Estrogen receptor-associated expression of keratinocyte growth factor and its possible role in the inhibition of apoptosis in human breast cancer

Abstract

Although estrogen is known to play a crucial role in the pathogenesis of breast cancer, the molecular mechanisms underlying the action of estrogen remain elusive. In the present study, we focused on keratinocyte growth factor (KGF) and its receptor (KGFR) in the pathogenesis of breast cancer, as a growth factor mediating estrogen action, since significant roles of KGF were demonstrated in various steroid hormone-dependent tissues. First, using paraffin-embedded specimens from 42 breast cancer patients, we examined expression patterns of KGF and KGFR by both immunohistochemistry using newly generated antibodies and nonradioactive in situ hybridization with T-T dimerized synthetic oligonucleotide probes. We next compared the results with the expression of estrogen receptor (ER) a and b, proliferative activity and apoptotic frequency (TUNEL staining). Also, the similar approaches were taken to analyze the expression and role of KGF in ERpositive (MCF7, ZR-75-1) and ER-negative (SK-BR-3, MDA-MB-231) human breast cancer cell lines in vitro. In the surgical specimens, KGF was expressed in cancer cells as well as stromal cells in 19/42 cases (45%), while KGFR was found in cancer cells in 24/42 cases (57%). The distribution of protein and mRNA in the analysis of both KGF and KGFR expression generally coincided. Moreover, KGF expression was closely associated with the expression of ER a, and the coexpression of KGF and KGFR significantly correlated with lower TUNEL index, but not with proliferative activity. In accordance with the in vivo findings, KGF expression was detected only in ER a-positive MCF7 and ZR-75-1 cells in vitro. And more importantly, we found the inhibitory effect of KGF upon the induction of apoptosis by anticancer drugs in MCF7 cells. Collectively, our results indicate that ER a may be involved in KGF expression, and that KGF may play antiapoptotic roles, rather than mitogenic, in human breast cancer. Keywords: apoptosis; breast cancer; estrogen receptor; immunohistochemistry; in situ hybridization; keratinocyte growth factor; TUNEL staining Breast cancer is the most frequent malignant tumor of women in the USA and European countries. In Japan, the frequency of breast cancer has rapidly increased during the last decade, and currently approximately 20 000 women develop breast cancer per year. However, our knowledge of the development and progression of breast cancer is still largely limited. The proliferation and differentiation of breast cancer cells are influenced by estrogen, 1-3 which exerts its action through binding to estrogen receptor (ER). Currently, ER is categorized into two subtypes, ER a and b, and both are believed to act as an active transcription factor, which binds to a specific DNA segment such as the estrogen responsive element (ERE) and AP-1 site, to regulate the expression of a variety of genes. 4,5 The majority of human breast cancer cells express both ER a and ER b. 6 While ER a is regarded as an indicator of

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