Fibrinogen activates focal adhesion kinase (FAK) promoting colorectal adenocarcinoma growth

Background: We previously showed that fibrinogen is a major determinant of the growth of a murine model of colorectal cancer (CRC).

Objective: Our aim was to define the mechanisms coupling fibrin(ogen) to CRC growth.

Results: CRC tumors transplanted into the dorsal subcutis of Fib^- mice were less proliferative and demonstrated increased senescence relative to those grown in Fib⁺ mice. RNA-seq analyses of Fib⁺ and Fib^- tumors revealed 213 differentially regulated genes. One gene highly upregulated in tumors from Fib^- mice was stratifin, encoding 14-3-3σ, a master regulator of proliferation/senescence. In a separate cohort, we observed significantly increased protein levels of 14-3-3σ and its upstream and downstream targets (i.e., p53 and p21) in tumors from Fib^- mice. In vitro analyses demonstrated increased tumor cell proliferation in a fibrin printed three-dimensional environment compared with controls, suggesting that fibrin(ogen) in the tumor microenvironment promotes tumor growth in this context via a tumor cell intrinsic mechanism. In vivo analyses showed diminished activation of focal adhesion kinase (FAK), a key negative regulator of p53, in Fib^- tumors. Furthermore, nuclear magnetic resonance-based metabolomics demonstrated significantly reduced metabolic activity in tumors from Fib^- relative to Fib⁺ mice. Together, these findings suggest that fibrin(ogen)-mediated engagement of colon cancer cells activates FAK, which inhibits p53 and its downstream targets including 14-3-3σ and p21, thereby promoting cellular proliferation and preventing senescence.

Conclusions: These studies suggest that fibrin(ogen) is an important component of the colon cancer microenvironment and may be exploited as a potential therapeutic target.