Rat liver dipeptidylpeptidase IV contains competing apical and basolateral targeting information.
Madin-Darby canine kidney (MDCK) cells deliver endogenous apical and basolateral proteins directly to the appropriate domains. We are investigating the molecular signals on a model plasma membrane hydrolase, dipeptidylpeptidase IV (DPPIV). Most newly synthesized rat liver DPPIV is delivered directly to the apical surface of transfected MDCK cells; however, about 20% is delivered first to the basolateral surface and reaches the apical surface via transcytosis (Casanova, J. E., Mishumi, Y., Ikehara, Y., Hubbard, A. L., and Mostov, K. E. (1991) J. Biol. Chem. 266, 24428-24432). A soluble form of DPPIV (solDPPIV) containing only the lumenal domain of the protein was efficiently transported and secreted by stably transfected MDCK cells. If this domain contains apical sorting information, we would expect 80% of the soluble protein to be secreted apically. Surprisingly, 95% of the secreted solDPPIV was found in the apical medium. The high efficiency of apical secretion suggested that the transmembrane domain and cytoplasmic tail of DPPIV might contain competing basolateral targeting information. To test this hypothesis, we investigated the trafficking of a chimera in which the cytoplasmic tail and transmembrane domains of DPPIV were joined to lysozyme, an exogenous protein which should not contain sorting information. This protein was delivered predominantly to the basolateral surface. Our results suggest that the lumenal domain of DPPIV carries dominant apical sorting information while the transmembrane domain and cytoplasmic tail of the molecule contains competing basolateral sorting information.
Department of Cell Biology and Anatomy, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205.
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Weisz
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Machamer
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Hubbard
D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D001692:Biological Transport; D002451:Cell Compartmentation; D002462:Cell Membrane / Q000378:metabolism; D016764:Cell Polarity; D002478:Cells, Cultured; D018819:Dipeptidyl Peptidase 4; D004152:Dipeptidyl-Peptidases and Tripeptidyl-Peptidases / Q000378:metabolism*; D004285:Dogs; D066298:In Vitro Techniques; D008099:Liver / Q000201:enzymology*; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D009838:Oligodeoxyribonucleotides / Q000737:chemistry; D051381:Rats; D013329:Structure-Activity Relationship
D009838:Oligodeoxyribonucleotides; D004152:Dipeptidyl-Peptidases and Tripeptidyl-Peptidases; D018819:Dipeptidyl Peptidase 4