Roles of SIRT1 in leukemogenesis

Deciphering avian hematopoietic stem cells by surface marker screening and gene expression profiling

BACKGROUND

Avian species have played a pivotal role in developmental hematopoiesis research, leading to numerous critical discoveries. Avian influenza, particularly the H5N1 strain, poses a significant threat to poultry and has zoonotic potential for humans. Infections often result in abnormal hematologic profiles, highlighting the complex interplay between avian diseases and hematopoiesis. Many avian diseases can suppress immune cells in the bone marrow (BM), impacting immune responses. Studying hematopoietic stem cells (HSCs) in avian BM is crucial for understanding these processes and developing effective vaccines and protection strategies for both avian and human health.

METHODS

This study adapted methods from mouse studies to isolate avian HSCs as Lineage-negative (Lin-) cells. These isolated cells were further identified as Lin-Sca1+c-Kit+ (LSK) and were found to be more prevalent than in control groups. RT-PCR analyses were conducted, showing that genes like MEIS1 and TSC1 were upregulated, while SIRT1, FOXO1, and AHR were downregulated in these stem cells. Screening for LSK markers revealed ten unique surface antigens in the Sca1+c-Kit+ cell populations, including highly enriched antigens such as CD178, CD227, and CD184. Additionally, studies on quail HSCs demonstrated that similar labeling techniques were effective in quail BM.

RESULTS

The research demonstrated that the identification of avian HSC-specific surface antigens provides valuable insights into the pathogenesis of avian influenza and other diseases, enhancing our understanding of how these diseases suppress HSC function. Notably, the upregulation of MEIS1 and TSC1 genes in LSK cells underscores their critical roles in regulating hematopoietic processes. Conversely, the downregulation of SIRT1, FOXO1, and AHR genes provides important clues about their roles in differentiation and immune response mechanisms.

DISCUSSION

The findings of this study deepen our understanding of the effects of avian diseases on the immune system by identifying surface markers specific to avian HSCs. The suppression of HSC function by pathogens such as influenza highlights the importance of understanding these cells in developing targeted vaccines. These results represent a significant step towards improving global health security by mitigating risks associated with avian pathogens.

Role of SIRT1 in Chemoresistant Leukemia

Leukemias of the AML, CML, and CLL types are the most common blood cancers worldwide, making them a major global public health problem. Furthermore, less than 24% of patients treated with conventional chemotherapy (low-risk patients) and 10-15% of patients ineligible for conventional chemotherapy (high-risk patients) survive five years. The low levels of survival are mainly due to toxicity and resistance to chemotherapy or other medication, the latter leading to relapse of the disease, which is the main obstacle to the treatment of leukemia. Drug resistance may include different molecular mechanisms, among which epigenetic regulators are involved. Silent information regulator 2 homolog 1 (SIRT1) is an epigenetic factor belonging to the sirtuin (SIRT) family known to regulate aspects of chromatin biology, genome stability, and metabolism, both in homeostasis processes and in different diseases, including cancer. The regulatory functions of SIRT1 in different biological processes and molecular pathways are dependent on the type and stage of the neoplasia; thus, it may act as both an oncogenic and tumor suppressor factor and may also participate in drug resistance. In this review, we explore the role of SIRT1 in drug-resistant leukemia and its potential as a therapeutic target.

Loss of G0/G1 switch gene 2 (G0S2) promotes disease progression and drug resistance in chronic myeloid leukaemia (CML) by disrupting glycerophospholipid metabolism

Tyrosine kinase inhibitors (TKIs) targeting BCR::ABL1 have turned chronic myeloid leukaemia (CML) from a fatal disease into a manageable condition for most patients. Despite improved survival, targeting drug-resistant leukaemia stem cells (LSCs) remains a challenge for curative CML therapy. Aberrant lipid metabolism can have a large impact on membrane dynamics, cell survival and therapeutic responses in cancer. While ceramide and sphingolipid levels were previously correlated with TKI response in CML, the role of lipid metabolism in TKI resistance is not well understood. We have identified downregulation of a critical regulator of lipid metabolism, G0/G1 switch gene 2 (G0S2), in multiple scenarios of TKI resistance, including (1) BCR::ABL1 kinase-independent TKI resistance, (2) progression of CML from the chronic to the blast phase of the disease, and (3) in CML versus normal myeloid progenitors. Accordingly, CML patients with low G0S2 expression levels had a worse overall survival. G0S2 downregulation in CML was not a result of promoter hypermethylation or BCR::ABL1 kinase activity, but was rather due to transcriptional repression by MYC. Using CML cell lines, patient samples and G0s2 knockout (G0s2-/- ) mice, we demonstrate a tumour suppressor role for G0S2 in CML and TKI resistance. Our data suggest that reduced G0S2 protein expression in CML disrupts glycerophospholipid metabolism, correlating with a block of differentiation that renders CML cells resistant to therapy. Altogether, our data unravel a new role for G0S2 in regulating myeloid differentiation and TKI response in CML, and suggest that restoring G0S2 may have clinical utility.

Loss of SIRT1 inhibits hematopoietic stem cell aging and age-dependent mixed phenotype acute leukemia

Aging of hematopoietic stem cells (HSCs) is linked to various blood disorders and malignancies. SIRT1 has been implicated in healthy aging, but its role in HSC aging is poorly understood. Surprisingly, we found that Sirt1 knockout improved the maintenance of quiescence of aging HSCs and their functionality as well as mouse survival in serial bone marrow transplantation (BMT) recipients. The majority of secondary and tertiary BMT recipients of aging wild type donor cells developed B/myeloid mixed phenotype acute leukemia (MPAL), which was markedly inhibited by Sirt1 knockout. SIRT1 inhibition also reduced the growth and survival of human B/myeloid MPAL cells. Sirt1 knockout suppressed global gene activation in old HSCs, prominently the genes regulating protein synthesis and oxidative metabolism, which may involve multiple downstream transcriptional factors. Our results demonstrate an unexpected role of SIRT1 in promoting HSC aging and age-dependent MPAL and suggest SIRT1 may be a new therapeutic target for modulating functions of aging HSCs and treatment of MPAL.

Benzimidazoles Against Certain Breast Cancer Drug Targets: A Review

BACKGROUND

Benzimidazoles are widely used scaffolds against various types of cancer including breast cancer. To this end, anticancer agents must be developed using the knowledge of the specific targets of BC.

OBJECTIVE

In this study, we aim to review the compounds used against some of the biomolecular targets of breast cancer. To this end, we present information about the various targets, with their latest innovative studies.

CONCLUSION

Benzimidazole ring is an important building block that can target diverse cancer scenarios since it can structurally mimic biomolecules in the human body. Additionally, many studies imply the involvement of this moiety on a plethora of pathways and enzymes related to BC. Herein, our target-based collection of benzimidazole derivatives strongly suggests the utilization of benzimidazole derivatives against BC.

Silent Information Regulator 1 Promotes Proliferation, Migration, and Invasion of Cervical Cancer Cells and Is Upregulated by Human Papillomavirus 16 E7 Oncoprotein

OBJECTIVE

Silent information regulator 1 (SIRT1), an NAD+-dependent III class histone deacetylase, plays crucial roles in cell proliferation, apoptosis, senescence, metabolism, and stress responses. Nevertheless, the role of SIRT1 in tumorigenesis remains unclear.

METHODS

In the present study, we measured expression levels of SIRT1 and HPV16 E7 protein in cervical cancer (CC) tissue and calculated their correlations. We measured the effect of silencing SIRT1 on the proliferation, migration, invasion, and apoptosis in human CC SiHa cells.

RESULTS

Immunohistochemistry results revealed that the expression of SIRT1 was upregulated with progression from CIN II-III to CC, but was not expressed in normal cervical tissues and CIN I. There was a positive correlation between SIRT1 expression and HPV16 E7 expression in CC tissues, and silencing of HPV16 E7 downregulated the expression of SIRT1. Depletion of SIRT1 downregulated SIRT1 expression, and inhibited proliferation, migration, and invasion of SiHa cells, inducing apoptosis.

CONCLUSIONS

Taken together, the data suggest that SIRT1 promotes CC carcinogenesis. SIRT1 inhibition is a potential treatment strategy for CC.

A Review on the Therapeutic Role of TKIs in Case of CML in Combination With Epigenetic Drugs

Chronic myeloid leukemia is a malignancy of bone marrow that affects white blood cells. There is strong evidence that disease progression, treatment responses, and overall clinical outcomes of CML patients are influenced by the accumulation of other genetic and epigenetic abnormalities, rather than only the BCR/ABL1 oncoprotein. Both genetic and epigenetic factors influence the efficacy of CML treatment strategies. Targeted medicines known as tyrosine-kinase inhibitors have dramatically improved long-term survival rates in CML patients during the previous 2 decades. When compared to earlier chemotherapy treatments, these drugs have revolutionized CML treatment and allowed most people to live longer lives. Although epigenetic inhibitors' activity is disrupted in many cancers, including CML, but when combined with TKI, they may offer potential therapeutic strategies for the treatment of CML cells. The epigenetics of tyrosine kinase inhibitors and resistance to them is being studied, with a particular focus on imatinib, which is used to treat CML. In addition, the use of epigenetic drugs in conjunction with TKIs has been discussed. Resistance to TKIs is still a problem in curing the disease, necessitating the development of new therapies. This study focused on epigenetic pathways involved in CML pathogenesis and tumor cell resistance to TKIs, both of which contribute to leukemic clone breakout and proliferation.

Surtuin 1 as a potential prognostic biomarker in very elderly patients with colorectal cancer

BACKGROUND/AIMS

Colorectal cancer (CRC) rate increases with aging. Aging-related proteins, such as sirtuins (SIRTs) may be a potential therapeutic target in the elderly patients with CRC. The clinical implications of SIRT1 and SIRT2 have not been reported for elderly patients with cancer. The aim of this study was to evaluate the impact of expression of SIRT1 and SIRT2 on clinical outcome in two extreme age groups of patients with CRC.

METHODS

The expression of SIRT1 and SIRT2 were evaluated in CRC tissues of 101 patients aged ≥ 80 years and 29 patients aged ≤ 40 years by immunohistochemistry. We defined the patients aged ≥ 80 years as the very elderly and patients aged ≤ 40 years as the young patients. Correlations between the expression of these proteins and clinicopathological features were analyzed.

RESULTS

The prognosis for the very elderly patients with high expressions of SIRT1 was significantly worse than that for patients showing low expression (median survival, 24.9 months vs. 38.6 months, p = 0.027) whereas high expression of SIRT2 better prognosis (median survival, 37.9 months vs. 17.3 months, p = 0.006). However, the young patients did not show any difference in prognosis according to expression of SIRT1 and SIRT2. In multivariate analysis, high SIRT1 expression retained statistical significance as a poor prognostic factor in the very elderly patients with CRC.

CONCLUSION

The results suggest that high SIRT1 expression could be predictive of a poor outcome for very elderly patients with CRC.

The Lyn-SIRT1 signaling pathway is involved in imatinib resistance in chronic myeloid leukaemia

BACKGROUND

Imatinib resistance is commonly associated with the activation of BCR-ABL signaling in chronic myeloid leukaemia (CML). The activation of Lyn can result in imatinib resistance by regulating the formation of BCR-ABL protein complexes. SIRT1 is a novel survival pathway activated by BCR-ABL expression in haematopoietic progenitor cells. This study aimed to investigate whether the signaling pathway of Lyn/BCR-ABL/SIRT1 could mediate imatinib resistance in CML.

METHODS

The MTT assay was used to detect cell viability. Apoptosis was measured by a flow cytometry assay. Protein expression was detected by Western blotting. Knockdown CML cells were constructed by shRNA interference. The CML mouse model was used to investigate the role of SIRT1 in CML in vivo.

RESULTS

Lyn was overexpressed in K562R cells. BCR-ABL phosphorylation and activation were promoted by Lyn. Imatinib suppressed BCR-ABL phosphorylation in both K562 and K562R cells. BCR-ABL positively regulated SIRT1 and Foxo1 but negatively regulated acetylated Foxo1 (Ac-Foxo1) and p53 expression. Pharmacological inhibition of SIRT1 or knockdown of SIRT1 increased apoptosis and reduced growth in vitro and in vivo. Foxo1 was downregulated by SIRT1 inhibition or knockdown, while Ac-Foxo1 and p53 were upregulated. In vivo experiments showed that imatinib and/or SIRT1 inhibition both prolonged the survival of the CML mouse model and that the effects of imatinib were enhanced in combination with SIRT1 inhibition.

CONCLUSION

We proposed a novel molecular mechanism of imatinib resistance in CML in which the high expression of Lyn in imatinib-resistant cells inhibited Ac-Foxo1 and p53 expression through the BCR-ABL/SIRT1/Foxo1 signaling pathway, thus reducing apoptosis and mediating imatinib resistance.

A new SIRT1 inhibitor, MHY2245, induces autophagy and inhibits energy metabolism via PKM2/mTOR pathway in human ovarian cancer cells

Ovarian cancer is a common gynecological cancer that is found worldwide. Class III histone deacetylase (HDAC) inhibitors, a new class of anticancer agents, induce autophagy in various human cancer cells. The aim of the present study was to investigate the antitumor activity of MHY2245, a new synthetic SIRT inhibitor, on human ovarian cancer cells. We found that MHY2245 exhibited potent cytotoxicity to SKOV3 cells in a time- and concentration-dependent manner. The cytotoxicity of MHY2245 (IC50=0.32 µM) was higher than that of doxorubicin (DOX, IC50=1.38µM) against SKOV3 cells. MHY2245 significantly inhibited SIRT1 enzyme activity, reduced the expression of SIRT1, increased cell cycle arrest at G2/M phase, and induced apoptotic cell death in SKOV3 cells via expression of cytochrome c, cleaved-PARP, cleaved caspase-3, and Bax. This might be associated with blocking of the pyruvate kinase M2 (PKM2)/mTOR pathway. MHY2245 also inhibited tumor growth and reduced tumor size when SKOV3 cells were transplanted into nude mice. Our results indicate that MHY2245 exerts antitumor activity against ovarian cancer cells by blocking the PKM2/mTOR pathway. We suggest that MHY2245 is a promising anticancer agent that disrupts ovarian cancer cell metabolism.

Nicotinamide Overcomes Doxorubicin Resistance of Breast Cancer Cells through Deregulating SIRT1/Akt Pathway

BACKGROUND AND PURPOSE

Breast cancer is one of the leading causes of cancer deaths in female worldwide. Doxorubicin represents the most common chemotherapy for breast cancer, whereas side effects and development of resistance impede its effect on chemotherapy. Nicotinamide (NAM), serves as the sirtuins' inhibitor, effectively suppressing various types of cancer. However, the effects of NAM on drug resistance of breast cancer are need to be fully investigated.

METHODS

Breast cancer doxorubicin-resistant cells MCF-7/ADR and doxorubicin-sensitive cells MCF-7 were applied in this study. Cell proliferation was assessed by CCK8 and colony-forming assays. Cell migration was evaluated by scratch test and transwell assay while cell apoptosis was measured by TUNEL analysis. Expression levels of SIRT1, phosphate Akt (P-Akt, Ser-473) and Akt were measured using western blot analysis. The interrelation between SIRT1 and Akt was investigated by co-immunoprecipitation assay.

RESULTS

Treatment of nicotinamide combined with doxorubicin effectively inhibited cell growth, suppressed cell migration, and promoted cell apoptosis of MCF7/ADR cells. Mechanistically, nicotinamide translocated SIRT1 from the cell nucleus to cytoplasm, dissociated the connection between SIRT1 and Akt, and consequently decreased expressions of SIRT1, and P-Akt, thereby inhibiting the growth of MCF7/ADR cells.

CONCLUSIONS

Our results suggested that the value of nicotinamide is a potential therapeutic agent for breast cancer treatment through downregulating SIRT1/Akt pathway, leading to the valid management of breast cancer patients.

Epigenetic Reprogramming and Emerging Epigenetic Therapies in CML

Chronic myeloid leukemia (CML) is a hematopoietic stem cell disorder characterized by BCR-ABL1, an oncogenic fusion gene arising from the Philadelphia chromosome. The development of tyrosine kinase inhibitors (TKIs) to overcome the constitutive tyrosine kinase activity of the BCR-ABL protein has dramatically improved disease management and patient outcomes over the past 20 years. However, the majority of patients are not cured and developing novel therapeutic strategies that target epigenetic processes are a promising avenue to improve cure rates. A number of epigenetic mechanisms are altered or reprogrammed during the development and progression of CML, resulting in alterations in histone modifications, DNA methylation and dysregulation of the transcriptional machinery. In this review these epigenetic alterations are examined and the potential of epigenetic therapies are discussed as a means of eradicating residual disease and offering a potential cure for CML in combination with current therapies.

SIRT1: a potential tumour biomarker and therapeutic target

SIRT1, which is highly homologous to yeast silent information regulator 2, has recently garnered tremendous attention because of its various regulatory effects in several pathological conditions. Numerous studies have found that SIRT1 is highly expressed in a broad range of tumours compared with the paracancerous tissue. However, the role of SIRT1 in malignancies has yet to be systematically elucidated, and its use as a promising biomarker or therapeutic target for tumours has not been well-reported. Herein, we focus on the roles of SIRT1 in cancers and summarise the potential use of SIRT1 as a promising tumour biomarker or therapeutic target.

Dual Tumor Suppressor and Tumor Promoter Action of Sirtuins in Determining Malignant Phenotype

Sirtuins (SIRTs), class III histone deacetylases, are differentially expressed in several human cancers, where they display both oncogenic and tumor-suppressive properties depending on cellular context and experimental conditions. SIRTs are involved in many important biological processes and play a critical role in cancer initiation, promotion, and progression. A growing body of evidence indicates the involvement of SIRTs in regulating three important tumor processes: epithelial-to-mesenchymal transition (EMT), invasion, and metastasis. Many SIRTs are responsible for cellular metabolic reprogramming and drug resistance by inactivating cell death pathways and promoting uncontrolled proliferation. In this review, we summarize current knowledge on the role of SIRTs in cancer and discuss their puzzling dual function as tumor suppressors and tumor promoters, important for the future development of novel tailored SIRT-based cancer therapies.

SIRT1 promotes formation of breast cancer through modulating Akt activity

The silent information regulation factor 1 (sirtuin Type 1, SIRT1), as a kind of NAD⁺ dependent class III histone deacetylation enzyme, has been found to be involved in tumor proliferation, invasion, and metastasis. The roles of SIRTl in breast cancer is multifaceted depending on its substrate from upstream or downstream signaling pathway. In this study, we sought to make clear the regulating effects of SIRT1 in breast cancer cells, and to explore the underlying mechanisms through which SIRT1 regulates breast cancer. First, our results showed that SIRT1 was significantly up-regulated in breast cancer tissues and cells, which correlated with histological grade, tumor size, as well as lymph node metastasis. Then we established SIRT1-overexpressed and SIRT1- knockdown breast cancer cell lines to investigate the functions of SIRT1 in regulating colony formation, cell proliferation, cell cycle, cell apoptosis and migration. We found that overexpression of SIRT1 significantly promoted breast cancer growth both in vitro and in vivo, whereas knockdown of SIRT1 inhibited these phenotypes. Furthermore, SIRT1 was found to interact with Akt directly, consequently promoting the activity of Akt in breast cancer cells in vitro and positively correlating with expression of Akt, P-Akt, in breast cancer tissues in vivo. Down regulation the activity of Akt partially weakened the proliferative effect mediated by SIRT1. Taken together, our results demonstrated SIRT1's tumor promotion function and potential mechanisms in breast cancer, thus providing valuable therapeutic targets for breast cancer.

SIRT1 overexpression is an independent prognosticator for patients with esophageal squamous cell carcinoma

BACKGROUND

Sirtuin 1 (SIRT1) regulates DNA repair and metabolism by deacetylating target proteins. SIRT1 may be oncogenic because its overexpression has been detected in many cancers. The aim of the present study was to clarify the prognostic role of SIRT1 in patients with esophageal squamous cell carcinoma (ESCC) and evaluate the effect of SIRT1 inhibitor in vitro.

METHODS

The expression of SIRT1 was evaluated immunohistochemically in 155 surgically resected ESCC and the staining results were evaluated semiquantitatively by the Immunoreactive Scoring System. The clinical features and treatment outcome were analyzed. The effect of SIRT1 inhibitor, SIRT 1 inhibitor IV, (S)-35, was investigated in vitro on ESCC cell lines.

RESULTS

The expression of SIRT1 on ESCC did not correlate with age, gender, tumor location, stage, T classification, N classification, surgical margin or histology. Univariate analysis showed that SIRT1 overexpression was associated with inferior overall survival (P = 0.004) and disease-free survival (P = 0.004). In multivariate comparison, SIRT1 overexpression remained independently associated with worse overall survival (P = 0.009, hazard ratio = 1.776) and disease-free survival (P = 0.017, hazard ratio = 1.642). In cell lines, SIRT1 inhibitor inhibited ESCC growth.

CONCLUSIONS

Our study suggests that SIRT1 overexpression is an independent prognosticator for patients with ESCC and the SIRT1 inhibitor suppressed cell proliferation of ESCC cell lines. Our findings suggest that inhibition of SIRT1 signaling may be a promising novel target for ESCC.

Non ABL-directed inhibitors as alternative treatment strategies for chronic myeloid leukemia

The introduction of ABL Tyrosine Kinase Inhibitors (TKIs) has significantly improved the outcome of Chronic Myeloid Leukemia (CML) patients that, in large part, achieve satisfactory hematological, cytogenetic and molecular remissions. However, approximately 15-20% fail to obtain optimal responses according to the current European Leukemia Network recommendation because of drug intolerance or resistance.Moreover, a plethora of evidence suggests that Leukemic Stem Cells (LSCs) show BCR-ABL1-independent survival. Hence, they are unresponsive to TKIs, leading to disease relapse if pharmacological treatment is discontinued.All together, these biological events generate a subpopulation of CML patients in need of alternative therapeutic strategies to overcome TKI resistance or to eradicate LSCs in order to allow cure of the disease.In this review we update the role of "non ABL-directed inhibitors" targeting signaling pathways downstream of the BCR-ABL1 oncoprotein and describe immunological approaches activating specific T cell responses against CML cells.

The impact of Mir-9 regulation in normal and malignant hematopoiesis

MicroRNA-9 (MiR-9) dysregulation has been observed in various cancers. Recently, MiR-9 is considered to have a part in hematopoiesis and hematologic malignancies. However, its importance in blood neoplasms is not yet well defined. Thus, this study was conducted in order to assess the significance of MiR-9 role in the development of hematologic neoplasia, prognosis, and treatment approaches. We have shown that a large number of MiR-9 targets (such as FOXOs, SIRT1, CCND1, ID2, CCNG1, Ets, and NFkB) play essential roles in leukemogenesis and that it is overexpressed in different leukemias. Our findings indicated MiR-9 downregulation in a majority of leukemias. However, its overexpression was reported in patients with dysregulated MiR-9 controlling factors (such as MLLr). Additionally, prognostic value of MiR-9 has been reported in some types of leukemia. This study generally emphasizes on the critical role of MiR-9 in hematologic malignancies as a prognostic factor and a therapeutic target.

Hypoxia-inducible factor 1 alpha promotes cancer stem cells-like properties in human ovarian cancer cells by upregulating SIRT1 expression

Ovarian cancer have a poor overall survival rate in patients, and late disease presentation and chemoresistance are the main factors that lead to the mortality of ovarian cancer. Cancer stem cells (CSCs), a small subpopulation of cancer cells, have been associated with resistance to chemo- and radio-therapy in cancer treatment. Hypoxia is a common characteristic of many malignant tumors, and increased HIF-1α expression predicts the poor prognosis of ovarian cancer. In this study, we reported the relationship between hypoxia and cancer stem cells-like properties in human ovarian cancer cell lines SKOV3 and HO8910, we found that hypoxia induced cancer stem cells-like properties in ovarian cancer cells. Moreover, SIRT1 was found to be the downstream target gene of HIF-1α, which was involved in the promotion of cancer stem cells-like features in ovarian cancer cells by hypoxia, and NF-κB signaling pathway was involved in hypoxia-induced SIRT1 up-regulation. Our results hinted that HIF1α and SIRT1 might serve as potential therapeutic targets for ovarian cancer.

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.

Over-expression of Sirt1 contributes to chemoresistance and indicates poor prognosis in serous epithelial ovarian cancer (EOC)

Ovarian cancer is the most lethal malignancy in female patients, and chemoresistance is the major contribution to low over survival rate. We aim to investigate the correction between Sirt1 expression and chemoresistance in serous epithelial ovarian cancer (EOC) and prognosis significance of Sirt1. Immunochemistry was used to determine the location pattern and expression of Sirt1 in a total of 63 serous EOC patients (28 cases of chemoresistance patients and 35 chemosensitive).The relationship between Sirt1 expression and clinicopathological features of serous EOC was analyzed. Univariate analysis and multifactor logistic regression analysis were applied to investigate risk factor for chemoresistance. Cox proportional hazards regression model and Kaplan-Meier survival analysis were applied to determine the prognosis factor and survival time. Immunohistochemistry proved that over-expression of nuclear Sirt1 was related to chemoresistance (P = 0.039). Multivariate logistic regression analysis proved that the nuclear expression of Sirt1 (P = 0.018) and the lymph node metastasis (P = 0.037) was independent risk factors for chemoresistance in serous epithelial ovarian cancer. Multivariate Cox regression result indicated that expression of Sirt1 (P = 0.026, RR 2.434, 95 % CI 1.109-5.339) and stage (P = 0.005, RR 2.366, 95 % CI 1.288-4.345) was independent prognostic factors. Kaplan-Meier analysis showed that the survival rate is significantly decreased in the Sirt1 highly expressed group. Western blot result showed that the protein level of Sirt1 was significantly higher in chemoresistant group compared with in sensitive group. In conclusion, our results proved that over-expression of Sirt1 could play an important role in chemoresistance of serous EOC and could be a prognosis indicator for the patient's survival outcome.

CD150(-) Side Population Defines Leukemia Stem Cells in a BALB/c Mouse Model of CML and Is Depleted by Genetic Loss of SIRT1

Leukemia stem cells (LSCs) of chronic myeloid leukemia (CML) are refractory to tyrosine kinase inhibitor treatment, persist in the residual disease, and are important source for disease recurrence. Better understanding CML LSCs will help devise new strategies to eradicate these cells. The BALB/c mouse model of CML using retroviral bone marrow transduction and transplantation is a widely used mouse model system for CML, but LSCs in this model are poorly characterized. Here, we show that lineage negative CD150(-) side population (CD150(-)SP), but not CD150(+)SP, are CML LSCs in this model, although both CD150(-)SP and CD150(+)SP cells are enriched for long-term hematopoietic stem cells in normal BALB/c mice. We previously showed that BCR-ABL transformation activates protein lysine deacetylase SIRT1 and inhibition of SIRT1 sensitizes CML stem/progenitor cells to tyrosine kinase inhibitors by acetylating and activating p53. In this study, we demonstrate that SIRT1 homozygous knockout substantially reduces CD150(-)SP CML LSCs, and compromises the maintenance of CML LSCs in the BALB/c model. We identified several molecular alterations in CD150(-)SP LSCs that included the elevated expression of cyclin-dependent kinase Cdk6 facilitating LSC activation and significantly reduced p53 expression. SIRT1 knockout suppressed Cdk6 expression and likely increases p53 protein functions through deacetylation without increasing its expression. Our results shed novel insight into CML LSCs and support a crucial role of SIRT1 in CML LSCs. Our study also provides a novel means for assessing new agents to eradicate CML LSCs.

Post transcriptional control of the epigenetic stem cell regulator PLZF by sirtuin and HDAC deacetylases

BACKGROUND

The transcriptional repressor promyelocytic leukemia zinc finger protein (PLZF) is critical for the regulation of normal stem cells maintenance by establishing specific epigenetic landscape. We have previously shown that CBP/p300 acetyltransferase induces PLZF acetylation in order to increase its deoxynucleotidic acid (DNA) binding activity and to enhance its epigenetic function (repression of PLZF target genes). However, how PLZF is inactivated is not yet understood.

RESULTS

In this study, we demonstrate that PLZF is deacetylated by both histone deacetylase 3 and the NAD+ dependent deacetylase silent mating type information regulation 2 homolog 1 (SIRT1). Unlike other PLZF-interacting deacetylases, these two proteins interact with the zinc finger domain of PLZF, where the activating CBP/p300 acetylation site was previously described, inducing deacetylation of lysines 647/650/653. Overexpression of histone deacetylase 3 (HDAC3) and SIRT1 is associated with loss of PLZF DNA binding activity and decreases PLZF transcriptional repression. As a result, the chromatin status of the promoters of PLZF target genes, involved in oncogenesis, shift from a heterochromatin to an open euchromatin environment leading to gene expression even in the presence of PLZF.

CONCLUSIONS

Consequently, SIRT1 and HDAC3 mediated-PLZF deacetylation provides for rapid control and fine-tuning of PLZF activity through post-transcriptional modification to regulate gene expression and cellular homeostasis.

SIRT1 expression is associated with poor prognosis of lung adenocarcinoma

Several studies have reported that the overexpression of Sirtuin 1 (SIRT1) was associated with poor prognosis in various human cancers. However, little is known regarding the prognostic value of SIRT1 in lung adenocarcinoma. Therefore, the aim of this study is to evaluate the role of SIRT1 in the prognosis of lung adenocarcinoma patients. Using a tissue microarray, we detected SIRT1 expression by immunohistochemistry in lung adenocarcinoma tissue, as well as in corresponding noncancerous tissues (NCTs). A high expression level of SIRT1 was observed in 74.7% (56/75) of patients with lung adenocarcinoma and 6.7% (5/75) of NCTs (P<0.001). SIRT1 expression was significantly associated with high pathological stage. Importantly, we found that SIRT1 expression was associated with worse overall survival in these lung adenocarcinoma patients (67.0 months vs 104.5 months; P=0.005). In addition, anaplastic lymphoma kinase, epidermal growth factor receptor, vascular endothelial growth factor (VEGF), and Survivin expression were evaluated by fluorescent in situ hybridization or immunohistochemistry, respectively. We found that VEGF and Survivin were both highly expressed in the lung adenocarcinoma tissues, as compared to NCTs. Moreover, the SIRT1 and VEGF expression statuses were significantly positively correlated (r=0.238, P=0.039), while SIRT1 and Survivin expression status were not significantly correlated (r=0.220, P=0.058). Correlation analysis showed a positive correlation between VEGF and Survivin expression (r=0.436, P<0.001). However, we found that VEGF and Survivin expression were not associated with the prognosis of lung adenocarcinoma patients (P=0.334; P=0.433, respectively). Taken together, our findings suggest that SIRT1 plays a role in the progression of lung adenocarcinoma and may be a significant prognostic indicator for lung adenocarcinoma patients.

Genetic events other than BCR-ABL1

The BCR-ABL1 oncoprotein is the cause of chronic myeloid leukemia and occurs as a consequence of the translocation t(9;22), a well-defined genetic event that results in the formation of the Philadelphia chromosome. While this genomic aberration is recognized to be the main culprit of the chronic phase of chronic myeloid leukemia, the natural clonal evolution of this myeloproliferative neoplasm involves the accumulation of secondary alterations through genomic instability. Thus, efforts to dissect the frequency and nature of the genomic events at diagnosis and at later stages are producing valuable insights into understanding the mechanisms of blastic transformation and development of resistance in chronic myeloid leukemia. The identification of alternative BCR-ABL1-dependent and BCR-ABL1-independent targets that sustain the survival of leukemic blasts and/or leukemia-initiating cells will facilitate the development of novel viable therapeutic options for patients who become resistant or intolerant to the currently available therapeutic options based on tyrosine kinase inhibitors.

Repression of SIRT1 promotes the differentiation of mouse induced pluripotent stem cells into neural stem cells

The use of transplanting functional neural stem cells (NSCs) derived from induced pluripotent stem cells (iPSCs) has increased for the treatment of brain diseases. As such, it is important to understand the molecular mechanisms that promote NSCs differentiation of iPSCs for future NSC-based therapies. Sirtuin 1 (SIRT1), a NAD(+)-dependent protein deacetylase, has attracted significant attention over the past decade due to its prominent role in processes including organ development, longevity, and cancer. However, it remains unclear whether SIRT1 plays a role in the differentiation of mouse iPSCs toward NSCs. In this study, we produced NSCs from mouse iPSCs using serum-free medium supplemented with retinoic acid. We then assessed changes in the expression of SIRT1 and microRNA-34a, which regulates SIRT1 expression. Moreover, we used a SIRT1 inhibitor to investigate the role of SIRT1 in NSCs differentiation of iPSCs. Data revealed that the expression of SIRT1 decreased, whereas miRNAs-34a increased, during this process. In addition, the inhibition of SIRT1 enhanced the generation of NSCs and mature neurocytes. This suggests that SIRT1 negatively regulated the differentiation of mouse iPSCs into NSCs, and that this process may be regulated by miRNA-34a.

SIRT1 expression is associated with the chemotherapy response and prognosis of patients with advanced NSCLC

Aim

The role of Sirtuin 1 (SIRT 1) in carcinogenesis is controversial. This study was to explore the association between the SIRT1 expression and the clinical characteristics, the responsiveness to chemotherapy and prognosis in Non-small cell lung cancer (NSCLC).

Methods

We enrolled 295 patients with inoperable advanced stage of NSCLC, namely, stage III (A+B) and IV NSCLC. All patients had received platinum-based chemotherapy after diagnosis and the chemotherapy response were evaluated. All patients were followed up for overall survival (OS) and progression free survival (PFS). Invitro, H292 cells were tranfected with SIRT1 small interfering RNA (siRNA). The cell biological behaviors and chemosensitivity to cisplatin treatment were studied. The invivo tumorgenesis and metastasis assays were performed in nude mice.

Results

We found that the SIRT1 expressions were significantly associated with the tumor stage, tumor size and differentiation status. Patients with high SIRT 1 expressions had a significantly higher chance to be resistant to chemotherapy than those with low SIRT 1 expression. Patients with high expression of SIRT1 had significantly shorter OS and DFS than those with low expression. Cox analyses confirmed that the SIRT 1 expression was a strong predictor for a poor OS and PFS in NSCLC patients underwent Platinum-based chemotherapy. Invitro studies revealed that the reduced expression SIRT 1 by siRNA technique significantly inhibited cell proliferation, migration and invasion. More importantly, SIRT1 si-RNA significantly enhanced the chemosensitivity of H292 cells to cisplatin treatment. The invivo tumorgenesis and metastasis assays showed that SIRT1 knockdown dramatically reduced the tumor volume and the metastatic ability in nude mice.

Conclusion

Collectively, our data suggest that the SIRT1 expression may be a molecular marker associated with the NSLCLC clinical features, treatment responsiveness and prognosis of advanced NSCLC.