A dileucine motif targets E-cadherin to the basolateral cell surface in Madin-Darby canine kidney and LLC-PK1 epithelial cells

E-cadherin is a major adherens junction protein of epithelial cells, with a central role in cell-cell adhesion and cell polarity. Newly synthesized E- cadherin is targeted to the basolateral cell surface, We analyzed targeting information in the cytoplasmic tail of E-cadherin by utilizing chimeras of E-cadherin fused to the ectodo- main of the interleukin-2 alpha (IL-2 alph a) receptor expressed in Madin-Darby canine kidney and LLC-PK1 epithelial c ells, Chimeras containing the full-length or membrane-proximal half of the E-cadherin cytoplasmic tail were correctly targeted to the basolateral doma in. Sequence analysis of the membrane-proximal tail region revealed the pre sence of a highly conserved dileucine motif, which was analyzed as a putati ve targeting signal by mutagenesis. Elimination of this motif resulted in t he loss of Tac/E-cadherin basolateral localization, pinpointing this dileuc ine signal as being both necessary and sufficient for basolateral targeting of E-cadherin, Truncation mutants unable to bind beta -catenin were correc tly targeted, showing, contrary to current understanding, that beta -cateni n is not required for basolateral trafficking. Our results also provide evi dence that dileucine mediated targeting is maintained in UC-PK, cells despi te the altered polarity of basolateral proteins with tyrosine-based signals in this cell line, These results provide the first direct insights into ho w E-cadherin is targeted to the basolateral membrane.