The Yes-associated protein (YAP) is a transcription coactivator that plays a crucial role in organ size control by promoting cell proliferation and inhibiting apoptosis. The Hippo tumor suppressor pathway inhibits YAP through phosphorylation-induced cytoplasmic retention and degradation. Here we report a novel mechanism of YAP regulation by angiomotin (AMOT) family proteins via a direct interaction. Knockdown of AMOT family protein AMOTL2 in polarized Madin-Darby canine kidney (MDCK) cells leads to YAP activation, as indicated by decreased YAP tight junction localization, attenuated YAP phosphorylation, accumulation of nuclear YAP, and induction of YAP target gene expression. Transcriptional coactivator with PDZ-binding motif (TAZ), the YAP paralog, is also regulated by AMOT in a similar fashion. Furthermore, AMOTL2 knockdown results in loss of cell contact inhibition in a manner dependent on the functions of YAP and TAZ. Our results indicate a potential tumor-suppressing role of AMOT family proteins as components of the Hippo pathway, and demonstrate a novel mechanism of YAP and TAZ inhibition by AMOT-mediated tight junction localization. These observations provide a potential link between the Hippo pathway and cell contact inhibition.

The TAZ transcription co-activator has been shown to promote cell proliferation and to induce epithelial-mesenchymal transition. Recently we have demonstrated that TAZ is phosphorylated and inhibited by the Hippo tumor suppressor pathway, which is altered in human cancer. The mechanism of TAZ-mediated transcription is unclear. We demonstrate here that TEAD is a key downstream transcription factor mediating the function of TAZ. Disruption of TEAD-TAZ binding or silencing of TEAD expression blocked the function of TAZ to promote cell proliferation and to induce epithelial-mesenchymal transition, demonstrating TEAD as a key downstream effector of TAZ. We also identified CTGF, a gene that regulates cell adhesion, proliferation, and migration, as a direct target of TAZ and TEAD. Our study establishes a functional partnership between TAZ and TEAD under negative regulation by the Hippo signaling pathway.

The TAZ transcription co-activator promotes cell proliferation and epithelial-mesenchymal transition. TAZ is inhibited by the Hippo tumor suppressor pathway, which promotes TAZ cytoplasmic localization by phosphorylation. We report here that TAZ protein stability is controlled by a phosphodegron recognized by the F-box protein β-TrCP and ubiquitylated by the SCF/CRL1^β-TrCP E3 ligase. The interaction between TAZ and β-TrCP is regulated by the Hippo pathway. Phosphorylation of a phosphodegron in TAZ by LATS primes it for further phosphorylation by CK1ϵ and subsequent binding by β-TrCP. Therefore, the Hippo pathway negatively regulates TAZ function by both limiting its nuclear accumulation and promoting its degradation. The phosphodegron-mediated TAZ degradation plays an important role in negatively regulating TAZ biological functions.

The conversion of serine and glycine that is accomplished by serine hydroxymethyltransferase 2 (SHMT2) in mitochondria is significantly upregulated in various cancers to support cancer cell proliferation. In this study, we observed that SHMT2 is acetylated at K95 in colorectal cancer (CRC) cells. SIRT3, the major deacetylase in mitochondria, is responsible for SHMT2 deacetylation. SHMT2-K95-Ac disrupts its functional tetramer structure and inhibits its enzymatic activity. SHMT2-K95-Ac also promotes its degradation via the K63-ubiquitin–lysosome pathway in a glucose-dependent manner. TRIM21 acts as an E3 ubiquitin ligase for SHMT2. SHMT2-K95-Ac decreases CRC cell proliferation and tumor growth in vivo through attenuation of serine consumption and reduction in NADPH levels. Finally, SHMT2-K95-Ac is significantly decreased in human CRC samples and is inversely associated with increased SIRT3 expression, which is correlated with poorer postoperative overall survival. Our study reveals the unknown mechanism of SHMT2 regulation by acetylation which is involved in colorectal carcinogenesis.

The Hippo pathway regulates organ size by controlling both cell proliferation and apoptosis. TAZ functions as a transcriptional co-activator downstream of the Hippo pathway and has been implicated in human cancer development. A key step in the Hippo-TAZ pathway is phosphorylation of TAZ by LATS kinase, which leads to TAZ inhibition by both cytoplasmic retention and degradation. However, the mechanism of TAZ dephosphorylation and the responsible phosphatase are unknown. Here, we identified PP1 as a bona fide TAZ phosphatase. PP1A dephosphorylates TAZ at Ser-89 and Ser-311, promotes TAZ nuclear translocation, and stabilizes TAZ by disrupting the binding to the SCF E3 ubiquitin ligase. Furthermore, ASPP2 facilitates the interaction between TAZ and PP1 to promote TAZ dephosphorylation. As a result, PP1 and ASPP2 increase TAZ-dependent gene expression. This study demonstrates that PP1A and ASPP2 play a critical role in promoting TAZ function by antagonizing the LATS kinase through TAZ dephosphorylation.