Induction of antiproliferative connective tissue growth factor expression in Wilms' tumor cells by sphingosine-1-phosphate receptor 2

Connective tissue growth factor (CTGF), a member of the CCN family of secreted matricellular proteins, regulates fibrosis, angiogenesis, cell proliferation, apoptosis, tumor growth, and metastasis. However, the role of CTGF and its regulation mechanism in Wilms' tumor remains largely unknown. We found that the bioactive lipid sphingosine-1-phosphate (S1P) induced CTGF expression in a concentration- and time-dependent manner in a Wilms' tumor cell line (WiT49), whereas FTY720-phosphate, an S1P analogue that binds all S1P receptors except S1P₂, did not. Further, the specific S1P₂ antagonist JTE-013 completely inhibited S1P-induced CTGF expression, whereas the S1P₁ antagonist VPC44116 did not, indicatingthat this effect was mediated by S1P₂. This was confirmed by adenoviral transduction of S1P₂ in WiT49 cells, which showed that overexpression of S1P ₂ increased the expression of CTGF. Induction of CTGF by S1P was sensitive to ROCK inhibitor Y-27632 and c-Jun NH₂-terminal kinase inhibitor SP600125, suggesting the requirement of RhoA/ROCK and c-Jun NH2-terminal kinase pathways for S1P-induced CTGF expression. Interestingly, the expression levels of CTGF were decreased in 8 of 10 Wilms' tumor tissues compared with matched normal tissues by quantitative real-time PCR and Western blot analysis. In vitro, human recombinant CTGF significantly inhibited the proliferation of WiT49 cells. In addition, overexpression of CTGF resulted in significant inhibition of WiT49 cell growth. Taken together, these data suggest that CTGF protein induced by S1P₂ might act as a growth inhibitor in Wilms' tumor.