Prostaglandin E2 and its receptor EP2 trigger signaling that contributes to YAP-mediated cell competition

Calcium transients trigger switch-like discharge of prostaglandin E2 in an extracellular signal-regulated kinase-dependent manner

Prostaglandin E2 (PGE2) is a key player in a plethora of physiological and pathological events. Nevertheless, little is known about the dynamics of PGE2 secretion from a single cell and its effect on the neighboring cells. Here, by observing confluent Madin-Darby canine kidney (MDCK) epithelial cells expressing fluorescent biosensors, we demonstrate that calcium transients in a single cell cause PGE2-mediated radial spread of PKA activation (RSPA) in neighboring cells. By in vivo imaging, RSPA was also observed in the basal layer of the mouse epidermis. Experiments with an optogenetic tool revealed a switch-like PGE2 discharge in response to the increasing cytoplasmic Ca2+ concentrations. The cell density of MDCK cells correlated with the frequencies of calcium transients and the following RSPA. The extracellular signal-regulated kinase (ERK) activation also enhanced the frequency of RSPA in MDCK and in vivo. Thus, the PGE2 discharge is regulated temporally by calcium transients and ERK activity.

Prostaglandin E2 attenuates lung fibroblast differentiation via inactivation of yes-associated protein signaling

Prostaglandin E2 (PGE2 ) has been implicated in counteracting fibroblast differentiation by TGFβ1 during pulmonary fibrosis. However, the precise mechanism is not well understood. We show here that PGE2 via EP2 R and EP4 R inhibits the expression of mechanosensory molecules Lysyl Oxidase Like 2 (LOXL2), myocardin-related transcription factor A (MRTF-A), ECM proteins, plasminogen activation inhibitor 1 (PAI-1), fibronectin (FN), α-smooth muscle actin (α-SMA), and redox sensor (nicotinamide adenine dinucleotide phosphate (NADPH) oxidase 4 (NOX4)) required for TGFβ1-mediated fibroblast differentiation. We further demonstrate that PGE2 inhibits fibrotic signaling via Yes-associated protein (YAP) but does so independently from its actions on SMAD phosphorylation and conserved cylindromatosis (CYLD; deubiquitinase) expression. Mechanistically, PGE2 phosphorylates/inactivates YAP downstream of EP2 R/Gαs and restrains its translocation to the nucleus, thus inhibiting its interaction with TEA domain family members (TEADs) and transcription of fibrotic genes. Importantly, pharmacological or siRNA-mediated inhibition of YAP significantly downregulates TGFβ1-mediated fibrotic gene expression and myofibroblast formation. Notably, YAP expression is upregulated in the lungs of D. farinae-treated wild type (WT) mice relative to saline-treated WT mice. Our results unravel a unique role for PGE2 -YAP interactions in fibroblast differentiation, and that PGE2 /YAP inhibition can be used as a novel therapeutic target in the treatment of pathological conditions associated with myofibroblasts like asthma.

Pleiotropic effects of cell competition between normal and transformed cells in mammalian cancers

PURPOSE

In the course of tumor progression, cancer clones interact with host normal cells, and these interactions make them under selection pressure all the time. Cell competition, which can eliminate suboptimal cells and optimize organ development via comparison of cell fitness information, is found to take place between host cells and transformed cells in mammals and play important roles in different phases of tumor progression. The aim of this study is to summarize the current knowledge about the roles and corresponding mechanisms of different cell competition interactions between host normal cells and transformed cells involved in mammalian tumor development.

METHODS

We reviewed the published relevant articles in the Pubmed.

RESULTS

So far, the role of several cell competition interactions have been well described in the different phases of mammalian tumor genesis and development. While cell competitions for trophic factors and epithelial defense against cancer (EDAC) prevent the emergence of transformed cells and suppress carcinogenesis, fitness-fingerprints-comparison system and Myc supercompetitors promote the local expansion of transformed cells after the early tumor lesion is formatted. In addition, various preclinical tumor-suppression models which based on the molecular mechanisms of these competition interactions show potential clinical value of boosting the fitness of host normal cells.

CONCLUSION

Cell competition between host and transformed cells has pleiotropic effects in mammalian tumor genesis and development. The clarification of specific molecular mechanisms shed light on novel ideas for the prevention and treatment of cancer.

Physiological and pathological roles of the Hippo-YAP/TAZ signaling pathway in liver formation, homeostasis and tumorigenesis

The liver plays central homeostatic roles in metabolism and detoxification, and has a remarkable capacity to fully recover from injuries caused by the various insults to which it is constantly exposed. To fulfill these functions, the liver must maintain a specific size and so must regulate its cell numbers. It must also remove senescent, transformed, and/or injured cells that impair liver function and can lead to diseases such as cirrhosis and liver cancer. Despite their importance, however, the mechanisms governing liver size control and homeostasis have resisted delineation. The discovery of the Hippo intracellular signaling pathway and its downstream effectors, the transcriptional coactivators Yes‐associated protein (YAP) and transcriptional coactivator with PDZ‐binding motif (TAZ), has provided partial elucidation of these mechanisms. The Hippo‐YAP/TAZ pathway is considered to be a cell’s sensor of its immediate microenvironment and the cells that surround it, in that this pathway responds to changes in elements such as the ECM, cell–cell tension, and cell adhesion. Once triggered, Hippo signaling negatively regulates the binding of YAP/TAZ to transcription factors such as TEAD and Smad, controlling their ability to drive gene expression needed for cellular responses such as proliferation, survival, and stemness. Numerous KO mouse strains lacking YAP/TAZ, as well as transgenic mice showing YAP/TAZ hyperactivation, have been generated, and the effects of these mutations on liver development, size, regeneration, homeostasis, and tumorigenesis have been reported. In this review, I summarize the components and regulation of Hippo‐YAP/TAZ signaling, and discuss this pathway in the context of liver physiology and pathology.

YAP drives cell competition by activating choline metabolism

Cell competition is a phenomenon that eliminates unfit cells from cell society, a function vital for maintaining cellular and organismal homeostasis. We previously showed that Madin-Darby canine kidney (MDCK) epithelial cells expressing the active form of the transcriptional coactivator Yes-associated protein (YAP) are apically extruded when surrounded by normal MDCK cells. Although we demonstrated that the arachidonic acid (AA) cascade is involved in YAP-dependent apical extrusion, the metabolic events leading to this outcome remained unclear. Here, we present the results of metabolomic analysis that identified phosphatidylcholine (PC) biosynthesis as the most significant player in this process. Removal of the PC biosynthetic components choline and methionine from culture medium inhibited YAP-dependent apical extrusion. Inhibition of either choline uptake or metabolic cycles involving choline or methionine also decreased YAP-dependent apical extrusion. At the molecular level, active YAP induced expression of the genes encoding glycerophosphocholine phosphodiesterase 1 (GPCPD1) and lecithin-cholesterol acyltransferase (LCAT), which are involved in choline metabolism. Our results indicate that YAP-dependent cell competition depends on YAP-mediated activation of the choline metabolic cycle.

Blockade of AMPK-Mediated cAMP-PKA-CREB/ATF1 Signaling Synergizes with Aspirin to Inhibit Hepatocellular Carcinoma

Simple Summary

Epidemiological and experimental studies have demonstrated that aspirin (acetylsalicylic acid) may prevent the incidence of some types of human cancer, including colorectal cancer and hepatocellular carcinoma (HCC). In addition, preclinical studies indicate that aspirin in combination with other treatments may achieve a more significant anti-cancer effect for established tumors. This study aims to improve the anti-cancer effect of aspirin by targeting signaling pathways related to aspirin and its targets. We find that aspirin may induce cAMP–PKA–CREB/ATF1 signaling in HCC via AMPK and its downstream target carbamoyl-phosphate synthase 1 (CPS1). Blockade of PKA–CREB/ATF1 signaling by the natural agent berbamine could sensitize HCC to aspirin. This research indicates that the combination of two inexpensive drugs, aspirin and berbamine, holds promise in preventing and treating HCC.

Abstract

Aspirin can prevent or inhibit inflammation-related cancers, such as colorectal cancer and hepatocellular carcinoma (HCC). However, the effectiveness of chemotherapy may be compromised by activating oncogenic pathways in cancer cells. Elucidation of such chemoresistance mechanisms is crucial to developing novel strategies to maximize the anti-cancer effects of aspirin. Here, we report that aspirin markedly induces CREB/ATF1 phosphorylation in HCC cells, which compromises aspirin’s anti-HCC effect. Inhibition of AMP-activated protein kinase (AMPK) abrogates the induction of CREB/ATF1 phosphorylation by aspirin. Mechanistically, activation of AMPK by aspirin results in decreased expression of the urea cycle enzyme carbamoyl-phosphate synthase 1 (CPS1) in HCC cells and xenografts. Treatment with aspirin or CPS1 knockdown stimulates soluble adenylyl cyclase expression, thereby increasing cyclic AMP (cAMP) synthesis and stimulating PKA–CREB/ATF1 signaling. Importantly, abrogation of aspirin-induced CREB/ATF1 phosphorylation could sensitize HCC to aspirin. The bis-benzylisoquinoline alkaloid berbamine suppresses the expression of cancerous inhibitor of protein phosphatase 2A (CIP2A), leading to protein phosphatase 2A-mediated downregulation of CREB/ATF1 phosphorylation. The combination of berbamine and aspirin significantly inhibits HCC in vitro and in vivo. These data demonstrate that the regulation of cAMP-PKA-CREB/ATF1 signaling represents a noncanonical function of CPS1. Targeting the PKA–CREB/ATF1 axis may be a strategy to improve the therapeutic effects of aspirin on HCC.

Nectin-4 and p95-ErbB2 cooperatively regulate Hippo signaling-dependent SOX2 gene expression, enhancing anchorage-independent T47D cell proliferation

Nectin-4, upregulated in various cancer cells, cis-interacts with ErbB2 and its trastuzumab-resistant splice variants, p95-ErbB2 and ErbB2∆Ex16, enhancing DNA synthesis through the PI3K-AKT signaling in human breast cancer T47D cells in an adherent culture. We found here that nectin-4 and p95-ErbB2, but not nectin-4 and either ErbB2 or ErbB2∆Ex16, cooperatively enhanced SOX2 gene expression and cell proliferation in a suspension culture. This enhancement of T47D cell proliferation in a suspension culture by nectin-4 and p95-ErbB2 was dependent on the SOX2 gene expression. In T47D cells, nectin-4 and any one of p95-ErbB2, ErbB2, or ErbB2∆Ex16 cooperatively activated the PI3K-AKT signaling, known to induce the SOX2 gene expression, to similar extents. However, only a combination of nectin-4 and p95-ErbB2, but not that of nectin-4 and either ErbB2 or ErbB2∆Ex16, cooperatively enhanced the SOX2 gene expression. Detailed studies revealed that only nectin-4 and p95-ErbB2 cooperatively activated the Hippo signaling. YAP inhibited the SOX2 gene expression in this cell line and thus the MST1/2-LATS1/2 signaling-mediated YAP inactivation increased the SOX2 gene expression. These results indicate that only the combination of nectin-4 and p95-ErbB2, but not that of nectin-4 and either ErbB2 or ErbB2∆Ex16, cooperatively regulates the Hippo signaling-dependent SOX2 gene expression, enhancing anchorage-independent T47D cell proliferation.

The role of Hippo-YAP signaling in squamous cell carcinomas

The Hippo‐YAP pathway regulates organ size, tissue homeostasis, and tumorigenesis in mammals. In response to cell density, external mechanical pressure, and/or other stimuli, the Hippo core complex controls the translocation of YAP1/TAZ proteins to the nucleus and thereby regulates cell growth. Abnormal upregulation or nuclear localization of YAP1/TAZ occurs in many human malignancies and promotes their formation, progression, and metastasis. A key example is squamous cell carcinoma (SCC) genesis. Many risk factors and crucial signals associated with SCC development in various tissues accelerate YAP1/TAZ accumulation, and mice possessing constitutively activated YAP1/TAZ show immediate carcinoma in situ (CIS) formation in these tissues. Because CIS onset is so rapid in these mutants, we propose that many SCCs initiate and progress when YAP1 activity is sustained and exceeds a certain oncogenic threshold. In this review, we summarize the latest findings on the roles of YAP1/TAZ in several types of SCCs. We also discuss whether targeting aberrant YAP1/TAZ activation might be a promising strategy for SCC treatment.

Prostaglandin E2 and its receptor EP2 trigger signaling that contributes to YAP-mediated cell competition

Cell competition is a biological process by which unfit cells are eliminated from “cell society.” We previously showed that cultured mammalian epithelial Madin‐Darby canine kidney (MDCK) cells expressing constitutively active YAP were eliminated by apical extrusion when surrounded by “normal” MDCK cells. However, the molecular mechanism underlying the elimination of active YAP‐expressing cells was unknown. Here, we used high‐throughput chemical compound screening to identify cyclooxygenase‐2 (COX‐2) as a key molecule triggering cell competition. Our work shows that COX‐2‐mediated PGE₂ secretion engages its receptor EP2 on abnormal and nearby normal cells. This engagement of EP2 triggers downstream signaling via an adenylyl cyclase‐cyclic AMP‐PKA pathway that, in the presence of active YAP, induces E‐cadherin internalization leading to apical extrusion. Thus, COX‐2‐induced PGE₂ appears a warning signal to both abnormal and surrounding normal cells to drive cell competition.