TGN38 RECYCLES BASOLATERALLY IN POLARIZED MADIN-DARBY CANINE KIDNEY-CELLS

Sorting of newly synthesized plasma membrane proteins to the apical or basolateral surface domains of polarized cells is currently thought t o take place within the trans-Golgi network (TGN). To explore the rela tionship between protein localization to the TGN and sorting to the pl asma membrane in polarized epithelial cells, we have expressed constru cts encoding the TGN marker, TGN38, in Madin-Darby canine kidney (MDCK ) cells. We report that TGN38 is predominantly localized to the TGN of these cells and recycles via the basolateral membrane. Analyses of th e distribution of Tac-TGN38 chimeric proteins in MDCK cells suggest th at the cytoplasmic domain of TGN38 has information leading to both TGN localization and cycling through the basolateral surface. Mutations o f the cytoplasmic domain that disrupt TGN localization also lead to no npolarized delivery of the chimeric proteins to both surface domains. These results demonstrate an apparent equivalence of basolateral and T GN localization determinants and support an evolutionary relationship between TGN and plasma membrane sorting processes.