Regulation of the Hippo Pathway by Phosphatidic Acid-Mediated Lipid-Protein Interaction.

The Hippo pathway plays a crucial role in organ size control and tumor suppression, but its precise regulation is not fully understood. In this study, we discovered that phosphatidic acid (PA)-related lipid signaling is a key regulator of the Hippo pathway. Supplementing PA in various Hippo-activating conditions activates YAP. This PA-related lipid signaling is involved in Rho-mediated YAP activation. Mechanistically, PA directly interacts with Hippo components LATS and NF2 to disrupt LATS-MOB1 complex formation and NF2-mediated LATS membrane translocation and activation, respectively. Inhibition of phospholipase D (PLD)-dependent PA production suppresses YAP oncogenic activities. PLD1 is highly expressed in breast cancer and positively correlates with YAP activation, suggesting their pathological relevance in breast cancer development. Taken together, our study not only reveals a role of PLD-PA lipid signaling in regulating the Hippo pathway but also indicates that the PLD-PA-YAP axis is a potential therapeutic target for cancer treatment.

Primary and metastatic tumors exhibit systems-level differences in dependence on mitochondrial respiratory function.

The Warburg effect, aerobic glycolysis, is a hallmark feature of cancer cells grown in culture. However, the relative roles of glycolysis and respiratory metabolism in supporting in vivo tumor growth and processes such as tumor dissemination and metastatic growth remain poorly understood, particularly on a systems level. Using a CRISPRi mini-library enriched for mitochondrial ribosomal protein and respiratory chain genes in multiple human lung cancer cell lines, we analyzed in vivo metabolic requirements in xenograft tumors grown in distinct anatomic contexts. While knockdown of mitochondrial ribosomal protein and respiratory chain genes (mito-respiratory genes) has little impact on growth in vitro, tumor cells depend heavily on these genes when grown in vivo as either flank or primary orthotopic lung tumor xenografts. In contrast, respiratory function is comparatively dispensable for metastatic tumor growth. RNA-Seq and metabolomics analysis of tumor cells expressing individual sgRNAs against mito-respiratory genes indicate overexpression of glycolytic genes and increased sensitivity of glycolytic inhibition compared to control when grown in vitro, but when grown in vivo as primary tumors these cells down-regulate glycolytic mechanisms. These studies demonstrate that discrete perturbations of mitochondrial respiratory chain function impact in vivo tumor growth in a context-specific manner with differential impacts on primary and metastatic tumors.

Control of metastatic niche formation by targeting APBA3/Mint3 in inflammatory monocytes.

Cancer metastasis is intricately orchestrated by both cancer and normal cells, such as endothelial cells and macrophages. Monocytes/macrophages, which are often co-opted by cancer cells and promote tumor malignancy, acquire more than half of their energy from glycolysis even during normoxic conditions. This glycolytic activity is maintained during normoxia by the functions of hypoxia inducible factor 1 (HIF-1) and its activator APBA3. The mechanism by which APBA3 inhibition partially suppresses macrophage function and affects cancer metastasis is of interest in view of avoidance of the adverse effects of complete suppression of macrophage function during therapy. Here, we report that APBA3-deficient mice show reduced metastasis, with no apparent effect on primary tumor growth. APBA3 deficiency in inflammatory monocytes, which strongly express the chemokine receptor CCR2 and are recruited toward chemokine CCL2 from metastatic sites, hampers glycolysis-dependent chemotaxis of cells toward metastatic sites and inhibits VEGFA expression, similar to the effects observed with HIF-1 deficiency. Host APBA3 induces VEGFA-mediated E-selectin expression in the endothelial cells of target organs, thereby promoting extravasation of cancer cells and micrometastasis formation. Administration of E-selectin-neutralizing antibody also abolished host APBA3-mediated metastatic formation. Thus, targeting APBA3 is useful for controlling metastatic niche formation by inflammatory monocytes.

Loss of YAP1 defines neuroendocrine differentiation of lung tumors.

YAP1, the main Hippo pathway effector, is a potent oncogene and is overexpressed in non-small-cell lung cancer (NSCLC); however, the YAP1 expression pattern in small-cell lung cancer (SCLC) has not yet been elucidated in detail. We report that the loss of YAP1 is a special feature of high-grade neuroendocrine lung tumors. A hierarchical cluster analysis of 15 high-grade neuroendocrine tumor cell lines containing 14 SCLC cell lines that depended on the genes of Hippo pathway molecules and neuroendocrine markers clearly classified these lines into two groups: the YAP1-negative and neuroendocrine marker-positive group (n = 11), and the YAP1-positive and neuroendocrine marker-negative group (n = 4). Among the 41 NSCLC cell lines examined, the loss of YAP1 was only observed in one cell line showing the strong expression of neuroendocrine markers. Immunostaining for YAP1, using the sections of 189 NSCLC, 41 SCLC, and 30 large cell neuroendocrine carcinoma (LCNEC) cases, revealed that the loss of YAP1 was common in SCLC (40/41, 98%) and LCNEC (18/30, 60%), but was rare in NSCLC (6/189, 3%). Among the SCLC and LCNEC cases tested, the loss of YAP1 correlated with the expression of neuroendocrine markers, and a survival analysis revealed that YAP1-negative cases were more chemosensitive than YAP1-positive cases. Chemosensitivity test for cisplatin using YAP1-positive/YAP1-negative SCLC cell lines also showed compatible results. YAP1-sh-mediated knockdown induced the neuroendocrine marker RAB3a, which suggested the possible involvement of YAP1 in the regulation of neuroendocrine differentiation. Thus, we showed that the loss of YAP1 has potential as a clinical marker for predicting neuroendocrine features and chemosensitivity.

The Hippo pathway kinases LATS1 and LATS2 attenuate cellular responses to heavy metals through phosphorylating MTF1.

Heavy metals are both integral parts of cells and environmental toxicants, and their deregulation is associated with severe cellular dysfunction and various diseases. Here we show that the Hippo pathway plays a critical role in regulating heavy metal homeostasis. Hippo signalling deficiency promotes the transcription of heavy metal response genes and protects cells from heavy metal-induced toxicity, a process independent of its classic downstream effectors YAP and TAZ. Mechanistically, the Hippo pathway kinase LATS phosphorylates and inhibits MTF1, an essential transcription factor in the heavy metal response, resulting in the loss of heavy metal response gene transcription and cellular protection. Moreover, LATS activity is inhibited following heavy metal treatment, where accumulated zinc directly binds and inhibits LATS. Together, our study reveals an interplay between the Hippo pathway and heavy metals, providing insights into this growth-related pathway in tissue homeostasis and stress response.

Nf1-Mutant Tumors Undergo Transcriptome and Kinome Remodeling after Inhibition of either mTOR or MEK.

Loss of the tumor suppressor NF1 leads to activation of RAS effector pathways, which are therapeutically targeted by inhibition of mTOR (mTORi) or MEK (MEKi). However, therapeutic inhibition of RAS effectors leads to the development of drug resistance and ultimately disease progression. To investigate molecular signatures in the context of NF1 loss and subsequent acquired drug resistance, we analyzed the exomes, transcriptomes, and kinomes of Nf1-mutant mouse tumor cell lines and derivatives of these lines that acquired resistance to either MEKi or mTORi. Biochemical comparisons of this unique panel of tumor cells, all of which arose in Nf1+/- mice, indicate that loss of heterozygosity of Nf1 as an initial genetic event does not confer a common biochemical signature or response to kinase inhibition. Although acquired drug resistance by Nf1-mutant tumor cells was accompanied by altered kinomes and irreversibly altered transcriptomes, functionally in multiple Nf1-mutant tumor cell lines, MEKi resistance was a stable phenotype, in contrast to mTORi resistance, which was reversible. Collectively, these findings demonstrate that Nf1-mutant tumors represent a heterogeneous group biochemically and undergo broader remodeling of kinome activity and gene expression in response to targeted kinase inhibition.

Defining the ATPome reveals cross-optimization of metabolic pathways.

Disrupted energy metabolism drives cell dysfunction and disease, but approaches to increase or preserve ATP are lacking. To generate a comprehensive metabolic map of genes and pathways that regulate cellular ATP-the ATPome-we conducted a genome-wide CRISPR interference/activation screen integrated with an ATP biosensor. We show that ATP level is modulated by distinct mechanisms that promote energy production or inhibit consumption. In our system HK2 is the greatest ATP consumer, indicating energy failure may not be a general deficiency in producing ATP, but rather failure to recoup the ATP cost of glycolysis and diversion of glucose metabolites to the pentose phosphate pathway. We identify systems-level reciprocal inhibition between the HIF1 pathway and mitochondria; glycolysis-promoting enzymes inhibit respiration even when there is no glycolytic ATP production, and vice versa. Consequently, suppressing alternative metabolism modes paradoxically increases energy levels under substrate restriction. This work reveals mechanisms of metabolic control, and identifies therapeutic targets to correct energy failure.

Hippo signaling dysfunction induces cancer cell addiction to YAP.

Over the past decades, the Hippo has been established as a crucial pathway involved in organ size control and cancer suppression. Dysregulation of Hippo signaling and hyperactivation of its downstream effector YAP are frequently associated with various human cancers. However, the underlying significance of such YAP activation in cancer development and therapy has not been fully characterized. In this study, we reported that the Hippo signaling deficiency can lead to a YAP-dependent oncogene addiction for cancer cells. Through a clinical compound library screen, we identified histone deacetylase (HDAC) inhibitors as putative inhibitors to suppress YAP expression. Importantly, HDAC inhibitors specifically targeted the viability and xenograft tumor growth for the cancer cells in which YAP is constitutively active. Taken together, our results not only establish an active YAP-induced oncogene addiction in cancer cells, but also lay the foundation to develop targeted therapies for the cancers with Hippo dysfunction and YAP activation.

The ERK signaling target RNF126 regulates anoikis resistance in cancer cells by changing the mitochondrial metabolic flux.

Loss of anchorage to the extracellular matrix leads to apoptosis (anoikis) in normal cells, but cancerous cells are usually resistant to such stress. Here we report the pivotal role of an E3 ubiquitin ligase, ring-finger protein 126 (RNF126), in the resistance of cancer cells to the stress associated with non-adherent conditions. Non-adherent cancer cells exhibited increased flux through the tricarboxylic acid cycle via increased conversion of pyruvate to acetyl-CoA. RNF126 was found to act as a ubiquitin ligase for pyruvate dehydrogenase kinases (PDKs), resulting in their proteasomal degradation. This decrease in PDK levels allowed pyruvate dehydrogenases to catalyze the conversion of pyruvate to acetyl-CoA. Moreover, depletion of RNF126 or increased expression of PDK1 in cancer cells suppressed colony formation in soft agar as well as tumorigenicity in mice. RNF126 expression in cancer cells was found to be under the control of the extracellular signal-regulated kinase signaling pathway, which is essential for anoikis resistance. Thus, RNF126 is an attractive molecule for treating cancer by selectively targeting anchorage-independent growth.

Mint3/Apba3 depletion ameliorates severe murine influenza pneumonia and macrophage cytokine production in response to the influenza virus.

Influenza virus (IFV) infection is a common cause of severe pneumonia. Studies have suggested that excessive activation of the host immune system including macrophages is responsible for the severe pathologies mediated by IFV infection. Here, we focused on the X11 protein family member Mint3/Apba3, known to promote ATP production via glycolysis by activating hypoxia inducible factor-1 (HIF-1) in macrophages, and examined its roles in lung pathogenesis and anti-viral defence upon IFV infection. Mint3-deficient mice exhibited improved influenza pneumonia with reduced inflammatory cytokines/chemokine levels and neutrophil infiltration in the IFV-infected lungs without alteration in viral burden, type-I interferon production, or acquired immunity. In macrophages, Mint3 depletion attenuated NF-κB signalling and the resultant cytokine/chemokine production in response to IFV infection by increasing IκBα and activating the cellular energy sensor AMPK, respectively. Thus, Mint3 might represent one of the likely therapeutic targets for the treatment of severe influenza pneumonia without affecting host anti-viral defence through suppressing macrophage cytokine/chemokine production.

NECAB3 Promotes Activation of Hypoxia-inducible factor-1 during Normoxia and Enhances Tumourigenicity of Cancer Cells.

Unlike most cells, cancer cells activate hypoxia inducible factor-1 (HIF-1) to use glycolysis even at normal oxygen levels, or normoxia. Therefore, HIF-1 is an attractive target in cancer therapy. However, the regulation of HIF-1 during normoxia is not well characterised, although Mint3 was recently found to activate HIF-1 in cancer cells and macrophages by suppressing the HIF-1 inhibitor, factor inhibiting HIF-1 (FIH-1). In this study, we analysed Mint3-binding proteins to investigate the mechanism by which Mint3 regulates HIF-1. Yeast two-hybrid screening using Mint3 as bait identified N-terminal EF-hand calcium binding protein 3 (NECAB3) as a novel factor regulating HIF-1 activity via Mint3. NECAB3 bound to the phosphotyrosine-binding domain of Mint3, formed a ternary complex with Mint3 and FIH-1, and co-localised with Mint3 at the Golgi apparatus. Depletion of NECAB3 decreased the expression of HIF-1 target genes and reduced glycolysis in normoxic cancer cells. NECAB3 mutants that binds Mint3 but lacks an intact monooxygenase domain also inhibited HIF-1 activation. Inhibition of NECAB3 in cancer cells by either expressing shRNAs or generating a dominant negative mutant reduced tumourigenicity. Taken together, the data indicate that NECAB3 is a promising new target for cancer therapy.