Fundamental research on breast cancer in Belgium

Rosita Winkler

• Medline search for « breast cancer » and Belgium limits: english, posted in the last 5 years.

• Result: 484 papers - fundamental / clinical - according to the abstracts ????

• Identified the following topics – A. The breast cancer cell :

1. The estrogen receptor (ER) 2. ERBB2 gene3. Expression of other breast cancer associated genes 4. Breast cancer genomics

B. Invasion, metastasis1. Epithelial to mesenchymal transition (EMT)2. Proteases3. Metastasis

1. Estrogen Receptor (G. Leclercq, Bordet Inst.)

ER17pP295 T311

The P295-T311 sequence:

involved in ER transcriptional activity and stability

Calmodulin (CaM) binding site -> transcriptional activity, stability

ER17p

ER17p: estrogenic response in ERexpressing breast cancer cells

proliferation, transcription

ER expression

CaM binding

Binds ER

Dissociates the ER /HSP70 complex-> activation of ER

hypothesis: P295-T311 sequence in the full length ER has a repressive function

Hypothesis: ER17p could be produced endogenously by ER degradation by the proteasome and exert estrogenic effects in breast cancer cells

; production could be enhanced by treatment with hormone and hormone agonist -> sustained estrogenic effect.

2. Mechanisms of ERBB2/HER2 overexpression in breast cancers

In ± 20% breast cancers erbB2/HER2 protein level is very high.

Main mechanisms:

-gene amplification

-Increased transcription rates

HER2/ERBB2 gene amplification (Vanden Bempt I., De Wolf-Peeters C, KUL)

Characterization of the ERBB2 amplicon -

Identification of 4 chromosomal regions (≠ ERBB2 gene) over-expressed in ERBB2 gene amplified breast cancers; ex : MMP9

Other co-amplified chromosomal regions but no pattern common to all breast cancers with ERBB2 gene amplification.

High level over-expression associated with gene amplification not with chromosome 17 polyploidy

ERBB2/HER2 gene expression regulation (ULg)

ERBB2

Identification of :

•Several enhancer regions, bound by

•Activator proteins - AP-2 family transcription factors - overexpressed in ERBB2 positive breast cancer cells and in subpopulation of ERBB2 positive primary breast cancers

3. pRB/E2F: regulate the expression of Brip1, CHK1 genes in breast cancers: (Verstuyf A., KUL)

Brip1 - (BRCA1 interacting protein) / CHK1 mutations -> increased breast cancer risk.Brip1 and CHK1 expression: •associated with cell proliferation •controlled by E2F transcription factor•Brip1 Increased in grade 3 ER-/PR-/HER2+ cancers•CHK1 increased in grade 3 ER-/PR-/HER2- cancers

S-phase - proliferation

Brip1/BRCA1

A.4 Identification of new breast cancer susceptibility

genes: rat model (Szpirer, ULB)

10-15% of human breast cancers are associated with susceptibility genes - only 30% of these have been identified. How identify low penetrance genes?

Rat mammary tumours interesting model :

•similar developments and histological features as human breast cancers

•strongly hormone dependent

•no virus involvement

•susceptible and resistant strains

Comparison of the genome of resistant / susceptible strains:

•Different genes involved in chemically/hormone induced cancers

•Different loci control tumour multiplicity, latency, and aggressiveness.

B. Breast cancer cells invade and metastasize

1. They acquire the capacity to move (EMT)

2. They produce or stimulate the stromal cells to produce proteases necessary for invasion, angiogenesis, metastasis

3. They form distant metastasis

Epithelial to Mesenchymal Transition - EMT

(G. Berx Ghent, C. Gilles, Liège)

Epithelial cells are tightly bound by “adherens junction” and their basal surface lies on a basal membrane.

EMT: epithelial to mesenchymal transition: transient process during which epithelial cells loose their epithelial characteristics and acquire mesenchymal properties: loss of adherens junctions, increased motility; described during embryogenesis - gastrulation. Involved in the metastatic process. Probably followed by mesenchymal to epithelial transition (MET).

For EMT cells are reprogrammed by re-expressing “Master regulators”: Twist, Snail , Slug transcription factors.

Twist, Snail , Slug:

•control embryonic EMT

•upregulated in metastatic cancers.

• induce the replacement of the epithelial specific proteins by mesenchymal proteins.

Sip1

Sip1

E-cadherin

Vimentin

Sip1 inhibits E-cadherin expression and stimulates vimentin expression in breast cancer cells

(Berx G. RUG, Gilles C. Ulg)

(Berx G., Ghent)

(Gilles C., Liège)

NanosNanos(Van Roy, Ghent)(Van Roy, Ghent)

MCP-1MCP-1(Gilles C, Lg)(Gilles C, Lg)

MMP produced by tumoral and stromal cells during tumour

progression

Proteases and breast cancer progression

uPAR/ uPA/PAI/plasmin system controls angiogenesis

MT1-MMP expressed by myofibroblasts in contact with the cancerous cells

MMP2 (activated by MT1-MMP) expressed by several cell types

MT4-MMP protein is over-expressed in primary breast cancers and node metastasis but mRNA levels are not increased

MT4-MMP over-expression accelerates the growth of mammary

cancer cells in immunodeficient mice. (Noel A., Foidart JM, Liege) SNP in MMP8 gene promoter associated with the expression level of the gene (Paridaens and Ye, KUL).

Bone metastasis (Castronovo, Lg)

Osteotropic breast cancer cells express bone extracellular matrix proteins

Regulatory factors and promoter regions are being identified