Actin nucleation activity of Adenomatous Polyposis Coli (APC) regulates cellular organization, remodeling and migration in 3D-preclinical models

Tight coordination between the microtubule and actin cytoskeletons is essential for a wide range of processes, including directed cell migration. Molecules bridging both cytoskeletons mediate this coordination, but precise mechanisms remain unclear. The tumor suppressor protein Adenomatous Polyposis Coli (APC) is known as the ‘gatekeeper’ gene in human colorectal tumorigenesis. Mutations
or alterations in the C-terminal of APC, most of which result in truncations, have been found in >80% of colorectal cancer cases. The C-terminal ‘Basic’ domain of APC binds to both microtubules and actin. Using a separation-of-function mutant of APC (APC-m4) as a tool that abolishes its actin nucleation activity, we demonstrated that this activity promotes microtubule-induced focal adhesion turnover to facilitate directionality of cells on a culture dish. However, whether/how this actin activity contributes to gut homeostasis and/or tumorigenesis is unknown. Here we have generated stable colorectal cell lines
expressing APC-m4 in preclinical models such as spheroids which recapitulate patient response. Using live-cell imaging, we have visualized that loss of actin nucleation activity of APC alters 3D-spheroid cell size, organization/shape and remodeling motility-associated events. Our findings offer a new perspectiv
to explore the importance of APC’s cytoskeletal functions in gut epithelium architecture/maintenance, and their dysfunction leading to disease