The AE2 anion exchanger is necessary for the structural integrity of the Golgi apparatus in mammalian cells

Abstract

The structural integrity of the Golgi apparatus is known to be dependent on multiple factors, including the organizational status of microtubules, actin and the ankyrin/spectrinbased Golgi membrane skeleton, as well as vesicular tra⁄cking and pH homeostasis. In this respect, our recently identi¢ed Golgi-associated anion exchanger, AE2, may also be of importance, since it potentially acts as a Golgi pH regulator and as a novel membrane anchor for the spectrin-based Golgi membrane skeleton. Here, we show that inhibition ( s 75%) of AE2 expression by antisense oligonucleotides in COS-7 cells results in the fragmentation of the juxtanuclear Golgi apparatus and in structural disorganization of the Golgi stacks, the cisternae becoming generally shorter, distorted, vesiculated and/or swollen. These structural changes occurred without apparent dissociation of the Golgi membrane skeletal protein Ankyrin 195 , but were accompanied by the disappearance of the well-focused microtubule-organizing center (MTOC), suggesting the involvement of microtubule reorganization. Similar changes in Golgi structure and assembly of the MTOC were also observed upon transient overexpression of the EGFP-AE2 fusion protein. These data implicate a clear structural role for the AE2 protein in the Golgi and in its cytological positioning around the MTOC.

A Golgi-associated protein 4.1B variant is required for assimilation of proteins in the membrane

“…However, in contrast to the well-characterized erythrocyte membrane skeleton, even the identities of the components of this surmised network in the Golgi-associated membrane have been elusive. Specific isoforms of spectrin and ankyrin have been recognized in the Golgi, and a recent report has suggested that the AE2 anion exchanger, a member of the red blood cell band 3 (AE1) family, is necessary for the structural integrity of the Golgi complex (Holappa et al, 2004). In the present study, we have identified a previously unknown protein 4.1 variant, 4.1B 200 , as a Golgispecific component.…”

Actin filaments are involved in the maintenance of Golgi cisternae morphology and intra‐Golgi pH

“…The structural role of the AE2 protein in the Golgi complex would be linked to its function (the reversible electroneutral exchange of Cl À for HCO 3 À ), thus contributing to the regulation of intracellular pH, organelle volume, and chloride concentration. Strikingly, in AE2-depleted cells, Golgi stacks display numerous fenestrations and swollen cisternae [Holappa et al, 2004]. On the other hand, it has also been reported that actin-binding activity is a requirement for transport of (V)H þ -ATPase to and from the plasma membrane [Vitavska et al, 2003;Chen et al, 2004b] and therefore, it is reasonable to assume a role for microfilaments and actin dynamics in the delivery and/or activation of (V)H þ -ATPase in endomembrane systems, including the Golgi complex.…”

Accommodation of large cargo within Golgi cisternae

“…/H ? exchanger family has been reported to contribute to Golgi pH as has the anion exchanger AE2 (Holappa et al 2004). An anion transporter called GPHR (Golgi pH regulator) was recently shown to be essential for maintaining cisternal pH, and the absence of GPHR leads to reduced membrane traffic and morphological disruption of the Golgi complex (Maeda et al 2008).…”