Cell-Cycle Regulation Cell-Cycle Regulation and the Genetics of and the Genetics of

CancerCancer

Hartwell Genetics of CancerHartwell Genetics of Cancer The normal control of cell divisionThe normal control of cell division

Normal cell cycleNormal cell cycle Molecular signalsMolecular signals MachineryMachinery Checkpoints that regulate passage through cell cycleCheckpoints that regulate passage through cell cycle

How cancer arises from malfunctions in controls How cancer arises from malfunctions in controls over cell divisionover cell division Description of cancer phenotypesDescription of cancer phenotypes Analysis of clonal nature of tumorsAnalysis of clonal nature of tumors Explanation of mutation in protooncogenes and Explanation of mutation in protooncogenes and

tumor-supressor genestumor-supressor genes Comprehensive example describing progression Comprehensive example describing progression

of mutation leading to low-grade brain tumors to of mutation leading to low-grade brain tumors to aggressive brain canceraggressive brain cancer

Cancer phenotype results from accumulation Cancer phenotype results from accumulation of mutations in the clonal progeny of cellsof mutations in the clonal progeny of cells

Clone of cells overgrows due to Clone of cells overgrows due to accumulation of mutations accumulation of mutations controlling controlling proliferation. proliferation.

Forms tumor and stimulates formation of Forms tumor and stimulates formation of blood vessels (angiogenesis)blood vessels (angiogenesis)

Disseminates through bloodstream to other Disseminates through bloodstream to other parts of body (metasteses)parts of body (metasteses)

Forms tumors thereForms tumors there

General cancer phenotype includes General cancer phenotype includes many types of cellular abnormalitiesmany types of cellular abnormalities

Inappropriate cell-cycle Inappropriate cell-cycle controlcontrol

Autocrine stimulationAutocrine stimulation – tumor – tumor cells make their own signals to cells make their own signals to dividedivide

Loss of contact inhibitionLoss of contact inhibition – – lost property to stop dividing lost property to stop dividing when contacted by another cellwhen contacted by another cell

Loss of cell deathLoss of cell death – resistance – resistance to to apoptosisapoptosis

Loss of gap junctionsLoss of gap junctions – no – no channels for connecting to channels for connecting to neighbor cell and neighbor cell and communicating directlycommunicating directly

Feature Figure 18.16 a

Studies based on Studies based on early inactivation of 1 Xearly inactivation of 1 X chromosome in each cell of chromosome in each cell of womenwomen show tumors show tumors

are each clonal descendents of are each clonal descendents of one cellone cell

Fig. 18.18

Cancer arises by successive mutations in a Cancer arises by successive mutations in a clone of proliferating cellsclone of proliferating cells

Fig. 18.21

ONCOGENES were first ONCOGENES were first identified in tumor-causing identified in tumor-causing animal viruses:animal viruses:

One or 2 viral genes, not the whole One or 2 viral genes, not the whole virus, was required. virus, was required.

The “oncogene” was related to The “oncogene” was related to normal cellular genes involved in normal cellular genes involved in control of division – often called control of division – often called “protooncogenes”“protooncogenes”

Fig. 18.23 b, c

Mutations seen include: Oncogenes (dominant)Tumor suppressor genes (recessive)DNA repair genes

Changes that produce a potential for Changes that produce a potential for immortalityimmortality

Loss of limitations on the number of cell divisionsLoss of limitations on the number of cell divisions Ability to grow in culture – normal cells do not grow Ability to grow in culture – normal cells do not grow

well in culture on agar plateswell in culture on agar plates Restoration of telomerase activityRestoration of telomerase activity

Feature Figure 18.16 c

Changes that enable tumor to disrupt local Changes that enable tumor to disrupt local tissue and invade distant tissuestissue and invade distant tissues

Ability to Ability to metastasizemetastasize AngiogenesisAngiogenesis – secrete substances that cause blood – secrete substances that cause blood

vessels to grow toward tumorvessels to grow toward tumor Evasion of immune surveillanceEvasion of immune surveillance

Feature Figure 18.16 d

Tumor-cell karyotypes often Tumor-cell karyotypes often show gross rearrangementsshow gross rearrangements

Feature Figure 18.16 b (2)

The normal cell divisionThe normal cell division Cyclin-dependent Cyclin-dependent

kinaseskinases collaborate collaborate with cyclins to with cyclins to ensure the proper ensure the proper timing and timing and sequence of cell-sequence of cell-cycle eventscycle events The cell cycle has The cell cycle has

four phases: four phases: GG11, S , S GG22, and M, and M

Fig. 18.2

Cyclin-dependent kinasesCyclin-dependent kinases (CDKs) control the cell (CDKs) control the cell cycle by cycle by phosphorylatingphosphorylating other proteins other proteins

Fig. 18.7a

Normal gene product must be produced at a Normal gene product must be produced at a particular stage in cell cycle – Yeast mutants:particular stage in cell cycle – Yeast mutants:

Cell acquires ability to Cell acquires ability to complete a cell cycle the complete a cell cycle the moment the temperature-moment the temperature-sensitive protein has sensitive protein has fulfilled its function in that fulfilled its function in that cycle.cycle.

CDC28CDC28 gene is first step in gene is first step in cell cyclecell cycle After CDC28 step, cell is After CDC28 step, cell is

committed to finish cell cyclecommitted to finish cell cycle Alternative fates after first Alternative fates after first

cell cyclecell cycle Arrest of cell divisionArrest of cell division Fusing with a cell of opposite Fusing with a cell of opposite

mating typemating type Decision to pursue made in Decision to pursue made in

GG11 phase at “start” phase at “start”Fig. 18.6

CDKs mediate the transition from CDKs mediate the transition from the Gthe G11-to-S phase in human cells-to-S phase in human cells

Fig. 18.9

Mutations creating defective Mutations creating defective tumor-suppressortumor-suppressor alleles alleles release break on cell divisionrelease break on cell division and decrease accuracy of cell and decrease accuracy of cell reproduction: reproduction: e.g., retinoblastoma tumor-suppressor genee.g., retinoblastoma tumor-suppressor gene

Fig. 18.24

Target of an enzyme is its substrateTarget of an enzyme is its substrate

Nuclear laminsNuclear lamins CDK substratesCDK substrates Underlie inner surface of the nuclear membraneUnderlie inner surface of the nuclear membrane Probably provide structural support for nucleusProbably provide structural support for nucleus May also be site for assembly of DNA replication, transcription, RNA May also be site for assembly of DNA replication, transcription, RNA

transport, and chromosome structure proteinstransport, and chromosome structure proteins Dissolution of nuclear membrane during mitosis is triggered by CDK Dissolution of nuclear membrane during mitosis is triggered by CDK

phosphorylation of nuclear laminsphosphorylation of nuclear lamins

Fig. 18.7b

Human CDKs and cyclins can function in Human CDKs and cyclins can function in yeast in place of native proteinsyeast in place of native proteins

Fig. 18.8

Humans make the transition from G2-to-M Humans make the transition from G2-to-M similar to yeast which is controlled by similar to yeast which is controlled by

phosphorylation and dephosphorylationphosphorylation and dephosphorylation

Fig. 18.10

Checkpoints Checkpoints integrateintegrate repair repair of chromosome of chromosome damage with damage with events of cell cycleevents of cell cycle

G1-to-S checkpointG1-to-S checkpoint p53 – transcription factor that p53 – transcription factor that

induces expression of DNA induces expression of DNA repair genes and CDK inhibitor repair genes and CDK inhibitor p21p21

p53 pathway p53 pathway activated byactivated by ionizing radiation or UV light ionizing radiation or UV light (causing (causing DNA damageDNA damage) during ) during G1 phase G1 phase delays entry into Sdelays entry into S phasephase

DNA is repaired before cell cycle DNA is repaired before cell cycle continuescontinues

If If DNA is badly damagedDNA is badly damaged cells cells commit suicide (programmed cell commit suicide (programmed cell death or death or apoptosisapoptosis))

Fig. 18.11 a

Defective Repair:Defective Repair: p53p53 mutants mutants do not do not

induce p21 and cell induce p21 and cell cycle is not arrestedcycle is not arrested

Cells replicate Cells replicate damaged DNAdamaged DNA

Cells die or DNA is Cells die or DNA is degraded and cell is degraded and cell is engulfed and digested engulfed and digested by neighboring cells by neighboring cells (apoptosis, or (apoptosis, or programmed cell programmed cell death) death) – or: cancer – or: cancer risk increasesrisk increases

Fig. 18.11 c,d

Two checkpoints act at the GTwo checkpoints act at the G22-to-M cell-cycle transition-to-M cell-cycle transition double stranded breaks: problems with double stranded breaks: problems with MITOSISMITOSIS

Fig. 18.12a

Checkpoint in MCheckpoint in Mspindle damagespindle damage

Fig. 18.12b

Checkpoints ensure genomic Checkpoints ensure genomic stabilitystability

Defective checkpoints Defective checkpoints Chromosome aberrationsChromosome aberrations

AneuploidyAneuploidy Changes in ploidyChanges in ploidy

Single-stranded nicks – normally repaired in GSingle-stranded nicks – normally repaired in G11 phasephase

Chromosome loss or gain – normally corrected Chromosome loss or gain – normally corrected in Gin G22-to-M checkpoint-to-M checkpoint

Normal cells Cancerous cells

Fig. 18.13 b

Three classes of error lead to Three classes of error lead to aneuploidy in tumor cellsaneuploidy in tumor cells

Fig. 18.13a

Molecular components of each Molecular components of each signaling systemsignaling system

Growth factorsGrowth factors – hormones and cell-bound signals that – hormones and cell-bound signals that stimulatestimulate or or inhibitinhibit cell proliferation cell proliferation

ReceptorsReceptors – membrane bound proteins that accept signals – membrane bound proteins that accept signals signal-binding sitesignal-binding site transmembrane segmenttransmembrane segment intracellular domainintracellular domain

Fig. 18.15 a

Signal transducers relay messages and Signal transducers relay messages and transcription factors activate expression of genestranscription factors activate expression of genes

Fig. 18.15 b

The The protooncogene RAS protooncogene RAS causes activation of causes activation of intracellular targets after growth factor binds intracellular targets after growth factor binds

to receptor – leading to cell replicationto receptor – leading to cell replication

Fig. 18.15 d

Fig. 18.15 c

Cancer mutations occur in two formsCancer mutations occur in two forms

OncogenesOncogenes dominant dominant

mutationsmutations Mutant tumor-Mutant tumor-

suppressor suppressor genesgenes recessive recessive

mutationsmutations

Fig. 18.22

Oncogenes versus Tumor Suppressor GenesOncogenes versus Tumor Suppressor Genes : : cancer formation and survival of mice of various cancer formation and survival of mice of various

genotypes genotypes

Fig. 18.17

Most cancers result from exposures to mutagensMost cancers result from exposures to mutagens

If one sib or twin gets cancer, other usually does notIf one sib or twin gets cancer, other usually does not Populations that migrate – profile of cancer becomes more Populations that migrate – profile of cancer becomes more

like people indigenous to new locationlike people indigenous to new location

Cancer develops over timeCancer develops over time

Fig. 18.19

Some cancers run in families such as Some cancers run in families such as retinoblastomaretinoblastoma

Fig. 18.20

Two approaches to identifying oncogenesTwo approaches to identifying oncogenes

Analysis of tumor Analysis of tumor causing retrovirusescausing retroviruses

Fig. 18.23 a

Genetics of brain cancerGenetics of brain cancer Glioblastoma multiforme (GBM)Glioblastoma multiforme (GBM)

Aggressive cancer of glial cellsAggressive cancer of glial cells Heterogeneous condition resulting from mutation in different Heterogeneous condition resulting from mutation in different

subset of genessubset of genes Glial cellsGlial cells

Astrocytes – provide support for neuronsAstrocytes – provide support for neurons Oligodendrocytes – produce myelin sheathsOligodendrocytes – produce myelin sheaths Ependymal cells – line the brain cavities known as ventricles and Ependymal cells – line the brain cavities known as ventricles and

regulate cerebrospinal fluid productionregulate cerebrospinal fluid production Grades of gliomasGrades of gliomas

Lowgrade (II)Lowgrade (II) Anaplastic (III)Anaplastic (III) GBM (IV)GBM (IV) Low grades progress to higher gradesLow grades progress to higher grades

Many genes in various combinations produce GBMsMany genes in various combinations produce GBMsThree routes for evolution of GBM have been identifiedThree routes for evolution of GBM have been identified

Fig. 18.26

Pathway from grade II astrocytoma Pathway from grade II astrocytoma to malignant GBMto malignant GBM

Fig. 18.27

Some rapidly arising GBMs have no Some rapidly arising GBMs have no apparent precursorsapparent precursors

Oncogenic amplification of the Oncogenic amplification of the epidermal-growth-epidermal-growth-factor-receptorfactor-receptor ( (EGFREGFR) gene and loss of regions ) gene and loss of regions from 10p and 10qfrom 10p and 10q

Arise Arise de novode novo or so rapidly no precursors are or so rapidly no precursors are detectabledetectable

Rarely occur in astrocytoma-derived GBM tumors Rarely occur in astrocytoma-derived GBM tumors with with p53p53 mutations and 17q deletions mutations and 17q deletions

Occur in significantly older adults than GBMs Occur in significantly older adults than GBMs with mutant with mutant p53p53 and chromosome 17 deletions and chromosome 17 deletions

SummarySummary GBM phenotypesGBM phenotypes

Develop by different combinations of mutations in Develop by different combinations of mutations in different pathwaysdifferent pathways Lower-grade astrocytomas via p53 and RB gene Lower-grade astrocytomas via p53 and RB gene

inactivationsinactivations Oligodendroglial tumors via deletions of chromosome 1 and Oligodendroglial tumors via deletions of chromosome 1 and

1919 de novode novo via EGFR gene activation via EGFR gene activation

Mutational pathways are often more complicatedMutational pathways are often more complicated Not every GBM shows all genetic changes describedNot every GBM shows all genetic changes described Some GBMs derived from one type of cell have mutations Some GBMs derived from one type of cell have mutations

associated with another type of cellassociated with another type of cell

Experiments with yeast helped identify Experiments with yeast helped identify genes that control cell divisiongenes that control cell division

Properties of yeast Properties of yeast Grow as haploid or diploid organismsGrow as haploid or diploid organisms

Can identify recessive mutations in haploidsCan identify recessive mutations in haploids Complementation analysis in diploidsComplementation analysis in diploids

Budding – daughter cell arises on surface of Budding – daughter cell arises on surface of mother cell and grows in size during cell cycle. mother cell and grows in size during cell cycle. Helps determine stage of cell cycle.Helps determine stage of cell cycle.

Isolation of temperature-sensitive Isolation of temperature-sensitive mutants in yeastmutants in yeast

Mutants grow Mutants grow normally at permissive normally at permissive temperaturetemperature

Mutants loses gene Mutants loses gene function at restrictive function at restrictive temperaturetemperature

Thousands of cell cycle Thousands of cell cycle mutants have been mutants have been identifiedidentified

Fig. 18.3

A cell-cycle mutant in yeastA cell-cycle mutant in yeast (a) growth at permissive (a) growth at permissive

temperature displays temperature displays buds of all sizesbuds of all sizes

(b) growth at restrictive (b) growth at restrictive temperature shows cells temperature shows cells have finished first cell have finished first cell cycle and arrested in the cycle and arrested in the secondsecond

Fig. 18.4

70 cell-cycle genes identified through 70 cell-cycle genes identified through temperature-sensitive mutation screenstemperature-sensitive mutation screens

Changes that produce genomic and Changes that produce genomic and karyotypic instabilitykaryotypic instability

Defects in DNA Defects in DNA replication machinery replication machinery – lost capability to – lost capability to reproduce genome reproduce genome faithfullyfaithfully

Increase rate of Increase rate of chromosomal chromosomal aberrations – fidelity of aberrations – fidelity of chromosome chromosome reproduction greatly reproduction greatly diminisheddiminished

Feature Figure 18.16 b (1)