Conclusions
These findings demonstrate the oncogenic role of KLK6 in the mutant Apc-mediated intestinal tumorigenesis and suggest the utility of KLK6 for early diagnosis of colorectal tumors.
Results
The presence of KLK6 protein in the adenomatous areas was confirmed by immunohistochemistry and optical coherence tomography/laser-induced fluorescence (OCT/LIF) imaging. To assess the contribution of the KLK6 expression on the Apc-mutant intestinal and colon tumorigenesis, we engineered a mouse with floxed alleles of the Klk6 gene (Klk6lox/lox) and crossed it with a mouse expressing the truncated APC protein under control of the intestinal tract-specific human CDX2P9.5-NLS Cre transgene (CPC;Apcfl/fl;Klk6+/+). We found that CPC;Apcfl/fl mice with disrupted Klk6 gene expression (CPC;Apcfl/fl;Klk6fl/fl) had a significantly smaller average size of the small intestinal and colon crypts (p < 0.001 and p = 0.04, respectively) and developed a significantly fewer adenomas (p = 0.01). Moreover, a decrease in high-grade adenomas (p = 0.03) and adenomas with a diameter above 2 mm (p < 0.0001) was noted in CPC;Apcfl/fl;Klk6fl/fl mice. Further molecular analysis showed that Klk6 gene inactivation in the small intestine and colon tissues of CPC;Apcfl/fl;Klk6fl/fl mice resulted in a significant suppression of transforming growth factor β2 (TGF-β2) protein (p ≤ 0.02) and mitogen-activated protein kinase (MAPK) phosphorylation (p ≤ 0.01). Conclusions: These findings demonstrate the oncogenic role of KLK6 in the mutant Apc-mediated intestinal tumorigenesis and suggest the utility of KLK6 for early diagnosis of colorectal tumors.