Deubiquitinating enzyme BAP1 is mutated in a hereditary cancer syndrome with increased risk of mesothelioma and uveal melanoma. Somatic BAP1 mutations occur in various malignancies. We show that mouse Bap1 gene deletion is lethal during embryogenesis, but systemic or hematopoietic-restricted deletion in adults recapitulates features of human myelodysplastic syndrome (MDS). Knock-in mice expressing BAP1 with a 3xFlag tag revealed that BAP1 interacts with HCF-1, OGT, and the polycomb group proteins ASXL1 and ASXL2 in vivo. OGT and HCF-1 levels were decreased by Bap1 deletion, indicating a critical role for BAP1 in stabilizing these epigenetic regulators. Human ASXL1 is mutated frequently in chronic myelomonocytic leukemia (CMML) so an ASXL/BAP1 complex may suppress CMML. A novel BAP1 catalytic mutation found in a MDS patient implies that BAP1 loss of function has similar consequences in mouse and man.

No abstract

The Hippo signaling pathway is responsible for regulating the function of TEAD family transcription factors in metazoans. TEADs, with their co-activators YAP/TAZ, are critical for controlling cell differentiation and organ size through their transcriptional activation of genes involved in cell growth and proliferation. Dysregulation of the Hippo pathway has been implicated in multiple forms of cancer. Here, we identify a novel form of regulation of TEAD family proteins. We show that human TEADs are palmitoylated at a universally conserved cysteine, and report the crystal structures of the human TEAD2 and TEAD3 YAP-binding domains in their palmitoylated forms. These structures show a palmitate bound within a highly conserved hydrophobic cavity at each protein's core. Our findings also demonstrate that this modification is required for proper TEAD folding and stability, indicating a potential new avenue for pharmacologically regulating the Hippo pathway through the modulation of TEAD palmitoylation.

The Hippo pathway remains a central focus in both basic and translational research and is a key modulator of developmental biology. Dysregulation of the pathway is associated with a plethora of human cancers and there are multiple efforts to target key components of the pathway for disease intervention. In this review, we briefly highlight the latest research advances around the core components of the Hippo pathway in cancer. More specifically, we discuss several genetic aberrations of these factors as mechanisms for the development of cancers, including genetic amplification, deletion, and gene fusions. Additionally, we highlight the role of the Hippo pathway in cancer therapy resistance and tumor immunogenicity. Last, we summarize the ongoing efforts to target the pathway in cancers. The Hippo Pathway The Hippo pathway is a highly conserved signaling pathway across higher-order vertebrates that modulates key target genes to regulate a multitude of biological processes including cellular proliferation, survival, differentiation, cellular fate determination, organ size, and tissue homeostasis (Figure 1). At the core of the pathway are serine/threonine kinases, sterile 20-like kinase 1/2 (MST1/2), and large tumor suppressor 1/2 (LATS1/2). Recently, MAP4K and TAOK kinases have been shown to directly phosphorylate LATS1/2, thus acting in parallel with MST1/2 [1]. These kinases, along with the adaptor proteins, Salvador homolog 1 (SAV1) and MOB kinase activator 1A/B (MOB1A/B), phosphorylate and inhibit downstream effector proteins, Yesassociated protein (YAP1), and its paralog transcriptional coactivator with PDZ-binding motif (TAZ) (also known as WWTR1) and sequestrates them in the cytoplasm by binding to 14-3-3 proteins [2]. Notably, the tumor suppressor neurofibromin 2 (NF2) (also known as Merlin) participates upstream of these kinases to inhibit YAP and TAZ activity by promoting the activation of the pathway. Additional phosphorylation of YAP/TAZ leads to proteasome-mediated degradation facilitated by binding to β-TrCP [3,4]. Such regulation prevents YAP/TAZ from accumulating in the nucleus and from binding to a family of sequence-specific transcription factors called TEA DNA-binding proteins (TEAD1-4) that mediate proliferative and prosurvival genes such as CTGF, CRY61, BIRC5, ANKRD1, and AXL (Figure 2). Besides TEADs, YAP/TAZ also cooperates with RUNT-related transcription factors (RUNX1 and 2), T-box transcription factor 5 (TBX5), and SMADs as among others [2,5]. Hippo Pathway Deregulation in Cancer Overexpression of Hippo Pathway Effector Proteins Aberration of the Hippo pathway is associated with the hallmarks of oncogenesis and, more recently, has been linked to other cellular processes such as regulation of T cell functionality [6]. These hallmarks include the induction of hyperproliferation, cellular invasion, and metastasis, as well as a role in cancer cell maintenance and chemotherapeutic resistance mechanisms. Analysis of over 9000 tumors showed that YAP and TAZ are frequently amplified in head and nec...

Among more than 200 BAP1 -mutant families affected by the "BAP1 cancer syndrome, " nearly all individuals inheriting a BAP1 mutant allele developed one or more malignancies during their lifetime, mostly uveal and cutaneous melanoma, mesothelioma, and clear-cell renal cell carcinoma. These cancer types are also those that, when they occur sporadically, are more likely to carry somatic biallelic BAP1 mutations. Mechanistic studies revealed that the tumor suppressor function of BAP1 is linked to its dual activity in the nucleus, where it is implicated in a variety of processes including DNA repair and transcription, and in the cytoplasm, where it regulates cell death and mitochondrial metabolism. BAP1 activity in tumor suppression is cell type-and context-dependent. BAP1 has emerged as a critical tumor suppressor across multiple cancer types, predisposing to tumor development when mutated in the germline as well as somatically. Moreover, BAP1 has emerged as a key regulator of gene-environment interaction.