Role of MYO1C in Golgi apparatus morphology and function

CAPMANY A; GOUD B; SCHAUER K

Carry-le-Rouet

Congreso; Club Exocytose-Endocytose 2015; 2015

Sociedad de Neurociencias y Sociedad de Biologia Celular de Francia

In their efforts to maintain intracellular vesicular transport and the position of organelles, cells use molecular motors, including myosins that interact or move on actin filaments. To date, 35 classes of myosin motor proteins have been described in mammalian cells. To determine which myosins participate in the positioning and morphology of the Golgi apparatus we performed a screening against 37 mammalian myosins. We took advantage of the ?micropatterning technique?, which brings cells to adopt a highly reproducible shape, and probabilistic density mapping, which quantifies spatial organization of a particular compartment. Our studies revealed that the knockdown of MYO1C causes Golgi apparatus fragmentation and changes the positioning of this organelle within the cell. MYO1C is a single-headed class I myosin that is enriched in dynamic regions of the plasma membrane (PM) distinguished by the presence of lamellipodia, filopodia, and membrane ruffles. This myosin has been previously reported to participate in exocytosis, recycling and delivery of several raft-associated cargoes such as GLUT4, AQP2 and VEGFR to the cell surface. However, its specific functions and partners remain to be elucidated and it is not known how this myosin affects the homeostasis of different organelles, particularly the Golgi apparatus. Follow up live cell experiments confirmed that MYO1C-depletion affects post-Golgi transport, reflected by a slower movement of Rab6-positive secretory vesicles. Additionally, we found that MYO1C interacts with the Golgi-specific Brefeldin A-resistance factor 1 (GBF1) by mass spectrometry and co-immune precipitation. GBF1 is a guanine-nucleotide-exchange factor (GEF) of Arf1 and regulates the ER-Golgi interface. The activation of Arf1 by GBF1 promotes the recruitment of COP-I involved in the retrograde transport of proteins from the Golgi to the ER. We observed that MYO1C colocalizes with a pool of GBF1 that is found at the PM, and interestingly, the presence of this PM pool of GBF1 is lost upon depletion of MYO1C. We are currently testing whether the absence of MYO1C at the PM induces an increased level of GBF1 at the Golgi, modifying Golgi transport homeostasis, including the secretory pathway, and disrupting Golgi morphology.