To further broaden our investigation into the mechanism ofRP1 functioning in breast cancer cells, werestored p27kip1 in MCF-7 and SKBR3 cells with overexpressed RP1. BrdU assays showed that p27kip1 significantlyinhibited the proliferation of MCF-7 and SKBR3 cells with overexpressed RP1 (Fig. 4a).Conversely, we repressed p27kip1 expression in MDA-MB-231 and BT549 cells withRP1 knockdown, and showed that theproliferation of these cells was remarkably enhanced compared with each controlgroup (Fig. 4b). This evidence concerns the gene RP1 and breast carcinoma.