The estrogen receptor α (ERα)-mediated pathway plays a critical role in breast cancer development and progression. KiSS1 was previously described as a metastasis suppressor gene in certain carcinomas. However, the role of KiSS1/GPR54 in breast cancer remains controversial. Whether the function of the KiSS1/GPR54 system depends on estrogen signaling in the breast cancer cell remains to be determined. This study aimed to determine the expression profiles of the KiSS1/GPR54, ERα, ERβ, aromatase and cyclin D1 genes in human breast cancer tissues, and to identify a possible link between the expression levels of the studied genes and the selected clinical and pathological features. The study subjects comprised 59 females treated surgically for primary breast cancer. Total RNA was extracted from frozen breast cancer tissues, and expression levels were examined to determine any correlations. We observed strong positive correlations between the expression levels of the studied genes. The expression of ERα correlated positively with progesterone receptors (PRs), and in these tumors we also observed positive correlations between KiSS1, GPR54 and cyclin D1 mRNAs and the ERα protein. ER-positive breast tumors exhibited higher KiSS1 and GPR54 levels than the ER-negative tumors. The expression levels of the ERα and GPR54 transcripts were higher in the moderately differentiated tumors (G2) compared to the poorly differentiated high-grade (G3) cancers. We also found that HER-2/neu status in breast cancer is negatively associated with GPR54 mRNA expression. Decreasing GPR54 mRNA expression levels in HER-2/neu (+) tumors may be associated with the deregulation of the classical estrogen-mediated signaling pathway in breast tumors, and therefore, with promotion of tumor invasiveness. Our findings indicate that genes involved in the KiSS1/GPR54 system, as well as in the estrogen signaling pathway, may be utilizable molecular factors in pathogenesis studies of breast cancer.

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