The Hippo pathway restricts the activity of transcriptional co-activators TAZ and YAP by phosphorylating them for cytoplasmic sequestration or degradation. In this report, we describe an independent mechanism for the cell to restrict the activity of TAZ and YAP through interaction with angiomotin (Amot) and angiomotin-like 1 (AmotL1). Amot and AmotL1 were robustly co-immunoprecipitated with FLAG-tagged TAZ, and their interaction is dependent on the WW domain of TAZ and the PPXY motif in the N terminus of Amot. Amot and AmotL1 also interact with YAP via the first WW domain of YAP. Overexpression of Amot and AmotL1 caused cytoplasmic retention of TAZ and suppressed its transcriptional outcome such as the expression of CTGF and Cyr61. Hippo refractory TAZ mutant (S89A) is also negatively regulated by Amot and AmotL1. HEK293 cells express the highest level of Amot and AmotL1 among nine cell lines examined, and silencing the expression of endogenous Amot increased the expression of CTGF and Cyr61 either at basal levels or upon overexpression of exogenous S89A. These results reveal a novel mechanism to restrict the activity of TAZ and YAP through physical interaction with Amot and AmotL1.

The transcriptional coactivators YAP and TAZ are downstream targets inhibited by the Hippo tumor suppressor pathway. The expression level of TAZ is recently shown to be elevated in invasive breast cancer cells and some primary breast cancers. TAZ is important for breast cancer cell migration, invasion, and tumorigenesis, but the underlying mechanism is not defined. In this study, we show that TAZ interacts with TEAD transcriptional factors. Knockdown of TEADs suppresses TAZmediated oncogenic transformation of MCF10A cells. Uncoupling TAZ from Hippo regulation by S89A mutation enhances its transforming ability. Several residues located in the N-terminal region of TAZ are identified to be important for interaction with TEADs, and these same residues are equally important for TAZ to transform MCF10A cells. Mechanistically, TAZ mutants defective in interaction with TEADs fail to accumulate in the nucleus. Live cell imaging of enhanced green fluorescent protein-TAZ and its mutant defective in TEAD interaction suggests that TEAD interaction mediates nuclear retention. These results reveal a novel mechanism for TEADs to regulate nuclear retention and thus the transforming ability of TAZ.

The Hippo pathway is an evolutionally conserved protein kinase cascade involved in regulating organ size in vivo and cell contact inhibition in vitro by governing cell proliferation and apoptosis. Deregulation of the Hippo pathway is linked to cancer development. Its first core kinase Warts was identified in Drosophila more than 15 years ago, but it gained much attention when other core components of the pathway were identified 8 years later. Major discoveries of the pathway were made during past several years. The core kinase components Hippo, Salvador, Warts, and Mats in the fly and Mst1/2, WW45, Lats1/2, and Mob1 in mammals phosphorylate and inactivate downstream transcriptional co-activators Yorkie in the fly, Yes-associated protein (YAP) and transcriptional co-activator with PDZ-binding motif (TAZ) in mammals, respectively. Phosphorylated Yorkie, YAP, and TAZ are sequestered in the cytoplasm by interaction with 14-3-3 proteins. Here we review recent progresses of this pathway by focusing on how these proteins communicate with each other and how loss of regulation results in cancers.

Exfoliation syndrome (XFS) is the commonest known risk factor for secondary glaucoma and a significant cause of blindness worldwide. Variants in two genes, LOXL1 and CACNA1A have been previously associated with XFS. To further elucidate the genetic basis of XFS, we collected a global sample of XFS cases to refine the association at LOXL1, which previously showed inconsistent results between populations, and to identify new variants associated with XFS. We identified a rare, protective allele at LOXL1 (p.407Phe, OR = 25, P =2.9 × 10−14) through deep resequencing of XFS cases and controls from 9 countries. This variant results in increased cellular adhesion strength compared to the wild-type (p.407Tyr) allele. A genome-wide association study (GWAS) of XFS cases and controls from 24 countries followed by replication in 18 countries identified seven genome-wide significant loci (P < 5 × 10−8). Index variants at the new loci map to chromosomes 13q12 (POMP), 11q23.3 (TMEM136), 6p21 (AGPAT1), 3p24 (RBMS3) and 5q23 (near SEMA6A). These findings provide biological insights into the pathology of XFS, and highlight a potential role for naturally occurring rare LOXL1 variants in disease biology.

The transcriptional co-activators YAP and TAZ are downstream targets inhibited by the Hippo tumor suppressor pathway. YAP and TAZ both possess WW domains, which are important protein–protein interaction modules that mediate interaction with proline-rich motifs, most commonly PPXY. The WW domains of YAP have complex regulatory roles as exemplified by recent reports showing that they can positively or negatively influence YAP activity in a cell and context-specific manner. In this study, we show that the WW domain of TAZ is important for it to transform both MCF10A and NIH3T3 cells and to activate transcription of ITGB2 but not CTGF, as introducing point mutations into the WW domain of TAZ (WWm) abolished its transforming and transcription-promoting ability. Using a proteomic approach, we discovered potential regulatory proteins that interact with TAZ WW domain and identified Wbp2. The interaction of Wbp2 with TAZ is dependent on the WW domain of TAZ and the PPXY-containing C-terminal region of Wbp2. Knockdown of endogenous Wbp2 suppresses, whereas overexpression of Wbp2 enhances, TAZ-driven transformation. Forced interaction of WWm with Wbp2 by direct C-terminal fusion of full-length Wbp2 or its TAZ-interacting C-terminal domain restored the transforming and transcription-promoting ability of TAZ. These results suggest that the WW domain-mediated interaction with Wbp2 promotes the transforming ability of TAZ.