Regulation of aquaporin-2 abundance by TAZ  in the kidney collecting duct cells
Background: The transcriptional coactivator with a PDZ-binding motif (TAZ), a downstream effector of the Hippo signaling pathway, regulates the expression of target genes by acting as a transcription cofactor. TAZ knockout (KO) mice exhibit polycystic kidneys and polyuria. This study aimed to investigate the role of TAZ in vasopressin-induced AQP2 regulation. Methods: 1) TAZ knockdown mediated by siRNA in mpkCCDc11 cells; 2) qRT-PCR, semiquantitative immunoblotting, and immunocytochemistry of AQP2; and 3) Next Generation Sequencing (NGS) in mpkCCDc11 cells, a mouse collecting duct cell line. Results: Endogenous expression of AQP2 was induced in mpkCCDc11 cells by treatment with dDAVP (10-9 M) treatment. Treatment with dDAVP (10-9 M) for 24 h increased AQP2 mRNA (12,608 ± 177% of control) and AQP2 protein levels (287 ± 15%). On the contrary, the increase induced by dDAVP in AQP2 mRNA (9,240 ± 241% of the control) and protein levels (215 ± 23%) was significantly reduced in TAZ-KD cells. TonEBP protein levels remained unchanged in TAZ-KD cells. NGS identified several potential AQP2 transcription factors (TF), including Klf6, Irf3, Cebpb, and Nr4a1, selected based on previous in silico database analysis. Among these, Nr4a1 was chosen for further investigation due to its significantly reduced expression of mRNA in TAZ-KD cells, as confirmed by qRT-PCR. Conclusion: TAZ appears to affect dDAVP-induced AQP2 trafficking through mechanisms not mediated by the cAMP/PKA pathway, suggesting the involvement of other non-canonical pathways. TAZ may also regulate AQP2 abundance, potentially through interaction with several transcription factors, including Nr4a1. Overall design: To investigate the impact of TAZ on regulation of aquaporin-2 in kidney collecting duct cells , TAZ knockdown was induced in mpkCCDc11 cells, a mouse cortical kidney collecting duct cell line, by treating them with TAZ-siRNA and vasopressin, followed by observation of changes. Subsequently, we conducted RNA-sequencing using three samples from each group treated with control-siRNA,TAZ-siRNA and vasopressin, respectively, to analyze transcriptomics. Changes in genes involved in aquaporin-2 transcription were analyzed based on NGS data.