Sex hormone binding globulin mRNA in human breast cancer: Detection in cell lines and tumor samples

Sex hormone binding globulin (SHBG) is a high affinity binding protein for estrogens and androgens. SHBG has been found in breast tissue and cell lines through immunostaining. The goal of this series of experiments was to determine whether mRNA for SHBG is expressed in breast cancer cell lines and tumor tissue. Reverse transcriptase-polymerase chain reaction (RT-PCR) was used to detect SHBG and β-2 microglobulin (control for tissue extractions). Three breast cancer cell lines, ZR-75-1, MCF-7, and MDA-MB-231 and 56 breast tissue samples were collected and analysed for SHBG mRNA expression. mRNA was successfully extracted from 30 of these breast tissue samples. SHBG mRNA was detected in ZR-75-1, MCF-7 and MDA-MB-231 cells, and in 11 of the breast tissue samples. Two PCR products were routinely amplified from the breast cancer cell line RNA, one at approximately 500 bp and another at approximately 300 bp. The DNA sequence of the 300 bp PCR produce was consistent with alternate splicing of the SHBG mRNA, where exon 7 is deleted, and is accompanied by a point deletion at the beginning of exon 8. SHBG protein production from the three breast cancer cell lines was detected by immunoprecipitation using an affinity purified SHBG antibody. SHBG mRNA was found in 11 of 30 samples of breast tissue. Some samples expressed only the 500 bp or the 300 bp PCR product, whereas others expressed both PCR products. The presence of SHBG mRNA in these samples was not associated with either the presence or absence of steroid receptors. SHBG mRNA is thus expressed in breast cancer cell lines, and in some breast tissue samples.