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First published online 18 December 2002
doi: 10.1242/jcs.00260
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Research Article |

Department of Molecular Sciences, University of Tennessee Health Science
Center, 858 Madison Avenue, Memphis, Tennessee 38163, USA
* Present address: Department of Medicine, Washington University School of
Medicine at Barnes-Jewish Hospital, St Louis, MO 63110, USA
Author for correspondence (e-mail:
jcox{at}utmem.edu)
Accepted 6 November 2002
AE1/Fc receptor chimeras have been used to define the sequences
that direct the basolateral sorting, recycling and cytoskeletal association of
the chicken AE1-4 anion exchanger in MDCK cells. These analyses revealed that
amino acids 1-63 of AE1-4 were sufficient to redirect a cytoplasmic tailless
murine IgG FcRII B2 receptor from the apical to the basolateral
membrane of MDCK cells, where Fc1-63 associated with elements of
the actin cytoskeleton. In contrast to Fc1-63, chimeras containing
amino acids 1-37 (Fc1-37) or 38-63 (Fc38-63) of AE1-4
accumulated in intracellular membrane compartments that overlapped late
endosomes and the trans-Golgi network (TGN), respectively. Internalization
assays indicated that the patterns of localization observed for
Fc1-37 and Fc38-63 resulted from the recycling of these
chimeras from the cell surface. These assays further indicated that
Fc1-37 and Fc38-63 each possess a basolateral sorting
activity. Mutagenesis studies revealed that the endocytic and basolateral
sorting activities in Fc1-37 are dependent upon serine 25, which is
located in a sequence similar to a sorting signal in the polymeric
immunoglobulin receptor. In addition, the sorting activities associated with
Fc38-63 were dependent upon tyrosine 47 and leucine 50. These
residues resided within the sequence, YVEL, which matches the YXX
motif
(where X is any amino acid and
is a hydrophobic residue) that functions
as an endocytic and TGN recycling signal for other membrane proteins. Our data
indicate that amino acids 1-63 of AE1-4 contain sorting and cytoskeletal
binding activities that account for most of the properties previously
associated with AE1-4 in MDCK cells. Furthermore, the alternative localization
patterns exhibited by chimeras containing various combinations of these
activities suggest that interplay between these cytoplasmic activities is
critical for specifying AE1-4 localization in epithelial cells.
Key words: Sorting signal, Actin, Recycling, TGN, Late endosomes
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