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The story of Retinoblastoma
Tumor Suppressor Genes
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Retinoblastoma is a cancerous disease
1/20,000 children; 300 peryearAera!e a!e is 1" months
Treatment#enucleation $ eye remoal
%ro!nosis is !ood afterenucleationoer &0' surial (ith earlydetection and treatment
Leukocoria or “white pupil”
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) Sporadic cancer in **)+*' of
all cases) Sporadic cancers areunilateral
Rb is either sporadic or familial
ereditary childhood cancer#) bilateral tumors in -.*' of
cases) unilateral tumors in -2*' ofcases
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hildren (ith bilateral familialRb hae a hi!h ris of deelopin!
non)retinal tumors
Germ)line mutations in the Rb
!ene lead to predisposition to
Sporad
ic
Familia
l
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n cancer patients (ith a familyhistory of Retinoblastoma# the
inheritance seems to be 4
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Rb tumors are associated (ith adeleted re!ion in chromosome 13
5eletion $ loss)of)functionprobably a recessie mutation in
the Rb !ene
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The 6nudson7s 8T(o it9 ypothesisfor the Generation of R:
Alfred Knudson, PNAS 68:820 (1971)
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The 6nudson7s 8t(o hit9 hypothesisfor the !eneration of R:
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Retinoblastoma is inherited as adominant trait, but it is recessive
at the cellular level
%eople (ith familialRetinoblastoma carry onemutated copy in A theircells< ells that (ould !et asecond hit (ill deelop Rb or
later, other cancers
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oss of hetero=y!osity > in a cell
represents the loss of normal function of oneallele of a !ene in (hich the other allele (as
already inactiated
oss of hetero=y!osity >
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Normalpatern
al
Mutated
maternal
Mutated
maternal
-/+
-/-
-/-
-/-
Mutatedpaternal
The mutatedmaternal
chromosome was
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The presence of one mutated copyincreases the chances of a second
mutated copy
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Rb is ?ust one e@ample
nheritance of brca1(lf) mutation
results in predisposition forbreast cancer
Rb $ A Tumor SuppressorGene
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Retinoblastoma is inherited as adominant trait, but it is recessive
at the cellular level
%eople (ith familialRetinoblastoma carry onemutated copy in A theircells< ells that (ould !et asecond hit (ill deelop Rb or
later, other cancers
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%redisposition is inheriteddominantly, but cancer is not
inherited The osprin! ABB>T inherit t(omutated !enes
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o( can (e clone a tumor)recessie!ene4
>nco!enes transform cells intocancerous cells
:ut TSGs are recessie
o( do (e test candidate !enes4
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Rb tumors are associated (ith adeleted re!ion in chromosome 13
5eletion $ loss)of)functionprobably a recessie mutation in
the Rb !ene
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Cse a fra!ment of the candidate !ene
as a probe for Southern :lot analysis
Search for absence of the !ene in tumorshopin! both mutated copies are deletions
Testin! a candidate!ene
More on this- Angier book, starting p !!"
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Rb !ene e@pression isabsent or altered in
retinoblastoma tumors
Friend e al! Naure(86) "ee e al! Science(87)
Borthern blotsmRBA
e@pression
#b tumors$T %ther
tumors
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De hae correlation
Dhat about causation4
The R: !ene is Enally
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Dr. David Abramson, RB expert at New ork !ospital
"ca. #$%&, Accordin' to Natalie An'ier(
“) believe that in *i*teen +ears, at the outside, well be able
to stop retinoblastoma be*ore it be'ins. )m so sure that
)ve alread+ 'iven the dru' a name. ) call it retino-revert,or retino-prevent. he dru' will be an analo'ue o* the
natural protein that is missin' in retinoblastoma cells /
0ell be able to dia'nose a child prenatall+ and start 'ivin'
this retino-revert to the mother to prevent retinoblastomas
*rom 'rowin' as the *etus is developin'. ) know )m 'oin'
out on a limb with this one, but / 1ome back to me in
233# and tell me i* ) wasnt ri'ht.”
Bold 4redictions, 5urther 0ork
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pRb# Dhat does it do4
p#b is a nuclear protein that under!oes
phosphorylation and dephospharylation in
Th di f th ll t l
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&'po-phosphorylated
or un)phosphorylated p#b inhibits the
cell from enterin!a ne( cell cycle
The !uardian of the cell at early)mid G1
Cpon further phosphorylation at the Rpoint, h'per)phosphorylated p#b
becomes inert and the cell cycle canroceed
'po p osp ory a e n s
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'po)p osp ory a e n s actiity of the F2 family of
transcription factors
yper)phosphorylation of
Rb seHuesters Rb,
F2s are needed
for transcriptionof !enes that areessential for thecell to enter thecell cycle
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ypo)phosphorylatedRb binds to F2s and#
) nhibits theirtranscriptionactiation sites) Recruits proteins that
(ill 8close9 thechromatin do(n
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Releasin! Rb fromthe F2s leads to#
) Release of theirtranscription actiation
sites) Recruitment of proteinsthat (ill 8open up9 thechromatin
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Rb, the retinoblastomaprotein re!ulates the cell
cycleell cycle $ >Rb binds to F2# notranscription, no
entry into S phase
ell cycle $ >B
Rb does not bind toF2# transcriptionand entry into Sphase
w/o ( copies o) #b* no cell
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pRb# Dhat does it do4
p#b is a nuclear protein that under!oes
phosphorylation and dephospharylation in
Rb ti it i ti htl l t d b
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Rb actiity is ti!htly re!ulated bythe cell cycle cloc
&'po-phosphorylation iscataly=ed by cyc5)56I/+
&'per-phosphorylation iscataly=ed by cycF)
562
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p#b is hyper)phosphorylated andinhibited and released from its role as a
!uardian, only upon c'c epression
Rb ti it i ti htl l t d b
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Rb actiity is ti!htly re!ulated bythe cell cycle cloc
o(eer, F)562 can phosphorylateRb, only ATFR Rb is phosphorylated by
cyc5)56I/+
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>nly after (e hae enou!h mito!en si!nalin!and, as a result, enou!h cyc5)56I/+
actiity, cycF can phosphorylate Rb and allo(
entry to the cell cycle
ae !ro(n enou!h4
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F2s hae more than 100tar!et !enes, mostly
inoled in the Erst stepsof NA replication>ne of thetar!ets# the
cycE gene Transcription ofcycE starts a
positie)eedback loop
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As F2s are necessary fore@pression of cycE, thin ho(
critical negative regulation b' #bis for cell cycle control
(Fs
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Rb !ene alteration is inoled many tumors
n the ma?ority of tumors you (ill End
mutation inoled in the R site
Cncontrolled crossin! of the R site can be
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Cncontrolled crossin! of the R site can bedue to loss of Rb function e<!< mutation,loss of 6s or onco!enic actiity of cyclins
F and 5
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Dhat not to focus on
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Dhat to focus on
ell cyclecontrolRe!ulation of 56s
Jito!ens and the cellcycleRb# !enetics
The restriction point# cyc5, cycF, F2s,
1+ d #b
5etails of the cell cycle e<!< (hat happens inprometaphase
Dhat not to focus on
Jolecular details of ubiHu< pre)replicatiecomple@, etc<
er)2