Helicobacter pylori-induced epithelial cell signalling in gastric carcinogenesis

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Helicobacter pylori-induced epithelial cell
signalling in gastric carcinogenesis

• Manoj Kumar
• Dairy microbiology Division
• N.D.R.I KARNAL
• INDIA

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Helicobacter pylori

• Spiral-shaped Gram-negative, oxidase and
  catalase-positive motile bacterium with 4-6
  flagella
• Microaerophilic, i.e. it requires oxygen but
  at lower levels than those contained in the
  atmosphere
• With its flagella and its spiral shape, the
  bacterium drills into the mucus layer of
  the stomach, and can either be found
  suspended in the gastric mucosa or attached
  to epithelial cells

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• Produces adhesins which bind to membrane-
  associated lipids and carbohydrates and help
  its adhesion to epithelial cells
• Breaks down urea (NH2CONH2) to NH4 and CO2
• Stomach acidity ?
• Possible for H. pylori to survive

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Contd

• Highly successful human microbial pathogen
• classified as a class I carcinogen
• cellular and molecular signalling pathways are
  used during H. pylori infection to promote
  epithelial hyperproliferation and transformation
• Gastric inflammation
• Chronic gastritis
• peptic ulcers
• gastric cancer
• gastric adenocarcinoma
• mucosa associated lymphoid tissue (MALT) lymphoma
• gastric epithelial hyperproliferation.

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H. pylori virulence factors associated with
gastriccancer
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H. pylori
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Ulcerated gastric adenocarcinoma
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Intestinal type gastric adenocarcinoma
Abnormal gland
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Typical endoscopic, endosonographic and
histological pictures in MALT-lymphoma
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Epithelial cell proliferation is increased with
gastric Helicobacter pylori infection
Bromodeoxyuridine staining
(b) a gerbil thirty-six weeks post-infection with
H. pylori (SS1 strain).
(a) an uninfected gerbil
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Epithelial cell proliferation is increased with
gastric Helicobacter pylori infection
Gastric pathology in (c) H. pylori uninfected
(d) H. pylori- infected Mongolian gerbils.
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Sequence of histological and endoscopic events in
H. pylori infected stomach with accompanying
transformation of chronic atrophic gastritis to
chronic active gastritis with polyp, intestinal
metaplasia and dysplasia to cancer.
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Progression to intestinal-type gastric
adenocarcinoma.
Helicobacter pylori colonization usually occurs
during childhood and, over a period of days to
weeks, leads to superficial gastritis. The
presence of host TP53 mutations, host
polymorphisms that promote high expression levels
of the cytokine interleukin (IL)-1ß, and the cag
island within infecting H. pylori isolates all
contribute to the development of atrophic
gastritis, intestinal metaplasia, dysplasia and,
eventually, gastric adenocarcinoma over the
course of many years. Additional mutations in
oncogenes that encode RAS or deleted in
colorectal cancer (DCC) might also contribute to
intestinal-type gastric carcinogenesis.
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Influence of H. pylori strains on epithelial
proliferation

• H. pylori is a genomically diverse pathogen and
  several bacterial virulence factors, are
  considered to have a key role in disease
  pathogenesis
• Only strains containing the cag PAI trigger
  signalling cascades in gastric epithelial cells,
  resulting in nuclear factor kappa B (NF-kB)
  activation and multiple associated changes in
  epithelial gene expression

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H. pylori affects apoptosis and cell cycle
control

• Apoptosis and cell cycle control are processes
  required for the regulation of cellular
  homeostasis
• chronic imbalance between apoptosis and cell
  proliferation is the first step of gastric
  carcinogenesis, as in all tumours.
• H. pylori infection could lead to an overall
  increase in cellular turnover and persistence of
  mutated cells, which will favour the development
  of neoplasia
• The cell cycle, the programme for cell growth and
  division (proliferation), consists of four phases
  that are known as G1 and G0, S, G2 and M. The
  important protein families used during this cycle
  include the cyclins, the cyclin dependent kinases
  (Cdks), the Cdk inhibitors and the
  tumour-supressor genes (in particular, Rb and p53)

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H. pylori affects apoptosis and cell cycle
control(2)

• The H. pylori toxin VacA induces gastric
  epithelial cell apoptosis, suggesting that
  differences in levels of gastric mucosal
  apoptosis among infected persons might result
  from strain-dependent variations in VacA
  structure.
• In another study, apoptosis of gastric epithelial
  cells was mediated by elevated levels of Smad5 as
  a result of cag PAI-dependent H. pylori infection.

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H. pylori affects apoptosis and cell cycle
control(3)

• Exposure of epithelial cells to H. pylori alters
  cell cycle control both in vitro and in vivo.
  Mucosal expression of cyclin D1, the
  tumour-suppressor p53 and the cell cycle
  inhibitor p21 was significantly higher in H.
  pylori- infected patients with intestinal
  metaplasia
• A clear effect of H. pylori on cell cycle
  progression has been described in infected
  patients with intestinal metaplasia that
  overexpress cyclin D2 and show reduced expression
  of the cell cycle inhibitor p27

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H. pylori cag strains can induce or prevent
gastric epithelial-cell apoptosis.
L
Proliferator activated receptor
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Epithelial cell signalling under the direct
control ofH. pylori

• The ability of a cell to respond to its
  extracellular environment involves a complex and
  highly organized series of events referred to as
  cellular signalling.
• These signalling processes regulate fundamental
  cellular responses and their abrogation can lead
  to the development of various human diseases,
  such as cancer.

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Epithelial cell signalling(a)
muropeptide
MAP3KINASES
GASTRITIS
INFLAMMATION
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Epithelial cell signalling(a)

• Cancer could arise from sites of infection,
  chronic irritation and inflammation..
• The physical contact between H. pylori and
  gastric epithelial cells leads to the activation
  of signal transduction pathways
• Muropeptides (GM) translocated by the T4SS
  of H. pylori are recognized by the intracellular
  receptor molecule NOD1, which directs activation
  of the transcription factor NF-?B.
• In addition, H. pylori-induces the kinases PAK1,
  NIK and the IKK complex leading to the
  phosphorylation of I?B molecules and nuclear
  translocation of active NF-?B.
• Activation of the transcription factor AP-1 is
  triggered by PAK1 which activates an unknown MAP
  3 kinase (MKKK), MKK4 and JNK. In addition, p38
  kinase is strictly induced by H. pylori strains
  carrying a T4SS.

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Epithelial cell signalling(b)
Enhancce Motogenic response
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Epithelial cell signalling(b)

• The T4SS of H. pylori translocates CagA, an
  effector protein which becomes tyrosine
  phosphorylated by Src kinases.
• CagA may disrupts epithelial tight junction in a
  process which comprises co-localisation of CagA
  with JAM molecules and the scaffolding protein
  ZO-1.
• Further, CagA directly binds to the cytoplasmic
  domain of the phosphorylated and active c-Met
  receptor and enhances the motogenic response
  (cell scattering). In addition, CagA recruits
  PLC? to the c-Met receptor.

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• The cell scattering involves Cdc42 and Rac1 which
  are activated in a cag PAI-dependent manner as
  well as the activity of MEK and ERK which are cag
  PAI independently activated.
• The phosphatase SHP-2 associates with
  phosphorylated CagA, and in an autoregulatory
  loop the interaction between CagA and the kinase
  CSK stimulates phosphorylation and inactivation
  of Src kinases leading to less phosphorylation of
  CagA.

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Proliferation-associated signalling cascades

• Cell growth and differentiation in response to
  extracellular stimuli is mediated through various
  intracellular signal transduction pathways.
• The mitogen-activated proteinkinase (MAPK)
  pathway is a major player in this kinase
  signalling cascade from growth factors to the
  cell nucleus.
• The pathway involves kinases at two levels
• 1. MAP kinases,also known as extracellular
  signal-regulated kinases(ERKs) and
• 2.MAP kinase kinases, also known as MEKs or
  MAPKERK kinases.
• MEK is activated by the phosphorylation of two
  serine residues by upstream kinases, MEK
  catalyzes the phosphorylation of threonine and
  tyrosine residues of ERK.

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• The activated ERK then phosphorylates and
  activates transcription factors in the nucleus,
  such as the ternary complex factor (TCF)Elk-1,
  which regulate early genes including c-myc, fos
  and jun.
• MEK and ERK enzymes are known to be essential
  for normal cell proliferation and
  differentiation, deregulation (overexpression,
  hyperactivity or gene mutation) of the MAPK
  signal transduction pathway might lead to
  proliferative diseases, cancer Therefore, cancer
  can be considered as a disease of communication
  at the molecular level.

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Activation of tyrosine kinase receptors

• Tyrosine kinase receptors have an important role
  in gastric carcinogenesis .
• Recent studies have demonstrated that H. pylori
  activates EGFR, HER2Neu (ErbB-2) and c-Met in
  gastric epithelial cells .
• EGFR activation is dependent on extracellular
  transmembrane metalloprotease cleavage of
  proheparin binding epidermal growth factor
  (proHB-EGF) and signalling by mature HB-EGF.

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• The upregulation of HB-EGF gene transcription by
  H. pylori requires metalloprotease, EGFR and MEK1
  activities , indicating the involvement of the
  triple membrane-passing signal (TMPS) for EGFR
  transactivation .
• Disruption of epithelial tight junctions by the
  interaction of translocated CagAwith the
  scaffolding protein ZO-1 and VacA-mediated
  phosphorylation of G protein-coupled receptor
  kinase-interactor 1 (Git1)probably promotes
  binding of EGF ligands to the EGFR located on
  basolateral membranes of the epithelial cells .

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Helicobacter pylori activates receptor tyrosine
kinases.
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Helicobacter pylori stimulates epidermal
growth-factor receptor (EGFR transactivation via
a triple membrane-passing signal (TMPS) cascade.
The EGF activation involves G-protein coupled
receptor (GPCR) activity and the TMPS for EGFR
transactivation, which is dependent on
extracellular transmembrane metalloprotease
cleavage of pro-heparin binding epidermal growth
factor (proHB-EGF) and signalling by mature
HB-EGF .
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CellCell and cellmatrix interactions and the
motogenic response

• Decreased cellcell or cellmatrix interactions
  are common in gastric cancer and might be related
  to the tendency to produce metastasis.
• In polarized epithelial cells H. pylori affects
  the scaffolding protein ZO-1 and the tight
  junctional adhesion protein (JAM) in a
  CagA-dependent manner, and disrupts
  junction-mediated epithelial barrier functions .
• Among the many types of adhesion molecules,
  E-cadherin serves as a prime mediator of
  cellcell adhesion within the zonula adherens
  junctions. Downregulation of E-cadherin in antral
  biopsies of H. pylori- infected patients has been
  described .
• The cytoplasmic domains of E-cadherin interact
  with catenins(a and b), and alterations in this
  system have been ascribed an important role in
  tumour initiation and progression

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Helicobacter pylori affects epithelial tight
junctions
Ptn tyrosin phophatase
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Conclusion

• A characteristic of H. pylori infection in humans
  is gastritis, which persists for decades without
  causing serious damage in most cases.
• The clinical complications of H. pylori
  infection, such as peptic ulcer disease and
  gastric cancer, appear to represent an imbalance
  in gastric homeostasis.

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• The induction of the motogenic response by H.
  pylori in epithelial cells represents an example
  of how a human microbial pathogen can activate
  growth-factor receptor tyrosine kinases, and
  modify signal transduction in the cell using
  translocated bacterial proteins.
• It will be essential to deepen our understanding
  of receptor crosstalk in H. pylori- infected
  epithelium and its contribution to EGFR, Her2Neu
  and c-Met activation.
• The study of signalling pathways that regulate
  EGFR, Her2Neu and c-Met expression and activity
  in H. pylori infection may identify promising
  therapeutic targets for suppression of
  transformation, and offer novel potential targets
  for the treatment and/or prevention of
  malignancies .
• To down regulate the expression of anti-apoptotic
  genes is another potential therapeutic approach.

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Thanks for your kind attention