Download Expression of the Epithelial Mesenchymal Transition Regulator

Expression of the Epithelial Mesenchymal Transition Regulator Snail in
Metaplastic Breast Carcinomas with Chondroid Differentiation
K Gwin, A Contreras, M Tretiakova, A Montag The University of Chicago Medical Center, Chicago, IL
Score
The epithelial mesenchymal transition (EMT) is an essential process
during normal embryogenesis in which polarized, immotile epithelia
acquire a highly motile, fibroblastoid phenotype. EMT is characterized by
the loss of cell-cell adhesion, apical-basal cell polarity and increased
motility of cells. In epithelial tumors, EMT is an important process during
tumor progression and development of metastasis. Tumor cells gain the
ability to invade tissues and to migrate to distant regions.
EMT is regulated by transcription factors such as Snail that downregulate
epithelial and upregulate mesenchymal genes. The transcription factor
Snail is considered one of the key regulators of EMT as it particularly
functions in repression of transcription of E-Cadherin. Metaplastic breast
carcinomas with chondroid differentiation (MBC) show a combined
epithelial and mesenchymal chondromyxoid matrix with features
reminiscent of EMT. MBC may therefore be a potential in vivo model for
EMT, and increased expression of Snail in both tumor components might
be present.
Archival paraffin embedded material of 12 MPC, as defined by the 2003
WHO classification, and 1 lymph node metastasis were retrieved from the
files of the Pathology Department. The lymph node metastases showed
only the epithelial component.
Selected 4 m thick formalin-fixed deparaffinized sections were stained
with primary anti-human Rabbit Polyclonal antibody SNAI1 (Aviva
Systems Bio).
Cytoplasmic and nuclear expression in the areas of strongest positivity
was determined in 50-100 tumor cells separately for both tumor
components. In accordance with previous studies nuclear snail expression
was evaluated as follows: 0, immunoreactivity of < 1% of tumor cells; 1+,
immunoreactivity of 1% of tumor cells; 2+ immunoreactivity of 2-5% of
tumor cells; 3+, immunoreactivity of >5% of tumor cells.
A
D
B
Figure 2. (A) Axillary lymph node metastases with positive nuclear and
cytoplasmic Snail expression (B) Normal breast parenchyma reveals no
expression of Snail.
Location
Infiltrating ductal
component
LN metastases
0, Negative
1
0
-
1+, Positive
0
1
-
2+, Positive
10
1
-
3+, Positive
1
10
1
The one axillary lymph node metastasis available for review, composed only of
the epithelial component of the primary breast carcinoma, showed nuclear
Snail expression in 12% of tumor cells. Of interest, the corresponding primary
breast tumor exhibited nuclear Snail expression in only in 4% of tumor cells of
the infiltrating ductal carcinoma, but in 70% of the metaplastic carcinoma
component. Snail was not expressed in adjacent normal mammary tissue.
Figure 1. : MBC (A) On low magnification, a significant difference of Snail
expression in both tumor components is found (B) The interphase of ductal
carcinoma and metaplastic chondroid matrix shows an increase in nuclear
expression (C) Infiltrating ductal component with mostly cytoplasmic staining.
(D) Metaplastic chondroid component with predominantly nuclear staining.
A
Metaplastic chondroid
component
Table 2: Nuclear Snail expression in breast carcinoma with chondroid differentiation (n=12)
B
C
Infiltrating duct
component
Chondroid
component
LN metastases
Nuclear
4.00%
33.70%
12%
94.80%
66.30%
88%
Cytoplasmic
Table 1: A total of 91.6% of MBC revealed simultaneous nuclear and
cytoplasmic staining in both the regular infiltrating ductal and in the metaplastic
chondroid component. The tumor cells with metaplastic features revealed a
significantly higher frequency of nuclear Snail expression (33.7) than those of
regular ductal carcinoma (4.0%) (p< 0.005)
Gene expression studies have demonstrated a distinctive gene expression
profile for MBC that is supportive of our findings showing that several of the
overexpressed genes, including Snail, were functionally related to adhesion,
motility, migration and extracellular matrix formation.
Of interest is the location and distribution between cytoplasmic and nuclear
expression of Snail in the two tumor components in our study. In addition to
being tightly regulated at the transcriptional level, the activity of Snail is also
influenced by its subcellular localization. Snail can cycle between nucleus and
cytosol. Two kinases, GSK-3 and PAK-1 are known regulate the function of
Snail. There is now mounting evidence that Snail protein expression in the
cytoplasm represents an inactive form of the protein.
Our study found expression of nuclear-localized, active Snail protein
predominantly in the chondroid matrix and to a lesser amount in the ductal
component. Nuclear expression was especially high at the interphase of both
components. These finding suggest that the metaplastic Snail positive cells
underwent EMT and acquired a mesenchymal phenotype. Another notable
finding was the increase in active Snail protein in the LN metastasis. As Snail
has also a recognized function in blocking the cell cycle and conferring
resistance to cell death, preserved Snail expression might be a capacity for
survival of metastasis.