Module 2.5: Other Flashcards
Features of h pylori
• It is a spiral shaped/curved organism that increases acid production
• It is a model of disease as it produces a range of diseases:
o Acute gastritis – not very symptomatic
o GU and chronic gastritis: majority of patients (90% of cases of chronic antral gastritis)
o DU: almost all patients (DU: duodenal ulcer)
o Also associated with gastric cancer (adenocarcinoma) and lymphoma
Hence if H.Pylori is treated, a lot of diseases can be treated also.
Epidemiology of H Pylori
• H. Pylori infection is associated with: o Crowding o Poor sanitation o Limited education o Poverty o Immigrant
• Worldwide: 10-90% colonisation rates
o Given that <1% of H. Pylori infected individuals will develop gastric cancer and lymphoma it may not seem like a big problem. However, H. Pylori infection is very prevalent and so this can affect millions of people hence helicobacter is a big cause of gastric cancers (+ lymphoma)
- In high prevalence countries it is acquired in childhood
- Various routes of transmission e.g. endoscopes (interestingly ,H. Pylori is highest among gastroenterologists)
Pathogenesis of h pylori
• Mainly an antral gastritis associated with increased acid production despite decreased gastrin
o Remember this is an alternate source of acid production that is not affected by gastrin but will contribute to gastrin reduction
• May progress to a multifocal atrophic gastritis with decreased acid
• Adapted to live in the gastric mucin – rarely invades tissue
Factors associated with h pylori Virulence
• Flagella
• Urease – produces ammonia from urea raising the pH
o This is its protective mechanism so that it can live in the stomach lining
o This is the basis of screening test
• Adhesins – mediate adherence to surface foveolar cells
• Toxins – cytotoxin-associated gene A (CagA) which is associated with ulcer development and cancer
o Virulent damaging toxin interacts with p53
o Toxin injected through Type IV secretion system
Pathology caused by h pylori
• Organism can usually be seen on biopsy in the mucus of the surface and neck regions
• Best diagnosed on an antral biopsy
o On biopsy, H. Pylori gastritis can be acute (neutrophil) or chronic (lymphocyte)
• Inflammation
o Neutrophils in the lamina propria, which may extend into the pits
o Plasma cells in the superficial lamina propria, which produces rugal fold thickening
o Lymphoid follicles often present = induced MALT
This is a marker of chronic inflammation as it is not present in normal mucosa
• Mucosa:
o Intestinal metaplasia with absorptive cells and goblet cells and Paneth cells
o Atrophy
o Dysplasia can lead to flat dysplasia pathway
Acute Inflammation – crypts packed with neutrophil polymorphs
Chronic inflammation – crypts contain increased numbers of plasma cells. Lymphoid follicles seen with germinal centres (blue circle).
Intestinal metaplasia – hallmark is goblet cells as can be seen on slide.
Dysplasia
• Nuclei are big (high nuclear:cytoplasmic ratio), hyperchromatin
H. Pylori Infection confers an increased risk of:
• Adenocarcinoma • Genotype of hlo associated cancers • Lymphoma • Reversibility of lymphoma o i.e. in a patient with low grade lymphoma, if you treat the H. Pylori infection, this can be reversed not reversible in high grade
Extra-intestinal Manifestations of Helicobacter Pylori
• Cardiovascular diseases o Epidemiological evidence is most convincing for this • Ischaemic heart disease • Noncardioembolic ischaemic stroke • Pre-eclampsia • Raynaud phenomenon • Migraine • Diabetes mellitus • The metabolic syndrome • Neurodegenerative diseases • Multiple sclerosis • Neuromyelitis optica
CVS effects of H. Pylori
- Especially caused by CagA+ve strains
- These induce anti-CagA antibodies from the host, which promote atherosclerotic plaque formation
• Biopsy o Histology o Rapid urease test o Culture o PCR • Serology • Faecal bacterial detection • Urea breath test o Detect ammonia production
Treatment
• Antibiotics and proton pump inhibitors (PPIs) triple therapy
• May relapse
Define cancer
Definition: a disease caused by an uncontrolled division of abnormal cells in a part of the body.
• Common Carcinomas o Lung o Breast (women) o Colon o Bladder o Prostate (men)
• Leukaemias
o Bloodstream
• Lymphomas
o Lymph nodes
• Common Sarcomas
o Fat
o Muscle
o Bone
two types of programmed cell death
o Apoptosis: an energy-dependent process that suppresses inflammation and allows for maintenance of plasma membrane integrity and ordered DNA fragmentation. Process: cells first shrink, nuclei condense and form ‘apoptotic bodies’
o Necrosis: an energy-independent process that induces inflammation whereby plasma membrane integrity is lost and there is random DNA fragmentation. Process: cell swells, ruptures and during its demise there is release of cellular contents
Define Transcription Factors
proteins involved in the regulation of gene expression that bind to the regulatory regions upstream of genes and either facilitate or inhibit transcription
• Transcription factors are composed of two essential functional regions:
o DNA-binding domain consists of amino acids that recognise specific DNA bases near the start of transcription
o Transactivator domain interacts with components of the transcriptional apparatus (RNA Polymerase) and with other regulatory proteins, thereby affecting the efficiency of DNA binding
What is NFkB
key nuclear transcription factor
- Consists of a protein family of inducible dimeric TFs which recognise the kB site
- This factor is thought to be involved in 80% of cancer. This is not mutated but is the main transcription factor to be dysregulated.
o In normal cells, NFkB is bound and deactivated by inhibitor-kappa B proteins (IkB)
o During stress and exposure to microbial productions/cytokines/mitogens, IkB protein is phosphorylated by inhibitor kappa-B kinase (IKK)
o This inactivation releases NFkB can enter the nucleus and affect transcription
Describe the Classical NFkB Pathway
• Expression of NFkB’s gene products mediate:
o Immunity
o Inflammation
o Development
o Cell survival problematic in malignancy as NFB effectively inhibits apoptosis
• Summary:
o IKK kinases activated by microbial product/mitogens/cytokines/stress
o IKK phosphorylates IkB, thereby releasing NFkB
o NFkB is now activated and so, migrates to the nucleus and binds to specific sites on DNA that are upstream of certain genes genes involved mediate above
N.B: An alternative NFkB pathway: activated in response to specific cytokines. This is involved in stimulating lymphoid organogenesis, as well as activating other chemokines and cytokines.
Protein Kinase (Definition)
A kinase is an enzyme that modifies other proteins by adding phosphate groups (phosphorylation).
Phosphorylation usually results in a functional change of the target protein (substrate).
The activity of a kinase involves removing a phosphate group from ATP and covalently attaching it to an amino acid that has a free hydroxyl group.
Most kinases act on both serine and threonine (others act on tyrosine).
By contrast, phosphatase is an enzyme that removes phosphate group from its substrate.
Pro-survival activity of NFkB in Disease
- Cellular responses to triggering of TNF-Rs, TRAIL-Rs and Fas
- B-Lymphopoeisis
- Bone morphogenesis
- B- and T-cell Costimulation (CD40, CD28, etc)
- Liver development
NFkB in Disease
• Its amplification allows development of cancer
o Not considered an oncogene but is regulated by oncoproteins e.g. Ras which is thought to phosphorylate in cancer
o This causes inhibition of programmed cell death and differentiation, enhancement of proliferation, invasion and metastasis
o Hence NFkB is associated with survival of late stage tumours e.g. breast, Hodgkin’s, colorectal cancer (and resistance to anti-cancer therapy)
• Implicated in cancer chemo- and radio-resistance
• Chronic inflammatory disease (IBD, RA)
• Metabolic and vascular disease (atherosclerosis)
Molecular Mechanism by which NFkB controls PCD
• TNF-alpha binding to its receptor – TNF-R1 – stimulates the death through the TRADD/TRAF pathway, causing the production of MAP3K, MAP2K and JNKs (mitogen activated protein kinases)
• JNKs interact with caspases (cysteine-aspartic proteases), leading to activation of cytochrome C and activation of all caspases DNA fragmentation and cell death
• However, a pro-survival pathway can also activated by NFkB (if dysregulated)
o MEKK3 leads to IKK activation inhibition of IkB activation of NFkB
o NFkB transcribes pro-survival genes that inhibit MAPKs
Distinct Mechanisms of PCD Inhibition
genes targeted by NFkB at different stages of the TRADD/TRAF pathway
• JNK is the end-product of this pathway and is itself, phosphorylated by MKK7
• Gadd45beta/Myd118 is a specific inhibitor of JNK cascade via inhibition of MKK7 (Papa S, et al, Nat. Cell Biol, 2004)
o Gadd45-beta is a 21kDa peptide predominantly found in the nucleus. It is a member of the Gadd45 family of inducible factors (others: Gadd45-alpha and –gamma)
o It inhibits MKK7 via its ATP-binding site (lysine 149) no ATP binding site mans no phosphorylation of JNK no caspases no cell death
o Peptides can therefore be devised e.g. peptide 1 which are synthetic competitive inhibitors of Gadd45-beta. This would restore MKK7 function and allow programmed cell death to return. This is an example of a peptide currently undergoing clinical trials for multiple myeloma.
NFkB blockers as a future therapy
o Inhibition of NFkB by either glucocorticoid or proteasome inhibitors is beneficial in certain malignancies such as Hodgkin’s lymphoma or multiple myeloma.
o However, current compounds can only achieve partial inhibition of NFkB and have considerable side effects, thereby limiting their use in humans.
• Gadd45beta and FHC blockers may present new targets
o Blocking molecules directly involved in the pro-survival pathway downstream of NFkB should display beter results with fewer side-effects as other functions of NFkB would not be affected
define mutation
• Definition: a mutation is a change in the normal base pair sequence of DNA
• Mutations can occur in either coding or noncoding regions
o These may be silent have no effect on resulting protein. This is especially true if they occur in noncoding regions of the DNA. Even small base-pair changes in the coding region may be silent because of the redundancy of the code.
o Point mutations a single base change that results in the change of an amino acid in the structure
o Deletions, insertions, translocations involve larger sections of DNA
Summarise Cancer Development
multistage process that involves inherited and somatic mutations of cellular genes
o Somatic mutations
Occur frequently (1 mutation/cell division)
Normally inconsequential (not passed on to next generation)
Dangerous if occurs on specific genes
E.g. BRCA1
o Germline mutations
Occurs rarely
Present in all somatic cells of affected individual
Cancer develops only in specific tissue/organ
Increased risk of cancer passed on to future generation
• Cancers are clonal
o Many mutations in several different distinct genes are required for normal cells to become cancerous
o This progressive accumulation of these multiple hits explains the age-incidence of cancer
o All the cells in a tumour originate from a single ancestral cell
o But, not all cells in a tumour have the same genotype because cancer cells are genetically unstable
o Variation gives rise to selection
o Clonal selection of variant progeny with the most robust growth properties play major contributing roles
Describe Cancer-associated Mutations
- Cancer-associated mutations, whether somatic or germline, point mutations or large deletions, alter key proteins and their functions in the human bio-system. A wide variety of mutations arw involved including those in non-coding regions
- Mutation can result in under- or over-expression of proteins needed for normalcy
• Mutations can affect: o Growth factors, cytokines o Receptors genes o Cell signalling genes o Transcription factor genes o Cell cycle control genes o Cell death and survival genes o DNA repair genes o Cellular differentiation genes
Describe Normal Cell Growth
• Most cells remain in interphase for at least 90% of cell cycle
o First phase of interphase: G1 rapid growth and metabolic activity (including synthesis of RNA and proteins)
o Followed by S phase (DNA synthesis)
o Followed by G2 cell grows and prepares for division
• Cell division happens in M phase (mitosis)
• Cells that do not divide for long periods do not replicate their DNA – G0 phase
- In normal cells TS genes act as braking signals during G1 to stop or slow the cell cycle before S phase
- DNA repair genes are active throughout cycle, particularly during G2 after DNA replication
- Oncogenes allow progression from G1 to S phase
Definition of a Protooncogone:
a normal gene that can become an oncogene, either after mutation or increased expression. Proto-oncogenes code for proteins that help regulate cell growth and differentiation. Proto-oncogenes are often involved in signal transduction and execution of mitogenic signals. Upon activation, a proto-oncogene becomes a tumour-inducing agent, which is named oncogene.
o Growth factors
o Growth factor receptors
o Signal relaying molecules
o Nuclear transcription factors (proteins that bind to genes to start transcription)
- When proto-oncogene is mutated or overregulated, it is called an oncogene
- Only one mutation in a single allele enough to trigger oncogenic role
- The chance will increase as a person ages
Definition of a TS Gene:
gene that protects a cell from uncontrolled cell growth. When this gene is mutated to cause a loss or reduction in its function, the cell can progress to cancer, usually in combination with other genetic changes.
both copies of tumour suppressor genes must be lost or mutated for cancer
o Person who carries a germline mutation in a tumour suppressor gene has only one functional copy of the gene in all cells
o For this person, it is more likely for the second hit to occur for cancer progression
• Act as negative regulators of cancer growth: o inhibit proliferation o induce apoptosis, o inhibit angiogenesis o induce cell adhesion • Act to maintain chromosome integrity
Examples of Oncogenes
RAS (e.g. colon cancer)
• Protein subfamily of small GTPases that are involved in cellular signal transduction
• Activation causes cell growth, differentiation and survival
C-MYC (e.g. overexpressed in colon cancer, amplified in lung, rearranged in lymphoma)
• Encodes transcription factor that regulate expression of 15% of all genes through binding on Enhancer Box sequences (E-boxes) + recruiting histone acetyltransferases (HATs)
• So in addition to its role as a classical transcription factor, c-myc also functions to regulate global chromatin structure by regulating histone acetylation both in gene-rich regions and other sites far from known genes
Others • CDK4 (familial melanoma) • MET (hereditary papillary renal cancer) • BCR/ABL (chronic myelogenic leukaemia) • BCL2 (follicular lymphoma)
Examples to TSG
o Rb
o P53
o APC
Describe retinablastoma
• Paediatric intraocular tumour accounting for 5% of childhood blindness
• Occurs as an inherited disease with autosomal dominant transmission + 90% penetrance
• Sporadic cases also known, but differ from typical hereditary disease
• May cause thickening of optic nerve due to extension of tumour + displace normal retina
• Several curative treatments
o Surgery and radiotherapy
Describe the two hit model
• The first insult is inherited in the DNA + any second insult
• In non-inherited retinoblastoma, two hits had to take place, explaining the age difference
• The development of malignancy depended both on the activation of proto-oncogene + deactivation of tumour suppressors
o First hit in an oncogene would not necessarily lead to cancer as normally functioning tumour suppressors would counterbalance
o Conversely, a damaged tumour suppressor (Rb1) would not lead to cancer unless there is a growth impetus from activated oncogene
