumorigenesis. Thus, by demonstrating the essential role of p38? in intestinal tumorigenesis in mouse models and the therapeutic activity of its pharmacological inhibitor pirfenidone, the proposed research is highly relevant to the NIH?s mission of extending healthy life and reducing the burdens of illness.
