The Golgi apparatus is a membranous organelle that plays a central role in the processing, sorting, and transport of proteins and lipids. In animal cells, the Golgi apparatus is known as a major microtubule-organizing center and requires microtubules for its organization and function. However, mechanisms underlying the microtubule organization and regulation of the Golgi apparatus have not been fully understood. In this study, I have found that myomegalin variant 8 (MMG8), a newly identified myomegalin isoform that is expressed in epithelial cells and fibroblasts, localizes to the cis-Golgi through the interaction with AKAP450. This interaction is necessary for the stability of MMG8 and AKAP450. In addition, depletion of MMG8 results in Golgi fragmentation and affects endoplasmi...[ Read more ]

The Golgi apparatus is a membranous organelle that plays a central role in the processing, sorting, and transport of proteins and lipids. In animal cells, the Golgi apparatus is known as a major microtubule-organizing center and requires microtubules for its organization and function. However, mechanisms underlying the microtubule organization and regulation of the Golgi apparatus have not been fully understood. In this study, I have found that myomegalin variant 8 (MMG8), a newly identified myomegalin isoform that is expressed in epithelial cells and fibroblasts, localizes to the cis-Golgi through the interaction with AKAP450. This interaction is necessary for the stability of MMG8 and AKAP450. In addition, depletion of MMG8 results in Golgi fragmentation and affects endoplasmic reticulum (ER)-to-Golgi transport. MMG8 participates in the attachment of γ-tubulin to the Golgi membranes, and thus is involved in the organization of Golgi-derived microtubules. MMG8 is also required for the Golgi localization of microtubule end-binding protein 1 (EB1), which plays a role in ER-to-Golgi transport. Moreover, I have found that the Golgi localization of the MMG8–AKAP450 complex and Golgi-derived microtubules are regulated by ER-to-Golgi transport. The Golgi localization of the MMG8–AKAP450 complex is also dynamic during the cell cycle. These findings have revealed a regulatory mechanism for the organization of Golgi-derived microtubules during the cell cycle.