ИСТИНА

In eukaryotic cells secretory proteins exit endoplasmic reticulum (ER) in special cites called ERES (ER exit sites). ERESes are covered with COPII coat consisting of inner layer formed by Sec23-Sec24 heterodimer and outer layer by Sec13-Sec31 proteins. Post-ER transport containers represent either vesicles or membrane tubes and they move to Golgi area. The mechanism of their movement remains rather illusive. It is assumed that ERES-derived containers are driven by dynein to the Gogi. ERES itself also moves chaotically and sporadically, and such a movement was confirmed in our experiments with live cell imaging. We have found that ERESes undergo chaotic low-amplitude movements in cells. They are located along the microtubules, and the destruction of microtubules or the inhibition of dynein leads to a further decrease in their mobility. Using VSVG release assay we have shown that ERES long range movements are frequently compelled with transport container formation and departure. Sar1a[H79G] GTPase expression induced COPII coat stabilization, and ERESes formed a cluster. Formation of the cluster depends on microtubules and on dynein activity. After microtubule disruption or dynein inhibition cluster dispersed and spread in cytoplasm. Restoration of microtubules lead to discontinuous movement of vesicles to central part of the cell and cluster rebuilding. What is the basis for such discontinuity of motion? Indeed, Sec23 in known to bind transitory to p150Glued dynactin protein. Inhibition of p150-Sec23 interaction with C-terminal fragment of p150Glued didn’t influence ERES clustering in Sar1a[H79G] expression. C-terminal fragment of p150Glued also didn’t inhibit ERES MT interaction suggesting another protein should be responsible for ERES MT binding, Increase of ERES motility in the same direction of cargo carrier displacement can be caused by the fact that dynein may start pushing transport carrier prior to its full detachment from ERES. It seems that in this situation dynein is activated also by other than dynactin cofactor. This work is supported by RFBR grant 18-04-00742.