Symplekin Specifies Mitotic Fidelity by Supporting Microtubule Dynamics

Abstract

Using a pangenomic loss-of-function screening strategy, we have previously identified 76 potent modulators of paclitaxel responsiveness in non-small-cell lung cancer. The top hit isolated from this screen, symplekin, is a well-established component of the mRNA polyadenylation machinery. Here, we performed a high-resolution phenotypic analysis to reveal the mechanistic underpinnings by which symplekin depletion collaborates with paclitaxel. We find that symplekin supports faithful mitosis by contributing to the formation of a bipolar spindle apparatus. Depletion of symplekin attenuates microtubule polymerization activity as well as expression of the critical microtubule polymerization protein CKAP5 (TOGp). Depletion of additional members of the polyadenylation complex induces similar phenotypes, suggesting that polyadenylation machinery is intimately coupled to microtubule function and thus mitotic spindle formation. Importantly, tumor cells depleted of symplekin display reduced fecundity, but the mitotic defects that we observe are not evident in immortalized cells. These results demonstrate a critical connection between the polyadenylation machinery and mitosis and suggest that tumor cells have an enhanced dependency on these components for spindle assembly.

Supplemental material for this article may be found at http://mcb.asm.org/.

We thank Charlene Ross for support with animal studies and Mark Cronan for assistance with live-cell imaging.

This work was supported by the PHS grant CA128926, from the NCI to A.W.W., as well as the North Carolina University Cancer Research Fund. K.M.C. was supported by the NCI training grant CA071341-14 and general medicine training grant GM008719.