An ultrasensitive photoelectrochemical assay for tumor necrosis factor-alpha based on hollow CdS cubes as a signal generator and NiCo2O4-Au as a signal extinguisher.

Sensitive detection of tumor necrosis factor-alpha (TNF-α) in human serum is beneficial for finding cancer patients early due to overexpressed TNF-α being related to some cancers. Here, a photoelectrochemical (PEC) aptasensor was constructed for ultrasensitive TNF-α assay based on the signal generator of hollow CdS cubes (H-CdS) and the signal extinguishing activity of NiCo2O4-Au. In this work, compared with traditional solid CdS, H-CdS could greatly promote the PEC signal because its hollow structure could accelerate the separation of photogenerated charges, which also possesses abundant active sites and high light absorption capability. Moreover, H-CdS can be prepared facilely with Cd-based Prussian blue analogs as the precursor. Meanwhile, NiCo2O4-Au was fabricated and utilized as a signal extinguisher. In the presence of TNF-α, NiCo2O4-Au could be introduced onto the H-CdS modified electrode, producing competitive consumption of the electron donor effect, the p-n semiconductor quenching effect, and the mimetic enzymatic catalytic precipitation effect, which all can significantly reduce the PEC signal. Based on the signal extinguishing activity of NiCo2O4-Au and the signal generator of H-CdS, TNF-α can be detected sensitively with a lower detection limit (0.63 fg mL-1) and a wide linear range (1 fg mL-1- to 1 ng mL-1), which may have a potential application in the PEC bioanalysis field and the disease diagnostics field.

Light-driven uranyl-organic frameworks used as signal-enhanced photoelectrochemical sensors for monitoring anthrax.

The semiconductor-like characteristics and light absorption ability of metal-organic frameworks (MOFs) make it have the potential for photoelectrochemical sensing. Compared with composite and modified materials, the specific recognition of harmful substances directly using MOFs with suitable structures can undoubtedly simplify the fabrication of sensors. Herein, two photosensitive uranyl-organic frameworks (UOFs) named HNU-70 and HNU-71 were synthesized and explored as the novel "turn-on" photoelectrochemical sensors, which can be directly applied to monitor the biomarker of anthrax (dipicolinic acid). Both sensors have good selectivity and stability towards dipicolinic acid with the low detection limits of 1.062 and 1.035 nM, respectively, which are far lower than the human infection concentration. Moreover, they exhibit good applicability in the real physiological environment of human serum, demonstrating a good application prospect. Spectroscopic and electrochemical studies show that the mechanism of photocurrent enhancement results from the interaction between dipicolinic acid and UOFs, which facilitates the photogenerated electron transport.

Colorimetric and Photocurrent-Polarity-Switching Photoelectrochemical Dual-Mode Sensing Platform for Highly Selective Detection of Mercury Ions Based on the Split G-Quadruplex-Hemin Complex.

Mercury ion (Hg2+) is one of the most harmful heavy metal ions with the greatest impact on public health. Herein, based on the excellent catalytic activity toward 3,3',5,5'-tetramethylbenzidine (TMB) and the strong photocurrent-polarity-switching ability to SnS2 photoanode of the split G-quadruplex-hemin complex, the magnetic NiCo2O4@SiO2-NH2 sphere-assisted colorimetric and photoelectrochemical (PEC) dual-mode sensing platform was developed for the Hg2+ assay. First, the amino-labelled single-stranded DNA1 (S1) was immobilized on NiCo2O4@SiO2-NH2 and then partly hybridized with another single-stranded DNA2 (S2). When Hg2+ was present, the thymine-Hg2+-thymine base pairs between S1 and S2 were formed, causing the formation of the split G-quadruplex in the presence of K+. After addition of hemin, the split G-quadruplex-hemin complex was obtained and effectually catalyzed the H2O2-mediated oxidation of TMB. Thus, the color and absorbance intensity of the TMB solution were changed, resulting in the visual and colorimetric detection of Hg2+. The linear response range is 10 pM to 10 nM, and the detection limit is 3.8 pM. Meanwhile, the above G-quadruplex-hemin complex effectively switched the photocurrent polarity of SnS2-modified indium tin oxide electrode, leading to the sensitive and selective PEC assay of Hg2+ with a linear response range of 5 pM to 500 nM and a detection limit of 2.3 pM. Moreover, the developed dual-mode sensing platform provided mutual authentication of detection results in different modes, effectively improving the assay accuracy and confidence, and may have a good potential application in highly sensitive, selective, and accurate determination of Hg2+ in environmental fields.

Highly Selective Photoelectrochemical Assay of Arsenate Based on Magnetic Co3O4-Fe3O4 Cubes and the Negative-Background Signal Strategy.

Water pollution presents a significant environmental concern on earth. Herein, due to the serious environmental harmfulness of arsenate [As(V)], an iron phthalocyanine (FePc)-induced switchable photocurrent-polarity platform was developed for highly selective assay of As(V). First, magnetic Co3O4-Fe3O4 cubes were obtained by calcination of the CoFe Prussian blue analogue and then functionalized with oligonucleotide (S1). In the presence of As(V), S1 could be released based on the stronger affinity between As(V) and Co3O4-Fe3O4 cubes. After magnetic separation by Co3O4-Fe3O4 cubes, the released S1 was used to trigger the catalytic hairpin assembly (CHA) and hybridization chain reaction, resulting in the formation of lots of G-quadruplex structures on the AgInS2/ITO electrode. Then, the capture of FePc by the G-quadruplex led to the switch of the photocurrent polarity of the AgInS2/ITO electrode from the anode to the cathode. Thus, As(V) was sensitively assayed with a low detection limit of 1.0 nM and a wide linear response range from 10 nM to 200 µM. This meets the detection requirement of the World Health Organization for the arsenic concentration in drinking water [less than 10 µg L-1 (130 nM)]. In addition, whether it was cationic or anionic interferents except phosphate (PO43-), only As(V) could generate the cathodic photocurrent, effectively avoiding the false-positive or false-negative results during As(V) assay. Interestingly, As(V) was also simultaneously separated from the detection system by Co3O4-Fe3O4 magnetic cubes. The proposed photoelectrochemical platform may have a great potential application for the selective detection of As(V) in environmental fields.

A label-free photoelectrochemical biosensor with ultra-low-background noise for lead ion assay based on the Cu2O-CuO-TiO2 heterojunction.

Herein, a label-free and ultra-low-background-noise PEC biosensor was developed for lead ion (Pb2+) assay based on the Cu2O-CuO-TiO2 heterojunction. By calcination of cupric ion (Cu2+) doped-titanium based metal organic framework (MOF) material (NH2-MIL-125), the Cu2O-CuO-TiO2 heterojunction was synthesized. With Pb2+, lots of DNA single strands (S1) could be released based on the Pb2+ assisted cyclic amplification strategy and hybridized with hairpin DNA (HP1) on the modified electrode. The exposed phosphate groups on S1 can adsorb Cu2O-CuO-TiO2 heterojunction, which results in a large cathode photocurrent. Due to the good photoelectric property of Cu2O-CuO-TiO2 and Pb2+-triggering cyclic amplification strategy, the constructed PEC biosensor achieves a wide linear detection range (10 fM - 1 µM) and a low detection limit (6.8 fM), which provides potential applications in ultrasensitive determination of Pb2+ in environmental water samples and organisms.

Highly Selective and Sensitive microRNA-210 Assay Based on Dual-Signaling Electrochemical and Photocurrent-Polarity-Switching Strategies.

Highly sensitive and selective microRNA (miRNA) assay is of great significance for disease diagnosis and therapy. Herein, a magnetic-assisted electrochemistry (EC)-photoelectrochemistry (PEC) dual-mode biosensing platform was developed for miRNA-210 detection based on dual-signaling EC and photocurrent-polarity-switching PEC strategies. Porous magnetic Fe3O4 octahedra with a large surface area were synthesized by calcining Fe-based metal-organic frameworks. Subsequently, the magnetic photoelectric materials (Fe3O4@CdS) were developed by the successive ionic layer adsorption and reaction method in Cd2+ and S2- solutions. Then, the self-assembled DNA nanoprisms contained three thiols/hanging arms that could capture miRNA-210 efficiently and were anchored to the Fe3O4@CdS octahedra via the Cd-S bond. When miRNA-210 was present, the double-stranded DNA concatemers [the self-assembled duplex helixes based on a pair of methylene blue (MB)-labeled single-stranded DNAs (AP1 and AP2) through the hybridization chain reaction and then intercalated with adriamycin (Dox) into their grooves] were connected with the Fe3O4@CdS-DNA nanoprisms. MB and Dox not only acted as the electrochemical probes but also synergistically switched the photocurrent polarity of the Fe3O4@CdS octahedra. Thus, miRNA-210 was assayed sensitively and selectively via the proposed EC-PEC dual-mode biosensing platform. Additionally, the abovementioned recognition steps occurred in a homogeneous system, and the effects of the impurities and interferences on the miRNA-210 assay could be easily avoided by magnetic separation due to the good magnetic properties of Fe3O4 octahedra. The proposed EC-PEC dual-mode biosensing platform showed a wide range of potential applications in bioanalysis and early diagnosis of disease.

A photocurrent-polarity-switching biosensor for highly selective assay of mucin 1 based on target-induced hemin transfer from ZrO2 hollow spheres to G-quadruplex nanowires.

Herein, a photocurrent polarity switching platform for highly selective assay of mucin 1 (MUC1) was developed based on target-induced hemin transfer from ZrO2 hollow spheres (ZrO2 HSs) to G-quadruplex nanowires (G wires). In this system, SiO2 spheres were used as templates to synthesize the uniform and mesoporous ZrO2 HSs. As nanocontainers, ZrO2 HSs could load hemin in its cavity via pores. Then, the aptamers of MUC1, as bio-gates, blocked the pores of ZrO2 HSs based on the specific binding of Zr4+ and the phosphate groups of aptamer. In the presence of MUC1, the aptamer could specifically recognize and bind with MUC1, and then leave away from the surface of ZrO2 HSs, which resulted in the opening of the bio-gates and releasing of hemin. Assisted with the G wires formed on the Au NPs/In2S3/ITO, the released hemin was captured on the electrode through the formation of hemin/G-quadruplex structure, leading to the switch of the photocurrent polarity of the electrode from anodic photocurrent to cathodic photocurrent. The proposed photoelectrochemical biosensor showed outstanding performance for MUC1 assay with high selectivity, wide linear response range (1 fg mL-1 -10 ng mL-1) and lower detection limit (0.48 fg mL-1). And the strategy could be easily extended to a triple-mode detection of MUC1 because the hemin/G-quadruplex structure was widely used in electrochemical and colorimetric methods as a hydrogen peroxide mimetic enzyme, which might provide wide applications in biological or clinical studies.

Sensitive Dual-Mode Biosensors for CYFRA21-1 Assay Based on the Dual-Signaling Electrochemical Ratiometric Strategy and "On-Off-On" PEC Method.

Herein, an electrochemical (EC)-photoelectrochemical (PEC) dual-mode biosensor was constructed for cytokeratin 19 fragment 21-1 (CYFRA21-1) assay based on the dual-signaling electrochemical ratiometric strategy and "on-off-on" PEC method. The indium tin oxide (ITO) electrode was modified by 3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA)@C60 and gold nanoparticles (Au NPs), and the double-stranded DNA composed of thiol/methylene blue (MB)-labeled single-stranded DNA (ssDNA) (S0-MB) and antibody/ferrocene (Fc)-labeled ssDNA (Ab1-S1-Fc) was immobilized on the Au NPs/PTCDA@C60/ITO electrode via the Au-S bond between Au NPs and thiol of S0-MB. With the help of another antibody-labeled ssDNA (Ab2-S2), the presence of CYFRA21-1 triggered a typical antigen-antibody sandwich immune reaction (Ab1, CYFRA21-1, and Ab2) and proximity hybridization between Ab1-S1-Fc and Ab2-S2. This caused the release of Ab1-S1-Fc from the modified electrode and the change of S0-MB to a hairpin structure, resulting in a decrease (an increase) of the oxidation peak current of Fc (MB) and an increase of the photocurrent due to the enhancing (inhibiting) effect of MB (Fc) on the photoelectric performance of the Au NPs/PTCDA@C60/ITO electrode. Thus, CYFRA21-1 was detected by the developed EC-PEC dual-mode sensing platform sensitively, and the linear response ranges of 0.001-40 ng/mL with a detection limit of 0.3 pg/mL for the EC technique and 0.0001-4 ng/mL with a detection limit of 0.03 pg/mL for the PEC method were obtained. Furthermore, by changing the specific antibodies of disease-related biomarkers, the developed dual-mode biosensing platform could be readily extended to detect other antigens, implying its great potential applications in biological analysis and early disease diagnosis.

Peptide Cleavage-Mediated and Environmentally Friendly Photocurrent Polarity Switching System for Prostate-Specific Antigen Assay.

As the most important serum biomarker for prostate cancer, sensitive and accurate detection of prostate-specific antigen (PSA) is of great reference value for the clinical diagnosis and treatment of prostate cancer. Herein, a peptide cleavage-mediated and environmentally friendly photocurrent polarity switching system was developed for ultrasensitive and highly selective detection of PSA based on the efficiently switching of photocurrent polarity of silver indium sulfide nanoparticles (AgInS2 NPs)-coated indium tin oxide (ITO) electrode by amino-functionalized CuO cubes (NH2-CuO). The porous CuO cubes were synthesized by calcination of HKUST-1 and functionalized with aminosilane. In the presence of PSA, the biotin and rhodamine B-labeled peptide (Bio-Pep-RhB) was cleaved and part of the peptide (P-Pep-RhB) was obtained by magnetic separation. Through host-guest recognition between ß-CD and RhB, the P-Pep-RhB was immobilized on the ß-CD/AgInS2 NPs/ITO electrode. Then, the amino-rich sequence on P-Pep-RhB combined with NH2-CuO via glutaraldehyde results in the switch of anodic photocurrent to cathodic photocurrent. On account of the high-efficient peptide cleaving strategy and the new photocurrent polarity switching system of porous CuO cubes//AgInS2 NPs, the prepared sensing platform displayed outstanding analytical performance for PSA with a wide linear response range (0.1 pg mL-1-100 ng mL-1) and a lower detection limit of 0.06 pg mL-1. The proposed analytical method could be easily extended to analyze other proteins via changing the peptide sequence, which has a potential application in the fields of biological analysis and medical diagnosis.

Label-free and near-zero-background-noise photoelectrochemical assay of methyltransferase activity based on a Bi2S3/Ti3C2 Schottky junction.

Herein, a novel label-free photoelectrochemical (PEC) sensing platform with near-zero background noise was developed for M.SssI CpG methyltransferase (M.SssI MTase) activity assay based on a new Schottky junction of Bi2S3/Ti3C2 nanosheets. The proposed PEC sensor exhibited a low detection limit and a high signal-to-noise ratio for M.SssI MTase assay.

CuO-ZnO heterojunction derived from Cu2+-doped ZIF-8: A new photoelectric material for ultrasensitive PEC immunoassay of CA125 with near-zero background noise.

By direct calcination of Cu2+-doped ZIF-8 in oxygen atmosphere, a new photoelectric material, CuO-ZnO heterojunction, was prepared. The morphology and structure were investigated in detail by several methods, such as scanning electron microscopy, transmission electron microscopy, nitrogen adsorption-desorption method and X-ray diffraction. Under visible light irradiation, CuO-ZnO heterojunction exhibits excellent PEC behavior in aqueous media with the presence of ascorbic acid (AA) and dissolved oxygen at -0.3 V. Taking the CA125-antibody functionalized CuO-ZnO heterojunction (CuO-ZnO-Ab2) as a signal source, a novel photoelectrochemical (PEC) immunosensing platform was developed for ultrasensitive assay of CA125. Because of the target-induced introduction of photoelectric material to the sensing platform, the proposed PEC immunosensor has excellent performance for CA125 assay: near-zero background noise, wide linear response range (1 × 10-5 U/mL to 100 U/mL) and low detection limit (3.16 × 10-6 U/mL). The developed CuO-ZnO heterojunction and the related PEC sensing platform may have promising applications in ultrasensitive and highly accurate monitoring of various proteins in bioanalysis and disease diagnosis.

Highly Selective and Sensitive Photoelectrochemical Sensing Platform for VEGF165 Assay Based on the Switching of Photocurrent Polarity of CdS QDs by Porous Cu2O-CuO Flower.

Herein, a highly selective and sensitive photoelectrochemical (PEC) sensing platform was developed for vascular endothelial growth factor 165 (VEGF165) assay based on the porous Cu2O-CuO flower-induced photocurrent-polarity switching of the CdS quantum dots (QDs) modified indium-tin oxide (ITO) electrode. The porous Cu2O-CuO flower with uniform size and large surface area was successfully synthesized by taking Cu-MOF (HKUST-1) as the precursor. Through VEGF165-triggered catalytic hairpin assembly process, the porous Cu2O-CuO flower was introduced to the surface of the CdS QDs/ITO electrode, resulting in the switching of the photocurrent polarity from anodic current to cathodic current. Based on the uniform particle size, high specific surface area, good photoelectric conversion efficiency, and photocurrent polarity switching ability of porous Cu2O-CuO flower, the proposed sensing platform showed excellent assay performance for VEGF165 with a linear response range from 1 to 3000 fM, a detection limit of 0.3 fM, and high selectivity. By changing the specific aptamer, the proposed sensing platform could be easily extended to detect other proteins, and may have a promising application in bioanalysis and early disease diagnosis.

Graphene blended with SnO2 and Pd-Pt nanocages for sensitive non-enzymatic electrochemical detection of H2O2 released from living cells.

This paper described a novel, facile and nonenzymatic electrochemical biosensor to detect hydrogen peroxide (H2O2). The sensor was fabricated based on Pd-Pt nanocages and SnO2/graphene nanosheets modified electrode (PdPt NCs@SGN/GCE). The electrochemical behavior of PdPt NCs@SGN/GCE exhibited excellent catalytic activity toward H2O2 with fast response, high selectivity, superior sensitivity, low detection limit of 0.3 µM and large linear range from 1 µM to 300 µM. Under these obvious advantages, the constructed biosensor provided to be reliable for determination of H2O2 secreted from human cervical cancer cells (Hela cells). Hence, the proposed biosensor is a promising candidate for detection of H2O2 in situ released from living cells in clinical diagnostics.

Facile synthesized SnO2 decorated functionalized graphene modified electrode for sensitive determination of daidzein.

A one-step and facile method using SnCl2·H2O as reducing agent to reduce graphene oxide (GO) was performed in the aid of poly(diallyldimethylammonium chloride) solution (PDDA). SnCl2·H2O is not only a reducing agent for graphene oxide (GO), but also a precursor of SnO2. SnO2-PDDA-GR composite was characterized by various surface, structural and electrochemical analysis techniques, such as transmission electron microscopy (TEM), UV spectrum (UV-vis), Infrared Spectrum (IR), X-ray diffraction (XRD), Cyclic voltammograms (CV) and electrochemical impedance (EIS). The SnO2-PDDA-GR composite was used to constructed electrochemical sensor (SnO2-PDDA-GR/GCE) for the determination of daidzein. Under the optimized experimental condition, it was found that the response of peak current is linear to the concentration of daidzein in the ranges of 2.0×10-8 -1.0×10-6molL-1, and the detection limit was estimated to be 6.7×10-9mol L-1 (S/N=3). Furthermore, this sensor was successfully applied for the determination of daidzein in traditional Chinese medicine (pueraria lobata) and Daidzein tablets.

Sensitive, simultaneous determination of chrysin and baicalein based on Ta2O5-chitosan composite modified carbon paste electrode.

Chrysin and baicalein are the major flavonoids found in oroxylum indicum, an essential herb in traditional Chinese medicine (TCM). Owing to their similar characteristics and physiochemical property, it is a great challenge to detect both of them simultaneously. In this work, tantalum oxide (Ta2O5) particles and chitosan modified carbon paste electrode (Ta2O5-CTS-CPE) was prepared and characterized by scanning electron microscope (SEM), X-ray diffraction spectroscopy (XRD), Fourier transform infrared spectroscopy (FTIR), cyclic voltammetry (CV) and electrochemical impedance spectrum(EIS). Under the optimum conditions, the prepared Ta2O5-CTS-CPE exhibited excellent electrocatalytic activity toward the oxidation of chrysin and baicalein, and it could serve as the sensor for highly sensitive and simultaneous determination both of them. The linear range is 0.08-4.0µM for both of them, and the detection limits were determined to be 0.03 and 0.05µM (S/N=3) for chrysin and baicalein, respectively. Furthermore, the proposed electrochemical sensor displayed high sensitivity, excellent stability and got satisfactory results in oroxylum indicum samples analysis.

Autophagy induction by tetrahydrobiopterin deficiency.

Tetrahydrobiopterin (BH4) deficiency is a genetic disorder associated with a variety of metabolic syndromes such as phenylketonuria (PKU). In this article, the signaling pathway by which BH4 deficiency inactivates mTORC1 leading to the activation of the autophagic pathway was studied utilizing BH4-deficient Spr(-/-) mice generated by the knockout of the gene encoding sepiapterin reductase (SR) catalyzing BH4 synthesis. We found that mTORC1 signaling was inactivated and autophagic pathway was activated in tissues from Spr(-/-) mice. This study demonstrates that tyrosine deficiency causes mTORC1 inactivation and subsequent activation of autophagic pathway in Spr(-/-) mice. Therapeutic tyrosine diet completely rescued dwarfism and mTORC1 inhibition but inactivated autophagic pathway in Spr(-/-) mice. Tyrosine-dependent inactivation of mTORC1 was further supported by mTORC1 inactivation in Pah(enu2) mouse model lacking phenylalanine hydroxylase (Pah). NIH3T3 cells grown under the condition of tyrosine restriction exhibited autophagy induction. However, mTORC1 activation by RhebQ64L, a positive regulator of mTORC1, inactivated autophagic pathway in NIH3T3 cells under tyrosine-deficient conditions. In addition, this study first documents mTORC1 inactivation and autophagy induction in PKU patients with BH4 deficiency.

Differential effects of specific amino acid restriction on glucose metabolism, reduction/oxidation status and mitochondrial damage in DU145 and PC3 prostate cancer cells.

Selective amino acid restriction targets mitochondria to induce apoptosis of DU145 and PC3 prostate cancer cells. Biochemical assays and flow cytometry were uitilized to analyze the glucose consumption, lactate production, pyruvate dehydrogenase (PDH), nicotinamide adenine dinucleotide (NAD)/NADH and nicotinamide adenine dinucleotide phosphate (NADP)/NADPH ratios, mitochondrial glutathione peroxidase (GPx), manganese superoxide dismutase (SOD), glutathione, reactive oxygen species (ROS) and DNA damage in DU145 and PC prostate cancer cells cultured under various amino acid deprived conditions. Restriction of tyrosine and phenylalanine (Tyr/Phe), glutamine (Gln) or methionine (Met) differentially modulated glucose metabolism and PDH and antioxidant enzyme activity in the mitochondria of the two prostate cancer cell lines. In DU145 cells, Gln and Met restriction increased glucose consumption and decreased lactate production, but Tyr/Phe restriction did not. The examined restrictions increased mitochondrial PDH activity and accumulation of ROS. Gln and Met restriction increased GPx activity. Tyr/Phe and Met restriction increased SOD during the first 2 days of the restriction, and the activity returned to the basal level on day 4. All amino acid restrictions decreased reduced glutathione (GSH) and induced mitochondrial DNA damage. In PC3 cells, all amino acid restrictions reduced glucose consumption and lactate production. Gln restriction increased ROS and elevated GPx activity. Tyr/Phe restriction increased SOD activity. The amino acid restriction decreased GSH, but did not cause mitochondrial DNA damage. Specific amino acid dependency differentially regulates glucose metabolism, oxidation-reduction reactions of mitochondria and mitochondrial damage in DU145 and PC3 prostate cancer cell lines.

Cell death of prostate cancer cells by specific amino acid restriction depends on alterations of glucose metabolism.

Selective amino acid restriction targets mitochondria resulting in DU145 and PC3 prostate cancer cell death. This study shows that restriction of tyrosine and phenylalanine (Tyr/Phe), glutamine (Gln), or methionine (Met) differentially modulates glucose metabolism, glycogen synthase kinase 3beta (GSK3beta), p53, and pyruvate dehydrogenase (PDH) in these two cell lines. In DU145 cells, Gln and Met restriction increase glucose consumption, but Tyr/Phe restriction does not. Addition of glucose to culture media diminishes cell death induced by Tyr/Phe-restriction. Addition of pyruvate reduces cell death due to Tyr/Phe and Gln restriction. Tyr/Phe, Gln and Met restriction increase phosphorylation of GSK3beta-Ser(9), phosphorylation of p53-Ser(15) and reduce the mitochondrial localization of PDH. Addition of glucose or pyruvate to cultures significantly reverses the alterations in GSK3beta, p53 and PDH induced by amino acid restriction. In p53-null PC3 cells, Tyr/Phe, Gln and Met restriction decreases glucose consumption, reduces phosphorylation of Akt-Ser(473), and increases phosphorylation of GSK3beta-Ser(9). Addition of pyruvate or glucose reduces death of Met-restricted cells. Addition of glucose increases phosphorylation of Akt-Ser(473) in amino acid-restricted cells reduces phosphorylation of GSK3beta-Ser(9) in Tyr/Phe and Gln restricted cells and increases phosphorylation of GSK3beta-Ser(9) in Met restricted cells. Addition of pyruvate reduces phosphorylation of GSK3beta-Ser(9) in all amino acid-restricted cells. In summary, cell death induced by specific amino acid restriction is dependent on or closely related to the modulation of glucose metabolism. GSK3beta (DU145 and PC3) and p53 (DU145) are crucial switches connecting metabolism and these signaling molecules to cell survival during amino acid restriction.

Selective amino acid restriction differentially affects the motility and directionality of DU145 and PC3 prostate cancer cells.

We previously found that selective restriction of amino acids inhibits invasion of two androgen-independent human prostate cancer cell lines, DU145 and PC3. Here we show that the restriction of tyrosine (Tyr) and phenylalanine (Phe), methionine (Met) or glutamine (Gln) modulates the activity of G proteins and affects the balance between two actin-binding proteins, cofilin and profilin, in these two cell lines. Selective amino acid restriction differentially reduces G protein binding to GTP in DU145 cells. Tyr/Phe deprivation reduces the amount of Rho-GTP and Rac1-GTP. Met deprivation reduces the amount of Ras-GTP and Rho-GTP, and Gln deprivation decreases Ras-GTP, Rac-GTP, and Cdc42-GTP. Restriction of these amino acids increases the amount of profilin, cofilin and phosphorylation of cofilin-Ser(3). Increased PAK1 expression and phosphorylation of PAK1-Thr(423), and Ser(199/204) are consistent with the increased phosphorylation of LIMK1-Thr(508). In PC3 cells, Tyr/Phe or Gln deprivation reduces the amount of Ras-GTP, and all of the examined amino acid restrictions reduce the amount of profilin. PAK1, LIMK1 and cofilin are not significantly altered. These data reveal that specific amino acid deprivation differentially affects actin dynamics in DU145 and PC3. Modulation on Rho, Rac, PAK1, and LIMK1 likely alter the balance between cofilin and profilin in DU145 cells. In contrast, profilin is inhibited in PC3 cells. These effects modulate directionality and motility to inhibit invasion.

Specific amino acid dependency regulates the cellular behavior of melanoma.

Relative specific amino acid dependency is one of the metabolic abnormalities of melanoma cells and metabolic studies of this dependency are in their infancy. Herein, we review the current studies in this area and present new information that adds to the understanding of how tyrosine (Tyr) and phenylalanine (Phe) dependency as well as other amino acids regulate the cell behaviors of melanoma cells. Amino acid dependency of human melanoma cells is multifactorial and restricting Tyr and Phe to melanoma triggers a series of alterations in metabolic and signaling pathways in a time-ordered fashion to alter different cellular behaviors. For example, at early time points, the reduction of Tyr and Phe alters metabolic reactions quantitatively or qualitatively. The alterations include modulation of integrin/focal adhesion kinase (FAK)/G protein pathways and the plasminogen activator (PA)/PA inhibitor pathways to inhibit tumor cell invasion. At later time periods, a further drop in intracellular amino acids induces more metabolic alterations to impact the FAK/Ras/Raf and Bcl-2 pathways leading to apoptosis. The threshold effects and the targeting of multiple pathways by restriction of specific amino acids provide a connection between the metabolic alterations and signaling pathways that modulate the cellular behaviors of melanoma cells. Decoding the metabolic alterations that connect amino acid concentration to the crucial step(s) in signaling is important and an exciting area of cancer research.