Mucin gene expression in normal bladder and expression of MUC2 in TCC of the bladder
N'Dow JM., Pearson JP., Bennett M., Neal DE., Robson CN.
Introduction: Nine human mucin genes (MUC1-8) have been identified and their expression is both cell- and tissue-specific. Neoplastic transformation of epithelial cells is commonly associated with altered mucin synthesis and structure. The aims of this study were to define mucin gene expression in the normal urothelium, and to correlate immunolocalization of MUC2 with mRNA expression in bladder cancer by in situ hybridization (ISH). Materials and methods: ISH for MUC1-7 was performed on 10 normal bladders, in addition to NCL-MUC-1 and NCL-MÜC-2 immunohistochemistry (IHC). MUC2 mRNA and protein expression were also studied in 20 newly diagnosed bladder cancers (10 superficial and 10 muscle-invasive). Results: All normal cases expressed MUC1 mRNA and protein, and MUC4 mRNA was expressed in 80%. There was weak focal expression of MUC3 in 33%. MUC2, 5AC, SB, 6 & 7 mRNA were not expressed in normal urothelium. MUC2 was detected in 80% of superficial cancers by ISH and in 70% by IHC. In muscleinvasive cancers, MUC2 was detected in half by ISH and in 30% by IHC. The pattern of expression was more heterogeneous in muscle-invasive cancers, with a much weaker signal. Three patients who developed distant metastasis had identical patterns of MUC2 expression. Conclusions: MUC1 and MUC4 are the predominant mucin genes expressed in normal urothelium. MUC2 is absent in normal urothelium, but is expressed in most cases of superficial bladder cancer. Down-regulation of MUC2 expression in muscle-invasive cancers could reflect dysregulation. © 1998 British Journal of Urology.