The amplified WWP1 gene is a potential molecular target in breast cancer

The amplification of the q21 band of chromosome 8 (8q21) occurs in a large percentage of breast cancers. WWP1, an HECT domain-containing ubiquitin E3 ligase located in the 8q21 region, negatively regulates the TGF-beta tumor suppressor pathway. To characterize the role of WWP1 in breast cancer, we analyzed WWP1 gene dosage and expression level as well as WWP1's function. A copy number gain of WWP1 was found in 51% (18/35) of breast cancer cell lines and in 41% (17/41) of primary breast tumors. Expression of WWP1 mRNA,Nas analyzed with real-time RT-PCR, Northern blot, and Western blot. WWP1 mRNA is upregulated in 58% (19/33) of breast cancer cell lines, and overexpression of WWP1 is significantly correlated with a gene copy number gain. In a panel of cDNA from primary breast tumors and normal tissues, expression of WWP1 in tumors is significantly higher than that in normal tissues. Functionally, RNAi-mediated WWP1 knockdown significantly induced cell growth arrest and apoptosis in the MCF7 and HCC1500 breast cancer cell lines. Consistently, WWP1 inhibition activated caspases. Forced over-expression of WWP1 by the lentiviral system in 2 immortalized breast epithelial cell lines MCF10A and 184B5 promoted cell proliferation. These results suggest that genomic aberrations of WWP1 may contribute to the pathogenesis of breast cancer. (C) 2007 Wiley-Liss, Inc.