title: Ras mutation impairs epithelial barrier function to a wide range of nonelectrolytes.
abstract: Although ras mutations have been shown to affect epithelial architecture and polarity, their role in altering tight junctions remains unclear. Transfection of a valine-12 mutated ras construct into LLC-PK1 renal epithelia produces leakiness of tight junctions to certain types of solutes. Transepithelial permeability of D-mannitol increases sixfold but transepithelial electrical resistance increases >40%. This indicates decreased paracellular permeability to NaCl but increased permeability to nonelectrolytes. Permeability increases to D-mannitol (Mr 182), polyethylene glycol (Mr 4000), and 10,000-Mr methylated dextran but not to 2,000,000-Mr methylated dextran. This implies a "ceiling" on the size of solutes that can cross a ras-mutated epithelial barrier and therefore that the increased permeability is not due to loss of cells or junctions. Although the abundance of claudin-2 declined to undetectable levels in the ras-overexpressing cells compared with vector controls, levels of occludin and claudins 1, 4, and 7 increased. The abundance of claudins-3 and -5 remained unchanged. An increase in extracellular signal-regulated kinase-2 phosphorylation suggests that the downstream effects on the tight junction may be due to changes in the mitogen-activated protein kinase signaling pathway. These selective changes in permeability may influence tumorigenesis by the types of solutes now able to cross the epithelial barrier.
authors.affiliation: The Lankenau Institute for Medical Research, Wynnewood, PA 19096, USA. mullinj@mlhs.org
authors.forename: James M
authors.initials: JM
authors.lastname: Mullin
authors.forename: James M
authors.initials: JM
authors.lastname: Leatherman
authors.forename: Mary Carmen
authors.initials: MC
authors.lastname: Valenzano
authors.forename: Erika Rendon
authors.initials: ER
authors.lastname: Huerta
authors.forename: Jon
authors.initials: J
authors.lastname: Verrechio
authors.forename: David M
authors.initials: DM
authors.lastname: Smith
authors.forename: Karen
authors.initials: K
authors.lastname: Snetselaar
authors.forename: Mantao
authors.initials: M
authors.lastname: Liu
authors.forename: Mary Kay
authors.initials: MK
authors.lastname: Francis
authors.forename: Christian
authors.initials: C
authors.lastname: Sell
mesh_terms: D000818:Animals; D001692:Biological Transport; D002455:Cell Division; D002460:Cell Line; D002463:Cell Membrane Permeability; D003911:Dextrans / Q000378:metabolism; D004594:Electrophysiology; D011905:Genes, ras; D007668:Kidney; D008565:Membrane Proteins / Q000378:metabolism; D009154:Mutation; D012965:Sodium Chloride / Q000378:metabolism; D014162:Transfection; D019459:Urothelium / Q000502:physiology*
chemical_list: D003911:Dextrans; D008565:Membrane Proteins; D012965:Sodium Chloride; C014392:carboxymethyl dextran