Rb Spring 11 Stu

7/24/2019 Rb Spring 11 Stu

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The story of Retinoblastoma

Tumor Suppressor Genes



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”



) 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



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



n cancer patients (ith a familyhistory of Retinoblastoma# the

inheritance seems to be 4



Rb tumors are associated (ith adeleted re!ion in chromosome 13

5eletion $ loss)of)functionprobably a recessie mutation in

the Rb !ene



The 6nudson7s 8T(o it9 ypothesisfor the Generation of R:

Alfred Knudson, PNAS 68:820 (1971)



The 6nudson7s 8t(o hit9 hypothesisfor the !eneration of R:



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



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 >



Normalpatern

al

Mutated

maternal

Mutated

maternal

-/+

-/-

-/-

-/-

Mutatedpaternal

The mutatedmaternal

chromosome was



The presence of one mutated copyincreases the chances of a second

mutated copy



Rb is ?ust one e@ample

nheritance of brca1(lf) mutation

results in predisposition forbreast cancer

Rb $ A Tumor SuppressorGene



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



%redisposition is inheriteddominantly, but cancer is not

inherited The osprin! ABB>T inherit t(omutated !enes



o( can (e clone a tumor)recessie!ene4

>nco!enes transform cells intocancerous cells

:ut TSGs are recessie

o( do (e test candidate !enes4



Rb tumors are associated (ith adeleted re!ion in chromosome 13

5eletion $ loss)of)functionprobably a recessie mutation in

the Rb !ene



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 !!"



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



De hae correlation

Dhat about causation4

The R: !ene is Enally



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



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



&'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



'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



ypo)phosphorylatedRb binds to F2s and#

) nhibits theirtranscriptionactiation sites) Recruits proteins that

(ill 8close9 thechromatin do(n



Releasin! Rb fromthe F2s leads to#

) Release of theirtranscription actiation

sites) Recruitment of proteinsthat (ill 8open up9 thechromatin



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



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



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



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



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/+



>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



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



As F2s are necessary fore@pression of cycE, thin ho(

critical negative regulation b' #bis for cell cycle control

(Fs



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



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



Dhat not to focus on



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

Rb Spring 11 Stu

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