A bidirectional "alpha(v)beta(3) integrin-ERK1/ERK2 MAPK" connection regulates the proliferation of breast cancer cells

In addition to their role in cell migration and adhesion, integrins elicit a series of transduction events that regulate cell-cycle progression and apoptosis in a process known as "outside-in" signaling. A second mode of integrin regulation known as "inside-out" signaling, in which the activation of major cell transduction cascades can influence the activation status of some integrins, has also been described. Here, we have assessed the role of the extracellular signal-regulated kinase (ERK1)/ERK2, mitogen-activated protein kinase (MAPK), and phospoinositide 3-kinase (PI-3'K) signaling pathways in the expression and function of alpha(v)beta(3) integrin in breast cancer models. Pharmacological inhibition of MEK1 and MEK2 with U0126 drastically increased the levels of alpha(v)beta(3) in Heregulin (HRG)-overexpressing MDA-MB-231 cells (231/WT, 231/VEC) and derivatives transfected with the antisense orientation of the HRG-beta2 full length cDNA (231/ASPOOL, 231/AS31). Interestingly, this was related to a significant decrease of viability and of the S- and G2/M subcompartment of the cell cycle in MDA MB 231 cells in response to U0126. Furthermore, specific inhibition of the PI-3'K pathway with LY294002 also induced an increase of alpha(v)beta(3) levels but to a lesser extent. Moreover, pretreatment of MDA-MB-231 cells with U0126 antagonized the effects of small peptidomimetic alpha(v)beta(3) antagonists. Remarkably, inhibition of the PI-3'K/AKT pathway did not exert the same effects, thus suggesting that the "outside-in" as well as the "inside-out" alpha(v)beta(3)-mediated signaling goes primarily through the ERK1/ERK2 MAPK pathway in MDA MB 231 breast cancer cells. Collectively, these results strongly suggest the existence of a bidirectional molecular connection alpha(v)beta(3)-ERK1/ERK2 MAPK that would regulate breast cancer cells survival and proliferation.     

Inhibition of tumor-associated fatty acid synthase activity enhances vinorelbine (Navelbine)-induced cytotoxicity and apoptotic cell death in human breast cancer cells

The lipogenic enzyme fatty acid synthase (FAS) is differentially overexpressed and hyperactivated in a biologically aggressive subset of breast carcinomas and minimally in most normal adult tissues, rendering it an interesting target for anti-neoplastic therapy development. Current trends in the treatment of human breast cancer are with drug combinations that result in improved responses as well as the ability to use less toxic concentrations of the drugs. Here, we envisioned that combinations of conventional chemotherapeutic agents with novel compounds directed against breast cancer-associated FAS hyperactivity may provide increased efficacy over existing therapy for human breast cancer. Specifically, we examined the ability of the mycotoxin cerulenin, a potent and non-competitive inhibitor of FAS activity, to enhance the cytotoxic effects of vinorelbine (Navelbine), a derivative of vinca alkaloid that interferes with tubulin assembly and exhibits activity against metastatic breast cancer. SK-Br3, MCF-7 and MDA-MB-231 human breast cancer cell lines were employed as models of high, moderate and low levels of FAS ('cerulenin-target'), respectively. Combinations of cerulenin with vinorelbine were tested for synergism, additivity or antagonism using the isobologram and the median-effect plot (Chou-Talalay) analyses. Breast cancer cells were either simultaneously exposed to cerulenin and vinorelbine for 24 h or sequentially to cerulenin for 24 h followed by vinorelbine for 24 h. Concurrent exposure to cerulenin and vinorelbine resulted in synergistic interactions in MCF-7 and MDA-MB-231 cell lines, while additivity was found in SK-Br3 cells. Sequencing cerulenin followed by vinorelbine resulted in synergism for SK-Br3 and MDA-MB-231 cells, whereas it showed additive effects in MCF-7 cells. FAS activity blockade was found to synergistically enhance apoptosis-inducing activity of vinorelbine, as determined by an enzyme-linked immunosorbent assay for histone-associated DNA fragments. To the best of our knowledge this is the first study demonstrating that breast cancer-associated FAS is playing an active role in human breast cancer chemosensitivity. We suggest that pharmacological inhibition of FAS activity is a novel molecular approach to enhance the cytotoxic effects of existing chemotherapeutic agents in human breast cancer.     

CD9 gene deficiency does not affect smooth muscle cell migration and neointima formation after vascular injury in mice

The hypothesis that CD9, a member of the tetraspanin family, plays a role in smooth muscle cell (SMC) migration was tested with the use of a vascular injury model in wild-type (CD9+/+) and CD9-deficient (CD9-/-) mice. Neointima formation 3 weeks after electric injury of the femoral artery was not significantly different in CD9+/+ and CD9-/- mice (area of 0.019 +/- 0.0034 mm2 versus 0.013 +/- 0.0036 mm2; mean +/- SEM, n = 6). The medial areas were also comparable, resulting in intima/media ratio's of 1.3 +/- 0.15 and 0.90 +/- 0.22, respectively. Nuclear cell counts in cross-sectional areas of the injured region were comparable in media (33 +/- 5 versus 27 +/- 2) and neointima (135 +/- 16 versus 97 +/- 17) of CD9+/+ and CD9-/- arteries. Immunocytochemical analysis revealed expression of CD9 in the endothelium, by SMC in the media and by some fibroblasts in the adventitia of non-injured femoral arteries. Three weeks after injury, there appeared to be a gradient of increased CD9 expression from the adventitia to the neointima, in which SMC are abundantly present. Immunogold labeling and electron microscopy with non-injured femoral arteries of CD9+/+ mice confirmed the presence of CD9 at the surface of adventitial fibroblasts and in SMC or pericytes, as well as in the endothelium. Thus, in this model CD9 is highly expressed by migrating SMC, but deficiency of CD9 does not affect SMC migration or neointima formation after perivascular injury.     

Population and family studies of HLA-DR4 by use of oligonucleotide typing

Using PCR and DR4 group-specific primers and SSO's we have examined DRB1*04 nucleotide polymorphisms in a population of 123 DR4-positive individuals (86 NAC, 27 Hispanics and 10 African Americans) from New York carrying a total of 134 DR4 haplotypes. We found that the distribution of DRB1*04 alleles on DR4 haplotypes differs in these three ethnic groups. In this relatively small population, certain alleles such as DRB1*0406 and 0411 were encountered only in Hispanics, while others such as DRB1*0403, 0408 and 0409 were found only in NAC (North American Caucasians). Such differences may be important in studies of HLA-DR4 and disease associations. Evidence from MLC and PLT studies of an HLA-B/DR crossover family, which was informative for the segregation of HLA-DRB1*0406 and DRB1*0407, supports the concept that subtypes of HLA-DR4 and/or associated HLA-DP alleles elicit T-cell alloreactivity, and may thus play a role in transplantation.     

RNA interference-mediated silencing of the p53 tumor-suppressor protein drastically increases apoptosis after inhibition of endogenous fatty acid metabolism in breast cancer cells

Fatty acid synthase (FAS)-dependent endogenous fatty acid synthetic activity is abnormally elevated in a biologically-aggressive subset of breast carcinomas. Remarkably, tumor-associated FAS hyperactivity represents a novel target for anti-metabolic therapy because pharmacological inhibitors of FAS are selectively cytotoxic for tumor cells, triggering their apoptotic cell death. Since the p53 tumor-suppressor protein (TP53) is thought to play a novel role in cellular responses of a variety of non-genotoxic metabolic stresses, we characterized the involvement of TP53 in the response of breast cancer cells to FAS inhibition. MCF-7 breast cancer cells were selected for study because they have an intact TP53 pathway and undergo little apoptosis following FAS blockade. Two chemically distinct inhibitors of FAS (the natural mycotoxin cerulenin and the novel small-molecule inhibitor C75) were studied in parallel to provide a broad picture of consequences suffered by the loss of FAS function on TP53 signaling. Treatment with either cerulenin or C75 induced TP53 protein accumulation at 24 h in MCF-7 cells. To determine whether the up-regulation of TP53 following exposure to cerulenin or C75 was solely due to inhibition of endogenous fatty acid metabolism, we first evaluated the cytotoxic response to chemical FAS blockers on MCF-7 cells in which FAS gene expression was previously silenced by using the highly sequence-specific mechanism of RNA interference. MCF-7 cells became insensitive to C75-induced cytotoxicity when the expression of FAS was specifically suppressed by targeted knock-down with small interfering RNA (siRNA), whereas they partially retained their sensitivity to cerulenin. These results demonstrate that C75-induced cytotoxic damage to breast cancer cells is closely dependent on its ability to inhibit FAS-catalyzed endogenous fatty acid biogenesis, thus ruling out a significant direct effect of C75 on DNA. To determine the functional role of TP53 on breast cancer cell survival after FAS blockade, we evaluated FAS inhibitor-mediated apoptosis in MCF-7 cells transiently transfected with a pool of sequence-specific double-stranded RNA oligonucleotides targeting TP53 gene. In these conditions, TP53 protein levels were unchanged during the period of FAS-inhibitor exposure. Remarkably, siRNA-induced silencing of TP53 gene expression did result in a dramatic increase (approximately 300%) in apoptotic cell death following exposure to C75. Strikingly, there was no apparent relationship between the TP53 mutational status and sensitivity to chemical FAS inhibitor in a panel of human breast cancer cell lines. However, the degree of TP53 mRNA expression was predictive of sensitivity to C75-induced cytotoxicity, with low-TP53 mRNA expressing breast cancer cells showing hypersensitivity to FAS blockade. These findings strongly suggest that: a) TP53 is a novel molecular sensor of energy imbalance after the perturbation of endogenous fatty acid metabolism in breast cancer cells; b) TP53 function closely influences the decision between apoptosis and growth arrest following FAS blockade; and c) pharmacological inhibitors of FAS activity may be clinically useful against breast carcinomas exhibiting mutation or aberrant expression of TP53.