title: Polymeric immunoglobulin receptor traffics through two distinct apically targeted pathways in primary lacrimal gland acinar cells.
abstract: The polymeric immunoglobulin receptor (pIgR) mediates transcytosis of dimeric immunoglobulin A (dIgA) and its release into mucosal secretions. The present study reveals the complexity of the trafficking of pIgR to the apical plasma membrane in epithelial cells with exocrine secretory functions; in rabbit lacrimal gland acinar cells (LGACs), trafficking of pIgR involves both the transcytotic pathway and one arm of the regulated secretory pathway. By specifically tracking pIgR endocytosed from the basolateral membrane, we show here that the Rab11a-regulated transcytotic pathway mediates the basal-to-apical transport of pIgR, and that pIgR sorted into the transcytotic pathway does not access the regulated secretory pathway. However, previous work in LGACs expanded in the present study has shown that some pIgR is localized to Rab3D-enriched mature secretory vesicles (SVs). Myosin Vb and myosin Vc motors modulate release of proteins from the Rab11a-regulated transcytotic pathway and the Rab3D-enriched secretory pathway in LGACs, respectively. Confocal fluorescence microscopy and biochemical assays showed that inhibition of myosin Vb and myosin Vc activity by overexpression of their dominant-negative mutants each significantly but differentially impaired aspects of apically targeted pIgR trafficking and secretory component release, suggesting that these motors function to regulate pIgR trafficking in both the transcytotic and exocytotic pathways. Intriguingly, a second mature SV population enriched in Rab27b was devoid of pIgR cargo, suggesting the specialization of Rab3D-enriched mature SVs to carry a particular subset of cargo proteins from the trans-Golgi network to the apical plasma membrane.
authors.affiliation: Department of Pharmacology and Pharmaceutical Sciences, School of Pharmacy, University of Southern California, Los Angeles, CA 90033, USA.
authors.forename: Shi
authors.initials: S
authors.lastname: Xu
authors.forename: Linlin
authors.initials: L
authors.lastname: Ma
authors.forename: Eunbyul
authors.initials: E
authors.lastname: Evans
authors.forename: Curtis T
authors.initials: CT
authors.lastname: Okamoto
authors.forename: Sarah F
authors.initials: SF
authors.lastname: Hamm-Alvarez
mesh_terms: D061354:Acinar Cells / Q000378:metabolism*; D000818:Animals; D002478:Cells, Cultured; D004705:Endocytosis / Q000502:physiology*; D004847:Epithelial Cells / Q000378:metabolism / Q000502:physiology; D005089:Exocytosis / Q000502:physiology; D005260:Female; D007765:Lacrimal Apparatus / Q000378:metabolism*; D024701:Myosin Type V / Q000378:metabolism; D021381:Protein Transport / Q000502:physiology*; D011817:Rabbits; D019056:Receptors, Polymeric Immunoglobulin / Q000378:metabolism*; D012635:Secretory Component / Q000378:metabolism / Q000502:physiology; D022142:Secretory Vesicles / Q000378:metabolism / Q000502:physiology; D057900:Transcytosis / Q000502:physiology*; D020691:rab GTP-Binding Proteins / Q000378:metabolism; D020692:rab3 GTP-Binding Proteins / Q000378:metabolism; D021601:trans-Golgi Network / Q000378:metabolism; D000099193:rab11 GTP-Binding Proteins
chemical_list: D024701:Myosin Type V; D019056:Receptors, Polymeric Immunoglobulin; D012635:Secretory Component; D020691:rab GTP-Binding Proteins; D020692:rab3 GTP-Binding Proteins; D000099193:rab11 GTP-Binding Proteins
keywords: Myosin V; Polymeric immunoglobulin receptor; Rab11a; Rab27b; Rab3D; Secretion; Transcytosis