Ribosomal protein L6 promotes growth and cell cycle progression through upregulating cyclin E in gastric cancer cells

Our previous study revealed that human ribosomal protein L6 (RPL6) was upregulated in multidrug-resistant gastric cancer cells and over-expression of RPL6 could protect gastric cancer cells from drug-induced apoptosis. The present study was designed to explore the role of RPL6 in tumorigenesis and development of gastric cancer. The expression of RPL6 in gastric cancer tissues and normal gastric mucosa was evaluated by immunohistochemical staining. It was found RPL6 was expressed at a higher level in gastric cancer tissues than that in normal gastric mucosa. RPL6 was then genetically overexpressed or knocked down in human immortalized gastric mucosa epithelial GES cells. It was demonstrated that upregulation of RPL6 accelerated the growth and enhanced in vitro colony forming ability of GES cells whereas downregulation of RPL6 showed adverse effects. Moreover, over-expression of RPL6 could promote G1 to S phase transition of GES cells. It was further evidenced that upregulation of RPL6 resulted in elevated cyclin E expression while downregulation of RPL6 caused decreased cyclin E expression in GES cells. Taken together, these data indicated that RPL6 was overexpressed in human gastric cancer and its over-expression could promote cell growth and cell cycle progression at least through upregulating cyclin E expression.