SIRT1 catalytic activity has little effect on tumor formation and metastases in a mouse model of breast cancer

SIRT6 enhances oxidative phosphorylation in breast cancer and promotes mammary tumorigenesis in mice

BACKGROUND

Sirtuin 6 (SIRT6) is a NAD⁺-dependent deacetylase with key roles in cell metabolism. High SIRT6 expression is associated with adverse prognosis in breast cancer (BC) patients. However, the mechanisms through which SIRT6 exerts its pro-oncogenic effects in BC remain unclear. Here, we sought to define the role of SIRT6 in BC cell metabolism and in mouse polyoma middle T antigen (PyMT)-driven mammary tumors.

METHODS

We evaluated the effect of a heterozygous deletion of Sirt6 on tumor latency and survival of mouse mammary tumor virus (MMTV)-PyMT mice. The effect of SIRT6 silencing on human BC cell growth was assessed in MDA-MB-231 xenografts. We also analyzed the effect of Sirt6 heterozygous deletion, of SIRT6 silencing, and of the overexpression of either wild-type (WT) or catalytically inactive (H133Y) SIRT6 on BC cell pyruvate dehydrogenase (PDH) expression and activity and oxidative phosphorylation (OXPHOS), including respiratory complex activity, ATP/AMP ratio, AMPK activation, and intracellular calcium concentration.

RESULTS

The heterozygous Sirt6 deletion extended tumor latency and mouse survival in the MMTV-PyMT mouse BC model, while SIRT6 silencing slowed the growth of MDA-MB-231 BC cell xenografts. WT, but not catalytically inactive, SIRT6 enhanced PDH expression and activity, OXPHOS, and ATP/AMP ratio in MDA-MB-231 and MCF7 BC cells. Opposite effects were obtained by SIRT6 silencing, which also blunted the expression of genes encoding for respiratory chain proteins, such as UQCRFS1, COX5B, NDUFB8, and UQCRC2, and increased AMPK activation in BC cells. In addition, SIRT6 overexpression increased, while SIRT6 silencing reduced, intracellular calcium concentration in MDA-MB-231 cells. Consistent with these findings, the heterozygous Sirt6 deletion reduced the expression of OXPHOS-related genes, the activity of respiratory complexes, and the ATP/AMP ratio in tumors isolated from MMTV-PyMT mice.

CONCLUSIONS

Via its enzymatic activity, SIRT6 enhances PDH expression and activity, OXPHOS, ATP/AMP ratio, and intracellular calcium concentration, while reducing AMPK activation, in BC cells. Thus, overall, SIRT6 inhibition appears as a viable strategy for preventing or treating BC.

CCL11 increases the proportion of CD4+CD25+Foxp3+ Treg cells and the production of IL‑2 and TGF‑β by CD4+ T cells via the STAT5 signaling pathway

CD4⁺ regulatory T (Treg) cells are associated with immune tolerance and antitumor immunosuppression. The aim of the present study was to investigate the role and molecular mechanism of C-C motif chemokine ligand 11 (CCL11) in the regulation of Treg cells from patients with breast cancer (BC) and healthy individuals in vitro, and from tumor-bearing mice in vivo. CD4⁺ T cells isolated from patients with BC or healthy individuals were incubated with anti-CCL11 neutralizing antibodies or recombinant human CCL11 protein, in the presence or absence of a STAT5 inhibitor. The serum CCL11 level and proportion of Treg cells characterized as CD4⁺CD25⁺forkhead box P3⁺ (Foxp3) among the CD4⁺ T cells in patients with BC and healthy individuals were analyzed by ELISA and flow cytometry, respectively. CCL11, C-C motif chemokine receptor 3 (CCR3), Foxp3, phosphorylated-STAT5 and STAT5 expression levels were determined by western blotting. The serum CCL11 level and the proportion of CD4⁺CD25⁺Foxp3⁺ Treg cells were significantly increased in patients with BC compared with healthy individuals. CCL11 blockade reduced the proportion of CD4⁺CD25⁺Foxp3⁺ Treg cells, the expression of CCR3 and Foxp3, and the level of STAT5 activation in tumor-associated CD4⁺ T cells, in a dose-dependent manner. CCL11 blockade also reduced the proportion of CD4⁺CD25⁺Foxp3⁺ Treg cells and the serum levels of interleukin (IL)-2 and transforming growth factor (TGF)-β1 in tumor-bearing mice. The recombinant human CCL11 protein increased the proportion of CD4⁺CD25⁺Foxp3⁺ Treg cells, the expression of CCR3 and Foxp3, and the release of IL-2 and TGF-β1 in non-tumor-associated CD4⁺ T cells via the STAT5 signaling pathway. The results of the present study may aid in identifying therapeutics that could further modulate the immune system during BC.

Modulating SIRT1 activity variously affects thymic lymphoma development in mice

SIRT1 is a protein deacetylase with a broad range of biological functions, many of which are known to be important in carcinogenesis, however much of the literature regarding the role of SIRT1 in cancer remains conflicting. In this study we assessed the effect of SIRT1 on the initiation and progression of thymic T cell lymphomas. We employed mouse strains in which SIRT1 activity was absent or could be reversibly modulated in conjunction with thymic lymphoma induction using either the N-nitroso-N-methylurea (NMU) carcinogenesis or the nucleophosmin-anaplastic lymphoma kinase (NPM-ALK) transgene. Decreased SIRT1 activity reduced the development of thymic lymphomas in the NMU-treated mice but was permissive for the formation of lung adenomas. Conversely, in the NPM-ALK transgenic mice, decreased SIRT1 activity had a modest promoting effect in the development of thymic lymphomas. The results of the work presented here add to the growing body of evidence that sirt1 is neither an outright oncogene nor a tumor suppressor. These opposing results in two models of the same disease suggest that the influence of sirt1 on carcinogenesis may lie in a role in tumor surveillance.

SIRT7 antagonizes TGF-β signaling and inhibits breast cancer metastasis

Distant metastasis is the main cause of breast cancer-related death; however, effective therapeutic strategies targeting metastasis are still scarce. This is largely attributable to the spatiotemporal intratumor heterogeneity during metastasis. Here we show that protein deacetylase SIRT7 is significantly downregulated in breast cancer lung metastases in human and mice, and predicts metastasis-free survival. SIRT7 deficiency promotes breast cancer cell metastasis, while temporal expression of Sirt7 inhibits metastasis in polyomavirus middle T antigen breast cancer model. Mechanistically, SIRT7 deacetylates and promotes SMAD4 degradation mediated by β-TrCP1, and SIRT7 deficiency activates transforming growth factor-β signaling and enhances epithelial-to-mesenchymal transition. Significantly, resveratrol activates SIRT7 deacetylase activity, inhibits breast cancer lung metastases, and increases survival. Our data highlight SIRT7 as a modulator of transforming growth factor-β signaling and suppressor of breast cancer metastasis, meanwhile providing an effective anti-metastatic therapeutic strategy.Metastatic disease is the major reason for breast cancer-related deaths; therefore, a better understanding of this process and its players is needed. Here the authors report the role of SIRT7 in inhibiting SMAD4-mediated breast cancer metastasis providing a possible therapeutic avenue.

Reversible modulation of SIRT1 activity in a mouse strain

The SIRT1 protein deacetylase is reported to have a remarkably wide spectrum of biological functions affecting such varied processes as aging, cancer, metabolism, neurodegeneration and immunity. However, the SIRT1 literature is also full of contradictions. To help establish the role(s) of SIRT1 in these and other biological processes, we set out to create a mouse in which the SIRT1 activity could be toggled between on and off states by fusing the estrogen receptor ligand-binding domain (ER) to the C terminus of the SIRT1 protein. We found that the catalytic activity of the SIRT1-ER fusion protein increased 4–5 fold in cells treated with its ligand, 4-hydroxy-tamoxifen (4OHT). The 4OHT-induced activation of SIRT1-ER was due in large part to a 2 to 4-fold increase in abundance of the SIRT1-ER protein in cells in culture and in tissues in vivo. This increase is reversible and is a consequence of 4OHT-induced stabilization of the SIRT1-ER protein. Since changes in SIRT1 level or activity of 2–4 fold are frequently reported to be sufficient to affect its biological functions, this mouse should be helpful in establishing the causal relationships between SIRT1 and the diseases and processes it affects.

Association between SIRT1 Gene Polymorphisms and Breast Cancer in Egyptians

Background

Breast cancer is reported to cause the highest mortality among female cancer patients. Previous studies have explored the association of silent mating-type information regulator 2 homolog 1 (SIRT1) gene expression with prognosis in breast cancer. However, no studies exist, so far, on the role of SIRT1 gene polymorphism in breast cancer risk or prognosis. The present study aimed to assess the association between SIRT1 gene polymorphisms and breast cancer in Egyptians.

Methods

The study comprised 980 Egyptian females divided into a breast cancer group (541 patients) and a healthy control group (439 subjects). SIRT1 gene single nucleotide polymorphisms (SNPs) rs3758391, rs3740051 and rs12778366 were genotyped using real-time polymerase chain reaction (RT-PCR). Allelic and genotypic frequencies were determined in both groups and association with breast cancer and clinicopathological characteristics was assessed.

Results

Breast cancer patients exhibited elevated serum SIRT1 levels which varied among different tumor grades. SIRT1 rs3758391 and rs12778366 TT genotypes were more frequent, exhibited higher SIRT1 levels than CC and CT genotypes and were associated with histologic grade and lymph node status. SIRT1 rs12778366 TT genotype also correlated with negative estrogen receptor (ER) and progesterone receptor (PR) statuses. The T allele frequency for both SNPs was higher in breast cancer patients than in normal subjects. Combined GG and AG genotypes of rs3740051 were more frequent, showed higher serum SIRT1 levels than the AA genotype, and were associated with ER and PR expression. Furthermore, inheritance of the G allele was associated with breast cancer.

Conclusions

Our findings reveal that rs3758391 and rs12778366 polymorphisms of SIRT1 gene are associated with breast cancer risk and prognosis in the Egyptian population.

Oncogenic role of SIRT1 associated with tumor invasion, lymph node metastasis, and poor disease-free survival in triple negative breast cancer

The aim of this study is to evaluate the biological role and clinical implications of silent mating type information regulation 2 homolog 1 (SIRT1) as a novel candidate for target therapy in triple negative breast cancer (TNBC) for which there is no specific agent. 344 patients who received surgical resection for TNBC from January 2003 to December 2006 at Seoul National University Hospital were enrolled, and the role of SIRT1 protein was evaluated via immunohistochemistry on tissue samples. In vivo experiments to evaluate tumor invasiveness were carried out with three human TNBC cell lines following SIRT1-siRNA transfection. Expression of SIRT1 significantly correlated with lymph node metastasis (p = 0.008). In multivariate analysis, SIRT1 expression (p = 0.011), T stage (p = 0.014), and lymphatic invasion (p < 0.001) were revealed to be independent predictive factors for lymph node metastasis. Combination of these three parameters revealed predictive performance for lymph node metastasis with an area under the curve (AUC) of 0.689 on receiver operating characteristics (ROC) curves analysis. SIRT1 expression correlated with shorter disease-free survival (P = 0.003) but not with overall survival. Inhibition of SIRT1 with small interfering RNA (siRNA) conspicuously suppressed the invasiveness of TNBC cell lines. This study reveals the role of SIRT1 on tumor invasiveness and unfavorable clinical outcomes, and we suggest its potential role as a prognostic indicator as well as a novel therapeutic target in TNBC.

SIRT7 inactivation reverses metastatic phenotypes in epithelial and mesenchymal tumors

Metastasis is responsible for over 90% of cancer-associated mortality. In epithelial carcinomas, a key process in metastatic progression is the epigenetic reprogramming of an epithelial-to-mesenchymal transition-like (EMT) change towards invasive cellular phenotypes. In non-epithelial cancers, different mechanisms must underlie metastatic change, but relatively little is known about the factors involved. Here, we identify the chromatin regulatory Sirtuin factor SIRT7 as a key regulator of metastatic phenotypes in both epithelial and mesenchymal cancer cells. In epithelial prostate carcinomas, high SIRT7 levels are associated with aggressive cancer phenotypes, metastatic disease, and poor patient prognosis, and depletion of SIRT7 can reprogram these cells to a less aggressive phenotype. Interestingly, SIRT7 is also important for maintaining the invasiveness and metastatic potential of non-epithelial sarcoma cells. Moreover, SIRT7 inactivation dramatically suppresses cancer cell metastasis in vivo, independent of changes in primary tumor growth. Mechanistically, we also uncover a novel link between SIRT7 and its family member SIRT1, providing the first demonstration of direct interaction and functional interplay between two mammalian sirtuins. Together with previous work, our findings highlight the broad role of SIRT7 in maintaining the metastatic cellular phenotype in diverse cancers.

Distinctive role of SIRT1 expression on tumor invasion and metastasis in breast cancer by molecular subtype

The aim of this study was to evaluate silent mating type information regulation 2 homolog 1 (SIRT1) expression levels by subtype and evaluate its predictive power of axillary lymph node metastasis (LNM) and its association with clinical outcome. A total of 427 patients diagnosed with invasive ductal carcinoma were chosen, immunohistochemical staining for SIRT1 expression was performed on tissue microarrays, and in vitro experiments with each intrinsic subtype of human breast cancer cell line were carried out. Increased expression of SIRT1 in hormone receptor-positive breast cancer and HER2 breast cancer subtype significantly correlated with lower risks of LNM. On the contrary, in triple-negative breast cancer, increased SIRT1 expression was more frequently observed in LNM-positive subgroup than LNM-negative subgroup. Combination of statistically significant, independent parameters including SIRT1 revealed predictive performance for LNM with area under the curve of 0.602, 0.587, and 0.726 for hormone receptor-positive breast cancer, HER2 breast cancer, and triple-negative breast cancer subtype, respectively. Inhibition of SIRT1 expression with small interfering RNA suppressed tumor invasion in MDA-MB-231, specifically. This is the first study to examine SIRT1 expression in breast cancer by subtype, and we have observed the potentially different role of SIRT1 gene having tumor-suppressive or tumor-promoting influence depending on the subtype; thus, different associations between SIRT1 expression and prognosis by subtype should be considered in its target therapy.

Modulation of tumorigenesis by dietary intervention is not mediated by SIRT1 catalytic activity

The protein deacetylase SIRT1 is involved in the regulation of a large number of cellular processes that are thought to be required for cancer initiation and progression. Both SIRT1 activity and tumorigenesis can be influenced by dietary fat and polyphenolics. We set out to determine whether dietary modulations of tumorigenesis are mediated by SIRT1 catalytic functions. We introduced a mammary gland tumor-inducing transgene, MMTV-PyMT, into stocks of mice bearing a H355Y point mutation in the Sirt1 gene that abolishes SIRT1 catalytic activity. Tumor latency was reduced in animals fed a high fat diet but this effect was not dependent on SIRT1 activity. Resveratrol had little effect on tumor formation except in animals heterozygous for the mutant Sirt1 gene. We conclude that the effects of these dietary interventions on tumorigenesis are not mediated by modulation of SIRT1 catalytic activity.