No tight junctions in tight junction protein-1 expressing HeLa and fibroblast cells.

Tight junctions are important structures that form the barrier of cells and tissues, and they play key roles in maintaining homeostasis of our body. The backbone of the tight junction proteins are claudins, which composed more than twenty members. The tight junction protein 1 (TJP1), also called ZO-1 (Zonula Occludens-1), is one of the tight junction related proteins, and it is widely used in literature to label tight junctions. Here we showed that TJP1 (ZO-1) is highly expressed in cancerous HeLa cells, fibroblast cells, HUVEC as well as MDCK cells, while claudin-1 is highly expressed in HUVEC and MDCK cells, but not expressed in HeLa and fibroblast cells. We aimed to investigate whether tight junction is present in HeLa and fibroblast cells. We used transepithelial/transendothelial electrical resistance (TEER) to measure tight junction dynamics in these cells. The results showed that there is no TEERs in HeLa and fibroblast cells, while there is relatively high TEER in HUVEC and MDCK cells. Importantly, the TEER in MDCK cells is dramatically reduced after knockdown of TJP1 (ZO-1). These results suggest that TJP1 (ZO-1) cannot be used as a marker of tight junctions in a variety of cells, while TJP1 (ZO-1) may play an important role in regulation of tight junctions in MDCK cells.