title: Placental growth factor inhibition modulates the interplay between hypoxia and unfolded protein response in hepatocellular carcinoma.
abstract: BACKGROUND
  Hepatocellular carcinoma (HCC) is a leading cause of cancer-related mortality. We previously showed that the inhibition of placental growth factor (PlGF) exerts antitumour effects and induces vessel normalisation, possibly reducing hypoxia. However, the exact mechanism underlying these effects remains unclear. Because hypoxia and endoplasmic reticulum stress, which activates the unfolded protein response (UPR), have been implicated in HCC progression, we assessed the interactions between PlGF and these microenvironmental stresses.
  
  
  METHODS
  PlGF knockout mice and validated monoclonal anti-PlGF antibodies were used in a diethylnitrosamine-induced mouse model for HCC. We examined the interactions among hypoxia, UPR activation and PlGF induction in HCC cells.
  
  
  RESULTS
  Both the genetic and pharmacological inhibitions of PlGF reduced the chaperone levels and the activation of the PKR-like endoplasmic reticulum kinase (PERK) pathway of the UPR in diethylnitrosamine-induced HCC. Furthermore, we identified that tumour hypoxia was attenuated, as shown by reduced pimonidazole binding. Interestingly, hypoxic exposure markedly activated the PERK pathway in HCC cells in vitro, suggesting that PlGF inhibition may diminish PERK activation by improving oxygen delivery. We also found that PlGF expression is upregulated by different chemical UPR inducers via activation of the inositol-requiring enzyme 1 pathway in HCC cells.
  
  
  CONCLUSIONS
  PlGF inhibition attenuates PERK activation, likely by tempering hypoxia in HCC via vessel normalisation. The UPR, in turn, is able to regulate PlGF expression, suggesting the existence of a feedback mechanism for hypoxia-mediated UPR that promotes the expression of the angiogenic factor PlGF. These findings have important implications for our understanding of the effect of therapies normalising tumour vasculature.
authors.affiliation: Department of Hepatology and Gastroenterology, Ghent University Hospital, De Pintelaan 185, 1K12IE, B-9000, Ghent, Belgium. YvesPaul.Vandewynckel@ugent.be.
authors.forename: Yves-Paul
authors.initials: YP
authors.lastname: Vandewynckel
authors.affiliation: Department of Hepatology and Gastroenterology, Ghent University Hospital, De Pintelaan 185, 1K12IE, B-9000, Ghent, Belgium. Debby.Laukens@UGent.be.
authors.forename: Debby
authors.initials: D
authors.lastname: Laukens
authors.affiliation: Department of Hepatology and Gastroenterology, Ghent University Hospital, De Pintelaan 185, 1K12IE, B-9000, Ghent, Belgium. Lindsey.Devisscher@UGent.be.
authors.forename: Lindsey
authors.initials: L
authors.lastname: Devisscher
authors.affiliation: Department of Hepatology and Gastroenterology, Ghent University Hospital, De Pintelaan 185, 1K12IE, B-9000, Ghent, Belgium. eliene.bogaerts@gmail.com.
authors.forename: Eliene
authors.initials: E
authors.lastname: Bogaerts
authors.affiliation: Department of Hepatology and Gastroenterology, Ghent University Hospital, De Pintelaan 185, 1K12IE, B-9000, Ghent, Belgium. annelies.paridaens@ugent.be.
authors.forename: Annelies
authors.initials: A
authors.lastname: Paridaens
authors.affiliation: Department of Hepatology and Gastroenterology, Ghent University Hospital, De Pintelaan 185, 1K12IE, B-9000, Ghent, Belgium. Anja.VandenBussche@UGent.be.
authors.forename: Anja
authors.initials: A
authors.lastname: Van den Bussche
authors.affiliation: Department of Hepatology and Gastroenterology, Ghent University Hospital, De Pintelaan 185, 1K12IE, B-9000, Ghent, Belgium. Sarah.Raevens@UGent.be.
authors.forename: Sarah
authors.initials: S
authors.lastname: Raevens
authors.affiliation: Department of Hepatology and Gastroenterology, Ghent University Hospital, De Pintelaan 185, 1K12IE, B-9000, Ghent, Belgium. xavier.verhelst@ugent.be.
authors.forename: Xavier
authors.initials: X
authors.lastname: Verhelst
authors.affiliation: Department of Hepatology and Gastroenterology, Ghent University Hospital, De Pintelaan 185, 1K12IE, B-9000, Ghent, Belgium. ccvsteen@hotmail.com.
authors.forename: Christophe
authors.initials: C
authors.lastname: Van Steenkiste
authors.affiliation: ThromboGenics NV, Heverlee, Belgium. bart.jonckx@thrombogenics.com.
authors.forename: Bart
authors.initials: B
authors.lastname: Jonckx
authors.affiliation: Department of Pathology, Ghent University Hospital, Ghent, Belgium. LouisJ.Libbrecht@UGent.be.
authors.forename: Louis
authors.initials: L
authors.lastname: Libbrecht
authors.affiliation: Department of Hepatology and Gastroenterology, Ghent University Hospital, De Pintelaan 185, 1K12IE, B-9000, Ghent, Belgium. Anja.Geerts@UGent.be.
authors.forename: Anja
authors.initials: A
authors.lastname: Geerts
authors.affiliation: Laboratory of Angiogenesis and Neurovascular link, Vesalius Research Centre, KU Leuven, Leuven, Belgium. peter.carmeliet@vib-kuleuven.be.|Laboratory of Angiogenesis & Neurovascular Link, Vesalius Research Centre, VIB, Leuven, Belgium. peter.carmeliet@vib-kuleuven.be.
authors.forename: Peter
authors.initials: P
authors.lastname: Carmeliet
authors.affiliation: Department of Hepatology and Gastroenterology, Ghent University Hospital, De Pintelaan 185, 1K12IE, B-9000, Ghent, Belgium. Hans.VanVlierberghe@UGent.be.
authors.forename: Hans
authors.initials: H
authors.lastname: Van Vlierberghe
mesh_terms: D000818:Animals; D006528:Carcinoma, Hepatocellular / Q000139:chemically induced / Q000235:genetics* / Q000473:pathology; D015687:Cell Hypoxia / Q000187:drug effects / Q000235:genetics; D004052:Diethylnitrosamine / Q000633:toxicity; D004195:Disease Models, Animal; D059865:Endoplasmic Reticulum Stress / Q000235:genetics; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects; D006025:Glycosaminoglycans / Q000502:physiology; D056945:Hep G2 Cells; D006801:Humans; D008113:Liver Neoplasms / Q000139:chemically induced / Q000235:genetics* / Q000473:pathology; D051379:Mice; D018345:Mice, Knockout; D009389:Neovascularization, Pathologic / Q000235:genetics* / Q000473:pathology; D000072483:Placenta Growth Factor; D011257:Pregnancy Proteins / Q000096:biosynthesis* / Q000235:genetics; D059016:Tumor Microenvironment / Q000235:genetics; D056811:Unfolded Protein Response / Q000235:genetics; D019892:eIF-2 Kinase / Q000096:biosynthesis* / Q000235:genetics
chemical_list: D004052:Diethylnitrosamine; D006025:Glycosaminoglycans; D000072483:Placenta Growth Factor; D011257:Pregnancy Proteins; D019892:eIF-2 Kinase; C000608036:PGF protein, human; C000608037:Pgf protein, mouse; C007858:glucuronyl glucosamine glycan sulfate