Lecture 2 (slide 76-153)

HER2+

gBRCA mut

bekendste moleculaire subtypes borstkanker

HER2+ similar principle as in lung cancer: activation of growth factor receptor signaling

principe HER2+ als moleculair subtype borstkanker

NEU / ERBB2

synoniemen HER2

Herceptin

Kadcyla

oudere en nieuwe therapie voor borstkanker tegen HER2+ subklasse

Trastuzumab: monoclonal antibody against HER2 receptor

wat hebben herceptin en kadcyla gemeen?

kadcyla: also emtansine (a chemotherapeutic agent), which is also released into the cell

verschil kadcyla en herceptin

the antibody acts as a carrier for the chemotherapy agent = antibody-drug conjugate (blocking effect + additional chemotherapeutic effect)

principe antibody drug conjugate (ADC)

RAS cycle

guanine nucleotide exchange factor: switches RAS on

GEF

GTPase activating protein: switches RAS off

GAP

Hotspot activating mutations often occur at G12, G13 or Q61

oncogene mutaties in RAS

Oncogene

is RAS an oncogene or tumor suppressor?

NF1 (neurofibromatosis 1) is an example of a GAP, so a tumor suppressive gene

NF1 in context van RTK downstream pathways

HRAS

NRAS

KRAS

three main RAS isoforms

KRAS: very important

HRAS: not mutated at all

rol HRAS en KRAS in pancreatic cancer

KRAS has a strong preference for the codon 12 mutations

voor wat voor mutaties heeft KRAS een sterke voorkeur?

central nervous system tumors

voorbeeld tumor met weinig RAS mutaties

melanoma (skin cancer) has over 30-40% of patients with BRAF activation. So very important oncogene in skin cancer!

belangrijk oncogene in skin cancer

Know that patients with a BRAF hotspot mutation usually do not overlap with RAS mutations. Additional mutation in the same pathway gives little extra selective benefit

bestaat er overlap in BRAF en RAS mutaties?

Vemurafenib (BRAF inhibitor)

Trametinib (MEK inhibitor)

belangrijke therapieën tegen melanoma

V600E

belangrijke activating mutatie in BRAF

colorectal carcinoma

waar kan je nog BRAF mutaties vinden (buiten melanoma)?

Requirement of combination therapy

A: In the BRAF V600E cancer situation, the MAPK cascade drives proliferation with feedback regulation present

B: With BRAF inhibition (e.g. vemurafenib), mutant BRAF is blocked, but feedback release can reactivate upstream EGFR/RAS signaling and restore pathway activity, causing resistance

C: Therefore broader pathway blockade is needed, combining BRAF inhibition with EGFR and/or MEK/ERK inhibitors to suppress reactivation

waarom is combination therapy nodig bij BRAF V600E mutated tumors?

AKT PI3K pathway

naast RAS/MAPK nog een belangrijk pathway in kanker

Phosphatidylinositol 3-kinase

PI3K

a heterodimer lipid kinase consisting of an 85-kD subunit bound to a 110-kD catalytic subunit

hoe is PI3K opgebouwd?

cell growth

effect AKT PI3K pathway

PTEN is an important tumor suppressor in this pathway, antagonizing PI3K signaling

tumor suppressor in AKT PI3K pathway

Proteus syndrome

overgrowth syndrome

Usually germline cancer predisposition involves tumor suppressor genes rather than activating oncogenes

This case is an exception: postzygotic germline/mosaic activating mutation in the PI3K/AKT pathway (often AKT1), not inherited from the parents in the classic sense

waarom is Proteus syndrome zo belangrijk in onze context?

MAX is an important dimerization partner of MYC, promoting transcriptional activation

belangrijke partner MYC

MAD can compete with MYC for MAX binding, leading to repression / reduced mitogenic signaling

MAD in context MYC en MAX

RB is a key gatekeeper of the G1/S transition. E2F transcription factors drive passage through the R-point and are normally suppressed by RB

belang RB

RB is inactivated, E2F released, cell goes past the R-point

effect phosphorylatie van RB

CDK4 is an important example in many tumor types because, together with cyclin D, it promotes progression through G1 toward S-phase

hoe gaat een cel van G1, naar de S-phase?

The extent of RB phosphorylation increases through the cell cycle, with additional kinases such as CDK2 contributing later

kinases die actief worden later in de cell cyle

which gene encodes p21?

CDKN1A

p21 is an upstream inhibitor of CDK2 (and CDKs), so acts as a tumor suppressive regulator

is p21 een oncogene of suppresor?

Cyclin-dependent kinases (CDKs) can act as oncogenic drivers when overactive

zijn CDKs oncogenes of suppressors?

CCND1

which gene encodes cyclin D1?

More Cyclin D1 (cofactor of CDK4/6) → more CDK4/6 activity → more proliferation.

wat maakt van CCND1 een oncogene?

Glioblastoma

important kind of brain tumour

drives amplifcation/deletion of cell cycle regulators

Chromothripsis can lead to amplification of EGFR and CDK4, promoting strong proliferative signaling

waarom leidt chromothripsis tot glioblastoma?

Cell-cycle control is not an isolated event: cyclin-CDK complexes are tightly linked to DNA-damage signaling

waarom is cyclin-CDK complexes niet het enige belangrijke bij cell cycle regulation?

Fusion tyrosine kinase from t(9;22), classic driver of CML.

Wat is BCR-ABL

SAC is an important checkpoint controlling progression from metaphase to anaphase, ensuring chromosomes are correctly attached to the spindle

belang SAC

Spindle assembly checkpoint

afkorting SAC

APC/C is a very important complex here. Together with cofactor CDC20, it functions as an E3 ubiquitin ligase

APC/C–CDC20 promotes degradation of securin and cyclin B. Loss of cyclin B lowers CDK1 activity

Later, APC/C with cofactor CDH1 degrades additional mitotic regulators such as FOXM1, AURKA, AURKB and PLK1, helping mitotic exit and preventing reactivation of CDK1

belang APC/C in SAC

CDK1 together with cyclin B is a key driver of mitosis. High CDK1-Cyclin B activity keeps the cell in mitosis until chromosomes are properly aligned

belangrijke driver van mitosis

Pro-mitotic transcription factor.

G2/M transition and mitosis.

Often overexpressed and drives proliferation.

wat is FOXM1 en zijn belang in kanker?

pathways with eg p53 and RB stops cells with too short telomeres (senescence), but mutations can make cells go past this checkpoint, going to crisis.

Crisis is also overcome by activating telomerase or other mechanisms (TERT complex)

hoe overkomen kankercellen te korte telomeren?

Catalytic reverse transcriptase subunit of telomerase.

wat is TERT?

RNA template used by telomerase.

wat is TERC?

p53

het belangrijkste gen dat zorgt voor senescence

They develop drugs targeting senescent cells (senolytics) and drugs targeting telomerase/telomere maintenance

Therapie tegen tumoren met verhoogde telomerase activiteit

increased transcription, gain/amplification, mutation or genomic rearrangements

Promoter mutations can create new ETS/TCF transcription factor binding sites, leading to higher TERT expression and increased telomerase activity

Enhancer hijacking

hoe kan TERT meer actief worden?

ALT (alternative lengthening of telomeres)

alternatieve methode voor telomere maintenance

telomerase-independent telomere maintenance through homologous recombination-based mechanisms

ALT does not rely on telomerase enzyme activity and is often associated with more genomic instability

=> Telomerase-dependent versus telomerase-independent telomere maintenance

mechanisme ALT (Alternative Lengthening of Telomers)

Extrachromosomal circular C-rich telomeric DNA.

wat zijn c-circles?

ALT-positive tumors.

waar vind je c-circles?

Telomerase-positive telomeres are often more heterochromatic / compact, with repressive chromatin marks

ALT-positive telomeres are relatively more open / altered chromatin and show increased structures such as G4 DNA and R-loops

chromatin difference tussen ALT- en telomerase-positives

ATRX helps maintain normal telomeric chromatin structure (linked to H3.3 deposition); loss or mutation of ATRX is frequently associated with ALT-positive tumors

belang ATRX bij ALT- en telomerase-positives

TERRA is a telomeric non-coding RNA and is often increased/associated with ALT, together with markers such as C-circles and APBs

TERRA

Nucleotide subsitution

Promotor hijacking

gene fusion

enhancer hijacking

focal amplification

disruption of insulated neighborhoods

Verschillende types van oncogene activatie

Inactivating mutations are the most important mechanism of tumor suppressor loss; enhanced degradation is less common but possible

belangrijkste mechanisme van tumor suppressor loss

Tumor suppressor genes are often linked to hereditary cancer predisposition syndromes when one mutant allele is inherited in the germline

Familial predisposition means increased risk, not certainty, of developing a certain tumor type

tumor suppressor genen en erfelijkheid

A lot of tumor suppressor genes need to have both alleles inactivated for full loss of function

Knudson two hit hypothesis

Hypophosphorylated RB = active brake; hyperphosphorylated RB = released brake

hypo- and hyperphosphorylated RB1

13q14: Retinoblastoma

In this case, the translocation places the RB1 region on the derivative X chromosome. If that derivative X becomes inactivated in a subset of cells, RB1 can be functionally silenced

Loss/inactivation of RB1 leads to retinoblastoma (a retinal eye tumor)

typische kanker door RB1 translocation, ook belangrijk geweest voor de ontdekking

Finding a disease gene based on chromosomal location.

positional cloning

p16 and 15

suppressor CDK4

p53 is a sequence-specific DNA binding protein that regulates transcription

p53

two N-terminal transactivation domains

conserved proline-rich domain

a central DNA binding domain

C terminus encoding its nuclear localization signals

oligomerization domain needed for transcriptional activity.

onderdelen p53

DNA-damage by UV → phosphorylation of p53 / changes in MDM2 → p53 increase → activates p21 → inhibits cyclin-CDK complexes → stops cell cycle for DNA-repair

cascade DNA damage by UV en p53

Ubiquitinates p53 for degradation.

rol MDM2

inhibits MDM2

=> increases p53

effect ARF

p53 is often active as a tetramer

wat voor eiwit is p53? (in zin van opbouw)

p16 (INK4A) and p14 (ARF) (both tumor suppressors)

belangrijke eiwitten komende van CDKN2A

inhibiting CDK4/6

rol INK4A

E2F is a key transcription factor that promotes G1/S cell-cycle progression by activating genes needed for DNA replication and proliferation. Normally it is restrained by RB. When E2F becomes abnormally elevated, cells sense this oncogenic signal and induce ARF, which stabilizes p53 and can trigger apoptosis or growth arrest.

on / off switch

belang E2F

Fine-tuning of p53 response.

belang PTM’s bij p53

single hit is sufficient for accelerating cancer formation

is de two hit hypothesis geldig bij p53?

~50% of tumors

komen p53 mutaties frequent voor?

>75% of mutations (>15.000 known) are missense rather then nonsense

wat voor mutaties heb je bij p53?

Partial reduction of function

hypomorphs

gain of new oncogenic function

neomorphic mutant

GOF present, but less frequent

Mogelijke mutaties bij p53

adenomatosis polyposis coli – colon cancer

APC (de kanker, niet het complex)

FAP (Familial Adenomatous Polyposis)

HNPCC: hereditary nonpolyposis colon cancer:

two syndromen dat zorgt voor een hoog risico in colorectal cancer

APC, it normally controls Wnt by beta-catenin, but mutation in APC leads to a lot of Wnt, so a lot of growth

gen belangrijk in FAP

germline mutations leading to mismatch repair defect

oorzaak HNPCC

Gorlin syndrome (Sonic Hedgehog pathway)

syndroom gelinkt met medulloblastoma