Molecular Mechanisms Of Microtubule Dynamics Regulated By DDA3and MCAK In Cell Migration And Division

Microtubules (MTs) are dynamic in eukaryocyte, growing and shortening at their ends via α/β-tubulin dimer addition and loss. The dynamics is very important for maintaining the physical properties and functional plasticity on restructuring of the cytoskeleton, delivery of cellular cargos, and regulation of alignment and segregation of sister chromatids in mitosis. MT dynamics is regulated by a group of microtubule-associated proteins, including MT plus-end tracking proteins (+TIPs), which specially localize to the growing MT plus ends. However, the molecular mechanisms underlying regulation of MT dynamics by+TIPs remain elusive. Here, we demonstrate two representative+TIPs orchestrate MT dynamic instability in cell migration and division respectively. One of them is DDA3(differential display activated by p53), a novel MT plus-end tracking protein we identified. The other one is a known MT plus-end tracking protein, MCAK (mitotic centromere-associated kinesin), which is also famous as a microtubule depolymerase. They modulate cell migration and division respectively via regulating MT dynamics.MT dynamics is regulated by a complex network of many MT plus-end tracking proteins. Identification of new+TIPs is one of the most important directions in study of MT dynamic instability. Taking the advantage of bioinformatics analysis and biochemical experiments validation, we identified DDA3as a novel+TIP. Here, the results show that DDA3directly binds to EB1(end-binding protein1), a core protein in the+TIP network, via its SxIP/SxLP motifs within the C-terminal Pro/Ser-rich region. Thus, the plus-end loading and tracking of DDA3depend on the interaction of its SxIP/SxLP motifs and EB1. As a+TIP, DDA3is required for MT plus ends stabilization at cell cortex. Since selective stabilization of MTs is essential for cell migration, my results suggested that EB1-mediated loading of DDA3modulates MT dynamics and thereby facilitates directional cell migration.In addition to their critical function in interphase cells,+TIPs are also important in mitotic cells, which regulate spindle microtubule dynamics to orchestrate the dynamic interactions between the kinetochore and spindle microtubules and ensure faithful chromosome segregation. Among the+TIPs have already been identified, the regulatory mechanisms of some+TIPs are still unclear, including the microtubule depolymerase MCAK. MCAK is a key regulator for an accurate kinetochore-microtubule attachment in mitosis. Thus, it is much important to study the regulatory mechanism underlying precise MCAK depolymerase activity control during mitosis. Here, the results reveal that PLKl (polo-like kinase1) phosphorylates MCAK at Ser715, which promotes its MT depolymerase activity. The proper phosphorylation of MCAK by PLK1is essential for faithful chromosome segregation in mitosis. Importantly, blocking of the phosphorylation of MCAK prevents correction of erroneous kinetochore microtubule attachments, resulting in abnormal anaphase with chromosome bridges. Thus, I reason that PLKl orchestrates MCAK activity at the kinetochore, which is essential for timely correction of aberrant kinetochore attachment to ensure accurate chromosome segregation during mitosis.Taken together, we describe the cellular functions and regulatory mechanisms of two representative MT plus-end tracking proteins—DDA3and MCAK. The deep investigation of molecular mechanism of faithful chromosome segregation and directional cell migration is helpful to have a better understanding of developmental morphogenesis, tumor metastasis, pathogenesis of genomic instability and so on. These findings will make great contribution to the promotion of the human health. Here, the functional studies of DDA3and MCAK in cell migration and division provide a unifying view for understanding their potential roles in related human diseases.