RESUMO
RPA2, a subunit of the heterotrimeric replication protein A (RPA) complex, is overexpressed in various cancers. In this study, we showed a significant RPA2 upregulation in breast cancer tissues and cell lines. Ectopic expression of RPA2 in MCF7 and MDA-MB-231 cells promoted cell proliferation, adhesion, migration and invasion, and induced epithelial-mesenchymal transition (EMT) of MCF7 cells. Ablation of RPA2 in MDA-MB-231 cells induced apoptosis and suppressed colony formation, EMT and invasion. Binding assays indicated that menin, the multiple endocrine neoplasia type 1 (MEN1) tumor suppressor gene product, interacted with RPA2. Ectopic expression of RPA2 inhibited the formation of the menin-NK-κB p65 complex and repressed the inhibitory effect of menin on expression of NF-κB-regulated genes that contribute to tumor progression. Conversely, knockdown of RPA2 promoted formation of the menin-p65 complex and repressed the expression of NF-κB-mediated genes. RPA2 expression was induced via an E2F1-dependent mechanism in MCF7 and MDA-MB-231 cells treated with NF-κB activators, TNF-alpha or lipopolysaccharide (LPS). These results suggested that RPA2-dependent tumorigenicity was mediated via enhancement of NF-κB activity by relieving the antagonistic function of menin on NF-κB-regulated transcription in breast cancer cells.
Assuntos
Neoplasias da Mama/genética , Proliferação de Células/genética , Proteínas Proto-Oncogênicas/genética , Proteína de Replicação A/biossíntese , Apoptose/genética , Neoplasias da Mama/patologia , Carcinogênese/genética , Adesão Celular/genética , Movimento Celular/genética , Transição Epitelial-Mesenquimal/genética , Feminino , Regulação Neoplásica da Expressão Gênica , Humanos , Células MCF-7 , NF-kappa B/genética , Invasividade Neoplásica/genética , Invasividade Neoplásica/patologia , Proteínas Proto-Oncogênicas/metabolismo , Proteína de Replicação A/genética , Transdução de Sinais/genéticaRESUMO
Senescence and epithelial-mesenchymal transition (EMT) have opposing roles in tumor progression, in that, one is a barrier against tumorigenesis, whereas the other is required for invasive malignancies. Here, we report that the DNA damage response (DDR) protein hRAD9 contributes to induction of senescence and inhibition of EMT. Our data show that hRAD9 is frequently downregulated in breast and lung cancers. Loss of hRAD9 expression is associated with tumor stage in breast and lung cancers, as well as with acquisition of an invasive phenotype. Ectopic hRAD9 expression in highly invasive cancer cell lines, H1299 and MDA-MB 231, with low endogenous hRAD9 induced senescence by upregulation of nuclear p21, independent of the p53 status. Ectopic expression of hRAD9 also significantly attenuated cellular migration and invasion in vitro and tumor growth in a xenograft mouse model in vivo. In contrast, silencing hRAD9 in lower invasive cancer cell lines, A549 and MCF7, with high endogenous hRAD9 dramatically increased their migration and invasion abilities, and simultaneously activated EMT. Knockdown of hRAD9 increased, whereas ectopic expression of hRAD9 decreased, the expression of Slug. Moreover, hRAD9 directly bound to the promoter region of slug gene and repressed its transcriptional activity. Taken together, these results suggest that hRAD9 is a potential tumor suppressor in breast and lung cancers and that it is likely to function by upregulating p21 and inhibiting Slug to regulate tumorigenesis.