A SNARE geranylgeranyltransferase essential for the organization of the Golgi apparatus.
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ABSTRACT:
SUBMITTER: Shirakawa R
PROVIDER: S-EPMC7156963 | biostudies-literature |
REPOSITORIES: biostudies-literature
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Project description:The Golgi apparatus plays a pivotal role in the sorting and post-translational modifications of secreted and membrane proteins. In mammalian cells, the Golgi is organized in stacks of cisternae linked together to form a network with a ribbon shape. Regulation of Golgi ribbon formation is poorly understood. Here we find in an image-based RNAi screen that depletion of the ubiquitin-ligase CBLC induces Golgi fragmentation. Depletions of the close homologues CBL and CBLB do not induce any visible defects. In CBLC-depleted cells, Golgi stacks appear relatively unperturbed at both the light and electron microscopy levels, suggesting that CBLC controls mostly network organization. CBLC partially localizes on Golgi membranes and this localization is enhanced after activation of the SRC kinase. Inhibition of SRC reverts CBLC depletion effects, suggesting interplay between the two. CBLC's regulation of Golgi network requires its ubiquitin ligase activity. However, SRC levels are not significantly affected by CBLC, and CBLC knockdown does not phenocopy SRC activation, suggesting that CBLC's action at the Golgi is not direct downregulation of SRC. Altogether, our results demonstrate a role of CBLC in regulating Golgi ribbon by antagonizing the SRC tyrosine kinase.
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Project description:N-alpha-acetyltransferase 80 (NAA80) was recently demonstrated to acetylate the N-terminus of actin, with NAA80 knockout cells showing actin cytoskeleton-related phenotypes, such as increased formation of membrane protrusions and accelerated migration. Here we report that NAA80 knockout cells additionally display fragmentation of the Golgi apparatus. We further employed rescue assays to demonstrate that this phenotype is connected to the ability of NAA80 to modify actin. Thus, re-expression of NAA80, which leads to re-establishment of actin's N-terminal acetyl group, rescued the Golgi fragmentation, whereas a catalytic dead NAA80 mutant could neither restore actin Nt-acetylation nor Golgi structure. The Golgi phenotype of NAA80 KO cells was shared by both migrating and non-migrating cells and live-cell imaging indicated increased Golgi dynamics in migrating NAA80 KO cells. Finally, we detected a drastic increase in the amount of F-actin in cells lacking NAA80, suggesting a causal relationship between this effect and the observed re-organization of Golgi structure. The findings further underscore the importance of actin Nt-acetylation and provide novel insight into its cellular roles, suggesting a mechanistic link between actin modification state and Golgi organization.
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