Abstract
EB1 was discovered 25 years ago as a binding partner of the tumor suppressor adenomatous polyposis coli (APC) [1]; however, the significance of EB1-APC interactions has remained poorly understood. EB1 functions at the center of a network of microtubule end-tracking proteins (+TIPs) [2–5], and APC binding to EB1 promotes EB1 association with microtubule ends and microtubule stabilization [6, 7]. Whether EB1 interactions govern functions of APC beyond microtubule regulation has not been explored. The C-terminal basic domain of APC (APC-B) directly nucleates actin assembly, and this activity is required in vivo for directed cell migration and for maintaining normal levels of F-actin [8–10]. Here, we show that EB1 binds APC-B and inhibits its actin nucleation function by blocking actin monomer recruitment. Consistent with these biochemical observations, knocking down EB1 increases F-actin levels in cells, and this can be rescued by disrupting APC-mediated actin nucleation. Conversely, overexpressing EB1 decreases F-actin levels and impairs directed cell migration without altering microtubule organization and independent of its direct binding interactions with microtubules. Overall, our results define a new function for EB1 in negatively regulating APC-mediated actin assembly. Combining these findings with other recent studies showing that APC interactions regulate EB1-dependent effects on microtubule dynamics [7], we propose that EB1-APC interactions govern bidirectional cytoskeletal crosstalk by coordinating microtubule and actin dynamics.
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•EB1 inhibits APC-mediated actin assembly in vitro by blocking G-actin recruitment•EB1 negatively regulates APC-dependent actin assembly in cells•Altering EB1 levels results in defects in cell migration and focal adhesions•EB1 regulates cellular actin independent of its direct binding to microtubules
Juanes et al. show that EB1, a key regulator of microtubule dynamics, directly inhibits APC-mediated actin assembly in vitro and governs APC-dependent cellular F-actin levels and directed cell migration. These results suggest that EB1 promotes bidirectional cytoskeletal crosstalk by coordinating microtubule and actin dynamics.