Human relaxins in normal, benign and neoplastic breast tissue

Abstract

Immunoreactive relaxin is present in human breast cyst fluid and postpartum 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 relaxins in normal, benign and neoplastic breast tissues with the avidin-biotin immunostaining technique. In view of the similarities in amino acid sequence between H1 and H2 relaxins, these antibodies to H2 relaxin are likely to detect either or both relaxins present in tissue sections. Staining patterns with these antibodies were identical and showed positive diffuse cytoplasmic staining in normal, lobular and ductal epithelium and in myoepithelial cells in breast tissues from normal prepubertal, cyclic, gestational, lactational and postmenopausal females. Relaxin staining was also present in epithelial and myoepithelial cells of ducts and lobules in benign breast disease as well as in metaplastic epithelium of apocrine microcysts. All breast carcinomas (infiltrating ductal, tubular, medullary, intraductal and infiltrating lobular carcinomas) had strong uniform cytoplasmic staining within the neoplastic epithelial cells. All staining was abolished in normal and neoplastic 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 neoplastic 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 relaxin. 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 normal and 9 out of 12 neoplastic breast RNA samples. The H2 relaxin gene 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 expressed at higher copy number in the neoplastic tissues. This is the first demonstration of the cellular immunolocalization of relaxin and relaxin 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.

The R273H p53 mutation can facilitate the androgen-independent growth of LNCaP by a mechanism that involves H2 relaxin and its cognate receptor LGR7

“…These data support our finding that increased H2 relaxin expression is associated with AI growth of CaP. A functional role for H2 relaxin in the progression of other cancers has also been demonstrated (Stemmermann et al, 1994;Tashima et al, 1994). Treatment of a breast cancer cell line, MCF-7, with H2 relaxin increased both cell proliferation and invasiveness (Tashima et al, 1994).…”

“…A functional role for H2 relaxin in the progression of other cancers has also been demonstrated (Stemmermann et al, 1994;Tashima et al, 1994). Treatment of a breast cancer cell line, MCF-7, with H2 relaxin increased both cell proliferation and invasiveness (Tashima et al, 1994). Other studies have demonstrated that H2 relaxin plays a role in processes associated with cancer progression.…”

Uterotrophic effects of relaxin related to age and estrogen receptor activation in neonatal pigs

“…Studies in other species indicate that relaxin of maternal origin could be an important source of the hormone in the neonate by way of ingestion of colostrum and milk. Relaxin is detectable in human (Eddie et al 1989) and canine (Goldsmith et al 1994) colostrum and milk, and mammary tissue has been suggested as a local source of relaxin (Tashima et al 1994). Like other peptide growth factors in milk, relaxin may contribute to early neonatal development (Burrin et al 1997, Anderson et al 1999.…”

Analysis of the 5'-upstream regions of the human relaxin H1 and H2 genes and their chromosomal localization on chromosome 9p24.1 by radiation hybrid and breakpoint mapping

“…The systemic relaxin acting in this way is the H2 form and the only relaxin produced by the human corpus luteum (Hudson et al 1984). It has been shown, however, that relaxins are also autocrine/paracrine hormones in a number of other tissues such as prostate (Hansell et al 1991), placenta (Sakbun et al 1990), endometrium, decidua (Bryant-Greenwood et al 1993) and mammary gland (Tashima et al 1994). When relaxins are produced and act locally in this manner, both relaxin genes are expressed (Bryant-Greenwood & Schwabe 1994).…”