Targeting of the AE2 anion exchanger to the Golgi apparatus is cell type-dependent and correlates with the expression of Ank 195, a Golgi membrane skeletal protein

Abstract

Sodium-independent anion exchangers (AE1–4) show remarkable variability in their tissue-specific expression and subcellular localization. Currently, isoform-specific targeting mechanisms are considered to be responsible for this variable localization. Here, we report that targeting can also be cell type-specific. We show that the full-length AE2 protein and its green fluorescent protein- or DsRed-tagged variants localize predominantly either to the Golgi apparatus in COS-7 cells, or to the plasma membrane in HeLa cells. This alternative targeting did not seem to result from either translational or post-translational differences, but rather from differential expression of at least one of the Golgi membrane skeletal proteins, ankyrin 195 (Ank 195), between the two cell types. Comparative studies with several different cell lines revealed that the Golgi localization of the AE2 protein correlated strictly with the expression of Ank 195 in the cells. The two Golgi-associated proteins also co-localized well and similarly resisted detergent extraction in the cold, whereas the plasma membrane-localized AE2 in Ank 195-deficient cells was mostly detergent-soluble. Collectively, our results suggest that Ank 195 expression is a key determinant for the variable and cell type-dependent localization of the AE2 protein in the Golgi apparatus in mammalian cells.