In most organisms, the Golgi apparatus (GA) consists of stack of cisternae ordered in a polarized fashion. Whereas in plants, invertebrates and fungi the stacks exist as isolated entities, in mammalian cells they are laterally linked to form a ribbon-like membrane system. This ribbon is localized close to the nucleus surrounding the centrosome. Although this organization has been observed for a long time, its functional significance is not fully understood. We show here that the GA/CTR protein AKAP450 is a key regulator of the Golgi positioning. The ectopic expression of the N-terminal domain (AK1) of AKAP450 led to the separation of an intact and interconnected Golgi ribbon away from the centrosome. Interestingly, expression of a sub-fragment of AKl (AKl B) did not affect Golgi positioning, but produced fragmented Golgi membranes next to the centrosome. Expression of either fragment results in a failure of the Golgi to nucleate microtubules. Both AKl and AKl B were targeted to the Golgi through interactions with GM 130, but AKl B lacked the capacity to interact with the p150glued subunit of dynactin. This is likely the underlying cause of the distinction between the two phenotypes that arose by specific interference of each fragment with either Golgi-dependent or centrosome-dependent stages of Golgi assembly. Testing AKl and AKlB in wound healing assays revealed that major effects on directional cell migration were observed only when Golgi positioning was disrupted. Our work also provides a link between the Golgi organization and ciliogenesis. Finally, preliminary data suggests a potential role of AKAP450 in the mitotic checkpoint linked to pericentrosomal Golgi ribbon organization.

Peer reviewed