The polarity protein Par3 enhances renal cell carcinoma metastasis via YAP/TAZ activation

Partitioning defective protein 3 (Par3) has recently been found to have important roles in cancer progression. Interestingly, Par3’s functions vary among cancers: both Par3 elevation (in the prostate or liver) and loss (in the breast or lung) have been implicated in cancer metastasis. Although Par3 overexpression has been correlated with diminished survival in renal cell carcinoma (RCC), data indicating the role of Par3 in RCC metastasis are lacking. Given reports of interactions between Par3 and oncoproteins such as Yes-associated protein (YAP)/WW domain-containing transcription regulator 1 (TAZ), we investigated whether Par3-mediated RCC metastasis might be due to activation of the Hippo pathway components YAP and TAZ.

Par3 levels were analyzed in RCC cell lines and human RCC patient tissues by western blotting and immunohistochemical (IHC) staining, as appropriate. Co-immunoprecipitation (co-IP) and immunofluorescence studies were conducted to examine the interaction between Par3 and YAP. Quantitative PCR and luciferase assays were used to investigate the effects of Par3 on YAP target gene expression and co-transcriptional regulation. PDZ domain deletion mutants of Par3 were generated to elucidate the structural basis of the interaction between Par3 and YAP.

Higher Par3 levels were found in distant-organ-RCC-metastasis-derived ACHN sublines than wild type ACHN cell lines. Par3 levels were also higher in the patient tissue obtained from metastatic sites than in normal kidney and primary RCC tumor tissues. Co-IP and IHC experiments demonstrated that Par3 directly interacted and co-localized with YAP/TAZ proteins. Moreover, Par3 upregulated the transcription of YAP/TAZ downstream target genes and increased the luciferase activity of YAP/TAZ responsive elements. PDZ domain 3 in the PARD3 gene was demonstrated to be particularly important in the interactions between Par3 and YAP. Furthermore, Par3 was found to upregulate intracellular levels of YAP/TAZ molecules and promote nuclear translocation of YAP.

Together, these results indicate the role of Par3 in RCC metastasis, via driving metastatic RCC progression by promoting the YAP/TAZ pathway.