Sweetening of Glutamine Metabolism in Cancer Cells by Rho GTPases Through Convergence of Multiple Oncogenic Signaling Pathways

Comment on: Lukey MJ, Greene KS, Erickson JW, et al. The oncogenic transcription factor c-Jun regulates glutaminase expression and sensitizes cells to glutaminase-targeted therapy. Nat Commun 2016;7:11321

Methylseleninic Acid Elevates REDD1 and Inhibits Prostate Cancer Cell Growth Despite AKT Activation and mTOR Dysregulation in Hypoxia

Methylseleninic acid (MSeA) is a monomethylated selenium metabolite theoretically derived from subsequent β-lyase or transamination reactions of dietary Se-methylselenocysteine that has potent antitumor activity by inhibiting cell proliferation of several cancers. Our previous studies showed that MSeA promotes apoptosis in invasive prostate cancer cells in part by downregulating hypoxia-inducible factor HIF-1α. We have now extended these studies to evaluate the impact of MSeA on REDD1 (an mTOR inhibitor) in inducing cell death of invasive prostate cancer cells in hypoxia. In both PTEN+ and PTEN- prostate cancer cells we show that MSeA elevates REDD1 and phosphorylation of AKT along with p70S6K in hypoxia. Furthermore, REDD1 induction by MSeA is independent of AKT and the mTOR inhibition in prostate cancer cells causes partial resistance to MSeA-induced growth reduction in hypoxia. Our data suggest that MSeA induces REDD1 and inhibits prostate cancer cell growth in hypoxia despite activation of AKT and dysregulation of mTOR

A Survey of Oxidative Paracatalytic Reactions Catalyzed by Enzymes That Generate Carbanionic Intermediates: Implications for ROS Production, Cancer Etiology, and Neurodegenerative Diseases

Enzymes that generate carbanionic intermediates often catalyze paracatalytic reactions with O2 and other electrophiles not considered “normal” reactants. For example, pyridoxal 5′-phosphate (PLP)—containing pig kidney dopa decarboxylase oxidizes dopamine with molecular O2 to 3,4-dihydroxyphenylacetaldehyde at about 1% of the rate at which it catalyzes nonoxidative dopa decarboxylation. The mutant Y332F enzyme, however, catalyzes stoichiometric conversion of dopa to 3,4-dihydroxyphenylacetaldehyde, suggesting that even minor structural changes may alter or initiate paracatalytic reactions catalyzed by certain enzymes. Carbanions generated by several thiamine diphosphate (ThDP)—dependent enzymes react with different electrophiles, transforming some xenobiotics and endogenous compounds into potentially biologically hazardous products. The detrimental effects of paracatalytic reactions may be greatly increased by cellular compartmentation of enzymes and intermediates. For example, in two of the the three multienzyme complexes involved in oxidative α-keto acid decarboxylation, paracatalytic reactions of the third component inactivate the first carbanion-generating component. In this review we provide an outline of carbanion-generating enzymes known to catalyze paracatalytic reactions. We also discuss the potential of some of these reactions to contribute to irreversible damage in cancer and neurodegeneration through disease-induced alterations in the metabolic state and/or protein structure

Cystamine and Cysteamine As Inhibitors of Transglutaminases In Vivo

Cystamine is commonly used as a transglutaminase inhibitor. This disulfide undergoes reduction in vivo to the aminothiol compound, cysteamine. Thus, the mechanism by which cystamine inhibits transglutaminase activity in vivo could be due to either cystamine or cysteamine, which depends on the local redox environment. Cystamine inactivates transglutaminases by promoting the oxidation of two vicinal cysteine residues on the enzyme to an allosteric disulfide, whereas cysteamine acts as a competitive inhibitor for transamidation reaction catalyzed by this enzyme. The latter mechanism is likely to result in the formation of a unique biomarker, N -(gamma-glutamyl)cysteamine that could serve to indicate how cyst(e)amine acts to inhibit transglutaminases inside cells and the body

Activation of NQO1 in NQO1*2 Polymorphic Human Leukemic HL-60 Cells by Diet-Derived Sulforaphane

BACKGROUND: The NAD(P)H: quinone oxidoreductase (NQO1) confers protection against semiquinones and also elicits oxidative stress. The C609T polymorphism of the NQO1 gene, designated NQO1*2, significantly reduces its enzymatic activity due to rapid degradation of protein. Since down regulation of NQO1 mRNA expression correlates with increased susceptibility for developing different types of cancers, we investigated the link between leukemia and the NQO1*2 genotype by mining a web-based microarray dataset, ONCOMINE. Phytochemicals prevent DNA damage through activation of phase II detoxification enzymes including NQO1. Whether NQO1 expression/activity in leukemia cells that carry the labile NQO1*2 genotype can be induced by broccoli-derived phytochemical sulforaphane (SFN) is currently unknown. METHODS AND RESULTS: The ONCOMINE query showed that: (1) acute lymphoblastic leukemia and chronic myelogenous leukemia are associated with reduced NQO1 levels, and (2) under-expressed NQO1 was found in human HL-60 leukemia cell line containing the heterozygous NQO1*2 polymorphism. We examined induction of NQO1 activity/expression by SFN in HL-60 cells. A dose-dependent increase in NQO1 level/activity is accompanied by upregulation of the transcription factor, Nrf2, following 1-10 μM SFN treatment. Treatment with 25 µM SFN drastically reduced NQO1 levels, inhibited cell proliferation, caused sub-G1 cell arrest, and induced apoptosis, and a decrease in the levels of the transcription factor, nuclear factor-κB (NFκB). CONCLUSIONS: Up to 10 μM of SFN increases NQO1 expression and suppresses HL-60 cell proliferation whereas ≥ 25 μM of SFN induces apoptosis in HL-60 cells. Further, SFN treatment restores NQO1 activity/levels in HL-60 cells expressing the NQO1*2 genotype

Application of Open-Access Databases to Determine Functional Connectivity Between Resveratrol-Binding Protein QR2 and Colorectal Carcinoma

Colorectal cancer (CRC) is a major cause of cancer-associated deaths worldwide. Recently, oral administration of resveratrol (trans-3,5,4\u27-trihydroxystilbene) has been reported to significantly reduce tumor proliferation in colorectal cancer patients, however, with little specific information on functional connections. The pathogenesis and development of colorectal cancer is a multistep process that can be categorized using three phenotypic pathways, respectively, chromosome instability (CIN), microsatellite instability (MSI), and CpG island methylator (CIMP). Targets of resveratrol, including a high-affinity binding protein, quinone reductase 2 (QR2), have been identified with little information on disease association. We hypothesize that the relationship between resveratrol and different CRC etiologies might be gleaned using publicly available databases. A web-based microarray gene expression data-mining platform, Oncomine, was selected and used to determine whether QR2 may serve as a mechanistic and functional biotarget within the various CRC etiologies. We found that QR2 messenger RNA (mRNA) is overexpressed in CRC characterized by CIN, particularly in cells showing a positive KRAS (Kirsten rat sarcoma viral oncogene homolog) mutation, as well as by the MSI but not the CIMP phenotype. Mining of Oncomine revealed an excellent correlation between QR2 mRNA expression and certain CRC etiologies. Two resveratrol-associated genes, adenomatous polyposis coli (APC) and TP53, found in CRC were further mined, using cBio portal and Colorectal Cancer Atlas which predicted a mechanistic link to exist between resveratrol→QR2/TP53→CIN. Multiple web-based data mining can provide valuable insights which may lead to hypotheses serving to guide clinical trials and design of therapies for enhanced disease prognosis and patient survival. This approach resembles a BioGPS, a capability for mining web-based databases that can elucidate the potential links between compounds to provide correlations of these interactions with specific diseases

Anticancer Activities of Resveratrol in Colorectal Cancer

Resveratrol (3,5,4′-trihydroxy-trans-stilbene) is a dietary polyphenolic phytochemical that has demonstrated health benefits such as cardioprotection, the prevention of neurodegeneration and chemoprevention. Resveratrol has shown great potential in the prevention and treatment of carcinomas and clinical trials support resveratrol as anticancer compound in colorectal carcinoma. Colorectal cancer remains a major cause of cancer-related deaths for both men and women in industrialized countries. Because of this widespread prevalence, identifying major risk factors and initiating colorectal screening procedures provide the distinct advantage for recognizing early disease and addressing treatable forms of CRC. Epidemiological studies of fruit and vegetable consumption in relationship to developing CRC have led to the notion that safe and inexpensive chemopreventive agents might be a valuable tool in diminishing the morbidity and mortality of CRC. While clinical trials and in vivo data show positive effects of resveratrol in CRC, the mechanism of action is relatively unclear. In this review, we will evaluate the current literature on the actions of resveratrol in CRC and provide a more mechanistic view of resveratrol in relationship with CRC

Retired A Stars: The Effect of Stellar Evolution on the Mass Estimates of Subgiants

Doppler surveys have shown that the occurrence rate of Jupiter-mass planets appears to increase as a function of stellar mass. However, this result depends on the ability to accurately measure the masses of evolved stars. Recently, Lloyd (2011) called into question the masses of subgiant stars targeted by Doppler surveys. Lloyd argues that very few observable subgiants have masses greater than 1.5 Msun, and that most of them have masses in the range 1.0-1.2 Msun. To investigate this claim, we use Galactic stellar population models to generate an all-sky distribution of stars. We incorporate the effects that make massive subgiants less numerous, such as the initial mass function and differences in stellar evolution timescales. We find that these effects lead to negligibly small systematic errors in stellar mass estimates, in contrast to the roughly 50% errors predicted by Lloyd. Additionally, our simulated target sample does in fact include a significant fraction of stars with masses greater than 1.5 Msun, primarily because the inclusion of an apparent magnitude limit results in a Malmquist-like bias toward more massive stars, in contrast to the volume-limited simulations of Lloyd. The magnitude limit shifts the mean of our simulated distribution toward higher masses and results in a relatively smaller number of evolved stars with masses in the range 1.0-1.2 Msun. We conclude that, within the context of our present-day understanding of stellar structure and evolution, many of the subgiants observed in Doppler surveys are indeed as massive as main-sequence A stars.Comment: Accepted to ApJ, 5 pages, 3 figures; changed title, reworded introduction and conclusion

HDAC8 and STAT3 Repress BMF Gene Activity in Colon Cancer Cells

Histone deacetylase (HDAC) inhibitors are undergoing clinical trials as anticancer agents, but some exhibit resistance mechanisms linked to anti-apoptotic Bcl-2 functions, such as BH3-only protein silencing. HDAC inhibitors that reactivate BH3-only family members might offer an improved therapeutic approach. We show here that a novel seleno-α-keto acid triggers global histone acetylation in human colon cancer cells and activates apoptosis in a p21-independent manner. Profiling of multiple survival factors identified a critical role for the BH3-only member Bcl-2-modifying factor (Bmf). On the corresponding BMF gene promoter, loss of HDAC8 was associated with signal transducer and activator of transcription 3 (STAT3)/specificity protein 3 (Sp3) transcription factor exchange and recruitment of p300. Treatment with a p300 inhibitor or transient overexpression of exogenous HDAC8 interfered with BMF induction, whereas RNAi-mediated silencing of STAT3 activated the target gene. This is the first report to identify a direct target gene of HDAC8 repression, namely, BMF. Interestingly, the repressive role of HDAC8 could be uncoupled from HDAC1 to trigger Bmf-mediated apoptosis. These findings have implications for the development of HDAC8-selective inhibitors as therapeutic agents, beyond the reported involvement of HDAC8 in childhood malignancy