Downregulation of stromal BRCA1 drives breast cancer tumor growth via upregulation of HIF-1α, autophagy and ketone body production

Our recent studies have mechanistically demonstrated that cancer-associated fibroblasts (CAFs) produce energy-rich metabolites that functionally support the growth of cancer cells. Also, several authors have demonstrated that DNA instability in the tumor stroma greatly contributes to carcinogenesis. To further test this hypothesis, we stably knocked-down BRCA1 expression in human hTERT-immortalized fibroblasts (shBRCA1) using an shRNA lentiviral approach. As expected, shBRCA1 fibroblasts displayed an elevated growth rate. Using immunofluorescence and immunoblot analysis, shBRCA1 fibroblasts demonstrated an increase in markers of autophagy and mitophagy. Most notably, shBRCA1 fibroblasts also displayed an elevation of HIF-1α expression. In accordance with these findings, shBRCA1 fibroblasts showed a 5.5-fold increase in ketone body production; ketone bodies function as high-energy mitochondrial fuels. This is consistent with the onset of mitochondrial dysfunction in BRCA1-deficient fibroblasts. Conversely, after 48 h of co-culturing shBRCA1 fibroblasts with a human breast cancer cell line (MDA-MB-231 cell), mitochondrial activity was enhanced in these epithelial cancer cells. Interestingly, our preclinical studies using xenografts demonstrated that shBRCA1 fibroblasts induced an ~2.2-fold increase in tumor growth when co-injected with MDA-MB-231 cells into nude mice. We conclude that a BRCA1 deficiency in the tumor stroma metabolically promotes cancer progression, via ketone production.     

Immunolocalization of BRCA1 protein in tumor breast tissue: prescreening of BRCA1 mutation in Tunisian patients with hereditary breast cancer?

BRCA1 is a tumor suppressor gene which is inactivated by mutation in familial breast and ovarian cancers. Over 300 different disease causing germ-line mutations have been described; 60% are unique to an individual family. This diversity and the large size of the gene lead us to search for a prescreening method for BRCA1 mutations. Since BRCA1 is a nuclear protein in normal cells, but reported by some authors to be cytoplasmic in breast tumor cells of patients with BRCA1 mutation, we evaluated immunohistochemistry as a prescreening technique to identify BRCA1 mutations in patients with familial presentation of breast cancer. Using a monoclonal antibody against the carboxy-terminal region of BRCA1, we performed immunohistochemistry on 18 tumor samples from patients with hereditary breast cancer. Cytoplasmic staining of BRCA1 was observed in 10 cases. Of the 18 tumors, 12 (66%) showed either BRCA mutation or BRCA1 accumulation or both, indicating that BRCA1 function might be lost in breast tumor cells not only through mutation, but also via abnormal cytoplasmic location. The immunohistochemical test used in this study would not be efficient as a pre-screening method of deleterious mutations, but it appeared useful to investigate tumor physiology.     

Downregulation of protein kinase CK2 activity facilitates tumor necrosis factor-α-mediated chondrocyte death through apoptosis and autophagy

Despite the numerous studies of protein kinase CK2, little progress has been made in understanding its function in chondrocyte death. Our previous study first demonstrated that CK2 is involved in apoptosis of rat articular chondrocytes. Recent studies have suggested that CK2 downregulation is associated with aging. Thus examining the involvement of CK2 downregulation in chondrocyte death is an urgently required task. We undertook this study to examine whether CK2 downregulation modulates chondrocyte death. We first measured CK2 activity in articular chondrocytes of 6-, 21- and 30-month-old rats. Noticeably, CK2 activity was downregulated in chondrocytes with advancing age. To build an in vitro experimental system for simulating tumor necrosis factor (TNF)-α-induced cell death in aged chondrocytes with decreased CK2 activity, chondrocytes were co-treated with CK2 inhibitors and TNF-α. Viability assay demonstrated that CK2 inhibitors facilitated TNF-α-mediated chondrocyte death. Pulsed-field gel electrophoresis, nuclear staining, flow cytometry, TUNEL staining, confocal microscopy, western blot and transmission electron microscopy were conducted to assess cell death modes. The results of multiple assays showed that this cell death was mediated by apoptosis. Importantly, autophagy was also involved in this process, as supported by the appearance of a punctuate LC3 pattern and autophagic vacuoles. The inhibition of autophagy by silencing of autophage-related genes 5 and 7 as well as by 3-methyladenine treatment protected chondrocytes against cell death and caspase activation, indicating that autophagy led to the induction of apoptosis. Autophagic cells were observed in cartilage obtained from osteoarthritis (OA) model rats and human OA patients. Our findings indicate that CK2 down regulation facilitates TNF-α-mediated chondrocyte death through apoptosis and autophagy. It should be clarified in the future if autophagy observed is a consequence versus a cause of the degeneration in vivo.     

Vitamin D, tamoxifen and β-estradiol modulate breast cancer cell growth and interleukin-6 and metalloproteinase-2 production in three-dimensional co-cultures of tumor cell spheroids with endothelium

Reciprocal interactions between tumor cells and endothelial cells constitute the most important stage of tumor metastasis. There is growing evidence suggesting that β-estradiol and vitamin D modulate the progression of steroid-sensitive breast cancers. In keeping with those results, the purpose of the study reported here was to determine the cytotoxic and antiproliferative activity of tamoxifen (TAM) in the T47D human breast cancer cell line depending on the cell culture model (three-dimensional (3D, spheroid) or two-dimensional (2D, monolayer)) and to estimate the antiproliferative activity of vitamin D in balanced TAM/β-estradiol conditions. The study was also designed to investigate whether vitamin D might influence interleukin-6 (IL-6) and metalloproteinase-2 (MMP-2) production in a co-culture of T47D cell spheroids with an endothelial cell monolayer in the presence of β-estradiol and TAM. Spectrophotometric analysis with MTT revealed that the cytotoxic and antiproliferative activity of TAM was dependent on the culture model, the density of cell culture, and culture medium supplements. In balanced TAM/β-estradiol medium, vitamin D only slightly inhibited T47D cell proliferation in both 2D and 3D cultures. Direct contact of tumor cell spheroids with the endothelium induced production of MMP-2 and IL-6, which was significantly inhibited in TAM/β-estradiol balanced medium. Addition of vitamin D further inhibited MMP-2 production, but enhanced the production of IL-6 as was shown by ELISA assay. Our co-culture model in TAM/β-estradiol balanced medium proved to be useful for examining direct and paracrine interactions of tumor cells with the endothelium in conditions that were closer to in vivo conditions than in the standard 2D model.     

Ferulic acid augments angiogenesis via VEGF,PDGF and HIF-1α

Therapeutic angiogenesis is critical to wound healing and ischemic diseases such as myocardial infarction and stroke. For development of therapeutic agents, a search for new angiogenic agents is the key. Ferulic acid, a phytochemical found in many fruits and vegetables, exhibits a broad range of therapeutic effects on human diseases, including diabetes and cancer. This study investigated the augmenting effect of ferulic acid on angiogenesis through functional modulation of endothelial cells. Through endothelial cell migration and tube formation assays, ferulic acid (10^?6–10^?4 M) was found to induce significant angiogenesis in human umbilical vein endothelial cells (HUVECs) in vitro without cytotoxicity. With chorioallantoic membrane assay, ferulic acid (10^?6–10^?5 M) was also found to promote neovascularization in vivo. Using Western blot analysis and quantitative real-time polymerase chain reaction, we found that ferulic acid increased vascular endothelial growth factor (VEGF) and platelet-derived growth factor (PDGF) expression in HUVECs. Furthermore, the amounts of hypoxic-induced factor (HIF) 1α mRNA and protein, the major regulator of VEGF and PDGF, also showed up-regulation by ferulic acid. Electrophoretic migration shift assay showed that the binding activity of HIF-1α was also enhanced with ferulic acid treatment of HUVECs. Moreover, inhibitors of extracellular-signal-regulated kinase 1/2 and phosphoinositide-3 kinase (PI3K) abolished the binding activity of HIF-1α and the subsequent activation of VEGF and PDGF production by ferulic acid. Thus, both mitogen-activated protein kinase and PI3K pathways were involved in the angiogenic effects of ferulic acid. Taken together, ferulic acid serves as an angiogenic agent to augment angiogenesis both in vitro and in vivo. This effect might be observed through the modulation of VEGF, PDGF and HIF-1α.     

Hereditary ovarian cancer and two-compartment tumor metabolism: Epithelial loss of BRCA1 induces hydrogen peroxide production,driving oxidative stress and NFκB activation in the tumor stroma

Mutations in the BRCA1 tumor suppressor gene are commonly found in hereditary ovarian cancers. Here, we used a co-culture approach to study the metabolic effects of BRCA1-null ovarian cancer cells on adjacent tumor-associated stromal fibroblasts. Our results directly show that BRCA1-null ovarian cancer cells produce large amounts of hydrogen peroxide, which can be abolished either by administration of simple antioxidants (N-acetyl-cysteine; NAC) or by replacement of the BRCA1 gene. Thus, the BRCA1 gene normally suppresses tumor growth by functioning as an antioxidant. Importantly, hydrogen peroxide produced by BRCA1-null ovarian cancer cells induces oxidative stress and catabolic processes in adjacent stromal fibroblasts, such as autophagy, mitophagy and glycolysis, via stromal NFκB activation. Catabolism in stromal fibroblasts was also accompanied by the upregulation of MCT4 and a loss of Cav-1 expression, which are established markers of a lethal tumor microenvironment. In summary, loss of the BRCA1 tumor suppressor gene induces hydrogen peroxide production, which then leads to metabolic reprogramming of the tumor stroma, driving stromal-epithelial metabolic coupling. Our results suggest that new cancer prevention trials with antioxidants are clearly warranted in patients that harbor hereditary/familial BRCA1 mutations.     

Metabolic reprogramming of cancer-associated fibroblasts by TGF-β drives tumor growth: Connecting TGF-β signaling with “Warburg-like” cancer metabolism and L-lactate production

We have previously shown that a loss of stromal Cav-1 is a biomarker of poor prognosis in breast cancers. Mechanistically, a loss of Cav-1 induces the metabolic reprogramming of stromal cells, with increased autophagy/mitophagy, mitochondrial dysfunction and aerobic glycolysis. As a consequence, Cav-1-low CAFs generate nutrients (such as L-lactate) and chemical building blocks that fuel mitochondrial metabolism and the anabolic growth of adjacent breast cancer cells. It is also known that a loss of Cav-1 is associated with hyperactive TGF-β signaling. However, it remains unknown whether hyperactivation of the TGF-β signaling pathway contributes to the metabolic reprogramming of Cav-1-low CAFs. To address these issues, we overexpressed TGF-β ligands and the TGF-β receptor I (TGFβ-RI) in stromal fibroblasts and breast cancer cells. Here, we show that the role of TGF-β in tumorigenesis is compartment-specific, and that TGF-β promotes tumorigenesis by shifting cancer-associated fibroblasts toward catabolic metabolism. Importantly, the tumor-promoting effects of TGF-β are independent of the cell type generating TGF-β. Thus, stromal-derived TGF-β activates signaling in stromal cells in an autocrine fashion, leading to fibroblast activation, as judged by increased expression of myofibroblast markers, and metabolic reprogramming, with a shift toward catabolic metabolism and oxidative stress. We also show that TGF-β-activated fibroblasts promote the mitochondrial activity of adjacent cancer cells, and in a xenograft model, enhancing the growth of breast cancer cells, independently of angiogenesis. Conversely, activation of the TGF-β pathway in cancer cells does not influence tumor growth, but cancer cell-derived-TGF-β ligands affect stromal cells in a paracrine fashion, leading to fibroblast activation and enhanced tumor growth. In conclusion, ligand-dependent or cell-autonomous activation of the TGF-β pathway in stromal cells induces their metabolic reprogramming, with increased oxidative stress, autophagy/mitophagy and glycolysis, and downregulation of Cav-1. These metabolic alterations can spread among neighboring fibroblasts and greatly sustain the growth of breast cancer cells. Our data provide novel insights into the role of the TGF-β pathway in breast tumorigenesis, and establish a clear causative link between the tumor-promoting effects of TGF-β signaling and the metabolic reprogramming of the tumor microenvironment.     

Metabolic reprogramming of cancer-associated fibroblasts by TGF-β drives tumor growth: Connecting TGF-β signaling with “Warburg-like” cancer metabolism and L-lactate production

We have previously shown that a loss of stromal Cav-1 is a biomarker of poor prognosis in breast cancers. Mechanistically, a loss of Cav-1 induces the metabolic reprogramming of stromal cells, with increased autophagy/mitophagy, mitochondrial dysfunction and aerobic glycolysis. As a consequence, Cav-1-low CAFs generate nutrients (such as L-lactate) and chemical building blocks that fuel mitochondrial metabolism and the anabolic growth of adjacent breast cancer cells. It is also known that a loss of Cav-1 is associated with hyperactive TGF-β signaling. However, it remains unknown whether hyperactivation of the TGF-β signaling pathway contributes to the metabolic reprogramming of Cav-1-low CAFs. To address these issues, we overexpressed TGF-β ligands and the TGF-β receptor I (TGFβ-RI) in stromal fibroblasts and breast cancer cells. Here, we show that the role of TGF-β in tumorigenesis is compartment-specific, and that TGF-β promotes tumorigenesis by shifting cancer-associated fibroblasts toward catabolic metabolism. Importantly, the tumor-promoting effects of TGF-β are independent of the cell type generating TGF-β. Thus, stromal-derived TGF-β activates signaling in stromal cells in an autocrine fashion, leading to fibroblast activation, as judged by increased expression of myofibroblast markers, and metabolic reprogramming, with a shift toward catabolic metabolism and oxidative stress. We also show that TGF-β-activated fibroblasts promote the mitochondrial activity of adjacent cancer cells, and in a xenograft model, enhancing the growth of breast cancer cells, independently of angiogenesis. Conversely, activation of the TGF-β pathway in cancer cells does not influence tumor growth, but cancer cell-derived-TGF-β ligands affect stromal cells in a paracrine fashion, leading to fibroblast activation and enhanced tumor growth. In conclusion, ligand-dependent or cell-autonomous activation of the TGF-β pathway in stromal cells induces their metabolic reprogramming, with increased oxidative stress, autophagy/mitophagy and glycolysis, and downregulation of Cav-1. These metabolic alterations can spread among neighboring fibroblasts and greatly sustain the growth of breast cancer cells. Our data provide novel insights into the role of the TGF-β pathway in breast tumorigenesis, and establish a clear causative link between the tumor-promoting effects of TGF-β signaling and the metabolic reprogramming of the tumor microenvironment.     

GD₃ synthase expression enhances proliferation and tumor growth of MDA-MB-231 breast cancer cells through c-Met activation

The disialoganglioside G(D3) is overexpressed in ～50% of invasive ductal breast carcinoma, and the G(D3) synthase gene (ST8SIA1) displays higher expression among estrogen receptor-negative breast cancer tumors, associated with a decreased overall survival of breast cancer patients. However, no relationship between ganglioside expression and breast cancer development and aggressiveness has been reported. We have previously shown that overexpression of G(D3) synthase induces the accumulation of b- and c-series gangliosides (G(D3), G(D2), and G(T3)) at the cell surface of MDA-MB-231 breast cancer cells together with the acquisition of a proliferative phenotype in the absence of serum. Here, we show that phosphoinositide 3-kinase/Akt and mitogen-activated protein kinase/extracellular signal-regulated kinase pathways are constitutively activated in G(D3) synthase-expressing cells. Analysis of phosphorylation of tyrosine kinase receptors shows a specific c-Met constitutive activation in G(D3) synthase-expressing cells, in the absence of its ligand, hepatocyte growth factor/scatter factor. In addition, inhibition of c-Met or downstream signaling pathways reverses the proliferative phenotype. We also show that G(D3) synthase expression enhances tumor growth in severe combined immunodeficient mice. Finally, a higher expression of ST8SIA1 and MET in the basal subtype of human breast tumors are observed. Altogether, our results show that G(D3) synthase expression is sufficient to enhance the tumorigenicity of MDA-MB-231 breast cancer cells through a ganglioside-dependent activation of the c-Met receptor.     

After BRCA1 and BRCA2-what next? Multifactorial segregation analyses of three-generation, population-based Australian families affected by female breast cancer

Mutations in BRCA1 and BRCA2 that cause a dominantly inherited high risk of female breast cancer seem to explain only a small proportion of the aggregation of the disease. To study the possible additional genetic components, we conducted single-locus and two-locus segregation analyses, with and without a polygenic background, using three-generation families ascertained through 858 women with breast cancer diagnosed at age <40 years, ascertained through population cancer registries in Melbourne and Sydney, Australia. Extensive testing for deleterious mutations in BRCA1 and BRCA2, to date, has identified 34 carriers. Our analysis suggested that, after other possible unmeasured familial factors are adjusted for and the known BRCA1 and BRCA2 mutation carriers are excluded, there appears to be a residual dominantly inherited risk of female breast cancer in addition to that derived from mutations in BRCA1 and BRCA2. This study also suggests that there is a substantial recessively inherited risk of early-onset breast cancer. According to the best-fitting model, after excluding known carriers of mutations in BRCA1 and BRCA2, about 1/250 (95% confidence interval [CI] 1/500 to 1/125) women have a recessive risk of 86% (95% CI 69%-100%) by age 50 years and of almost 100% by age 60 years. Possible reasons that our study has implicated a novel strong recessive effect include our inclusion of data on lineal aunts and grandmothers, study of families ascertained through women with early-onset breast cancer, allowance for multiple familial factors in the analysis, and removal of families for whom the cause (i.e., BRCA1 or BRCA2) is known. Our findings may have implications for attempts to identify new breast cancer-susceptibility genes.     

Transforming growth factor-β signaling in tumor initiation,progression and therapy in breast cancer: an update

Transforming growth factor-β (TGF-β) is a ubiquitous cytokine playing an essential role in cell proliferation, differentiation, apoptosis, adhesion and invasion, as well as in cellular microenvironment. In malignant diseases, TGF-β signaling features a growth inhibitory effect at an early stage but aggressive oncogenic activity at the advanced malignant state. Here, we update the current understanding of TGF-β signaling in cancer development and progression with a focus on breast cancer. We also review the current approaches of TGF-β signaling-targeted therapeutics for human malignancies.