1,25-Dihydroxyvitamin D₃Binding in Estrogen-Responsive Rat Breast Tumor*

Abstract

Receptors for 1,25 dihydroxyvitamin D3 [1,25-(OH)2D3] have been reported in breast tissue; however, the presence of multiple binding sites and limited availability of human tumor tissue have precluded complete biochemical characterization of the receptor in breast cancer. In the present study, binding proteins for 1,25-(OH)2D3 in breast tumor tissue were analyzed using a rat model of breast cancer. Breast tumors were induced in adult female rats with the carcinogen nitrosomethylurea. Such tumors previously have been shown to possess high levels of estrogen receptors and are estrogen dependent. Binding proteins for 1,25-(OH)2D3 in 0.3 M KCl extracts of tumor tissue were analyzed on sucrose density gradients. Two binding proteins were detected: one sedimenting at 5-6 S representing binding of 1,25-(OH)2D3 to the 25 hydroxyvitamin D3 (25OHD3) binding protein and a second moiety sedimenting, like the rat intestinal receptor, at 3.3 S. Binding of the dihydroxy metabolite to the faster sedimenting protein could be eliminated by inclusion of radioinert 25OHD3 in the incubation medium. Receptor content of rat breast tumor was investigated using an hydroxylapatite assay by incubating tumor extracts with a saturating concentration of 1,25-(OH)2-[3H]D3, plus unlabeled 25OHD3 to eliminate binding of the hormone to the 5-6 S species. Scatchard analysis of 1,25-(OH)2D3 binding to the tumor extracts yielded an apparent dissociation constant (Kd) of 0.33 nM. In summary, breast tumors induced in rats by nitrosomethylurea were shown to contain high affinity 1,25-(OH)2D3 receptors with properties very similar to those reported for the receptor in other mammalian target organs. The presence of receptors for 1,25-(OH)2D3 in these rat breast tumors implies that the tissue is potentially responsive to the hormone.

Vitamin D and breast cancer: Past and present

“…In 1980, Colston and Feldman (1) were the first to demonstrate VDR expression, as identified by specific 1,25D binding, in normal breast tissue. Subsequent studies verified that the majority of breast tumors and established breast cancer cell lines retained some VDR expression (2–4). Although some early studies suggested that the presence of tumor VDR independently correlated with better prognosis in breast cancer patients, the cumulative data remains inconclusive (5).…”

Antiproliferative effects of 1,25-dihydroxyvitamin D3 on breast cells: a mini review

“…Receptors for 1,25-(OH) 2 D 3 in MCF-7, a cultured breast cancer cell line, were first shown by Eisman et al (10) in 1979 and later VDR expression was reported in carcinogen-induced rat mammary tumors as well (24). VDR was also detected in some normal breast tissues such as the mammary gland of pregnant and lactating rabbits but not in virgin rabbits (25).…”

The impact of vitamin D in breast cancer: genomics, pathways, metabolism

“…VDR expression is retained in the majority of rodent breast tumors, human breast cancers and established breast cancer cell lines (Colston et al, 1986; Buras et al, 1994; Zinser and Welsh, 2004b). In a study of 136 patients with primary breast cancer, it was found that women with VDR negative tumors relapsed significantly earlier than women with VDR positive tumors (Berger et al, 1991).…”