Epithelial permeability factor: A serum protein that condenses actin and opens tight junctions

An epithelial permeability factor (EPF) in human serum lowered, within 1 h, the transepithelial electrical resistance and opened the tight junctions of a cultured kidney epithelium (Madin-Darby canine kidney) when it came in contact with the basolateral surface of the kidney epithelium. Size-exclusion chromatography of serum or heat-inactivated serum resolved seven peaks of EPF activity (~15, ~30, ~45, ~60, ~120, and ~240 kDa and >240 kDa) with 65% of the activity at ~45, ~60, and ~120 kDa. Heat inactivation, which had no effect on total activity, caused a significant decrease in the activity at 120 kDa and an equivalent rise in activity at 45 kDa. Although acid charcoal extraction or lectin affinity chromatography did not remove activity, EPF activity was eliminated by pepsin. Heat-inactivated serum or fractions containing EPF had no effect on ZO-1 localization but did cause a dose- dependent focal condensation of the perijunctional actin ring at sites where three or more cells were in contact. These data suggest that EPF is a protein that appears to form multimers that interact with the basolateral surface of the epithelium and cause constriction of the cytoskeleton and an increase in permeability at specific sites along the tight junction.