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Yes-associated protein (YAP) is overexpressed and has an oncogenic role in hepatocellular carcinoma (HCC). However, whether membrane protein can serve not only as a tumor marker that reflects YAP function but also as a therapeutic target that stimulates tumorigenesis in HCC remains unknown. Here we report that the membrane protein melanoma cell adhesion molecule (MCAM) was under positive regulation by YAP and was highly elevated in HCC cells. Within the MCAM promoter, we found the presence of a cAMP Response Element (CRE; −32 to −25 nt), which is conserved among species and is essential for YAP- and CREB-dependent regulation. Moreover, the interaction between CREB and YAP at the CRE site was dependent on PTPIY-WW domain interactions. However, MCAM expression was low and could not be regulated by YAP in breast and colon cancer cells because of the low levels of the acetyltransferase p300. In HCC cells, high levels of p300 facilitated the binding of YAP to the MCAM promoter, which in turn enhanced histone acetylation and polymerase II recruitment through the dissociation of the deacetylase Sirt1. These results suggest that MCAM is an HCC-specific target of YAP. In clinical serum samples, we found that the serum levels of MCAM were highly elevated in patients with HCC compared with healthy controls and with patients with cirrhosis, hepatitis, colon cancer and breast cancer. MCAM levels were shown to be a slightly better indicator than serum alpha-fetoprotein for predicting HCC. We further demonstrated that MCAM is essential for the survival and transformation of HCC. Mechanistically, MCAM induced translation initiation and the transcriptional activities of c-Jun/c-Fos. In addition, AKT activation had an essential role in the MCAM-promoted binding of eukaryotic initiation factor 4E to c-Jun/c-Fos mRNA. In conclusion, we demonstrated that MCAM may be a potential tumor marker and therapeutic target for the diagnosis and treatment of HCC. [ABSTRACT FROM AUTHOR]

Estrogen receptor α (ERα) is initially expressed in the majority of breast cancers and promotes estrogen-dependent cancer progression by regulating the transcription of genes linked to cell proliferation. ERα status is of clinical importance, as ERα-positive breast cancers can be successfully treated by adjuvant therapy with antiestrogens or aromatase inhibitors. Complications arise from the frequent development of drug resistance that might be caused by multiple alterations, including components of ERα signaling, during tumor progression and metastasis. Therefore, insights into the molecular mechanisms that control ERα expression and stability are of utmost importance to improve breast cancer diagnostics and therapeutics. Here we report that the atypical E3 ubiquitin ligase RNF31 stabilizes ERα and facilitates ERα-stimulated proliferation in breast cancer cell lines. We show that depletion of RNF31 decreases the number of cells in the S phase and reduces the levels of ERα and its downstream target genes, including cyclin D1 and c-myc. Analysis of data from clinical samples confirms correlation between RNF31 expression and the expression of ERα target genes. Immunoprecipitation indicates that RNF31 associates with ERα and increases its stability and mono-ubiquitination, dependent on the ubiquitin ligase activity of RNF31. Our data suggest that association of RNF31 and ERα occurs mainly in the cytosol, consistent with the lack of RNF31 recruitment to ERα-occupied promoters. In conclusion, our study establishes a non-genomic mechanism by which RNF31 via stabilizing ERα levels controls the transcription of estrogen-dependent genes linked to breast cancer cell proliferation. [ABSTRACT FROM AUTHOR]

Epithelial ovarian cancer (EOC) is a highly lethal gynaecological malignancy. Cisplatin is the basal chemotherapeutic agent used to treat EOC, but resistance to cisplatin leads to chemotherapy failure. MicroRNAs are a novel class of regulators that function by controlling gene expression at the post-transcriptional level. Several recent reports have identified some microRNAs that are related to chemotherapy sensitivity. In this study, we found two microRNAs miR-152 and miR-185 that were significantly downregulated in the cisplatin-resistant ovarian cell lines SKOV3/DDP and A2780/DDP, compared with their sensitive parent line SKOV3 and A2780, respectively. Subsequently, the roles of miR-152 and miR-185 were evaluated in vitro and in vivo. The overexpression of miR-152 or miR-185 increased cisplatin sensitivity of SKOV3/DDP and A2780/DDP cells by inhibiting proliferation and promoting apoptosis, then we further confirmed that these miRNAs functioned through suppressing DNA methyltransferase 1 (DNMT1) directly. Concordantly, CD-1/CD-1 nude mice that were injected intraperitoneally with SKOV3/DDP cells transfected with miR-152 mimics exhibited upregulated cisplatin sensitivity in vivo. Interestingly, we found that there were no significant changes in the expression of these two microRNAs after treatment with decitabine (DAC), a traditional epigenetic therapeutic agent, suggesting these miRNAs represented two new regulators independent of DAC. Finally, the survival assay in A549 and HepG2 cells revealed that the two microRNAs involved in cisplatin sensitivity were related to cell types. Our results indicated that miR-152 and miR-185 were involved in ovarian cancer cisplatin resistance in vitro and in vivo by targeting DNMT1 directly. These molecules may serve as potential epigenetic therapeutic targets in other cancers. [ABSTRACT FROM AUTHOR]

Hypoxia changes the responses of cancer cells to many chemotherapy agents, resulting in chemoresistance. The underlying molecular mechanism of hypoxia-induced drug resistance remains unclear. Pim-1 is a survival kinase, which phosphorylates Bad at serine 112 to antagonize drug-induced apoptosis. Here we show that hypoxia increases Pim-1 in a hypoxia-inducible factor-1α-independent manner. Inhibition of Pim-1 function by dominant-negative Pim-1 dramatically restores the drug sensitivity to apoptosis induced by chemotherapy under hypoxic conditions in both in vitro and in vivo tumor models. Introduction of siRNAs for Pim-1 also resensitizes cancer cells to chemotherapy drugs under hypoxic conditions, whereas forced overexpression of Pim-1 endows solid tumor cells with resistance to cisplatin, even under normoxia. Dominant-negative Pim-1 prevents a decrease in mitochondrial transmembrane potential in solid tumor cells, which is normally induced by cisplatin (CDDP), followed by the reduced activity of Caspase-3 and Caspase-9, indicating that Pim-1 participates in hypoxia-induced drug resistance through the stabilization of mitochondrial transmembrane potential. Our results demonstrate that Pim-1 is a pivotal regulator involved in hypoxia-induced chemoresistance. Targeting Pim-1 may improve the chemotherapeutic strategy for solid tumors.Oncogene (2009) 28, 2581–2592; doi:10.1038/onc.2009.124; published online 1 June 2009 [ABSTRACT FROM AUTHOR]