Evidence for a Common Mechanism of SIRT1 Regulation by Allosteric Activators

Article (PDF Available)inScience 339(6124):1216-9 · March 2013with117 Reads
DOI: 10.1126/science.1231097 · Source: PubMed
Abstract
A molecule that treats multiple age-related diseases would have a major impact on global health and economics. The SIRT1 deacetylase has drawn attention in this regard as a target for drug design. Yet controversy exists around the mechanism of sirtuin-activating compounds (STACs). We found that specific hydrophobic motifs found in SIRT1 substrates such as PGC-1α and FOXO3a facilitate SIRT1 activation by STACs. A single amino acid in SIRT1, Glu230, located in a structured N-terminal domain, was critical for activation by all previously reported STAC scaffolds and a new class of chemically distinct activators. In primary cells reconstituted with activation-defective SIRT1, the metabolic effects of STACs were blocked. Thus, SIRT1 can be directly activated through an allosteric mechanism common to chemically diverse STACs.
ROS is also problematic. According to our data,
thiourea mildly inhibits cell growth (Fig. 1B),
indicating that this compound may have non-
specific effects, such as slowing down cell meta-
bolism, which would lead to increased tolerance
to killing. Indeed, we observed protective effect
of thiourea from antibiotic killing even under
anaerobic conditions (fig. S5). Reports of mu-
tants in the TCA cycle being more resistant to
killing could similarly result from these cells
having a slower metabolism. Finally, the use of
HPF as a detector of ROS is only valid if this
dye is a specific detector. However, we find that
antibiotics cause a shift in HPF fluorescence
under anaerobic conditions (fig. S6). Dying cells
apparently produce some products to which HPF
responds.
Taken together, our results show that killing
by antibiotics is unrelated to ROS production. This
finding will refocus efforts on unanswered ques-
tions on the mechanism of killing by antibiotic s.
For example, we do not know how b-lactams
induce autolysis, nor how exactly mistranslation
caused by aminoglycosides leads to cell death.
Better understanding of cell death will guide the
development of advanced cures to treat recalci-
trant infectious diseases (23).
References and Notes
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217 (1997).
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(2005).
23. K. Lewis, Nature 485,439(2012).
Acknowledgments: The authors thank V. Isabella for helpful
discussion of the manuscript. This work was supported by
NIH grant T-R01AI085585-01 and by Army Research Office
grants W9911NF-09-1-0265 and 55631-LS-RIP.
Supplementary Materials
www.sciencemag.org/cgi/content/full/339/6124/1213/DC1
Materials and Methods
Figs. S1 to S6
Reference (24)
13 November 2012; accepted 24 January 2013
10.1126/science.1232688
Evidence for a Common
Mechanism of SIRT1 Regulation
by Allosteric Activators
Basil P. Hubbard,
1
Ana P. Gomes,
1,2
Han Dai,
3
Jun Li,
1
April W. Case,
3
Thomas Considine,
3
Thomas V. Riera,
3
Jessica E. Lee,
4
Sook Yen E,
4
Dudley W. Lamming,
1
* Bradley L. Pentelute,
5
Eli R. Schuman,
3
Linda A. Stevens,
6
Alvin J. Y. Ling,
1
Sean M. Armour,
1
Shaday Michan,
1
Huizhen Zhao,
7
Yong Jiang,
7
Sharon M. Sweitzer,
7
Charles A. Blum,
3
Jeremy S. Disch,
3
Pui Yee Ng,
3
Konrad T. Howitz,
8
Anabela P. Rolo,
2,9
Yoshitomo Hamuro,
4
Joel Moss,
6
Robert B. Perni,
3
James L. Ellis,
3
George P. Vlasuk,
3
David A. Sinclair
1,10
§
A molecule that treats multiple age-related diseases would have a major impact on global health
and economics. The SIRT1 deacetylase has drawn attention in this regard as a target for drug
design. Yet controversy exists around the mechanism of sirtuin-activating compounds (STACs).
We found that specific hydrophobic motifs found in SIRT1 substrates such as PGC-1a and FOXO3a
facilitate SIRT1 activation by STACs. A single amino acid in SIRT1, Glu
230
,locatedinastructured
N-terminal domain, was critical for activation by all previously reported STAC scaffolds and a
new class of chemically distinct activators. In primary cells reconstituted with activation-defective
SIRT1, the metabolic effects of STACs were blocked. Thus, SIRT1 can be directly activated
through an allosteric mechanism common to chemically diverse STACs.
T
he nicotina mide adenine dinucleotide
(NAD
+
)dependent deacetylase SIRT1
is implicated in the prevention of many
age-related diseases such as cancer, Alzhei-
mersdisease,andtype2diabetes(1). At the
cellular level, SIRT1 controls DNA repair and
apoptosis, circadian clocks, inflammatory path-
ways, insulin secretion, and mitochondrial bio-
genesis (2, 3).
Naturally occurring STACs such as resveratrol
(4)andchemicallyunrelatedsyntheticSTACs
activate SIR T 1 in vitro by lowering its peptide
Michaelis constant (K
M
)andproducepharma-
cological changes consistent with SIR T1 activa-
tion (47). However , the legitimacy of STACs as
direct SIR T1 activators has been widely debated.
In previous studies, STACs increased SIR T1 ac-
tivity toward fluorophore-tagged substrates but
not toward corresponding nontagged peptides
(811). One explanation was that STACs were
bin d in g to the fluo r o p ho r e - li n k e d su b s t ra t e , w hi c h
would not occur in vivo (10). Alternatively, the
fluorescent groups might mimic a property of
natural substrates. Given that the fluorophores
used in previous studies are bulky and hydro-
phobic (4, 5), we tested whether these moieties
might substitute for hydrophobic amino acids
in endogenous substrates.
We used a SIRT1 activity assay whereby the
reaction product nicotinamide was converted to
1-alkylthiosubstituted isoindoles via the nicotin-
amidase PNC1 (12)andortho-phthalaldehyde
(OPT) (13)(fig.S1,AtoE).Asecondassaymea-
sured the SIRT1 product O-acetyl adenosine
diphosphate ribose (OAcADPR) by mass spec-
trometry (14)(fig.S2,AtoE).
AseriesofSTACs,includingSTAC-1(SRT1460)
(5)andSTAC-2[compound22in(15)] (fig. S3),
activated SIRT1 with an aminomethylcoumarin
(AMC)tagged peptide serving as a substrate via
apeptideK
M
-lowering mechanism, similar to the
action of resveratrol (fig. S4, A to C, and tables
S1 and S2) (4). The AMC moiety mediated ac-
tivation only when it was directly adjacent to
the acetylated Lys
9
of histone 3 (H3K9) at the
+1 position (16); this finding demonstrates that the
fluorophore has a positional requirement (Fig. 1A
and fig. S5A). The fluorophore moieties at
1
Department of Genetics, Harvard Medical School, Boston,
MA 02115, USA.
2
Center for Neurosciences and Cell Biology,
Department of Life Sciences, University of Coimbra, Coimbra
3004-517, Portugal.
3
Sirtris, a GSK Company, Cambridge , MA
02139, USA.
4
ExSAR Corporation, Monmouth Junction, NJ
08852, USA.
5
Department of Chemistry, Massachusetts Insti-
tute of Technology, Cambridge, MA 02139, USA.
6
NIH Car-
diovascular and Pulmonary Branch/National Heart, Lung and
Blood Institute, Bethesda, MD 20892, USA.
7
GlaxoSmithKline,
Collegeville, PA 19426, USA.
8
BIOMOL Research Laboratories
Inc. , Plym o ut h Mee ti n g, PA 194 62 , USA .
9
Department of Biol-
ogy, University of Aveiro, Aveiro 3810-193, Portugal.
10
Depart-
ment of Pharmacology, University of New South Wales, Sydney,
NSW 2052, Australia.
*Present address: Whitehead Institute for Biomedical Research,
Cambridge, MA 02142, USA.
Present address: Instituto Nacional de Geriatría, Institutos
Nacionales de Salud , xico D.F. 04510, xico.
Present address: Reaction Biology Corporation, Malvern,
PA 19355, USA.
§To whom correspondence should be addressed. E-mail:
david_sinclair@hms.harvard.edu
8MARCH2013 VOL339 SCIENCE www.sciencemag.org1216
REPORTS
positions +1 (4)or+6(5)weredispensableif
replaced with naturally occurring hydrophobic
amino acids (15)(Fig.1Bandfig.S5B).
We then tested whether native peptide se-
quences might also support activation (1724).
Sequences from two SIRT1 substrates supported
STAC-mediated activation: mouse peroxisome
proliferatoractivated receptor g coactiv ator
1a Lys
778
(PGC-1aK778) (22)andhumanfork-
head box O3a protein L ys
290
(FOXO3a-K290)
(19)(Fig.1C).STAC-mediatedactivationwas
dose-dependent (Fig. 1D), and relative activation
was similar between the SIR T1 assays (fig. S5C).
Isothermal titration calorimetry (ITC) did not
detect binding between saturating amounts of
PGC-1a peptide (2 mM) and STAC-1 (100 mM)
or STAC-2 (50 mM), arguing against activation
driven solely by substrate enhancement (fig. S6,
AandB)(15). Kinetic analysis of SIRT1 ac-
tivation by STAC-2 with the FOXO3a-K290
substrate revealed that rate enhancement was
mediated primarily through a lowering of pep-
tide K
M
(fig. S6C). Thus, the mechanism of
activation appeared to be independent of the
substrate used.
The PGC-1aK778 peptide contains aromat-
ic, hydrophobic amino acids at the +1 and +6
positions (relative to the acetylated lysine), as
does the FOXO3a-K290 peptide at position +1.
Alanine substitution of either the T yr at the +1
position or the Phe at the +6 position of the PGC-
1a peptide reduced activation, and substitution
of bo th abol i s he d acti v a t ion completely (Fig. 2A).
Similarly, for FOXO3a, substitution of the Trp
at the +1 position blocked activation (Fig. 2B),
but substitution of several N-terminal residues
did not (Fig. 2, A and B). A global search of nu-
clear acetylated proteins, conforming to the
sequences X
6
-K(Ac)-{Y,W,F}-X
5
,X
6
-K(Ac)-
X
5
-{Y,W, F} (16), and the union of the two sets,
identified more than 400 sequences (fig. S7A).
We t es t ed f iv e o f t h e se n at i v e s e q u en c e s and
found that three of them supported activation:
metallothionein-like 5 (MTL5), peptidylprolyl
isomerase A (PPIA), and eukaryotic translation
initiation factor 2a (eIF2a)(25)(fig.S7B).
An alternative peptide sequence from FOXO3a
(encompassing L ys
242
)wassequentiallyaltered
to resemble the FOXO3a-K290 sequence. Sub-
stitution of the Ser at +1 with Trp did not impart
the ability to activate (fig. S7C) unless in com-
bination with a Pro substitution at the +2 position
(fig. S7C). Thus, a hydrophobic residue at the
+1 position is necessary but not sufficient for
activation.
Fig. 2. Substrate sequence requirements and regions on SIRT1 necessary for
activation. (A and B)SIRT1activationbySTAC-2onpeptidesderivedfromPGC-
1aK778 (A) and FOXO3a-K290 (B) as measured by PNC1-OPT assay; data are
means T SEM (n =3).(C)Biochemicalscreenforactivation-compromisedmutants.
Abacterialexpressionplasmid(pET28a)carryingtheSIRT1genewasmutagenized
and used to generate recombinant SIRT1 proteins that were screened for activity in
the presence or absence of resveratrol using an AMC-based assay. (D)Activationof
wild-type SIRT1, E230K, and E230A mutants by 40 mMresveratrol,50mMSTAC-1,
5 mMSTAC-2,5mMSTAC-3,and10mMSTAC-4asmeasuredbyanAMCassay;
data are means T SD (n =3).Dimethylsulfoxide(DMSO)wasusedasacontrol.
Fig. 1. SIRT1 activation by STACs on native peptide sequences. (A)SIRT1activationby50m MSTAC-1
or 5 mM STAC-2 with peptides bearing an AMC moiety at the indicated positions, where X
n
represents
the number of amino acids between the acetylated lysine and the AMC. (B) SIRT1 activation by STACs
on hydrophobic patch peptides. Complete amino acid sequences of peptides bearing tryptophan (W)
or tryptophan and alanine substitutions (WAW) are provided in the supplementary materials. (C)
SIRT1 activation on native peptide sequences of known targets (detailed in the supplementary
materials). (D) Dose-response curves for STAC-2 as measured by PNC1-OPT assay; data are means T
SEM (n =3).
www.sciencemag.org SCIENCE VOL 339 8 MARCH 2013
1217
REPORTS
These data were consistent with an allosteric
mechanism of SIR T1 activation (4, 15). To elu-
cidate the determinants of activation in SIRT1,
we screened for SIRT1 mutant proteins lacking
activation (Fig. 2C). The ability of SIR T1 to be
activated by resveratrol was attenuated in one
mutant that substituted a lysine for a glutamate
at position 230 (E230K), whether an AMC-tagged
substrate (Fig. 2D) or a natural amino acid sub-
strate was used (fig. S8A). Substitution of Glu
230
with L y s or Ala attenuated SIRT1 activation by
117 chemically diverse ST ACs, independent of
the substrate used (Fig. 2D, Fig. 3, A to D, fig.
S8, B and C, and tables S3 and S4).
Glu
230
is immediately N-terminal to the cat-
alytic core of SIRT1 and is conserved from flies
to humans (fig. S8D). The E230K substitution
did not impair the basal catalytic activity of
SIRT1, nor did it significantly alter the maxi-
mum velocity of reaction (V
max
), the Michaelis
constant for NAD
+
(K
MNAD
+
), or the K
M
for
several peptides (fig. S9, A to E) or the median
inhibitory concentration (IC
50
)valuesforseveral
SIRT1 inhibitors (fig. S10, A to E and table S5).
Secondary structural eleme nt s, therm al dena tu r -
ation profiles (fig. S11, A to C and table S6),
melting temperatures (fig. S12, A and B), and
intracellular localizationpatterns(fig.S13A)of
wild-type and SIR T1-E230K were also similar .
To examine the entire structure of SIRT1,
we used hydrogen-deuterium exchange mass
spectrometry (HDXMS). No changes in protein
dynamics were detected between wild-type and
SIR T1-E230K. The catalytic core domain showed
slow exchange, consistent with a well-defined
structure (fig. S14, A and B). The N and C
termini showed fast exchange (fig. S14A), ex-
cept for a small C-terminal region around resi-
due 650 recently implicated in the regulation
of SIRT1 activity (26, 27)andasmallrigid
N-terminal region, residues 190 to 244, encom-
passing Glu
230
(Fig. 3E and fig. S14A).
The variable median effective concentration
(EC
50
)/dissociation constant (K
d
) ratios indi-
cate that the majority of synthetic STACs do
not interact strongly with SIRT1 and likely
bind to a steady-state form such as the enzyme-
substrat e comple x (15). SIRT1 truncations of
the fir st 183 re sidue s did not disrupt STAC
binding, but truncations to residues 195 and
225 did, coincident with a loss of activation
(table S7), whereas the E230K substitution had
variable effects on STAC binding (fig. S15). T o-
gether, these data indicate that SIR T1 has a struc-
tured N-terminal domain that is required for
STAC binding that encompasses Glu
230
,anamino
acid critical for activation across a broad class
of STACs.
Resveratrol and synthetic STACs increase
mitochondrial function in a SIRT1-dependent
manner (2830). However, it is unclear whether
this is a direct or indirect effect of STACs on
SIR T1. We therefore reconstituted primary SIR T1
knockout (KO) myoblasts (30)withwild-type
mouse SIR T1 or mouse SIR T1-E222K (the mu-
rine equivalent of human SIR T1-E230K) (Fig. 4A
and fig. S16A). ST ACs increased mitochondri a l
mass and adenosine triphosphate (ATP) content in
wild-type but not SIRT1 KO myoblasts (Fig. 4,
B and C, and fig. S16B). In myoblasts carrying
SIR T1-E222 K, the effects of ST ACs on mitochon-
drial mass and ATP levels were also blocked
(Fig. 4, B and C, and fig. S16B). In SIRT1 KO
mouse embryonic fibroblasts (MEFs) recon-
stituted with SIR T1-E222K (fig. S17A), the ability
of ST ACs to increase mitochondrial mass, A TP ,
and mitochondrial DNA copy number was also
blocked (fig. S17, B to D, and fig. S18A). At
these concentrations, there was no evidence for
SIRT1-independent adenosine monophosphate
(AMP)activated protein kinase phosphorylation
(fig. S19A) (30)orinhibitionofphosphodiesterase
isoforms (table S8). These findings argue against
these pathways directly mediating the effects
of STACs.
The data presented here favor a mechanism
of direct assisted allosteric activation mediated
by an N-terminal activation domain in SIRT1
(fig. S20, A and B) that is responsible for at
least some of the physiological effects of ST ACs.
Thus, allosteric activation of SIR T1 by ST ACs
remain s a viabl e thera pe utic intervent ion strategy
for many diseases associated with aging.
Fig. 3. Effects of SIRT1-E230 substitutions on activation andidentificationofanorderedactivationdomain.(A and B)
Dose-response titrations of STAC-5 (A) and STAC-8 (B) on the activity of wild-type SIRT1 and E230 mutants with the
Trp 5-mer peptide serving as the substrate, as measured by mass spectrometrybased OAcADPR assay. The sequence of the Trp 5-mer peptide is included in
the supplementary materials. data are means T SD (n =3).(C and D)Relativeactivationbyachemicallydiverse,117-compoundset(25mM) using the Trp 5-mer
substrate for wild-type versus E230K (C) or wild-type versus E230A (D), as meas ured by OAcADP R assay (n =2).Theredlinerepresentsy = x correlation. (E)
HDXMS heat map of deute ration levels of wild-type (W) and SIR T1-E230K (E) N termini at six different time points (15 to 5000 s).
8MARCH2013 VOL339 SCIENCE www.sciencemag.org
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REPORTS
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16. Single-letter abbreviations for amino acid residues:
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K, Lys; L, Leu; M, Met; N, Asn; P, Pro; Q, Gln; R, Arg;
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Acknowledgments: Supported by the Glenn Foundation for
Medical Research, the Ellison Medical Foundation, the Juvenile
Diabetes Research Foundation, the United Mitochondrial
Disease Foundation, NIH and NIAID grants, an NSERC
fellowship (B.P.H.), the Portuguese Science and Techn ology
Foundation (A.P.G.), the Intramural Research Program, and
NIH/NHLBI (L.A.S. and J.M.). D.A.S. is a consultant and
inventor on patents licensed to Sirtris, a GSK company. H.D.,
A.W.C., T.C., T.V.R., E.R.S., H.Z., Y.J., S.M.S., C.A.B., J.S.D.,
P.Y.N., R.B.P., J.L.E., and G.P.V. are employees of Sirtris,
aGSKcompany.DedicatedtothememoriesofJanaPerniand
Harmon Rasnow. A patent application on the PNC1-OPT sirtuin
assay has been filed by Harvard Medical School with D.A.S.
and B.P.H. as inventors. Patent applications related to sirtuin
activators have been filed by Sirtris and Biomol. Natural Sirt1
activators will be provid ed upon request. Synthetic STACs are
provided under a material transfer agreement from Sirtris.
Supplementary Materials
www.sciencemag.org/cgi/content/full/339/6124/1216/DC1
Materials and Methods
Figs. S1 to S20
Tables S1 to S8
Reference (31)
4October2012;accepted18January2013
10.1126/science.1231097
Aire-Dependent Thymic Development of
Tumor-Associated Regulatory T Cells
Sven Malchow,
1
Daniel S. Leventhal,
1
Saki Nishi,
1
Benjamin I. Fischer,
1
Lynn Shen,
1
Gladell P. Paner,
1
Ayelet S. Amit,
1
Chulho Kang,
2
Jenna E. Geddes,
3
* James P. Allison,
3
Nicholas D. Socci,
4
Peter A. Savage
1
Despite considerable interest in the modulation of tumor-associated Foxp3
+
regulatory T cells
(T
regs
) for therapeutic benefit, little is known about the developmental origins of these cells
and the nature of the antigens that they recognize. We identified an endogenous population of
antigen-specific T
regs
(termed MJ23 T
regs
) found recurrently enriched in the tumors of mice
with oncogene-driven prostate cancer. MJ23 T
regs
were not reactive to a tumor-specific antigen but
instead recognized a prostate-associated antigen that was present in tumor-free mice. MJ23 T
regs
underwent autoimmune regulator (Aire)dependent thymic development in both male and
female mice. Thus, Aire-mediated expression of peripheral tissue antigens drives the thymic
development of a subset of organ-specific T
regs
,whicharelikelycooptedbytumorsdeveloping
within the associated organ.
R
egulatory T (T
reg
)cellsarecriticalforthe
prevention of autoimmunity , the mainte-
nance of immune homeostasis, and the
suppression of antitumor immune responses (1, 2).
For many human cancers, the density of T
regs
within tumor lesions is predictive of poor clinical
outcome (3), suggesting that T
regs
play a func-
tional role in cancer progression. In this study, we
set out to establish a tractable animal model in
which a single specificity of naturally occurring
tumor-associated T
regs
could be studied in the
context of a genetically driven mouse model of
autochthonous cancer . In order to identify an
endogenous tumor -associated T
reg
response, we
analyzed the immune response in TRAMP mice,
which develop prostatic adenocarcinoma because
of the transgenic expression of the model oncogene
SV40 T antigen in the prostate (4, 5). Unlike t he
prostates of tumor-free mice, which contain very few
Fig. 4. mSIRT1-E222Kdependent ef-
fects of STACs on mitochondrial-related
parameters in cells. (A)Full-lengthmurine
SIRT1 (mSIRT1) transcripts in wild-type
and primary myoblasts reconstituted with
wild-type mSIRT1 or mSIRT1-E222K. The
SIRT1 exon 3-4 junction (SIRT1 E3-4) and
18S ribsosomal RNA, as an internal con-
trol for loading, were detected by reverse
transcription polymerase chain reaction.
(B and C)Effectof25mMresveratrol(B)
or 1 mMSTAC-4(C)onmitochondrial
mass and ATP in primary myoblasts; data
are means T SEM (n = 6). *P <0.05,
**P <0.01(t test versus DMSO control).
1
Department of Pathology, University of Chicago, Chicago, IL
60637, USA.
2
Cancer Research Laboratory, University of California,
Berkeley, CA 94720, USA.
3
Department of Immunology, Howard
Hughes Medical Institute, Memorial Sloan-Kettering Cancer Cen-
ter, New York, NY 10021, USA.
4
Bioinformatics Core, Memorial
Sloan-Kettering Cancer Center, New York, NY 10021, USA.
*Present address: Department of Immunology, Harvard Medical
School, Boston, MA 02115, USA.
Present address: Department of Immunology, The University
of Texas MD Anderson Cancer Center, Houston, TX 77030, USA.
To whom correspondence should be addressed. E-mail:
psavage@bsd.uchicago.edu
www.sciencemag.org SCIENCE VOL 339 8 MARCH 2013 1219
REPORTS
    • "Recently, direct SIRT1 activation has been confirmed, and it has been shown that there are subtle structural and positional requirements to detect SIRT1 activation with some of its natural substrates (e.g., FOXO3a and PGC-1α) [104, 114]. Moreover, E230K or E230A SIRT1 mutation abolishes enzyme activation as well as binding of SRT compounds, suggesting an assisted allosteric activation mechanism in which the activators bind and stabilize the enzymesubstrate complex promoting the deacetylation reaction [104]. Lastly, the crystal structure of a SRT compound bound to an engineered minimally functional hSIRT1 has been reported, unambiguously confirming the direct allosteric activation of SIRT1 by small molecules [115]. "
    [Show abstract] [Hide abstract] ABSTRACT: Sirtuins are NAD+-dependent histone deacetylases regulating important metabolic pathways in prokaryotes and eukaryotes and are involved in many biological processes such as cell survival, senescence, proliferation, apoptosis, DNA repair, cell metabolism, and caloric restriction. The seven members of this family of enzymes are considered potential targets for the treatment of human pathologies including neurodegenerative diseases, cardiovascular diseases, and cancer. Furthermore, recent interest focusing on sirtuin modulators as epigenetic players in the regulation of fundamental biological pathways has prompted increased efforts to discover new small molecules able to modify sirtuin activity. Here, we review the role, mechanism of action, and biological function of the seven sirtuins, as well as their inhibitors and activators.
    Full-text · Article · Dec 2016
    • "One of the key enzymes of this class is SIRT1 [151] which can be activated by resveratrol. Although it is questionable how resveratrol acts on SIRT1⎯directly or indirectly (e.g., mediated by AMPK activation) [152, 153], resveratrol efficiency in cancer therapy has been shown in colon cancer cell lines (HCT116, Caco2). Treatment with resveratrol leads to a decrease in glucose uptake by cells and to an attenuation of the activity of glycolytic enzymes, Akt and mTORC1 activity, as well as VEGF (vascular endothelial growth factor) production. "
    [Show abstract] [Hide abstract] ABSTRACT: The main objective of anticancer treatment is the elimination of degenerated cells by the induction of programmed cell death. Various chemotherapy drugs and radiation are able to activate cell death mechanisms in tumors. However, unfortunately, monotherapy will always be insufficiently effective because of the variety and virulence of tumors, as well as their ability to develop resistance to drugs. Moreover, monotherapy might constrain many negative side effects. Therefore, the combination of different approaches and/or drugs will increase the efficiency of treatment. One such promising approach is the combination of nutrient restriction (NR) and various chemotherapeutic drugs. This approach may not only affect the autophagy but also influence apoptotic cell death. This review is focused on the potential of NR use in anticancer therapy, as well as the molecular mechanisms underlying this approach.
    Full-text · Article · May 2016
    • "Interestingly, the debate rose again about the specificity of these STACs for SIRT1 [104]. Recent research, however, has provided new evidence showing that these STACs, and even more potent new generations (STAC- 5, STAC-9, and STAC-10), are indeed SIRT1 activators [105, 106]. Although the mechanism of action of resveratrol and other STACs may still need to be further investigated, it is clear that they provide beneficial effects against age-related disease in vivo. "
    [Show abstract] [Hide abstract] ABSTRACT: Sirtuins are a conserved family of NAD-dependent protein deacylases. Initially proposed as histone deacetylases, it is now known that they act on a variety of proteins including transcription factors and metabolic enzymes, having a key role in the regulation of cellular homeostasis. Seven isoforms are identified in mammals (SIRT1–7), all of them sharing a conserved catalytic core and showing differential subcellular localization and activities. Oxidative stress can affect the activity of sirtuins at different levels: expression, posttranslational modifications, protein-protein interactions, and NAD levels. Mild oxidative stress induces the expression of sirtuins as a compensatory mechanism, while harsh or prolonged oxidant conditions result in dysfunctional modified sirtuins more prone to degradation by the proteasome. Oxidative posttranslational modifications have been identified in vitro and in vivo , in particular cysteine oxidation and tyrosine nitration. In addition, oxidative stress can alter the interaction with other proteins, like SIRT1 with its protein inhibitor DBC1 resulting in a net increase of deacetylase activity. In the same way, manipulation of cellular NAD levels by pharmacological inhibition of other NAD-consuming enzymes results in activation of SIRT1 and protection against obesity-related pathologies. Nevertheless, further research is needed to establish the molecular mechanisms of redox regulation of sirtuins to further design adequate pharmacological interventions.
    Full-text · Article · Jan 2016
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