Growth differentiation factor-9 expression is inversely correlated with an aggressive behaviour in human bladder cancer cells

Abstract

Growth differentiation factor-9 (GDF-9) is a family member of bone morphogenetic proteins (BMPs), which belong to the TGF-β superfamily. There has been a recent surge of interest in the role of growth differentiation factors and other BMPs in the development and spread of cancer. However, the role of GDF-9 in bladder cancer remains unknown. The present study investigated the expression of GDF-9 in normal and malignant human bladder tissue and its molecular interactions within bladder cancer cells. The expression of GDF-9 in human bladder tissues and bladder cancer cell lines was assessed at both the mRNA and protein levels using RT-PCR and immunohistochemistry, respectively. Full-length GDF-9 cDNA was amplified from normal mammary tissues. GDF-9 was overexpressed in bladder cancer cell lines using a mammalian expression construct. The effect of GDF-9 on cellular functions, was examined in bladder cancer cells overexpressing GDF-9 using a variety of in vitro assays. In normal bladder tissues, stronger staining of GDF-9 was seen in transitional cells, both in the cytoplasm and in the nucleus. In contrast, the staining of GDF-9 was notably weak or absent in cancer cells of tumour tissues. Similarly, the bladder cancer cell lines RT112 and EJ138, expressed very low levels of GDF-9. Moreover, overexpression of GDF-9 reduced the growth, adhesion and migration of bladder cell lines in vitro. However, the overexpression of GDF-9 had little bearing on the invasion of bladder cell lines in vitro. In conclusion, GDF-9 is expressed at lower levels in human bladder cancer cells compared with normal transitional cells of the bladder. GDF-9 levels are inversely correlated with the growth, adhesion and migration of bladder cancer cells in vitro. The results of the present study suggest that GDF-9 is a potential tumour suppressor in human bladder cancer.