Role Of Cystathionine Beta-synthase Research Articles

Role of cystathionine beta synthase in lipid metabolism in ovarian cancer.

Elevated lipid metabolism is implicated in poor survival in ovarian cancer (OC) and other cancers; however, current lipogenesis-targeting strategies lack cancer cell specificity. Here, we identify a novel role of cystathionine beta-synthase (CBS), a sulphur amino acid metabolizing enzyme highly expressed in several ovarian cancer cell lines, in driving deregulated lipid metabolism in OC. We examined the role of CBS in regulation of triglycerides, cholesterol and lipogenic enzymes via the lipogenic transcription factors SREBP1 and SREBP2. CBS silencing attenuated the expression of number of key enzymes involved in lipid synthesis (FASN and ACC1). Additionally CBS abrogates lipid uptake in OC cells. Gene silencing of CBS or SREBPs abrogated cellular migration and invasion in OC, while ectopic expression of SREBPs can rescue phenotypic effects of CBS silencing by restoring cell migration and invasion. Mechanistically, CBS represses SREBP1 and SREBP2 at the transcription levels by modulating the transcription factor Sp1. We further established the roles of both CBS and SREBPs in regulating ovarian tumor growth in vivo. In orthotopic tumor models, CBS or SREBP silencing resulted in reduced tumor cells proliferation, blood vessels formation and lipid content. Hence, cancer-selective disruption of the lipid metabolism pathway is possible by targeting CBS and, at least for OC, promises a profound benefit.

S6-5 Role of cystathionine-beta synthase and its product, hydrogen sulfide in cancer biology

In colorectal and ovarian cancer, increased production of hydrogen sulfide (H2S) from cystathionine-β-synthase (CBS) plays an important role in promoting cellular bioenergetics, proliferation and migration. Pharmacological inhibition or genetic silencing of CBS exerts antitumor effects in vitro and in vivo, and potentiates the efficacy of current standard-of-care anticancer therapeutics. In this four-part presentation, we will first summarize recently published studies documenting a critical role for CBS-dependent H2S production in cancer cell proliferation and tumorigenesis. Second, we will discuss the state-of-the-art of CBS activity modulation with special reference to allosteric CBS activators (such as S-adenosylmethionine) and pharmacological CBS inhibitors of various classes including the complex pharmacology of aminooxyacetic acid. Third, we will present new experimental evidence designed to reconcile a controversy in the literature regarding the apparently contradictory effects of H2S donors on cancer cell proliferation and survival. Finally, we will discuss current and future strategies for targeting cancer cell H2S-production in the development of novel anticancer therapies.

P17 Modulatory effect of S-adenyl-methionine, an allosteric activator of cystathionine-beta-synthase on the proliferation and bioenergetics of colon cancer cells: Mechanism of action

Previous studies reported that S-adenosyl- l -methionine (SAM), an allosteric activator of cystathionine-beta-synthase (CBS) increases the production of hydrogen sulfide (H2S) in isolated enzyme preparations. Given the multiple pharmacological effects of SAM, the goal of our study was to probe the specific role of CBS in the effects of SAM in HCT116 colon cancer cells. SAM (0.1 μM–3 mM) concentration-dependently increased CBS-mediated H2S production. The effect of SAM on cell proliferation (assessed real time for up to 24 h by xCELLigence) was time-dependent. SAM (0.1–3 mM) enhanced HCT116 cell proliferation at all concentrations tested in the first 12 h following treatment, but induced cell death/inhibition of proliferation thereafter (12–24 h). The short-term stimulatory effects of SAM were attenuated by stable CBS silencing. In contrast, the anti-proliferative effects of SAM were maintained in cells with CBS silencing. Short-term exposure of HCT116 cells to SAM (0.1–1 mM, 1 h) concentration-dependently increased the oxygen consumption and bioenergetic function of HCT116 cells, while longer-term exposures resulted in a suppression of these parameters at all concentrations of SAM tested. While the stimulatory effect of SAM on proliferation and bioenergetics were attenuated in cells with stable CBS silencing, the inhibitory effects of SAM were largely unaffected by it. Thus, CBS in colon cancer cells produces H2S in a regulated fashion. H2S, when produced at low-to-intermediate levels, serves as an endogenous cancer cell growth and bioenergetic factor. While the short-term inhibition of cell proliferation by high concentrations of SAM may be partially related to “over-stimulation” of CBS, the long-term inhibitory effects of SAM on cell proliferation and bioenergetics are mainly CBS-independent.

P24 Renal protection through CBS/H2S pathway in mammalian hibernation: A natural model of hypothermic organ preservation during cold ischemia and reperfusion

Hydrogen sulfide (H2S) can induce a hypometabolic, hibernation-like state in small mammals when given in sublethal concentrations. Hibernating animals undergo a repetitive cycle of cooling (torpor) and rewarming without reperfusion injury or other ill effects. Recently, we observed in the ductus deferens cells of the Syrian hamster (hibernating animal) that one of the protective mechanisms against hypothermia-rewarming injury consists of endogenous production of H2S through the enzyme cystathionine-beta-synthase (CBS). We also showed that endogenous H2S is highly produced during torpor in hibernating hamsters and less produced when metabolism is normalized. Therefore in this study, we investigated the role of CBS and H2S in the induction of torpor and renal protection by blocking the CBS enzyme during torpor in hamsters. Our results show that hamsters during hibernation are able to preserve their kidney integrity through activation of CBS enzyme leading to endogenous H2S production under the extreme physiological conditions of torpor. The results demonstrate profound protective effects of CBS/H2S pathway on survival, renal function, and inflammation during hibernation. These findings might have therapeutic potential to protect kidneys that suffer from hypoxia during transplantation, ischemia–reperfusion and other related clinical conditions.

Abstract 1882: Role of cystathionine beta-synthase in ovarian cancer growth, metastasis and drug sensitivity.

Abstract Hydrogen sulfide (H2S), the third gasotransmitter, has recently attracted a lot of attention for its cytoprotective action and role in angiogenesis. Dysregulation of the major enzymes which produces H2S namely, cystathionine beta synthase (CBS), cystathionine gamma lyase (CSE) and 3-mercaptopyruvate sulfurtransferase (3-MST) have also been implicated in a large number of pathological conditions that range from neurological disorders to cardiovascular diseases. Surprisingly, studies on the role of these enzymes in cancer is scarce, especially, that of CBS. Relapse with a drug resistant and aggressive phenotype is a common occurrence in ovarian cancer with an overall 5-year survival of approximately 30%. Here we report that, CBS, a key enzyme required for sulphur amino acid metabolism, plays a critical role in promoting ovarian cancer growth, metastasis and drug resistance. Overexpression of CBS was observed in a majority of ovarian cancer cell lines utilized in our study compared to normal ovarian surface epithelial cells. Silencing CBS in A2780 cells using siRNA or a CBS-specific inhibitor, aminooxyacetic acid reduced proliferation of ovarian cancer cells by dramatically reducing total glutathione levels, H2S levels and thereby enhancing oxidative stress. Downregulation of CBS reduced activation of NF-kB and upregulated p53 protein levels thereby inactivating the antioxidant network of the cells. A deeper insight into the intracellular localization of CBS by confocal fluorescence microscopy demonstrated a mitochondria specific distribution and silencing CBS caused mitochondrial superoxide accumulation that resulted in decreased mitochondrial respiration, reduced ATP production and increased ADP-to-ATP ratio. Furthermore, silencing CBS, augmented the activity of cisplatin in vitro in A2780 cells and in vivo in an orthotopic model of advanced ovarian cancer. Nanoliposomal delivery of CBS siRNA significantly reduced the number of tumor nodules in a chemoresistant orthotopic mouse model of ovarian cancer. To our knowledge, this is the first study demonstrating the importance of CBS in ovarian cancer progression and drug resistance and therefore is a viable target for future anti-cancer therapies. Citation Format: Sounik Saha, Sanjib Bhattacharyya, Karuna Giri, Ian R. Lanza, K. Sreekumar Nair, Nicholas B. Jennings, Rakesh Kumar, Anil K. Sood, Resham Bhattacharya, Priyabrata Mukherjee. Role of cystathionine beta-synthase in ovarian cancer growth, metastasis and drug sensitivity. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 1882. doi:10.1158/1538-7445.AM2013-1882

The Production of Transgenic Mice Expressing Human Cystathionine Beta-Synthase to Study Down Syndrome

Down syndrome (DS) is the most common genetic cause of significant cognitive disability. We hypothesize that by identifying metabolic alterations associated with cognitive impairment, it may be possible to develop medical or dietary interventions to ameliorate cognitive disabilities in persons with DS. Evidence suggests that one-carbon/transsulfuration (1C-TS) metabolism is abnormal in persons with DS. Cystathionine beta-synthase (CBS) plays a critical role in this metabolic system. The gene for CBS is on human chromosome 21, and there is evidence of elevated CBS enzyme activity in tissues and cells from individuals with DS. To analyze the possible role of CBS in Down syndrome, we have produced several lines of transgenic mice expressing the human CBS gene. We describe the use of Florescence Situ Hybridization (FISH) analysis to characterize the transgene insertion site for each line. Our initial expression analysis of each transgenic line by RT-PCR shows that the tissue specificity of human CBS mRNA levels in these mice may differ from the tissue specificity of mouse CBS mRNA levels in the same animals. These mice will be invaluable for assessing the regulation of the CBS gene and the role of CBS in cognition. They can also be used to develop therapies that target abnormalities in 1C-TS metabolism to improve cognition in persons with DS.