title: Upregulation of surfactant synthesis triggers ABCA1-mediated basolateral phospholipid efflux.
abstract: Alveolar type II lung epithelia produce surfactant, an essential surface-active material highly enriched with disaturated phosphatidylcholine (DSPC), which requires a key regulatory enzyme, CTP:phosphocholine cytidylyltransferase alpha (CCTalpha), for its synthesis before its export apically into the alveolus. In this study, we examined whether surfactant phosphatidylcholine (PC) synthesis and export are physiologically linked. Stable overexpression of CCTalpha in lung epithelial cell lines increased rates of PC synthesis and cellular DSPC mass without altering total cellular PC content. Overexpression of CCTalpha was associated with i) increased basolateral, rather than apical, PC export catalyzed by ABCA1; ii) basolateral export of significant levels of unsaturated (nonsurfactant) PC; and iii) transcriptional activation of the ABCA1 gene via a liver X receptor/retinoic acid receptor-independent pathway. Cells exposed to PC vesicles exhibited a dose-dependent increase in ABCA1 transcriptional activity. These data provide the first evidence that surfactant PC synthesis is linked to its export via a basolateral lipid efflux pathway. This pathway is mediated, in part, by a phospholipid sensor, ABCA1, that appears to partake in the autoregulation of both cellular content and composition of PC, thereby providing a potentially novel exit route for a newly synthesized pool of PC distinct from surfactant.
authors.affiliation: Department of Internal Medicine, Roy J. and Lucille A. Carver College of Medicine, University of Iowa, Iowa City, IA 52242, USA.
authors.forename: Jiming
authors.initials: J
authors.lastname: Zhou
authors.forename: Yong
authors.initials: Y
authors.lastname: You
authors.forename: Alan J
authors.initials: AJ
authors.lastname: Ryan
authors.forename: Rama K
authors.initials: RK
authors.lastname: Mallampalli
mesh_terms: D064286:ATP Binding Cassette Transporter 1; D018528:ATP-Binding Cassette Transporters / Q000235:genetics / Q000378:metabolism*; D000818:Animals; D002460:Cell Line; D045744:Cell Line, Tumor; D019916:Choline-Phosphate Cytidylyltransferase / Q000235:genetics / Q000378:metabolism; D006801:Humans; D051379:Mice; D010713:Phosphatidylcholines / Q000096:biosynthesis* / Q000378:metabolism; D010743:Phospholipids / Q000378:metabolism*; D011663:Pulmonary Surfactants / Q000378:metabolism*; D015854:Up-Regulation
chemical_list: C577836:ABCA1 protein, human; D064286:ATP Binding Cassette Transporter 1; D018528:ATP-Binding Cassette Transporters; D010713:Phosphatidylcholines; D010743:Phospholipids; D011663:Pulmonary Surfactants; D019916:Choline-Phosphate Cytidylyltransferase