Relaxin-like factor (RLF) is differentially expressed in the normal and neoplastic human mammary gland

BACKGROUND. Expression of relaxin-like factor (RLF), a member of the relaxi n family, was studied in normal, benign, and malignant neoplastic human bre ast tissue. METHODS. Reverse transcription polymerase chain reaction (RT-PCR) and nonra dioactive in situ hybridization were employed to detect RLF transcripts. RL F epitopes were detected with a rabbit polyclonal antiserum generated again st the putative receptor binding domain of human RLF. The RLF antiserum was characterized by Western blot analysis on human testicular and placental t issues, recombinant glutathione S-transferase-RLF fusion protein, and bacul ovirus-derived recombinant marmoset-RLF and marmoset-relaxin. RESULTS. RT-PCR analysis revealed RLF amplicons in a cDNA library of normal human breast tissue and in malignant neoplastic breast tissue. RLF hybridi zation signals were localized exclusively in the tubuloalveolar and ductal breast epithelium but were absent in stromal cells. Benign breast disease d isplayed weaker RLF hybridization signals compared with normal tubuloalveol ar breast tissue. Malignant transformation of breast epithelial tissues res ulted in down-regulation of RLF gene expression. The weakest expression of RLF mRNA was observed in lymph node metastases of corresponding primary duc tal carcinomas. Immunoreactive RLF was exclusively expressed in breast epit helial cells. Despite strong RLF hybridization signals, the tubuloalveolar epithelial cells of normal breast tissue displayed only very weak immunorea ctive RLF. Benign breast disease showed clearly detectable levels of both R LF mRNA and immunoreactive protein. In contrast, epithelial cells in breast carcinoma and lymph node metastases displayed strong expression of immunor eactive RLF, although expression of RLF transcripts was weak. CONCLUSIONS. Results demonstrated that transcriptional and posttranscriptio nal mechanisms affected human RLF gene expression in normal and neoplastic epithelial breast cells. Cancer 2000;89:2161-8. (C) 2000 American Cancer So ciety.