Role of sclerostin in the occurrence and development of uveal melanoma and its biological mechanism

To investigate the effects of sclerostin (SOST) and WNT/CTNNB1 signaling pathway on the cell cycle, migration and invasion of human uveal melanoma (UM) cells and its related mechanism.

UM tissues from 20 cases of epithelioid UM and 16 cases of spindle cell type UM were collected.The contents of SOST, Wnt-1 and Catenin beta-1 proteins in the collected tissues were detected by immunohistochemical staining.Three human UM tissue derived cell lines OCM-1 (primary spindle cell type), Mum-2B (metastatic epithelioid) and Mum-2C (metastatic spindle cell type) were selected and divided into three groups, blank control group not transfected, empty vector group transfected with SOST negative control vector and SOST siRNA group transfected with SOST siRNA.After 24-hour transfection, the mRNA and protein expression levels of SOST, CTNNB1, WNT protein family 1 (WNT1), CCND1, matrix metalloproteinase (MMP)2 and MMP9 were detected by real-time fluorescence quantitative PCR and Western blot, respectively.The invasion and migration ability of the transfected cells were measured by transwell method, and the cell cycle distribution was detected by flow cytometry.Another 9 female BALB/c nude mice were selected and randomized into OCM-1 group, OCM-1 empty vector group and SOST shRNA group, inoculated with OCM-1 without lentivirus infection, OCM-1 with blank lentivirus infection and OCM-1 with SOST shRNA lentivirus infection, respectively.Six weeks after inoculation, the in situ formation of tumor was observed.The interaction between SOST and low density lipoprotein receptor related protein(LRP)-5/6 in OCM-1 cells was explored by co-immunoprecipitation assay.The study protocol was approved by the Ethics Committee of Tianjin Medical University Eye Hospital (2018KY[L]-20).

Immunohistochemical staining results showed that the SOST expression level was higher and the expression levels of Wnt-1 and Catenin beta-1 were lower in spindle cell type UM tissues than in epithelioid UM tissues, and the differences were all statistically significant (all at P<0.01). The real-time fluorescence quantitative PCR results showed that the relative expression of SOST mRNA was significantly lower and the relative expressions of CCND1, WNT1 and MMP9 mRNA were significantly higher in SOST siRNA groups than in corresponding empty vector groups in the three cell lines (all at P<0.05). In OCM-1 and Mum-2C cell lines, the relative expressions of CTNNB1 mRNA were significantly higher in SOST siRNA groups than in empty vector groups (all at P<0.01). Western blot results showed that the relative expression of SOST protein was significantly lower and the relative expressions of Wnt-1, Catenin beta-1, cyclin-D1, MMP2 and MMP9 proteins were significantly higher in SOST siRNA groups than in empty vector groups (all at P<0.01). Transwell assay showed that the cell invasion and migration ability of SOST siRNA group was significantly higher than that of blank control group and empty vector group in the three cell lines (all at P<0.01). Flow cytometry showed that the proportion of G1-phase cells and the G1/S-phase ratio were significantly lower in SOST siRNA group than in blank control groups and empty vector groups (all at P<0.01). The eyeball volume of OCM-1 group, OCM-1 empty vector group and SOST shRNA group was (42.7±4.6), (49.0±22.9) and (135.2±32.7)mm³, respectively, showing a significant overall difference (F=19.963, P<0.01). The eyeball volume of SOST shRNA group was larger than that of OCM-1 group and OCM-1 empty vector group, and the differences were statistically significant (both at P<0.05). Co-immunoprecipitation results showed that SOST could interact with LRP-5 and LRP-6 by binding to them, respectively.

Silencing SOST can promote the invasion and migration of UM cells, and increase the proportion of UM cells in the division phase.Silencing SOST can promote tumor growth in eyes of nude mice.SOST may play this function by interacting with the membrane receptor LRP-5/LRP-6 and then regulating the WNT/CTNNB1 signal pathway.