Identification of the cell surface and nuclear receptors for NGF in a breast carcinoma cell line

Nerve growth factor receptor immunoreactivity in breast cancer patients

Nerve growth factor receptor (NGF-R) has been shown to have antiproliferative, differentiative, or apoptotic effects on some types of tumor cells, whereas in others it may have mitogenic activity. The immunohistochemical distribution of NGF-R was analyzed in a series of tissue samples from breast cancer patients and its relationship with other clinical and pathological parameters was studied. The distribution of NGF-R was evaluated by immunohistochemistry in frozen tissue samples of 46 breast cancer patients (ME20-4 monoclonal anti-NGF-R). NGF-R immunoreactivity was localized in the plasma membrane of myoepithelial cells, differentiated ducts, neoplastic cells, blood vessels, and nerve fibers in 26 patients (57%). Less differentiated neoplastic tissues were usually NGF-R negative. NGF-R immunoreactivity was associated with estrogen receptor (ER) status (p = 0.02), small tumor dimension (pT) (p = 0.04), low histologic grade (G1-G2) (p < 0.05), old age (p = 0.02), menopause (p = 0.02), and long disease-free survival (DFS) (median follow up 86 months; p = 0.03; independently from ER, pT, age, menopause by multivariate analysis, p = 0.0078). The expression of NGF-R immunoreactivity by breast cancer patients with long DFS may represent a crucial step both in the differentiation status of neoplasia and in the host immune mechanism controlling tumor growth and metastasization.

Nerve growth factor stimulates proliferation and survival of human breast cancer cells through two distinct signaling pathways

We show here that the neurotrophin nerve growth factor (NGF), which has been shown to be a mitogen for breast cancer cells, also stimulates cell survival through a distinct signaling pathway. Breast cancer cell lines (MCF-7, T47-D, BT-20, and MDA-MB-231) were found to express both types of NGF receptors: p140(trkA) and p75(NTR). The two other tyrosine kinase receptors for neurotrophins, TrkB and TrkC, were not expressed. The mitogenic effect of NGF on breast cancer cells required the tyrosine kinase activity of p140(trkA) as well as the mitogen-activated protein kinase (MAPK) cascade, but was independent of p75(NTR). In contrast, the anti-apoptotic effect of NGF (studied using the ceramide analogue C2) required p75(NTR) as well as the activation of the transcription factor NF-kB, but neither p140(trkA) nor MAPK was necessary. Other neurotrophins (BDNF, NT-3, NT-4/5) also induced cell survival, although not proliferation, emphasizing the importance of p75(NTR) in NGF-mediated survival. Both the pharmacological NF-kappaB inhibitor SN50, and cell transfection with IkBm, resulted in a diminution of NGF anti-apoptotic effect. These data show that two distinct signaling pathways are required for NGF activity and confirm the roles played by p75(NTR) and NF-kappaB in the activation of the survival pathway in breast cancer cells.

Internalization of prolactin receptor and prolactin in transfected cells does not involve nuclear translocation

Prolactin (PRL) interacts with a specific, well characterized plasma membrane receptor (PRLR) that is coupled to signal transduction pathways involving Jak2, Fyn, and MAP kinases, and signal transducers and activators of transcription (STAT). Although a few previous studies have indicated nuclear translocation of PRL in IL-2 stimulated T lymphocytes, PRL-dependent Nb2 lymphoma cell lines and 235–1 lactotrophs, the mechanisms of nuclear targeting remain unknown and conflicting results have been reported concerning the putative nuclear translocation of the PRLR. We therefore decided to investigate nuclear translocation of PRLR and PRL in various cell lines transfected with an expression plasmid encoding PRLR, using confocal laser microscopy. We have constructed various cDNAs of the long and short forms of the rat PRLR containing an oligonucleotide encoding a Flag epitope inserted either just before the N-terminal amino acid or in the C-terminal end of the mature receptor (named N-terminal or C-terminal Flag-tagged PRLR). The corresponding receptors function as the PRLR in transfected cells: they are expressed at the plasma membrane and in compartments of the secretory pathway, they bind PRL with normal affinity (Kd= 4x10(−10) M) and have the same capacity to stimulate the transcriptional activity of a milk protein (beta-casein) gene as wild-type PRLR. In addition, the tagged receptors are much more efficiently immunodetected using anti-Flag antibodies, as compared to anti-PRL antibodies (U5 or U6). Immunofluorescence combined with detailed confocal laser microscopy showed that addition of PRL (0 to 12 hours) to COS-7, CHO and NIH-3T3 transfected fibroblasts induces rapid internalization of the receptor (long form), without any translocation to the nucleus. Using PRL-R tagged both in the N-terminal or C-terminal regions of the mature receptor excludes the possibility of a cleaved fragment which could have been subsequently imported into the nucleus. An absence of nuclear translocation of PRLR was also observed in a 293 cell line stably expressing the receptor, and in physiological targets for PRL, i.e. in Nb2 lymphoma cells expressing the Nb2 form of the receptor or in BGME mammary gland epithelial cells upon overexpression of a Flag-tagged PRLR. Similarly, the short form of the PRLR was not detected in nuclei of transfected COS cells upon PRL treatment. Clearly, our results provide evidence that internalization of the plasma membrane PRLR does not lead to nuclear translocation of the receptor, or part of it, in most fibroblasts and epithelial cells at physiological concentrations of PRL. Also, in co-localization experiments, PRL was internalized without nuclear translocation. Activation of STATs transcription factors and MAP kinases, as well as translocation of these proteins to the nucleus following their phosphorylation, probably remains the intracellular mechanism coupling stimulation to nuclear events.

Nuclear/growth factors

The now classical model for cell-cell communication espouses that information travels between cells in the form of molecules that bind specific cell-surface receptors and trigger signal-transducing mechanisms that eventually lead to transcriptional modifications. Here we gather the available information suggesting that some growth factors may also act by interfering directly with gene transcription, following their internalization and nuclear translocation. Among these factors are bona fide growth factors such as Fibroblast Growth Factor-1 and -2 and Schwannoma Derived Growth Factor, for which internalization and nuclear translocation have been demonstrated. Conversely, we propose that some isoforms of nuclear factors of the homeoprotein family could pass from cell to cell. The implications of the model are presented in the context of the specificity of cellular interactions.

Expression of transforming growth factor alpha, amphiregulin and cripto-1 in human breast carcinomas

The expression of three epidermal growth factor (EGF)-related peptides, transforming growth factor alpha (TGF-alpha), amphiregulin (AR) and cripto-1 (CR-1), was examined by immunocytochemistry (ICC) in 68 primary infiltrating ductal (IDCs) and infiltrating lobular breast carcinomas (ILCs), and in 23 adjacent non-involved human mammary tissue samples. Within the 68 IDC and ILC specimens, 54 (79%) expressed immunoreactive TGF-alpha, 52 (77%) expressed AR and 56 (82%) expressed CR-1. Cytoplasmic staining was observed with all of the antibodies, and this staining could be eliminated by preabsorption of the antibodies with the appropriate peptide immunogen. Cytoplasmic staining with all of the antibodies was confined to the carcinoma cells, since no specific immunoreactivity could be detected in the surrounding stromal or endothelial cells. In addition to cytoplasmic reactivity, the AR antibody also exhibited nuclear staining in a number of the carcinoma specimens. No significant correlations were found between the percentage of carcinoma cells that were positive for TGF-alpha, AR or CR-1 and oestrogen receptor status, axillary lymph node involvement, histological grade, tumour size, proliferative index, loss of heterozygosity on chromosome 17p or overall patient survival. However, a highly significant inverse correlation was observed between the average percentage of carcinoma cells that expressed AR in individual tumours and the presence of a point-mutated p53 gene. Likewise, a significantly higher percentage of tumour cells in the ILC group expressed AR as compared with the average percentage of tumour cells that expressed AR in the IDC group. Of the 23 adjacent, non-involved breast tissue samples, CR-1 could be detected by ICC in only three (13%), while TGF-alpha was found in six (26%) and AR in ten (43%) of the non-involved breast tissues. These data demonstrate that breast carcinomas express multiple EGF-related peptides and show that the differential expression of CR-1 in malignant breast epithelial cells may serve as a potential tumour marker for breast cancer.