Background: Recently, researchers have been using mass spectroscopy to study cancer. For use of proteomics spectra in a clinical setting, stringent quality-control procedures will be needed. Methods: We pooled samples of nipple aspirate fluid from healthy breasts and breasts with cancer to prepare a control sample. Aliquots of the control sample were used on two spots on each of three IMAC ProteinChip

Antibodies (Abs) raised against the estrogen receptor-alpha (ERalpha) were used to investigate the role of ERalpha proteins located at the plasma membrane in mediating the rapid, estrogen-stimulated secretion of prolactin (PRL) from rat pituitary GH(3)/B6/F10 cells. Exposure of the cells to 1 nM 17beta-estradiol (E(2)) significantly increased PRL release after 3 or 6 min. When ERalpha Abs that bind specifically to ERalpha but are too large to diffuse into cells were tested for activity at the cell membrane, Ab R4, targeted to an ERalpha hinge region sequence, increased PRL release in a time- and concentration-dependent fashion. Ab H151, directed against a different hinge region epitope, decreased PRL release and blocked the stimulatory action of E(2). Abs raised against the DNA binding domain (H226) or the carboxyl terminus (C542) were not biologically active. When each Ab was examined for recognition of ERalpha on the cell surface by immunocytochemistry, all except H151 generated immunostaining in aldehyde-fixed cells. In live cells, however, Ab H151 but not Ab R4 blocked the membrane binding of fluorescently tagged E(2)-BSA. Overall, the data indicate that plasma membrane ERalpha proteins mediate estrogen-stimulated PRL release from GH(3)/B6/F10 cells. These results may also convey information about conformationally sensitive areas of the membrane form of ERalpha involved in rapid, nongenomic responses to estrogens.

There is clear evidence of rapid, nongenomic responses to estrogen in a variety of neuronal model systems. To address the question of whether some of these rapid estrogen signals might be transduced by the classical estrogen receptor (ER) α or a closely related protein in nontransformed neurons, we undertook the present study using isolated fetal rat hippocampal neurons. Several antibodies developed to detect ERα were tested in this system and showed positive membrane staining in nonpermeabilized neurons. MC-20, an affinity purified anti-ERα, rabbit polyclonal IgG antibody which does not recognize ERβ was selected to carry out the majority of the experiments. When permeabilized, the hippocampal neurons exhibited low levels of nuclear staining for ERα, but abundant labeling for ERα throughout the entire cell including the neurites. In addition to traditional immunocytochemistry controls, incubation of neurons for 24 h in the presence of 10 µM antisense oligonucleotide directed against the translation start site of ERα reduced ERα immunoreactivity throughout the neurons providing further evidence that the immunostaining was specific for ERα. Confocal and conventional microscopy demonstrated that the antigen was predominately extranuclear and localization of ERα in the neurites suggests that the receptor is in close proximity to the plasma membrane. This localization is consistent with a role for ERα as a transducer of rapid, nongenomic estrogen responses in hippocampal neurons.

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New approaches are needed for the early detection of breast cancer. Proteomic profiling technologies, such as surface-enhanced laser desorption ionization mass spectrometry (SELDI-MS), may be able to identify tumor markers in biological fluids. The objective of this study was to determine whether there are differences in protein expression patterns in nipple aspirate fluid (NAF) from the cancerous and noncancerous breasts of patients with unilateral breast cancer and the breasts of healthy volunteers. Paired NAF samples were obtained from 23 women with stage I or II unilateral invasive breast carcinoma and five healthy female volunteers. Aliquots of the samples were applied to SELDI Protein-chip arrays (WCX2 and IMAC3-Cu++), and protein expression was analyzed using time-of-flight MS. A total of 463 distinct peaks were detected and analyzed. In breast cancer patients, no differences in protein expression were identified between the breast with the intact primary carcinoma and the contralateral noncancerous breast. Seventeen peaks were overexpressed in cancer-bearing breasts compared to breasts of healthy volunteers (p < 0.0005). When spectra from the nontumor-bearing breasts of breast cancer patients were compared with spectra from breasts of healthy volunteers, two peaks that were overexpressed in breast cancer patients and one peak that was underexpressed in breast cancer patients were detected (p < 0.0027). SELDI-MS was able to identify differences in the phenotypic proteomic profile of NAF samples obtained from patients with early-stage breast cancer and healthy women. Proteomic screening techniques such as SELDI-MS analysis of NAF may be useful for breast cancer screening and diagnosis.