Activation of  the YAP/KLF5 transcriptional cascade in renal tubular cells aggravates kidney injury
The Hippo/YAP pathway plays a critical role in early embryonic kidney development, but its functions in the adult kidney are less well understood. Our previous work has demonstrated that tubular YAP activation induced by double knockout of the upstream Hippo kinases Mst1 and Mst2 (Mst1/2 dKO) promotes tubular injury and renal inflammation under basal conditions. However, the importance of tubular YAP activation remains to be established in injured kidneys in which many other injurious pathways are simultaneously activated. Several secreted factors were found to be increased by YAP in tubular cells, but how the transcriptional network is altered by YAP  is largely unknown.  Here, we show that tubular YAP was already activated at 6 h after unilateral ureteral obstruction (UUO). Tubular YAP deficiency greatly attenuated tubular cell over-proliferation, tubular injury and renal inflammation induced by UUO or cisplatin. RNA-Seq, ChIP and luciferase assay revealed that YAP promoted the transcription of the transcription factor KLF5 whereas no interaction between YAP and KLF5 was observed. Consistently, the elevated expression of KLF5 and its target genes in Mst1/2 dKO or UUO kidneys was blocked by ablation of Yap in tubular cells. Inhibition of KLF5 prevented tubular cell over-proliferation, tubular injury and renal inflammation in Mst1/2 dKO kidneys. Therefore, our results demonstrate that tubular YAP is a key player in kidney injury. YAP and KLF5 form a transcriptional cascade, in which tubular YAP activation induced by kidney injury promotes KLF5 transcription. Activation of this cascade induces tubular cell over-proliferation, tubular injury and renal inflammation Overall design: HK-2 cells cultured in DMEM/F12 containing 1% FBS underwent electrotransfection with GFP or Yap and Taz plasmids. 5 h after electrotransfection, total RNA was extracted. RNA sequencing (RNA-seq) was performed on an Illumina Nova Seq 6000 System (Novogene Co., Ltd.).