Loss of polarity protein Par3, via transcription factor Snail, promotes bladder cancer metastasis

Bladder cancer (BLCA) remains the leading cause of cancer‐related mortality among genitourinary malignancies worldwide. BLCA metastasis represents the primary reason for its poor prognosis. In this study, we report that decreased expression of partitioning defective 3 (Par3), a polarity protein (encoded by PARD3), is associated with tumor aggressive phenotypes and poor prognosis in BLCA patients. Consistently, ablation of Par3 promotes the metastasis and invasion of BLCA cells in vitro and in vivo. Further studies reveal that zinc finger protein Snail represses the expression of Par3 by binding to E2‐box (CAGGTG) of PARD3 promoter‐proximal. Inhibition of GSK‐3β promotes the expression and nuclear localization of Snail and then reduces the expression of Par3, resulting in the metastasis and invasion of BLCA cells. Moreover, we detected the interaction between Par3 (936‐1356 aa) and ZO‐1 (1372‐1748 aa), which is involved in the maintenance of tight junction. Together, our results demonstrate that the GSK‐3β/Snail/Par3/ZO‐1 axis regulates BLCA metastasis, and Snail is a major regulator for Par3 protein expression in BLCA. We report here that (a) polarity protein Par3 is frequently lost in BLCA patients and is associated with muscle‐invasive phenotypes and poor prognosis; (b) Par3 deficiency is required for BLCA invasion and metastasis in vitro and in vivo; (c) Snail suppresses Par3 expression through its binding to PARD3 E2‐box; and (d) overexpression of Par3 abolishes LiCl‐ or Snail‐induced BLCA metastatic behaviors, suggesting a role of the GSK‐3β/Snail/Par3 axis in regulating BLCA metastasis.