Oligomerization and cellular localization of SLC26A11
The solute carrier family 26 (SLC26) encompasses multifunctional anion exchangers in all kingdoms of life. SLC26 proteins are known to assemble as dimers, and co-expression of multiple isoforms in certain cells raises the question whether different SLC26s can assemble into hetero-dimers. We focused on SLC26A11, a broadly expressed isoform that differs from other isoforms in its subcellular localization. Whereas the vast majority of SLC26-FP fusion proteins, i.e. SLC26A1, SLC26A2, SlC26A3, SLC26A4/pendrin, SLC26A5/prestin, SLC26A6, SlC26A7, and SLC26A9, localize to the surface membrane of transfected mammalian cells, we found exclusive lysosomal localization of SLC26A11. Renal collecting duct intercalated cells express SLC26A11 together with SLC26A4/pendrin and SLC26A7, and we therefore tested whether heterodimerization between these transporters might result in SLC26 transporter re-localization. Neither in HEK293T nor in immortalized intercalated cells co-expressing SLC26A11 with SLC26A4/pendrin or with SLC26A7, changes of SLC26A11 localization were observed. Moreover, native gel electrophoresis did not provide any evidence for heterodimerization of these isoforms. We next tested heterodimerization of SLC26A11 with SLC26A1, SLC26A2, SLC26A6 or SLC26A9 via co-expression in HEK293T cells and confocal imaging. For all combinations, no changes in subcellular distribution were observed. We conclude that SLC26A11 does not heterodimerize with other SLC26 proteins, and that heterodimerization does not target SLC26A11 to cellular surface membranes.