ENHANCED PARACELLULAR BARRIER FUNCTION OF RAT MESOTHELIAL CELLS PARTIALLY PROTECTS AGAINST CANCER CELL PENETRATION

To study pathophysiological roles of mesothelial barrier functions in protection against cancer cell invasion, we isolated mesothelial cells from the rat abdominal cavity and cultured them with 10(-6)M all-tran s-retinoic acid (RA) for 10 days. Mesothelial barrier function assesse d by measuring transcellular electrical resistance (TER) and the expre ssion of 7H6 tight junction-associated antigen at the cell border were induced by the treatment (10.01+/-0.8 vs 6.05+/-0.7 Omega cm(2) witho ut RA; mean+/-s.e.m., n=10). Then we quantified the attachment and pen etration of rat mammary cancer cells (SST-2 cells) into the mesothelia l cell monolayer by prelabelling of the cancer cells with fluorescent dye and by observing optical sections at different heights using a las er confocal scanning microscope. When SST-2 cells were overlaid onto t he mesothelial cell monolayer treated with RA, the number of cancer ce lls found at the basal level of the monolayer was significantly reduce d. These results showed that enhanced mesothelial barrier function at least partially prevents the penetration of cancer cells into mesothel ial cells and suggested that 7H6 antigen serves as a reliable immunocy tochemical marker for monitoring mesothelial barrier function.