Tumor suppressor NF2/merlin is a microtubule stabilizer

Cancer-associated mutations in oncogene products and tumor suppressors contributing to tumor progression manifest themselves, at least in part, by deregulating microtubule-dependent cellular processes that play important roles in many cell biological pathways, including intracellular transport, cell architecture, and primary cilium and mitotic spindle organization. An essential characteristic of microtubules in the performance of these varied cell processes is their ability to continuously remodel, a phenomenon known as dynamic instability. It is therefore conceivable that part of the normal function of certain cancer-causing genes is to regulate microtubule dynamic instability. Here, we report the results of a high-resolution live-cell image-based RNA interference screen targeting a collection of 70 human tumor suppressor genes to uncover cancer genes affecting microtubule dynamic instability. Extraction and computational analysis of microtubule dynamics from EB3-GFP time-lapse image sequences identified the products of the tumor suppressor genes NF1 and NF2 as potent microtubule-stabilizing proteins. Further in-depth characterization of NF2 revealed that it binds to and stabilizes microtubules through attenuation of tubulin turnover by lowering both rates of microtubule polymerization and depolymerization as well as by reducing the frequency of microtubule catastrophes. The latter function appears to be mediated, in part, by inhibition of hydrolysis of tubulin-bound GTP on the growing microtubule plus end.