Docstoc

Helicobacter pylori induced epithelial cell signalling in gastric

Document Sample
Helicobacter pylori induced epithelial cell signalling in gastric Powered By Docstoc
					 Helicobacter pylori-induced epithelial
cell signalling in gastric carcinogenesis




                             Manoj Kumar
                      Dairy microbiology Division
                           N.D.R.I KARNAL
                                INDIA
                    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
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
                                              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.
H. pylori virulence factors associated with gastric
                       cancer
H. pylori
Ulcerated gastric adenocarcinoma
Intestinal type gastric
   adenocarcinoma




                      Abnormal gland
Typical endoscopic, endosonographic and histological pictures in
MALT-lymphoma
    Epithelial cell proliferation is increased with
        gastric Helicobacter pylori infection




                           Bromodeoxyuridine staining


                                             (b) a gerbil thirty-six weeks
(a) an uninfected gerbil                     post-infection with H. pylori
                                             (SS1 strain).
  Epithelial cell proliferation is increased with
      gastric Helicobacter pylori infection




Gastric pathology in (c) H. pylori   (d) H. pylori- infected Mongolian
uninfected                           gerbils.
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.
     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)-1β, 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.
 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
  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)
 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.
 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
H. pylori cag+ strains can induce or prevent
      gastric epithelial-cell apoptosis.




            L




                               Proliferator activated receptor
Epithelial cell signalling under the direct control of
                        H. 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.
          Epithelial cell signalling(a)



muropeptide



                               MAP3KINASES




                                  GASTRITIS
              INFLAMMATION
             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-кB.

 In addition, H. pylori-induces the kinases PAK1, NIK and the
IKK complex leading to the phosphorylation of IкB molecules
and nuclear translocation of active NF-кB.

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.
Epithelial cell signalling(b)




                                Enhancce
                                Motogenic
                                response
            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 ץ‬to the c-Met receptor.
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.
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
MAPK–ERK 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.
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.
  Activation of tyrosine kinase receptors

Tyrosine kinase receptors have an important role in
gastric carcinogenesis .

Recent studies have demonstrated that H. pylori
activates EGFR, HER2–Neu (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.
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 .
Helicobacter pylori activates receptor
         tyrosine kinases.
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 .
Cell–Cell and cell–matrix interactions and the
            motogenic response
Decreased cell–cell or cell–matrix 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 cell–cell 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
Helicobacter pylori affects epithelial tight
               junctions



                                    Ptn tyrosin phophatase
                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.
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, Her2–
Neu and c-Met activation.

The study of signalling pathways that regulate EGFR, Her2–Neu
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.
Thanks for your kind
    attention