RPL27 contributes to colorectal cancer proliferation and stemness via PLK1 signaling

Although expression of ribosomal protein L27 (RPL27) is upregulated in clinical colorectal cancer (CRC) tissue, to the best of our knowledge, the oncogenic role of RPL27 has not yet been defined. The present study aimed to investigate whether targeting RPL27 could alter CRC progression and determine whether RPL27 gains an extra-ribosomal function during CRC development. Human CRC cell lines HCT116 and HT29 were transfected with RPL27-specific small interfering RNA and proliferation was assessed in vitro and in vivo using proliferation assays, fluorescence-activated cell sorting (FACS) and a xenograft mouse model. Furthermore, RNA sequencing, bioinformatic analysis and western blotting were conducted to explore the underlying mechanisms responsible for RPL27 silencing-induced CRC phenotypical changes. Inhibiting RPL27 expression suppressed CRC cell proliferation and cell cycle progression and induced apoptotic cell death. Targeting RPL27 significantly inhibited growth of human CRC xenografts in nude mice. Notably, polo-like kinase 1 (PLK1), which serves an important role in mitotic cell cycle progression and stemness, was downregulated in both HCT116 and HT29 cells following RPL27 silencing. RPL27 silencing reduced the levels of PLK1 protein and G2/M-associated regulators such as phosphorylated cell division cycle 25C, CDK1 and cyclin B1. Silencing of RPL27 reduced the migration and invasion abilities and sphere-forming capacity of the parental CRC cell population. In terms of phenotypical changes in cancer stem cells (CSCs), RPL27 silencing suppressed the sphere-forming capacity of the isolated CD133(+) CSC population, which was accompanied by decreased CD133 and PLK1 levels. Taken together, these findings indicated that RPL27 contributed to the promotion of CRC proliferation and stemness via PLK1 signaling and RPL27 may be a useful target in a next-generation therapeutic strategy for both primary CRC treatment and metastasis prevention.