ENKD1 is a centrosomal and ciliary microtubule-associated protein important for primary cilium assembly and Hedgehog signaling

Abstract

Centrioles and cilia are conserved, microtubule-based structures critical for cell function and development. Their structural and functional defects cause cancer and developmental disorders. How microtubules are organized into ordered structures by microtubule-associated proteins (MAPs) and tubulin modifications is best understood during mitosis but is largely unexplored for the centrioles and the ciliary axoneme, which are composed of remarkably stable microtubules that maintain their length at steady state. In particular, we know little about the identity of the centriolar and ciliary MAPs and how they work together during the assembly and maintenance of the cilium and centriole. Here, we identified Enkurin domain containing 1 (ENKD1) as a component of the centriole wall and the axoneme in mammalian cells, and showed that it has extensive proximity interactions with these compartments and MAPs. Using in vitro and cellular assays, we found that ENKD1 is a new MAP that promotes microtubule polymerization and regulates microtubule organization and stability. Consistently, overexpression of ENKD1 increased tubulin polymerization and acetylation and disrupted microtubule organization. Cells depleted for ENKD1 were defective in ciliary length and content regulation and failed to respond to Hedgehog pathway activation. Together, our results establish ENKD1 as a new centriolar and ciliary MAP that regulate primary cilium structure and function, and advances our understanding of the functional and regulatory relationship between MAPs and the primary cilium.