An association of a simultaneous nuclear and cytoplasmic localization of Fra-1 with breast malignancy

Abstract

Background: Overexpression of Fra-1 in fibroblasts causes anchorage-independent cell growth and oncogenic transformation. A high level of Fra-1 expression is found in various tumors and tumorigenic cell lines, suggesting that Fra-1 may be involved in malignant progression. This study aimed to investigate the significance of Fra-1 expression in breast carcinogenesis.

Methods: The expression of Fra-1 was investigated by immunohistochemistry in neoplastic breast diseases ranging from benign fibroadenoma to very aggressive undifferentiated carcinoma. The correlations of Fra-1 expression with other indicators of breast carcinoma prognosis (ER, PR and ErbB2 receptors) were analyzed.

Results: All neoplastic breast tissues, either benign or malignant breast tissues, were nuclear immunoreactive for Fra-1-recognizing antibody. The pattern of Fra-1 expression by benign neoplastic cells was predominantly nuclear. However, the nuclear/cytoplasmic concomitant immunoreactivity was observed in all types of breast carcinomas. A clear shift in Fra-1 immunoreactivity, from an exclusively nuclear to a simultaneous nuclear and cytoplasmic localization was noticed in ~90% of breast carcinomas.

Conclusion: The overall expression, pattern and intensity of Fra-1 proteins were correlated with breast oncogenesis. Overexpression of Fra-1, leading to a persistent high cytoplasmic accumulation, may play a role in the process of breast carcinogenesis.

Figure 1

The immunohistochemical staining of Fra-1 in benign breast tumors. Paraffin-embedded tissue sections were prepared. Endogenous peroxidase activity was quenched using 3% hydrogen peroxide before immunohistochemical staining. The Streptavidin-Biotin method was used to detect Fra-1 expression. The rabbit anti-human Fra-1 polyclonal antibody at a concentration of 5 μg/ml in PBS was applied for 60 minutes at 37°C or overnight at 4°C. The sections were then incubated with biotinylated anti-rabbit antibody at 37°C for 15 minutes. The streptavidin peroxidase reagent was applied at 37°C for 15 minutes. The color was developed by incubating with DAB solution. A, nonspecific immunoglobulin was used as a negative control. B, The nuclear immunoreactivity for Fra-1 was identified mostly in the epithelial cells of fibroadenomas. C, The strong nuclear immunostaining was present in fibroadenomas. D, Positive staining appeared largely on the apical epithelial layer on the luminal aspect, but myoepithelial layer was mostly negative. ×400 magnification.

Figure 2

The immunohistochemical staining of Fra-1 in breast carcinomas. A and B, strong nuclear and weak cytoplastic immunostaining were observed in two representative invasive ductal carcinomas. C and D, Strong nuclear and cytoplasmic double staining was very pronounced in two representative invasive ductal carcinomas. E, nonspecific immunoglobulin was used as a negative control. ×400 magnification.

Figure 3

The differential expression of Fra-1 protein in breast carcinomas. Fra-1 protein immunostaining was weak in adjacent peritumoural tissues and positive reactivity restricted to nuclear (A), but strong in poorer differentiated region in the same section and positive reactivity presented in nuclear and cytoplasmic simultaneously (B). ×400 magnification.