HUMAN RELAXINS IN NORMAL, BENIGN AND NEOPLASTIC BREAST-TISSUE

Immunoreactive relaxin is present in human breast cyst fluid and postp artum milk without concurrent detectable serum levels, suggesting that the breast is a site of relaxin synthesis. Monoclonal and polyclonal antibodies to human relaxin H2 have been used to immunolocalize relaxi ns in normal, benign and neoplastic breast tissues with the avidin-bio tin immunostaining technique. In view of the similarities in amino aci d sequence between H1 and H2 relaxins, these antibodies to H2 relaxin are likely to detect either or both relaxins present in tissue section s. Staining patterns with these antibodies were identical and showed p ositive diffuse cytoplasmic staining in normal, lobular and ductal epi thelium and in myoepithelial cells in breast tissues from normal prepu bertal, cyclic, gestational, lactational and postmenopausal females. R elaxin staining was also present in epithelial and myoepithelial cells of ducts and lobules in benign breast disease as well as in metaplast ic epithelium of apocrine microcysts. All breast carcinomas (infiltrat ing ductal, tubular, medullary, intraductal and infiltrating lobular c arcinomas) had strong uniform cytoplasmic staining within the neoplast ic epithelial cells. All staining was abolished in normal and neoplast ic tissues when the polyclonal antibody was preabsorbed with relaxin. It was necessary to distinguish between the possibilities of relaxins being sequestered by breast tissue and local synthesis: Therefore, the expression of the H1, H2 or both human relaxin genes in normal and ne oplastic breast tissues was studied by the isolation of RNA, synthesis of first strand cDNA and amplification by PCR using primer sets which amplified either both H1 and H2, or specifically only H1 or H2 relaxi n. The coamplification of both relaxin genes was verified by Southern analysis, diagnostic restriction enzyme digestion and sequencing. The primer set for H1 relaxin detected H1 gene expression in 1 out of 8 no rmal and 9 out of 12 neoplastic breast RNA samples. The H2 relaxin gen e was found to be expressed in 3 out of 8 of the normal samples but in all 12, of the neoplastic samples, suggesting that this gene is expre ssed at higher copy number in the neoplastic tissues. This is the firs t demonstration of the cellular immunolocalization of relaxin and rela xin gene expression in normal and neoplastic breast. This should allow further exploration of relaxin's role(s) in normal breast physiology and in its tumorigenesis.