Cone-rod homeobox transcriptionally activates TCF7 to promote the proliferation of retinal pigment epithelial and retinoblastoma cells in vitro.

Aim: To investigate the proliferation regulatory effect of cone-rod homeobox (CRX) in retinal pigment epithelium (RPE) and retinoblastoma (RB) cells to explore the potential application and side effect (oncogenic potential) of CRX-based gene therapy in RPE-based retinopathies.

Methods: Adult human retinal pigment epithelial (ARPE)-19 and human retinal pigment epithelial (RPE)-1 cells and Y79 RB cell were used in the study. Genetic manipulation was performed by lentivirus-based technology. The cell proliferation was determined by a CellTiter-Glo Reagent. The mRNA and protein levels were determined by quantitative real-time polymerase chain reaction (qPCR) and Western blot assay. The transcriptional activity of the promoter was determined by luciferase reporter gene assay. The bindings between CRX and transcription factor 7 (TCF7) promoter as well as TCF7 and the promoters of TCF7 target genes were examined by chromatin immunoprecipitation (ChIP) assay. The transcription of the TCF7 was determined by a modified nuclear run-on assay.

Results: CRX overexpression and knockdown significantly increased (n=3, P<0.05 in all the cells) and decreased (n=3, P<0.01 in all the cells) the proliferation of RPE and RB cells. CRX overexpression and knockdown significantly increased and deceased the mRNA levels of Wnt signaling target genes [including MYC proto-oncogene (MYC), JUN, FOS like 1 (FOSL1), CCND1, cyclin D2 (CCND2), cyclin D3 (CCND3), cellular communication network factor 4 (CCN4), peroxisome proliferator activated receptor delta (PPARD), and matrix metallopeptidase 7 (MMP7)] and the luciferase activity driven by the Wnt signaling transcription factor (TCF7). TCF7 overexpression and knockdown significantly increased and decreased the proliferation of RPE and RB cells and depletion of TCF7 significantly abolished the stimulatory effect of CRX on the proliferation of RPE and RB cells. CRX overexpression and knockdown significantly increased and decreased the mRNA level of TCF7 and the promoter of TCF7 was significantly immunoprecipitated by CRX antibody.

Conclusion: CRX transcriptionally activates TCF7 to promote the proliferation of RPE and RB cells in vitro. CRX is a potential target for RPE-based regenerative medicine. The potential risk of this strategy, tumorigenic potential, should be considered.