Abstract
SummaryBackgroundPhosphorylation of the transcriptional coactivator YAP1 is a key event in defining Hippo signaling outputs. Previous studies demonstrated that phosphorylation of YAP1 at serine 127 (S127) sequesters YAP1 in the cytoplasm and consequently inhibits YAP1 transcriptional activity. Mammalian tissue-culture experiments suggest that downstream of MST1/2 signaling, LATS1/2 function as YAP1-S127 kinases. However, studies of Mst1/2 knockout mouse models revealed that the identity of the physiological YAP1-S127 kinase(s) in certain tissues, such as the intestine, remains unknown.ResultsWe show that mammalian NDR1/2 kinases phosphorylate YAP1 on S127 and thereby negatively regulate YAP1 activity in tissue-cultured cells. By studying NDR1/2-deficient mice, we demonstrate the in vivo relevance of NDR1/2-mediated regulation of YAP1. Specifically, upon loss of NDR1/2 in the intestinal epithelium, endogenous S127 phosphorylation is decreased whereas total YAP1 levels are increased. Significantly, ablation of NDR1/2 from the intestinal epithelium renders mice exquisitely sensitive to chemically induced colon carcinogenesis. Analysis of human colon cancer samples further revealed that NDR2 and YAP1 protein expression are inversely correlated in the majority of samples with high YAP1 expression. Collectively, we report NDR1/2 as physiological YAP1-S127 kinases that might function as tumor suppressors upstream of YAP1 in human colorectal cancer.ConclusionsWe establish mammalian NDR1/2 as bona fide kinases that target YAP1 on S127 in vitro and in vivo. Our findings therefore have important implications for a broad range of research efforts aimed at decoding and eventually manipulating YAP1 biology in cancer settings, regenerative medicine, and possibly also noncancer human diseases.
Highlights
The transcriptional coactivator YAP1 and its fly counterpart Yorkie drive tissue and organ growth in flies and mammals [1]
We show that mammalian NDR1/2 kinases phosphorylate YAP1 on serine 127 (S127) and thereby negatively regulate YAP1 activity in tissue-cultured cells
By studying NDR1/2-deficient mice, we demonstrate the in vivo relevance of NDR1/2-mediated regulation of YAP1
Summary
The transcriptional coactivator YAP1 and its fly counterpart Yorkie drive tissue and organ growth in flies and mammals [1]. Delineated in flies, the Hippo kinase phosphorylates the Lats/Warts kinase, which in turn restricts Yorkie activity by phosphorylating serine 168 (S168) [2]. MST1/2 phosphorylate LATS1/2, which in turn phosphorylate YAP1 on serine 127 (S127), the mammalian equivalent of Yorkie S168 [3], resulting in cytoplasmic retention and decreased transcription of YAP1 target genes [4]. Subsequent mouse models demonstrated that MST1/2 kinases are required to suppress the oncogenic potential of YAP1 in the liver and the intestinal epithelium [7,8,9,10], yet none of these models provided strong evidence for LATS1/2 as direct YAP1S127 kinases. One study suggested that in the liver, MST1/2 activate a kinase distinct from LATS1/2 to phosphorylate YAP1 on S127 [9]. Ablation of MST1/2 kinase activity results in YAP1-dependent crypt hyperplasia [10, 11]. The YAP1-S127 kinase functioning downstream of MST1/2 was not addressed in the intestinal epithelium [10, 11]
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