Clinical and in vitro analysis of Osteopontin as a prognostic indicator and unveil its potential downstream targets in bladder cancer

Osteopontin (OPN) plays an important role in cancer progression, however its prognostic significance and its downstream factors are largely elusive. In this study, we have shown that expression of OPN was significantly higher in bladder cancer specimens with higher T-stage or tumor grades. In addition, a high level of OPN was significantly associated with poorer survival in two independent bladder cancer patient cohorts totaling 389 bladder cancer patients with available survival data. We further identified Matrix metallopeptidase 9 (MMP9) and S100 calcium-binding protein A8 (S100A8) were both downstream factors for OPN in bladder cancer specimens and bladder cancer cell lines. Expression of OPN was significantly positively associated with that of MMP9 and S100A8, while overexpression of OPN resulted in upregulation of MMP9 and S100A8, and knockdown of OPN showed consistent downregulation of MMP9 and S100A8 expression levels. Importantly, expression levels of both MMP9 and S100A8 were significantly associated with higher T-stage, higher tumor grade and a shorter survival time in the bladder cancer patients. Interestingly, OPN expression only predicted survival in MMP9-high, but not MMP9-low subgroups, and in S100A8-low but not S100A8-high subgroups. Our results suggest that OPN, MMP9 and S100A8 all play a significant role in bladder cancer progression and are potential prognostic markers and therapeutic targets in bladder cancer. The mechanistic link between these three genes and bladder cancer progression warrants further investigation.