Transmembrane protein KIRREL1 regulates Hippo signaling via a feedback loop and represents a therapeutic target in YAP/TAZ-active cancers.

The Hippo tumor-suppressor pathway is frequently dysregulated in human cancers and represents a therapeutic target. However, strategies targeting the mammalian Hippo pathway are limited because of the lack of a well-established cell-surface regulator. Here, we show that transmembrane protein KIRREL1, by interacting with both SAV1 and LATS1/2, promotes LATS1/2 activation by MST1/2 (Hippo kinases), and LATS1/2 activation, in turn, inhibits activity of YAP/TAZ oncoproteins. Conversely, YAP/TAZ directly induce the expression of KIRREL1 in a TEAD1-4-dependent manner. Indeed, KIRREL1 expression positively correlates with canonical YAP/TAZ target gene expression in clinical tumor specimens and predicts poor prognosis. Moreover, transgenic expression of KIRREL1 effectively blocks tumorigenesis in a mouse intrahepatic cholangiocarcinoma model, indicating a tumor-suppressor role of KIRREL1. Hence, KIRREL1 constitutes a negative feedback mechanism regulating the Hippo pathway and serves as a cell-surface marker and potential drug target in cancers with YAP/TAZ dependency.

Traditional Chinese medicine Yiqi Huoxue recipe attenuates hepatic fibrosis via YAP/TAZ signaling.

BACKGROUND/AIMS: The Yiqi Huoxue (YQHX) recipe has been shown to attenuate liver fibrosis, but precise mechanisms have not yet been elucidated. Recently, Yes-associated protein (YAP)/transcriptional coactivator with PDZ-binding motif (TAZ) signaling has been implicated in liver fibrogenesis. This study investigated whether the YAP/TAZ signaling is involved in the therapeutic effect of YQHX on hepatic fibrosis. MATERIALS AND METHODS: Wistar rats were used to generate a model of carbon tetrachloride (CCl4)-induced liver fibrosis. Chronic hepatitis B (CHB) patients with liver fibrosis were enrolled and assigned to receive either nucleoside/nucleotide analogues (NAs) or NAs plus YQHX. Histology, immunohistochemistry, qRT-PCR, and western blotting were conducted to mechanistically assess the therapeutic effects of YQHX on liver fibrosis. RESULTS: YQHX markedly alleviated morphological alterations in CCl4-induced liver fibrosis and decreased markers of hepatic fibrosis in rats. Furthermore, YQHX significantly suppressed CCl4-meidated activation of the transforming growth factor-beta (TGF-ß)/Smad signaling pathway. Notably, CCl4 induced up-regulation of YAP, TAZ, and connective tissue growth factor (CTGF), which were significantly abrogated by YQHX. Consistent with the above major findings in rats, CHB patients treated with NAs plus YQHX had greater improvement in liver fibrosis than those given NAs alone (71.4% vs. 28.6%; P = 0.057). In addition, hepatic and plasma levels of YAP were significantly decreased after YQHX treatment in CHB patients with liver fibrosis. CONCLUSION: YAP/TAZ signaling plays a role, at least in part, in the anti-fibrotic activity of YQHX. The findings may help to better understand the mechanisms of YQHX in the treatment of liver fibrosis.