Abstract: | The F508 mutation leads to retention of cystic fibrosistransmembrane conductance regulator (CFTR) in the endoplasmic reticulum and rapid degradation by the proteasome and other proteolytic systems.In stably transfected LLC-PK1(porcine kidney) epithelial cells, F508 CFTR conforms to thisparadigm and is not present at the plasma membrane. WhenLLC-PK1 cells or human nasal polyp cells derived from a F508 homozygous patient are grown on plastic dishes and treated with an epithelial differentiating agent (DMSO, 2%for 4 days) or when LLC-PK1 cellsare grown as polarized monolayers on permeable supports, plasmamembrane F508 CFTR is significantly increased. Moreover, whenconfluent LLC-PK1 cells expressing F508 CFTR were treated with DMSO and mounted in an Ussing chamber, afurther increase in cAMP-activated short-circuit current (i.e., ~7µA/cm2;P < 0.00025 compared with untreatedcontrols) was observed. No plasma membrane CFTR was detected after DMSOtreatment in nonepithelial cells (mouse L cells) expressing F508CFTR. The experiments describe a way to augment F508 CFTR maturationin epithelial cells that appears to act through a novel mechanism andallows insertion of functional F508 CFTR in the plasma membranes oftransporting cell monolayers. The results raise the possibility thatincreased epithelial differentiation might increase the delivery of F508 CFTR from the endoplasmic reticulum to the Golgi, where the F508 protein is shielded from degradative pathways such as theproteasome and allowed to mature. |