Autocrine and paracrine growth inhibitors of breast cancer cells

Role of insulin-like growth factor binding protein-3 in 1, 25-dihydroxyvitamin-d 3 -induced breast cancer cell apoptosis

Insulin-like growth factor I (IGF-I) is implicated in breast cancer development and 1, 25-dihydroxyvitamin D₃ (1, 25-D₃) has been shown to attenuate prosurvival effects of IGF-I on breast cancer cells. In this study the role of IGF binding protein-3 (IGFBP-3) in 1, 25-D₃-induced apoptosis was investigated using parental MCF-7 breast cancer cells and MCF-7/VD^R cells, which are resistant to the growth inhibitory effects of 1, 25-D₃. Treatment with 1, 25-D₃ increased IGFBP-3 mRNA expression in both cell lines but increases in intracellular IGFBP-3 protein and its secretion were observed only in MCF-7. 1, 25-D₃-induced apoptosis was not associated with activation of any caspase but PARP-1 cleavage was detected in parental cells. IGFBP-3 treatment alone produced cleavage of caspases 7, 8, and 9 and PARP-1 in MCF-7 cells. IGFBP-3 failed to activate caspases in MCF-7/VD^R cells; however PARP-1 cleavage was detected. 1, 25-D₃ treatment inhibited IGF-I/Akt survival signalling in MCF-7 but not in MCF-7/VD^R cells. In contrast, IGFBP-3 treatment was effective in inhibiting IGF-I/Akt pathways in both breast cancer lines. These results suggest a role for IGFBP-3 in 1, 25-D₃ apoptotic signalling and that impaired secretion of IGFBP-3 may be involved in acquired resistance to vitamin D in breast cancer.

IL-25 causes apoptosis of IL-25R-expressing breast cancer cells without toxicity to nonmalignant cells

As cells differentiate into tissues, the microenvironment that surrounds these cells must cooperate so that properly organized, growth-controlled tissues are developed and maintained. We asked whether substances produced from this collaboration might thwart malignant cells if they arise in the vicinity of normal tissues. Here, we identified six factors secreted by nonmalignant mammary epithelial cells (MECs) differentiating in three-dimensional laminin-rich gels that exert cytotoxic activity on breast cancer cells. Among these, interleukin-25 (IL-25/IL-17E) had the highest anticancer activity without affecting nonmalignant MECs. Apoptotic activity of IL-25 was mediated by differential expression of its receptor, IL-25R, which was expressed in high amounts in tumors from patients with poor prognoses but was low in nonmalignant breast tissue. In response to IL-25, the IL-25R on the surface of breast cancer cells activated caspase-mediated apoptosis. Thus, the IL-25/IL-25R signaling pathway may serve as a new therapeutic target for advanced breast cancer.

Effects of endogenous insulin-like growth factor binding protein-3 on cell cycle regulation in breast cancer cells

High tissue insulin-like growth factor binding protein-3 (IGFBP-3) expression in breast cancers is associated in some studies with rapid growth and poor outcome. This study examined the effects of endogenous IGFBP-3 in Hs578T breast cancer cells, which are IGF-unresponsive and grow aggressively despite relatively high IGFBP-3 expression. IGFBP-3 downregulation using siRNA was associated with increases in DNA synthesis, the percentage of cells in S phase and viable cell numbers, accompanied by increases in cyclins A and D1, a decrease in p27 expression, and increased phosphorylation of retinoblastoma (Rb) on Ser795. Downregulation of IGFBP-3 inhibited extracellular signal-regulated kinase (ERK) activation and cell migration in a monolayer wound healing assay. These results indicate that endogenous IGFBP-3 is anti-proliferative and pro-migratory in Hs578T cells and that these effects are IGF-independent. Poor outcome in breast tumours expressing high levels of IGFBP-3 may be due to the effects of IGFBP-3 on cell migration rather than cell growth.

Enhanced expression of Rab27A gene by breast cancer cells promoting invasiveness and the metastasis potential by secretion of insulin-like growth factor-II

In addition to the functions of transporting melanosome in melanocytes and releasing contents of lytic granules in CTLs, Rab27A was recently shown to be involved in exocytosis of insulin and chromaffin granules in endocrine cells; it was also reported to be expressed in an exceptionally broad range of specialized secretory cells. As autocrine and paracrine cytokines are essential for invasion and metastasis in some solid tumors, blocking them may be an effective strategy to prevent tumor dissemination. In the present study, we show that Rab27A is associated with invasive and metastatic potentials of human breast cancer cells. The overexpression of Rab27A protein redistributed the cell cycle and increased the invasive and metastatic abilities in breast cancer cells both in vitro and in vivo. We also certified that Rab27A conferred the invasive and metastatic phenotypes on breast cancer cells by promoting the secretion of insulin-like growth factor-II (IGF-II), which regulates the expression of p16, vascular endothelial growth factor, matrix metalloproteinase-9, cathepsin D, cyclin D1, and urokinase-type plasminogen activator. These data provide functional evidence that Rab27A acts as a novel mediator of invasion and metastasis promotion in human breast cancer cells, at least in part, through regulating the secretion of IGF-II, suggesting that synergistic suppression of Rab27A and IGF-II activities holds a promise for preventing breast cancer invasion and metastasis.

Breast cancer: when proteomics challenges biological complexity

Proteomics is now entering into the field of biomedicine with declared hopes for the identification of new pathological markers and therapeutic targets. Current proteomic tools allow large-scale, high-throughput analyses for the detection, identification, and functional investigation of low-abundant proteins. However, the major limitation of proteomic investigations remains the complexity of biological structures and physiological processes, rendering the path of exploration of related pathologies paved with various difficulties and pitfalls. The case of breast cancer illustrates the major challenge facing modern proteomics and more generally post-genomics: to tackle the complexity of life.

Chemopreventive agents induce a senescence-like phenotype in rat mammary tumours

Terminal replicative senescence (TRS) is a physiological process associated with terminal differentiation, shortening of the telomere, and lack of proliferative activity. Immortalised and tumour cells have lost their differentiation potential and the ability to develop a senescence phenotype. Recently, others and we [11] have observed that some antitumour agents and radiation induce a senescence-like phenotype (SLP) in human immortalized and tumour cell lines. The main purpose of this study was to identify senescence-like cells (SLC) in mammary tumours of rats and assess whether chemopreventive agents that have been used for the prevention and/or treatment of breast cancer can induce a SLP in tumour cells. Sprague-Dawley rats with N-methyl-N-nitrosourea (MNU)-induced mammary tumours were randomised and treated with tamoxifen, vorozole, 4-(hydroxyphenyl)retinamide (4-HPR), or 9-cis-retinoic acid (9cRA). The SLC in mammary tumours were identified and characterised by: (a) SA-beta-Gal staining method, which has been considered specific for human cells in TRS (b) staining for lipofuscin, which, although not specific, accumulates in the cytoplasm of cells in senescence; (c) lack of 5-Bromodeoxyuridine (BrdU) labelling after continuous (7 days) infusion of BrdU via osmotic pumps; (d) 90 degrees side light scatter (9OLS) as evaluated by flow cytometry; and (e) decreased telomerase activity. We found that in control tumours, SA-beta-Gal-positive cells were rare (below 1.0%) among the tumour cells, stroma fibroblast, myoepithelial and endothelial cells. SA-beta-Gal-positive cells increased significantly in the tumours treated with chemopreventive agents and this was associated with a lack of proliferative activity, increased cell granularity, lipofuscin accumulation, and decreased telomerase activity. Thus, in this study we provide for the first time evidence that cells in replicative senescence are present in mammary tumours of rats and that chemopreventive agents can suppress tumor growth by a novel cellular mechanism, inducing a SLP in the tumor cells.

Functional proteomics of breast cancer for signal pathway profiling and target discovery

The near completion of human genome sequencing and the introduction of mass spectrometry combined with advanced bioinformatics for protein identification have led to the emergence of proteomics as a powerful tool for characterizing new markers and therapeutic targets. Breast cancer proteomics has already identified proteins of potential clinical interest, such as the molecular chaperone 14-3-3 sigma and the heat shock protein HSP90, and technological innovations such as large scale and high throughput analysis are now driving the field. Methods in functional proteomics have also been developed to study the intracellular signaling pathways that underlie the development of breast cancer cells. As illustrated by fibroblast growth factor-2 and the H19 noncoding oncogenic mRNA, proteomics is a pertinent approach to identify signaling proteins and to decipher the complex signaling circuitry involved in tumor growth and metastasis. Together with genomics, proteomics is now providing a way to define molecular processes involved in breast carcinogenesis and to identify new therapeutic targets. The next challenge will be the introduction of proteomics as a tool for the clinic, for the establishment of diagnosis, prognosis, and the monitoring of treatment; however, this ambitious goal still requires further technological progress in the field.

Role of insulin-like growth factor binding protein-3 in breast cancer cell growth

The mitogenic effects of insulin-like growth factors (IGFs) are regulated by a family of insulin-like growth factor binding proteins (IGFBPs). One member of this family, IGFBP-3, mediates the growth-inhibitory and apoptosis-inducing effects of a number of growth factors and hormones such as transforming growth factor-beta, retinoic acid, and 1,25-dihydroxyvitamin D3. IGFBP-3 may act in an IGF-dependent manner by attenuating the interaction of pericellular IGFs with the type-I IGF receptor. It may also act in an IGF-independent manner by initiating intracellular signaling from a cell surface receptor, or by direct nuclear action, or both. The possibility of a membrane-bound receptor is strengthened by recent studies which have identified members of the transforming growth factor-beta receptor family as having a role, either directly or indirectly, in signaling from the cell surface by IGFBP-3. A number of growth factors and hormones stimulate the expression and secretion of cellular IGFBP-3, which then signals from the cell surface to bring about some of the effects attributed to the primary agents. Within the cell, the apoptosis-inducing tumor suppressor, p53, can also induce IGFBP-3 expression and secretion. Since IGFBP-3 upregulates the cell cycle inhibitor, p21(Waf1), and increases the ratio of proapoptotic to antiapoptotic members of the Bcl family, it appears to exert the same effects on major downstream targets of cell signaling as p53 does. The nuclear localization of IGFBP-3 has been described in a number of cell types. IGFBP-3 may act to import IGFs or other nuclear localization signal-deficient signaling molecules into the nucleus. It may also act directly in the nucleus by enhancing the activity of retinoid X receptor-alpha and thereby promote apoptosis. All of the above phenomena will be discussed with particular emphasis on the growth of breast cancer cells.

Normal breast epithelial cells induce p53-dependent apoptosis and p53-independent cell cycle arrest of breast cancer cells

Cancer development depends not only on the nature of cancerous cells themselves, but also on the regulatory effects of various normal cells. The present study was performed to investigate the effect of normal breast epithelial cells (NBEC) on the growth of breast cancer cells under various conditions. We demonstrated that NBEC-conditioned medium (NBEC-CM) inhibited growth of breast cancer cell lines in monolayer culture and three-dimensional collagen gel culture, as well as in soft agar. In MCF-7 and T-47D cells which have a functional p53, NBEC-CM induced apoptosis without modifying cell cycle progression. In MDA-MB-231 and BT-20 cells that have a non-functional p53, NBEC-CM did not induce apoptosis, although a slight G1 blokage was observed in MDA-MB-231 cells. Transient transfections of MCF-7 and T-47D cells demonstrated that NBEC-triggered apoptosis was mediated by endogenous p53. Moreover, pifithrin-alpha which specifically inhibits the transcriptional activity of p53, completely abolished NBEC-induced apoptosis in both MCF-7 and T-47D cells, indicating that p53 mediated apoptosis via its transcriptional activity. Finally, orthovanadate, a protein tyrosine phosphatase inhibitor, completely inhibited NBEC-triggered apoptosis, indicating that NBEC-triggered apoptosis was regulated by tyrosine phosphatases.

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.