The antagonistic regulation of human MUC4 and ErbB-2 genes by the Ets protein PEA3 in pancreatic cancer cells: implications for the proliferation/differentiation balance in the cells

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Abstract
The human transmembrane mucin MUC4 is aberrantly expressed in 75% of pancreatic ductal adenocarcinomas, whereas no expression is found in normal pancreas. Therefore MUC4 appears as a useful biological marker for the diagnosis of ductal adenocarcinomas. Since rat Muc4 was shown to interact with ErbB-2 tyrosine kinase receptor and to either promote cell survival and differentiation or cell proliferation, it is postulated that MUC4 may also participate in pancreatic carcinogenesis. Our aim was to investigate in parallel the role of the Ets factor PEA3 in MUC4 and ErbB-2 transcriptional regulation in pancreatic cancer cells. Two MUC4-expressing WD (well-differentiated) (CAPAN-1 and -2) and one MUC4-non-expressing poorly differentiated (PANC-1) cell lines were used. The three cell lines express ErbB-2 at different levels. By co-transfection and site-directed mutagenesis, we show that PEA3 is a transactivator of the MUC4 promoter and that the -216 and -2368 PEA3 binding sites of the MUC4 promoter are essential. We also demonstrate that PEA3 acts in synergy with c-Jun and specificity protein 1 to transactivate the proximal region of the MUC4 promoter and increase MUC4 mRNA levels in WD cells. These results suggest that MUC4 is a new target gene of the Ets factor PEA3 in pancreatic cancer cells. In contrast, PEA3 represses the transcriptional activity of two fragments of the ErbB-2 promoter in a dose-dependent manner and decreases the endogenous ErbB-2 mRNA levels in WD cell lines. Thus, PEA3, by its capacity to up-regulate the epithelial marker MUC4 and to down-regulate the ErbB-2 oncogene, appears as a key regulator of the differentiation/proliferation balance in pancreatic cancer cells.