L16-21 Flashcards
Genes that have direct involvement in causing cancer:
TSG’s and PO’s
Genes that have indirect involvement in causing cancer and control DNA damage?
DNA repair genes, genes involved in carcinogen metabolism.
Why would DNA repair fail?
If a mutation is present in a PO or a TSG.
Ataxia telangectasia:
Autosomal recessive & rare
AT symptoms/features:
loss of coordination, dilated capillaries, immune deficiency, sensitivity to ionising radiation, predisposition to lymphoma and leukaemia. Heterozygotes have increased cancer risk due to gene being an intermediate for breast cancer (low penetrance)
Gene involved in AT
ATM gene - involved in sensing DNA damage, has protein kinase activity and phosphorylates p53 after DNA damage. AT cells cannot arrest the cell cycle in response to DNA damage
How is the ATM protein held in its inactive and active states
Inactive state: oligomers that are phosphorylated, when sensing DNA damage, to monomers
Xeroderma pigmentosa:
Rare, AR
XP symptoms:
Dwarfism, mental retardation, blindness and deafness, severe UV sensitivity, skin and eye cancers (patients ALL have UV sensitivity but may not have any/all of the others)
What are the XP affected genes involved in?
gene excision and repair of thymine dimers, there are several genes involved, hence variable phenotype.
Bloom syndrome, symptoms and why?
AR, lymphoma, leukaemia, chronic lung disease and diabetes. Due to mutations in DNA helicase so DNA cannot be unwound correctly. Plus high levels of chromatin exchange in the cell.
Fanconis anaemia symptoms
AR, mental retardation, aniridia, skeletal abnormalities, leukaemia
How many genes in the fanconi anaemia complex and what do they do?
- All could mutate to give cancer. They act to ubiquitinate D2 and I protein subunits which then form a complex with three other proteins including BRCA2 to begin homologous recombination. This brings in BRCA1, RAD51 and RAD51C. Hom rec is a high fidelity way of repairing DNA damage, when it goes wrong, increased BC and FA risk.
Hereditary non-polyposis colon cancer key points:
AD, early onset colon cancer, few polyps, mutations in mismatch repair genes. MLH1 is affected in 51% of HNPCCs. Also, TGFbeta receptor gene has a repeat region in it which is known to be particularly susceptible to repeat changes and is common in HNPCC (increases risk of colon cancer)
Features of genetic predisposition to cancer?
Family history, early onset cancer, multiple cancers (bilateral organs)
Retinoblastoma:
Childhood eye cancer affects 1/20,000, high cure rates. 40% inherited, one parent affected = 95% penetrance. AD.
Difference between hereditary tumours and sporadic tumours:
Hereditary = early onset and bilateral organs/ multiple tumours Sporadic = later onset and one tumour in one organ
What is the two hit theory
That regardless of if a tumour is sporadic or hereditary, there are two ‘hits’ or limited events in cancer development.
Evidence of the two hit theory:
- chromosome deletions
- allele loss (LOH) - mechanisms: non-disjunction, non-disjunction and duplication, mitotic recombination, deletion. - no LOH = gene conversion, point mutation
- Somatic cell hybrids - heterokaryon (non-tumourigenic)
Oncogene dominant mutations are:
Point mutations, gene amplification, chromosome translocations - few inherited mutations
TSG recessive mutations causing cancer
point mutations, deletions, epigenetic silencing.
Does the two hit theory hold?
No, most cancers and more complex than that and there are multiple steps and multiple genes involved.
What is the most common change in human cancers?
p53 mutation
RB1 properties:
Rb TSG, mutated in all retinoblastomas, encodes a 110kD nuclear phosphoprotein, involved in cell cycle regulation
How can you get a RB1- cell to revert to a more normal phenotype?
insert a functional copy of RB1
How do tumour viruses affect Rb?
E1A of adenovirus binds in place of the phosphate and E7 binds to unphosphorylated Rb. Both causing the release of E2F and pushing the cell into S phase (so viral DNA is replicated). Normally highly regulated mitogenic signals disrupt the Rb:E2F interaction to trigger the cell cycle.
WT1 properties:
1/10,000 childhood kidney tumour 11p13 deletion
WT1 mutation symptoms
WAGR syndrome: Wilms tumour, Aniridia, GI abnormalities, mental Retardation
What does WT1 encode?
DNA/RNA binding zinc finger proteins
p53 properties:
Transcriptional regulator, levels rise in response to DNA damage causing G1 arrest and repair (or apoptosis)
What syndrome has p53 germline mutations?
Li-Fraumeni syndrome (cancer susceptibility)
How is p53 regulated and why is regulation stopped when p53 is mutated?
p53 up regulated production of mdm2 which forms a complex with p53 causing it to be degraded, mutant p53 does NOT up reg mdm2, so mutant p53 builds up = increased levels.
MEN2A is associated with what and shows what diseases:
(Multiple endocrine neoplasia 2a) and is associated with RET and mutations give three diseases:
- Thyroid cancer
- Parathyroid hyperplasia - (calcium metabolism)
- Pheochromocytoma - benign tumour in adrenal medulla, can kill you due to increased adrenaline spikes
MEN2B is similar to MEN2A but…
does not give parathyroid hyperplasia and instead can cause gangloineuromas
FMTC stands for? and is due to?
Familial medullary thyroid cancer and is due to a germline mutation in RET
RET function:
TK receptor thats ligand is GDNF (glial derived neurotrophic factor). GDNF ligand causes receptor dimerisation between GDNFalpha and RET. Mutations in RET cause ligand independent activation = constitutive activation of the pathway. RET is expressed on neural crest cells and affects the tissues they make up.
MET
Encodes receptor TK, ligand = hepatocyte growth factor, gene on C7
MET is mutated in
hereditary papillary renal carcinoma via a germline missense mutation causing constituative activation of the TK receptor.
KIT
Encodes TK receptor for stem cell factor and is important in development, somatic and germline mutations of KIT are found in GI stromal tumours.
ALK
TK receptor with unknown ligand, somatic and germline mutations in neuroblastoma
CDK4/Cyclin D complexes:
phosphorylate RB1 to allow S phase entry. p16 inhibits CDK4.
Germline p16 mutations are seen in
familial melanoma, mutations in p16 prevent it binding to CDK4
Ras pathway mutations cause
developmental/ cancer syndromes
Screening for cancer: indicators, tests and benefits
I: family history, early onset/ multiple tumours
T: Karyotype, sequence gene (known & unknown mutations)
B: Early screening, Counselling, prenatal diagnosis.
An example of using chromosome translocations to find cancer genes:
RT PCR with primers specific for fusion protein. i.e. Edwings tumour t(11;22) product only appears if fusion protein is present.
Gene therapy for cancer involves:
TSG replacement, Antisense RNA to oncogenes (to inhibit them), RNA interference (siRNA)
What does anti-p53 virus do
Selectively kill of cancer cells with mutant p53 (doesn’t work so well in vivo)
Rational drugs for cancer?
Gleevec and Gefetnib (EFGR in lung cancer)
B-cell receptors recognize:
native antigen
TCR recognise:
peptide fragment of antigen presented by an MHC molecule on the surface of an APC.
Professional APC’s are:
DC’s, macrophages, B lymphocytes. They express MHC I and MHC II
What are the 3 domains on a MHC I molecule:
alpha1, alpha2, alpha3
What do alpha1 and alpha2 of an MHC I molecule contribute to the peptide binding cleft?
an alpha helix and several beta pleated sheets.
In MHC II what chains contribute to the peptide binding cleft?
alpha 1 and beta 1
How does a TCR recognise MHC and peptide?
The TCR has hypervariable loops on its variable domains, which interact with the side chains of the alphahelices AND the peptide. It is essential that the T cells recognise the complex of peptide and MHC to allow them to scan for infected cells or APCs
Where do T cells and DC’s reside in the lymph node?
Paracorticol area
How do B cells get activated by T cells? *check this
T cells present peptide to B cells, B cells internalise foreign material and present in on the surface in the context of MHC, T cells recognize the antigen and then provide help to activate the B cell by trafficking to just under the LN capsule. Here B cells become blast cells and are activated to enlarge and differentiate to plasma cells which produces specific antibodies that are then secreted.
CD4 associates with which and were on an MHC?
MHC II on the beta2 domain
CD8 associates where and with which MHC?
MHCI and with alpha3
T helper cell function:
Cytokine production, macrophage activation, “help” for B cells (IL-4)
T cytotoxic cell function:
cytotoxic lysis of infected or tumour cells
Congenic mouse:
Mice that are genetically identical except at a single locus or region
How are congenic mice bred?
By cycles of backcrossing, interbreeding and skin grafting
The major histocompatibility locus in mice.
complex: H-2 MHC Class: I Region: K GP: H-2K Region: D GP: H-2D, H-2L MHC class: II Region: IA GP: IAalpbet Region IE GP: IEalpbet
What is the human leukocyte antigen regions and gene products in relation to class
check on paper if right p16 L19
HLA E, F & G are
non classical HLA
HLA locus is:
polymorphic
HLA genes are
polymorphic
Why are most people heterozygous for MHC?
One allele inherited from mother and one from father, there are many different polymorphisms so they are highly unlikely to be the same.
What is TAPBP and where is it encoded?
In the MHC class II locus, tapasin is a component that proteates transporters associated with antigen processing with MHC molecules
TAP1 and TAP2 are:
In the MHC class II locus and are part of a heterodimer that transports peptides from the cytosol into the ER so the peptide can be loaded in the MHC class I molecule.
LMP2 & LMP7 on the MHC II locus are:
Components of proteosomes which are multi-enzyme complexes that chew up protein within the cytosol and generate peptides to be transported by TAP etc…
Which HLA genes are highly polymorphic?
HLA A, B, C and DRB1
What chain are the polymorphic AA around the peptide-binding groove on MHC I?
alpha1 and alpha2
What chain are the polymorphic AA around the peptide-binding groove on MHC II?
beta1
What is the key function of HLA?
To present peptides to T cells.
