Rb Depletion Results in Deregulation of E-Cadherin and Induction of Cellular Phenotypic Changes that Are Characteristic of the Epithelial-to-Mesenchymal Transition

Abstract

The retinoblastoma tumor suppressor protein (Rb) is mutated or expressed at very low levels in several tumor types, including retinoblastoma and osteosarcoma, as well as small cell lung, colon, prostate, bladder, and breast carcinomas. Loss or reduction of Rb expression is seen most commonly in highgrade breast adenocarcinomas, suggesting that a relationship may exist between loss of Rb function and a less-differentiated state, increased proliferation, and high metastatic potential. In this study, we found that knockdown of Rb by small interfering RNA in MCF7 breast cancer cells disrupts cell-cell adhesion and induces a mesenchymal-like phenotype. The epithelial-to-mesenchymal transition (EMT), a key event in embryonic morphogenesis, is implicated in the metastasis of primary tumors. Additionally, Rb is decreased during growth factor-and cytokine-induced EMT and overexpression of Rb inhibits the EMT in MCF10A human mammary epithelial cells. Ectopic expression and knockdown of Rb resulted in increased or reduced expression of E-cadherin, which is specifically involved in epithelial cell-cell adhesion. Other EMTrelated transcriptional factors, including Slug and Zeb-1, are also induced by Rb depletion. Furthermore, we confirmed that Rb binds to an E-cadherin promoter sequence in association with the transcription factor activator protein-2A. Finally, in breast cancer specimens, we observed a concurrent downregulation of Rb and E-cadherin expression in mesenchymallike invasive cancers. These findings suggest that Rb inactivation contributes to tumor progression due to not only loss of cell proliferation control but also conversion to an invasive phenotype and that the inhibition of EMT is a novel tumor suppressor function of Rb. [Cancer Res 2008;68(13):5104-12]

A bioinformatical and functional approach to identify novel strategies for chemoprevention of colorectal cancer

“…We found that roscovitine induced changes in the expression of proteins involved in the Rb pathway. Several changes are likely to be the result of CDK2 inhibition, including the loss of phospho-Rb and the upregulation of p53 (Arima et al, 2008). However, other observed changes in the expression of Rb pathway proteins may be independent of CDK2 inhibition, but the result from CDK7/9 inhibition, such as the loss of cyclin D1 (Aldoss et al, 2009).…”

Regulation of miR106b cluster through the RB pathway

“…8,39 The mechanism underlying this process remains ill-defined. Recent studies have suggested a role for the RB pathway in regulating the epithelial-to-mesenchymal transition through miR200.…”

Cross-regulation between protein L-isoaspartyl O-methyltransferase and ERK in epithelial mesenchymal transition of MDA-MB-231 cells

“…As such, we sought to determine if PIMT expression is up-regulated during the induction of EMT by TGF-β and TNF-α. Previously, treatment with a combination of TGF-β and TNF-α was shown to induce EMT in some cell types [28] . Indeed, when MDA-MB-231 breast cancer cells were treated with TGF-β/TNF-α, a morphological change from an epithelial-like to a mesenchymal-like appearance was induced ( Figure 5A).…”