TMEM2 expression is downregulated as bladder cancer invades the muscle layer

Cell surface hyaluronidase transmembrane protein 2 (TMEM2), which also serves as a reportedly functions in malignancy of several solid tumors. However, TMEM2 involvement in bladder cancer (BCa) is unknown. Therefore, we investigate potential changes in expression of TMEM2 during BCa invasion and over the course of the epithelial mesenchymal transition (EMT). Immunohistochemical analysis of 127 clinical specimens revealed that TMEM2 expression changed with pathological stage (pT) and infiltration pattern (INF) and was highest in pTa-pT1 of INFa tumors and significantly lower at stages from pTa-pT1 to pT2 or 3 in INFb or INFc. E-cadherin expression was highest in INFa and lowest in INFc, a pattern comparable to TMEM2 expression. TMEM2 protein expression analysis of BCa cell lines showed that muscle-invasive T24 and YTS-1 cells with low TMEM2 expression exhibited EMT phenotypes in vitro, in contrast to high TMEM2-expressing non-muscle invasive RT4 cells. EMT-induced non-muscle invasive RT4 cells also showed significantly decreased plasma membrane expression of TMEM2. Our data suggested TMEM2 expression is higher in non-invasive cancers, whereas invasive cancer cells are less likely to express TMEM2 during muscle-invasion and "partial EMT".