jose mg izarzugaza, phd, assoc. prof. integrative systems...
TRANSCRIPT
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Understanding cancer genomics
Jose MG Izarzugaza, PhD, Assoc. Prof.
Integrative Systems Biology Group
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http://www.nature.com/scitable/topicpage/cell-division-and-cancer-14046590
What is cancer?
The disease caused by an uncontrolled division of abnormal cells in a part of the body
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Need for speed: Oncogenes vs Tumour suppressors
(ib.bioninja.com.au)
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Oncogenes: - Turn abnormal cell growth on- Mutated proto-oncogenes- 70 protooncogenes- gain of function genes- primarily somatic activated- [throttle pedal in a car]
(Adapted from Nat. Cancer Inst.)
“Oncogenes are mutated genes whose PRESENCE can stimulate the development of cancer”
Examples: HER-2/neu. RAS, MYC, SRC, hTERT
RAS, MYC, SRC are protein kinases Cell cycle regulation
Need for speed: Oncogenes vs Tumour suppressors
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Tumour suppressor genes: - Stop the cell cycle, G1 phase- Slow the cell cycle before S phase- Can induce apoptosis
- primarily somatic de-activated- loss-of-function mutations- [brake pedal in a car]
(Adapted from Nat. Cancer Inst.)
“Tumour suppressors are normal genes whose ABSENCE can stimulate the development of cancer”
Examples: p53, Rb, APC
Sometimes, a single functional copy (heterozygous) is enough to prevent cancer
Need for speed: Oncogenes vs Tumour suppressors
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DNA damage repair genes- Correct damage during DNA duplication- Active in cell cycle, primarily G2 - After DNA replication, before Chr divides
- loss-of-function mutations increased mutation burden
Examples: BRCA1 and BRCA2 in breast cancerAlso, mDDRG in hereditary colon cancer
(Adapted from Nat. Cancer Inst.)
Need for speed: DNA repair genes
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The hallmarks of cancer
The hallmarks of cancerHanahan and Weinberg, Cell 2000
- acquire functional capabilities
- cancer development
- various mechanistic strategies
(ib.bioninja.com.au)
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Cancer is a genetic disease: chromosomal aberrations
Chromosomal gain, lossTranslocation, inversionFocal amplification
Spectral karyotyping
What is cancer?
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Cancer is a genetic disease: point mutations SubstitutionInsertionDeletion
KRAS-wtATGACTGAATATAAACTTGTGGTAGTTGGAGCTGGTGGCGTAGGCAAG...-M--T--E--Y--K--L--V--V--V--G--A--G--G--V--G--K-...
KRAS-G12DATGACTGAATATAAACTTGTGGTAGTTGGAGCTGATGGCGTAGGCAAG...-M--T--E--Y--K--L--V--V--V--G--A--D--G--V--G--K-...
• Frequent driver mutation for tumors of the lung, colon, etc.• Predicts lack of benefit from EGFR inhibitors
What is cancer?
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Driver Confers selective advantageDisease associated, pathogenic
Passenger Present in the clonal progenitorFunctionally neutral
The drivers and passengers paradox
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Somatic Mutations-Present only in some cells
-Not transmitted to offspring-Do not fixate in population
Germline MutationsPresent in all cells
Transmitted to offspringFixate in population (SNP)
Germline vs Somatic mutations
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“Cancer is not a single disease, but rather 150+ different diseases.”
Prof. Dr. Mariano Barbacid, former director of the Spanish National Cancer Research Center and discoverer of the first oncogene, RAS.
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Top 20 cancers by incidence
In general, cancer is treated according to its tissue of origin
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Number of somatic mutations in different cancer types
Nature et al., 2013
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Mutation signatures in different cancer types
Alexandrov, Nature et al., 2013
E.g.: Signature 4
- Smoking induced mutations
- Lung cancers
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For the researcher: • Identify recurrent mutations that represent druggable targets• Identify specific mutations or patterns that predict benefit from
specific drugs• Study the evolutionary process -- mutation, selection
For the cancer patient:Identify “actionable” mutations - inform treatment decisionsAid in diagnosis
Why study cancer genomes?
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Measured in individual cells:- Cellular/tissue morphology- Protein expression- Gene copy number (FISH) - Karyotype
Measured in bulk tissue (usually):- Gene expression (from microarray)- Copy number profile (from SNP array)- WES/WGS/RNA-seq
Bulk tissue includes non-tumor cells!
@HS21_6684:1:1306:6031:9563#14CTTCCGATCTGGGTTAGGGTTAGGGTTAGGGTTAGGGTTAGGGTTAGGGTTAGGGTTAGGGTTAGGGTTAGGGTT+HS21_6684:1:1306:6031:9563#149((A=CA;2FDEEE>E=IIIIIIGGGIIHEF?CEHFDIGIIIGGGEGGHHHHIHFBBBGHEIHHFDHDDFDD?@@
Characterising a tumour specimen
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Histological characterization of a set of tumor specimens
Fine-needle aspiration (FNA) Core needle biopsy
Otherstromal*
Lymphocytes
Tumor
W. F. Symmans et al., Cancer 97:2960 (2003)
* Other stromal = fibroblasts, endothelials, histocytes, adipocytes
Caution 1: Tumour specimens are not just tumour cells
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Gerlinger et al. (2012) NEJM
Primary renal cell carcinoma
Caution 2: Tumour heterogeneity
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- Tumour heterogeneity differential
subclonal evolution
- Clones accumulate different mutations
as they diverge.
Caution 2: Tumour heterogeneity
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Driver Confers selective advantageDisease associated, pathogenic
Passenger Present in the clonal progenitorFunctionally neutral
The drivers and passengers paradox
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Treatment can re-shape tumour heterogeneity
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How to identify somatic mutations in a tumor
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Variant calling pipeline
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MuTect
K. Cibulskis et al., Nat Biotech (2013)
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Tumour
Blood (healthy)
(Healthy tissue in tumour fraction)
germlinegermline somatic
Matched samples for variant calling
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Somatic mutation calling vs.“regular” variant calling
1. We are interested in somatic mutations: differences between the tumor genome and the normal genome (NOT the reference genome).
2. The tumor data represents a mixture of reads from tumor cells and from normal cells, so we need deeper sequencing and more sensitive analysis to detect variants.
3. Tumors are often heterogeneous, and relevant mutations may be present at low allelic frequency. So we need even deeper sequencing.
Also: we are often interested in copy number changes, translocations, and clonal architecture
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M. Griffith et al., Cell Systems (2015)
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Cancer gene panel amplicon sequencing
ABL1 EGFR GNAS MLH1 RET
AKT1 ERBB2 HNF1A MPL SMAD4
ALK ERBB4 HRAS NOTCH1 SMARCB1
APC FBXW7 IDH1 NPM1 SMO
ATM FGFR1 JAK2 NRAS SRC
BRAF FGFR2 JAK3 PDGFRA STK11
CDH1 FGFR3 KDR PIK3CA TP53
CDKN2A FLT3 KIT PTEN VHL
CSF1R GNA11 KRAS PTPN11
CTNNB1 GNAQ MET RB1
TruSeq Amplicon - Cancer Panel Gene List
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Driver Confers selective advantageDisease associated, pathogenic
Passenger Present in the clonal progenitorFunctionally neutral
The drivers and passengers paradox
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Traditionally
PhenotypeFunction
Mechanism
1 Mutation=
1 Disease
Lots of hard work
Prediction ofPathogenicity /
Prioritization
X MutationsIn
Y PatientsAnd
Z Conditions Unfeasible
Now (High Throughput Sequencing, NGS)
Understanding variation in –omics times
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http://www.ensembl.org/Homo_sapiens/Info/Index
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Ensembl Variant Effect Predictor (I)
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Ensembl Variant Effect Predictor (II)
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Ensembl Variant Effect Predictor (Results)
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Predictors: SIFThttp://sift.jcvi.org/
- Based on the degree of conservation in a multiple sequence alignment (MSA)- MSA generated from PSI-BLAST results (closely related sequences)
- Deleterious if SIFT ≤ 0.05
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Predictors: Polyphen-2
MACHINE LEARNING - Naïve Bayes Classifier
SEQUENCE BASED FEATURES- Importance of site: DISULFID, CROSSLNK, BINDING, ACT_SITE,
LIPID, METAL, SITE, MOD_RES, CARBOHYD, NON_STD…- Importance of region: TRANSMEM, INTRAMEM, COMPBIAS,
REPEAT, COILED, SIGNAL, PROPEP…- PSIC conservation score
STRUCTURE BASED FEATURES- Likeness to destroy hydrophobic core, electrostatic interactions,
interactions with ligands, or other important features of proteins
http://genetics.bwh.harvard.edu/pph2/
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Predictors: Polyphen-2
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Automatic methods to predict the pathogenicity of mutations
Some of the (many) methods implemented during the last decade
MutationAssessor
Polyphen-2
PMUT
SNAP SIFT
Torkamani
SNPs&GO