Abstract: Background and purpose: A large number of studies have showed that retinoblastoma gene 1 (RB1) can inhibit the occurrence and development of many tumors, including neuroblastoma, small cell lung cancer, osteosarcoma, pancreatic cancer, breast cancer and so on. RB1 is also closely related to the regulation of cell cycle, differentiation, senescence, apoptosis, growth inhibition, etc. The goal of this article is to elucidate whether miR-222 promotes cell proliferation and invasion by targeting RB1, further to explore the molecular mechanism that miR-222 functions as an oncogene in retinoblastoma cells. Methods: miR-222 (miR-222 mimics) and RB1-wt, miR-NC and RB1-wt, miR-222 and RB1-mut, miR-NC (a controlled miR-222 mimics) and RB1-mut were co-transfected into Y79 cells, and luciferase activity was detected by single photon. Retinoblastoma cells were transfected with miR-222 mimics and miR-NC, and the expressions of RB1 protein were detected by Western blot. Retinoblastoma cell proliferation assays were performed by MTS assay when miR-222, miR-NC, RB1 (pcDNA3.1-RB1), vector (pcDNA3.1), miR-222+RB1 and miR-NC+vec- tor were transfected into Y79 cells. The growth and invasion ability of Y79 cells with ectopic expression of miR-222 were evaluated by MTS and Transwell invasion assays. Results: This study demonstrated that miR-222 could promote the luciferase activity of RB1-wt. The expression levels of luciferase reporter gene activity in Y79 cells after transfection with miR-222+RB1-wt were higher than those in the negative control cells (miR-NC+RB1-wt) (P<0.05). The protein expression levels of RB1 in Y79 cells after transfection with miR-222 were lower than those in miR-NC (P<0.05). Overexpression of RB1 inhibited the proliferation of retinoblastoma cells. miR-222 promoted the proliferation of retinoblastoma cells through targeting RB1 (P<0.05). Moreover, there was no significant difference between the cell survival rates of Y79 which were transfected with miR-222+pcDNA3.1-RB1 and miR-NC+pcDNA3.1 (P>0.05). After transfection with miR-222 mimics for 48 h, Transwell invasion assay showed that the number of cells through the basement membrane was (193±10). Compared with the control group (144±11), it could significantly accelerate the invasion of Y79 cells (P<0.01). There was no significant difference between the number of cells through the basement membrane which were transfected with miR-222+pcDNA3.1-RB1 and miR-NC+pcDNA3.1 (P>0.05). Conclusion: miR-222 promotes cell proliferation and invasion by targeting RB1 expression in retinoblastoma cells.

Key words: Retinoblastoma, miR-222, RB1, Growth, Invasion