Reduction of the tumorigenic potential of human retinoblastoma cell lines by TFF1 overexpression involves p53/caspase signaling and miR-18a regulation.

Trefoil factor family (TFF) peptides have been shown to play a pivotal role in oncogenic transformation, tumorigenesis and metastasis by changing cell proliferation, apoptosis, migration and invasion behavior of various cancer cell lines. In the study presented, we investigated the effect of TFF1 overexpression on cell growth, viability, migration and tumorigenicity of different retinoblastoma (RB) cell lines. Transient TFF1 overexpression significantly increases RB cell apoptosis levels. Stable, lentiviral TFF1 overexpression likewise decreases RB cell viability, proliferation and growth and significantly increases apoptosis as revealed by WST-1 assays, BrdU and DAPI cell counts. TFF1-induced apoptosis is executed via cleaved caspase-3 activation as revealed by caspase blockage experiments and caspase-3 immunocytochemistry. Results from pG13-luciferase reporter assays and Western blot analyses indicate that TFF1-induced apoptosis is mediated through transcriptional activity of p53 with concurrently downregulated miR-18a expression. In ovo chicken chorioallantoic membrane (CAM) assays revealed that TFF1 overexpression significantly decreases the size of tumors forming from Y79 and RB355 cells and reduces the migration potential of RB355 cells. Differentially expressed genes and pathways involved in cancer progression were identified after TFF1 overexpression in Y79 cells by gene expression array analysis, underlining the effects on reduced tumorigenicity. TFF1 knockdown in RBL30 cells revealed caspase-3/7-independent apoptosis induction, but no changes on cell proliferation level. In summary, the in vitro and in vivo data demonstrate for the first time a tumor suppressor function of TFF1 in RB cells which is at least partly mediated by p53 activation and miR-18a downregulation.