RNA inference-mediated caveolin-1 down-regulation decrease estrogen receptor alpha (ERα) signaling in human mammary epithelial cells.

Several evidences support that caveolin-1 is associated with mammary cell transformation and oncogenesis. We have previously reported that a cell line, named MCF10A-ST1 (ST1), which only expressed 30% Cav-1 compared with parental cells MCF10A (human mammary epithelial cell line) was isolated by gene trapping. The decreased expression of Cav-1 is sufficient for phenotypic transformation of MCF10A cells, which involved in the loss of anchorage-dependent growth and migration in nude mice with the existence of E2. The previous study in our lab on microarray assay showed that the expression of cyclin D1 (cell cycle protein) was up-regulated in ST1 cell line. Here, we not only confirmed the results by Western Blot but also demonstrated that Cav-1 down-regulation accelerate the progression of mammary cells from G1 phase into S phase by Flow Cytometry (FCM). This proposed that the Cav-1 down-regulation could change the progress of cell cycle in the mammary cells. Otherwise, microarray assay also showed that the transcription factor (c-Jun) was up-regulated. But, the original carcinoma gene (c-Fos) and transcription factor (AP-1) have not obviously changed compared with MCF10A. ST1 cells obtained the morigenicity in nude mice with the existence of E2, and the immunoprecipitation showed the interactions of Cav-1 with ERα in both MCF10A and ST1. ERα expression was increased as further down-regulation of Cav-1. So, we hypothesize that Cav-1 down-regulation could induce the activation of ERα-associated signaling pathway, in order to adjust the development and proliferation. By siRNA technology, the down regulation of Cav-1 could activate MAP kinase and Akt signaling pathway, including the phosphorylation of ERK1/2 and Akt. However, the mechanism of Cav-1 down-regulation in the early transformation and signaling transduction of mammary epithelial cells is unclear. Here, we report that down-regulation of caveolin-1 protein expression leads to deregulate estrogen receptor alpha (ERα) signaling and consequently early transformation in mammary epithelia.