IDENTIFICATION AND LOCALIZATION OF THE EXTRACELLULAR CALCIUM-SENSING RECEPTOR IN HUMAN BREAST

The extracellular calcium (Ca-o(2+))-sensing receptor (CaR) plays a cr itical role in maintaining Ca-o(2+), homeostasis in mammals by virtue of its presence in parathyroid gland and kidney. The breast is well re cognized as a Ca2+-handling organ, and the effects of altering Ca-o(2) on the proliferation of breast epithelial cells are well documented. To date there are no data regarding the expression and localization o f CaR in breast tissue. In the present study, we assessed the distribu tion of CaR messenger ribonucleic acid (mRNA) and protein in normal an d fibrocystic human breast tissue as well as in ductal carcinoma of th e breast using RT-PCR, Northern analysis, and immunohistochemistry wit h CaR-specific antisera. In all tissues, RT-PCR performed using sense and antisense primers based on the sequence of the human parathyroid C aR complementary DNA amplified a product of the size expected (425 bp) for genuine CaR transcripts. Nucleotide sequencing of RT-PCR products confirmed more than 99% homology with human parathyroid CaR complemen tary DNA. Although insufficient quantities of mRNA were isolated from normal and fibrocystic tissue for Northern analysis, a single 5.2-kb C aR transcript was expressed in malignant breast tissue similar to the major CaR transcript in human parathyroid. Localization of CaR protein by immunohistochemistry showed specific CaR staining of the ductal ep ithelial cells of the breast in all three tissue types. These findings indicate the presence of CaR mRNA and protein in the breast, providin g indirect evidence that the CaR may have some role(s) in the control of Ca2+ transport, epithelial cell proliferation, and/or other process es in normal and abnormal breast tissue.