Cell migration in higher organisms is essential for multiple physiological and pathophysiological processes, including embryonic development and immune responses. Alteration of cell motility in cancer cells is one of the most dangerous features of malignant tumors, as it builds up their invasive and metastatic potential. Polarized organization of microtubule arrays is essential for polarized cell motility. However, the principles of this regulation are not yet understood. It is generally assumed that microtubules in vertebrate cells are formed by the centrosome. We have recently demonstrated that a large number of microtubules originate from the Golgi apparatus (Efimov et al, 2007). We have identified two molecular players critical for this novel phenomenon: microtubule regulatory proteins CLASPs are required for the formation of Golgi-derived microtubules, and golgin GCC185 serves as an anchor for CLASPs at the trans-Golgi network (TGN) at the Golgi periphery. In sharp contrast to symmetric microtubule arrays organized by the centrosome, microtubules nucleated at the peripheral Golgi compartment are preferentially oriented toward the leading edge in motile cells. Preliminary data suggest that the migratory potential of cells lacking Golgi-originated microtubules is compromised. Within this proposal, we will test the hypothesis that asymmetric microtubule nucleation at the Golgi is critical for motile cell polarization. We will test whether Golgi-originated microtubules exert their effect on cell polarity via regulation of the actin cytoskeleton or directional post-Golgi transport to the cell front, or both. We will also address molecular mechanisms that regulate microtubule formation at the TGN.
Our specific aims are: 1. Determine the role of Golgi-derived microtubules in the cytoskeletal polarity of motile cells. 2. Determine the role of Golgi-derived microtubules in polarized Golgi trafficking in motile cells. 3. Determine if dynamic CLASP anchoring underlies the microtubule-organizing potential of the Golgi. PUBLIC HEALTH REVELANCE: Knowledge of the molecular events that underlie cell motility is critical for understanding major health-related processes, including embryonic morphogenesis, wound healing, the immune response and cancer invasiveness. As major anticancer therapies include microtubule-specific drugs, knowledge their potential targets is especially valuable. In this proposal, we will carry out research that will determine the role of a novel Golgi-derived asymmetric microtubule array in cell motility.
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