RNA Adenine Research Articles

REVIEW ARTICLE; ANTICANCER ACTIVITIES OF SOME FUSED HETEROCYCLIC MOIETIES CONTAINING NITROGEN AND/OR SULFUR HETEROATOMS

Cancer cells often have a high demand for antiapoptotic proteins in order to resist programmed cell death. Heterocyclic compounds present themselves as a fundamental division of organic chemistry. Most clinically effective antitumor agents are inhibitors of DNA, RNA or protein synthesis, enzyme inhibition and/or interfere with the metabolism of other cell components, frequently lacking or displaying poor selective antitumor activity. The majority of heterocycle compounds and typically common heterocycle fragments present in most pharmaceuticals currently marketed, alongside with their intrinsic versatility and unique physicochemical properties have poised them as true cornerstones of medicinal chemistry. The S-heterocyclic core (Thiophene) has been reported to possess significant importance in various fields from medicinal chemistry. Many diverse biologically active products were prepared, several of which exhibited antimicrobial, analgesic, anti-inflammatory, antioxidant, antitumor, local anesthetic, anticoagulant and antithrombotic activities. Many N-heterocyclic compounds that are broadly distributed in Nature, possess physiological and pharmacological properties and are constituents of many biologically important molecules, including many vitamins, nucleic acids, pharmaceuticals, antibiotics, dyes and agrochemicals, amongst many others. The base pairs of DNA and RNA (Guanine, cytosine, adenine, and thymine) are also made up of N-heterocyclic compounds, namely purines, pyrimidines, etc. These nitrogen-containing heterocyclic molecules with distinct characteristics and applications have gained prominence in the rapidly expanding fields of organic and medicinal chemistry and the pharmaceutical industry. Finally, many of these compounds have higher activity against cancer cells using the standard MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide)assay.

Caffeine: Benefits, Risks and Effects-A Review

Caffeine, the world’s most widely consumed psychoactive drug is a central nervous system(CNS) stimulantof the methylxanthine class. It is a white crystalline purine, a methylxanthine alkaloid which is bitter in taste.Caffeine is structurally related to the adenine and guanine bases of DNA and RNA. It is found in the nuts,seeds or leaves of a number of plants native to East Asia, Africa, and South America, and its natural functionis to prevent germination of nearby seeds and to protect them against predator insects. Caffeine can haveboth positive and negative impact on human health. It can be used to treat and prevent the premature infantbreathing disorders such as bronchopulmonary dysplasia of prematurity and apnea of prematurity. Caffeinecitrate is on the WHO Model List of Essential Medicines which confers a modest protective effect againstsome diseases, including Parkinson’s disease. Caffeine is classified by the US FDA as generally recognizedas safe(GRAS). Toxic doses are over 10 gm/day for an adult, which are much higher than the typical doseof under 500 mg/day. However, pure powdered caffeine, available as a dietary supplement, can be lethal intablespoon-sized amounts. In this review article, we discuss about the health benefits and adverse effects ofcaffeine along with its future prospects.

Selectively Disrupting m6A-Dependent Protein-RNA Interactions with Fragments.

We report a crystallographic analysis of small-molecule ligands of the human YTHDC1 domain that recognizes N6-methylated adenine (m6A) in RNA. The 30 binders are fragments (molecular weight < 300 g mol-1) that represent 10 different chemotypes identified by virtual screening. Despite the structural disorder of the binding site loop (residues 429-439), most of the 30 fragments emulate the two main interactions of the -NHCH3 group of m6A. These interactions are the hydrogen bond to the backbone carbonyl of Ser378 and the van der Waals contacts with the tryptophan cage. Different chemical groups are involved in the conserved binding motifs. Some of the fragments show favorable ligand efficiency for YTHDC1 and selectivity against other m6A reader domains. The structural information is useful for the design of modulators of m6A recognition by YTHDC1.

Evaluation and Correlation of Solubility and Solvation Thermodynamics of Some DNA and RNA Bases in Aqueous Mixtures of Dipolar Aprotic N,N-Dimethyl Formamide

In this article we report the solubilities of some DNA and RNA bases, viz., uracil (U), thymine (T), cytosine (C) and adenine (A) at five equidistant temperatures from 288.15 to 308.15 K under the experimental pressure p = 0.1 MPa, in aqueous mixtures of dipolar aprotic N,N-dimethyl formamide (DMF) and, hence, standard Gibbs energies and entropies of transfer (∆ $$ S_{\text{t}}^{0} $$ ) from water to aqueous mixtures of DMF have been evaluated at 298.15 K. The chemical effects of the transfer Gibbs energies $$ \Delta G_{\text{t,chem}}^{ 0} (i) $$ and entropies of transfer ( $$ \Delta S_{\text{t,chem}}^{ 0} (i) $$ ) have been obtained after elimination of the cavity effect, dipole–dipole interaction and dipole–induced-dipole interactions. The cavity effect has been estimated by the scaled particle theory; on the other hand dipole–dipole interaction and dipole–induced-dipole interactions have been computed from the Keesom orientation expressions. The observed $$ \Delta G_{\text{t}}^{ 0} (i) $$ and $$ T\Delta S_{\text{t}}^{ 0} (i) $$ versus composition profiles are non-uniform because of the various interaction effects. Elimination of the effect due to dispersion interaction from the total chemical interaction yields the corresponding effects of the hydrophilic and hydrophobic sites of the solutes with the components of the solvent mixtures as compared to those present in water. In the case of transfer entropies, the relative structuredness of solvents is a guiding factor. However, the overall $$ \Delta G_{\text{t}}^{ 0} $$ behavior reflects increased stabilization of the DNA-RNA bases, which leads us to conclude that DMF induces denaturation of the double-stranded nucleic acid helix.

Binding and structural studies of the complexes of type 1 ribosome inactivating protein from Momordica balsamina with uracil and uridine.

Ribosome inactivating protein (RIP) catalyzes the cleavage of glycosidic bond formed between adenine and ribose sugar of ribosomal RNA to inactivate ribosomes. Previous structural studies have shown that RNA bases, adenine, guanine, and cytosine tend to bind to RIP in the substrate binding site. However, the mode of binding of uracil with RIP was not yet known. Here, we report crystal structures of two complexes of type 1 RIP from Momordica balsamina (MbRIP1) with base, uracil and nucleoside, uridine. The binding studies of MbRIP1 with uracil and uridine as estimated using fluorescence spectroscopy showed that the equilibrium dissociation constants (KD ) were 1.2 × 10-6 M and 1.4 × 10-7 M respectively. The corresponding values obtained using surface plasmon resonance (SPR) were found to be 1.4 × 10-6 M and 1.1 × 10-7 M, respectively. Structures of the complexes of MbRIP1 with uracil (Structure-1) and uridine (Structure-2) were determined at 1.70 and 1.98 Å resolutions respectively. Structure-1 showed that uracil bound to MbRIP1 at the substrate binding site but its mode of binding was significantly different from those of adenine, guanine and cytosine. However, the mode of binding of uridine was found to be similar to those of cytidine. As a result of binding of uracil to MbRIP1 at the substrate binding site, three water molecules were expelled while eight water molecules were expelled when uridine bound to MbRIP1.

Characterization of a Plasmodium falciparum rRNA methyltransferase

The ribosomal RNA adenine dimethyltransferases (rAD) of KsgA/Dim1 family are universally conserved with eukaryotic rADs separated into distinct cytosolic Dim1 and organellar KsgA/TFB homologs. Among the two putative KsgA proteins encoded by the Plasmodium falciparum genome, we found that PfKsgA1 was dually localised in the cytoplasm and the mitochondrion. The protein interacted specifically with small ribosomal subunit as detected by ribosome pull-down using anti-PfKsgA1 antibodies. Recombinant PfKsgA1 exhibited methyltransferase activity which was further confirmed by complementation in an Escherichia coli KsgA knockout strain. Similar to the human mitochondrial KsgA homologs that can additionally function as transcription regulators, PfKsgA1 also interacted with DNA in a sequence non-specific manner suggesting more than one functional role of an important ribosome biogenesis protein in Plasmodium.

Position-dependent effects of regioisomeric methylated adenine and guanine ribonucleosides on translation.

Reversible methylation of the N6 or N1 position of adenine in RNA has recently been shown to play significant roles in regulating the functions of RNA. RNA can also be alkylated upon exposure to endogenous and exogenous alkylating agents. Here we examined how regio-specific methylation at the hydrogen bonding edge of adenine and guanine in mRNA affects translation. When situated at the third codon position, the methylated nucleosides did not compromise the speed or accuracy of translation under most circumstances. When located at the first or second codon position, N1-methyladenosine (m1A) and m1G constituted robust blocks to both Escherichia coli and wheat germ extract translation systems, whereas N2-methylguanosine (m2G) moderately impeded translation. While m1A, m2G and N6-methyladenosine (m6A) did not perturb translational fidelity, O6-methylguanosine (m6G) at the first and second codon positions was strongly and moderately miscoding, respectively, and it was decoded as an adenosine in both systems. The effects of methylated ribonucleosides on translation could be attributed to the methylation-elicited alterations in base pairing properties of the nucleobases, and the mechanisms of ribosomal decoding contributed to the position-dependent effects. Together, our study afforded important new knowledge about the modulation of translation by methylation of purine nucleobases in mRNA.

Determination of DNA and RNA Methylation in Circulating Tumor Cells by Mass Spectrometry.

DNA methylation (5-methylcytosine, 5-mC) is the best characterized epigenetic mark that has regulatory roles in diverse biological processes. Recent investigation of RNA modifications also raises the possible functions of RNA adenine and cytosine methylations on gene regulation in the form of "RNA epigenetics." Previous studies demonstrated global DNA hypomethylation in tumor tissues compared to healthy controls. However, DNA and RNA methylation in circulating tumor cells (CTCs) that are derived from tumors are still a mystery due to the lack of proper analytical methods. In this respect, here we established an effective CTCs capture system conjugated with a combined strategy of sample preparation for the captured CTCs lysis, nucleic acids digestion, and nucleosides extraction in one tube. The resulting nucleosides were then further analyzed by liquid chromatography-electrospray ionization-tandem mass spectrometry (LC-ESI-MS/MS). With the developed method, we are able to detect DNA and RNA methylation (5-methyl-2'-deoxycytidine, 5-methylcytidine, and N(6)-methyladenosine) in a single cell. We then further successfully determined DNA and RNA methylation in CTCs from lung cancer patients. Our results demonstrated, for the first time, a significant decrease of DNA methylation (5-methyl-2'-deoxycytidine) and increase of RNA adenine and cytosine methylations (N(6)-methyladenosine and 5-methylcytidine) in CTCs compared with whole blood cells. The discovery of DNA hypomethylation and RNA hypermethylation in CTCs in the current study together with previous reports of global DNA hypomethylation in tumor tissues suggest that nucleic acid modifications play important roles in the formation and development of cancer cells. This work constitutes the first step for the investigation of DNA and RNA methylation in CTCs, which may facilitate uncovering the metastasis mechanism of cancers in the future.

2-Thiouracil deprived of thiocarbonyl function preferentially base pairs with guanine rather than adenine in RNA and DNA duplexes.

2-Thiouracil-containing nucleosides are essential modified units of natural and synthetic nucleic acids. In particular, the 5-substituted-2-thiouridines (S2Us) present in tRNA play an important role in tuning the translation process through codon–anticodon interactions. The enhanced thermodynamic stability of S2U-containing RNA duplexes and the preferred S2U-A versus S2U-G base pairing are appreciated characteristics of S2U-modified molecular probes. Recently, we have demonstrated that 2-thiouridine (alone or within an RNA chain) is predominantly transformed under oxidative stress conditions to 4-pyrimidinone riboside (H2U) and not to uridine. Due to the important biological functions and various biotechnological applications for sulfur-containing nucleic acids, we compared the thermodynamic stabilities of duplexes containing desulfured products with those of 2-thiouracil-modified RNA and DNA duplexes. Differential scanning calorimetry experiments and theoretical calculations demonstrate that upon 2-thiouracil desulfuration to 4-pyrimidinone, the preferred base pairing of S2U with adenosine is lost, with preferred base pairing with guanosine observed instead. Therefore, biological processes and in vitro assays in which oxidative desulfuration of 2-thiouracil-containing components occurs may be altered. Moreover, we propose that the H2U-G base pair is a suitable model for investigation of the preferred recognition of 3′-G-ending versus A-ending codons by tRNA wobble nucleosides, which may adopt a 4-pyrimidinone-type structural motif.

Engineering Escherichia coli for functional expression of membrane proteins.

A major bottleneck in the characterization of membrane proteins is low yield of functional protein in recombinant expression. Microorganisms are widely used for recombinant protein production, because of ease of cultivation and high protein yield. However, the target proteins do not always obtain their native conformation and may end up in a nonfunctional state, in insoluble aggregates. For screening of functional protein, it is thus important to readily discriminate aggregated, mistargeted protein from globally well-folded, membrane-inserted protein. We developed a robust strategy for expression screening of functional proteins in bacteria, which is based on directed evolution. In this strategy, the C-terminus of the target membrane protein is tagged with two additional protein domains in tandem. The first one is green fluorescent protein (GFP), which functions as a reporter of the global folding state of the fusion protein. The other one is the erythromycin resistance protein (23S ribosomal RNA adenine N-6 methyltransferase, ErmC), which confers a means to select for enhanced expression. By gradually increasing the antibiotic concentration in the medium, we force the cells to evolve in a way that allows more functional target-GFP-ErmC to be expressed. The acquired genomic mutations can be generic or membrane protein specific. This strategy is readily adopted for the expression of any protein and ultimately yields a wealth of genomic data that may provide insight into the factors that limit the production of given classes or types of proteins.

Effects of Hypoxanthine Substitution in Peptide Nucleic Acids TargetingKRAS2Oncogenic mRNA Molecules: Theory and Experiment

Genetic disorders can arise from single base substitutions in a single gene. A single base substitution for wild type guanine in the twelfth codon of KRAS2 mRNA occurs frequently to initiate lung, pancreatic, and colon cancer. We have observed single base mismatch specificity in radioimaging of mutant KRAS2 mRNA in tumors in mice by in vivo hybridization with radiolabeled peptide nucleic acid (PNA) dodecamers. We hypothesized that multimutant specificity could be achieved with a PNA dodecamer incorporating hypoxanthine, which can form Watson-Crick base pairs with adenine, cytosine, thymine, and uracil. Using molecular dynamics simulations and free energy calculations, we show that hypoxanthine substitutions in PNAs are tolerated in KRAS2 RNA:PNA duplexes where wild type guanine is replaced by mutant uracil or adenine in RNA. To validate our predictions, we synthesized PNA dodecamers with hypoxanthine, and then measured the thermal stability of RNA:PNA duplexes. Circular dichroism thermal melting results showed that hypoxanthine-containing PNAs are more stable in duplexes where hypoxanthine-adenine and hypoxanthine-uracil base pairs are formed than single mismatch duplexes or duplexes containing hypoxanthine-guanine opposition.

Evolved Escherichia coli Strains for Amplified, Functional Expression of Membrane Proteins

The major barrier to the physical characterization and structure determination of membrane proteins is low protein yield and/or low functionality in recombinant expression. The enteric bacterium Escherichia coli is the most widely employed organism for producing recombinant proteins. Beside several advantages of this expression host, one major drawback is that the protein of interest does not always adopt its native conformation and may end up in large insoluble aggregates. We describe a robust strategy to increase the likelihood of overexpressing membrane proteins in a functional state. The method involves fusion in tandem of green fluorescent protein and the erythromycin resistance protein (23S ribosomal RNA adenine N-6 methyltransferase, ErmC) to the C-terminus of a target membrane protein. The fluorescence of green fluorescent protein is used to report the folding state of the target protein, whereas ErmC is used to select for increased expression. By gradually increasing the erythromycin concentration of the medium and testing different membrane protein targets, we obtained a number of evolved strains of which four (NG2, NG3, NG5 and NG6) were characterized and their genome was fully sequenced. Strikingly, each of the strains carried a mutation in the hns gene, whose product is involved in genome organization and transcriptional silencing. The degree of expression of (membrane) proteins correlates with the severity of the hns mutation, but cells in which hns was deleted showed an intermediate expression performance. We propose that (partial) removal of the transcriptional silencing mechanism changes the levels of proteins essential for the functional overexpression of membrane proteins.

Probing electronic coupling between adenine bases in RNA strands from synchrotron radiation circular dichroism experiments

Circular dichroism spectra (176-330 nm) of RNA adenine oligomers, (rA)(n) (n = 1-10, 12, 15, and 20), reveal electronic coupling between two bases in short strands. The number of interacting bases in long strands is more and larger than that reported previously for the corresponding DNA strands.

Cryptic diversity and morphological convergence in threatened species of fossorial skinks in the genus Scelotes (Squamata: Scincidae) from the Western Cape Coast of South Africa: Implications for species boundaries, digit reduction and conservation

We investigated the evolutionary relationships among populations of two threatened Red Data Book fossorial skinks, Scelotes gronovii and Scelotes kasneri, along the Western Cape Coast of South Africa. The genus Scelotes shows considerable variation in limb and digit reduction. We sampled four localities purported to contain S. gronovii and seven of S. kasneri, encompassing all of each species’ limited distribution. Each of these species lack forelimbs, and differ by the number of digits on the hind limbs, among other morphological characters; S. gronovii bears a single digit and S. kasneri bears two digits on the hind limbs. Sequence data obtained from three mtDNA (16S ribosomal RNA, cytochrome b, and nicotinamide adenine dinucleotide dehydrogenase 1 unit; 2035bp ttl.) and two nuclear (dynein axonemal heavy chain 3 and the natural killer tumor recognition; 1848bp ttl.) gene regions were used to reconstruct the evolutionary relationships among the two focal species and several other co-distributed species (Scelotes bipes, Scelotes montispectus, and Scelotes sexlineatus). Phylogenetic results (Bayesian and parsimony) revealed that several populations previously considered S. kasneri actually belong to other species, and others are paraphyletic with respect to one another. Additionally, populations of S. gronovii were also found to be paraphyletic, with populations south of the Berg River supported as sister to S. bipes, and populations north of the Berg River sister the remaining sampled species. Our results require a redefinition of S. sexlineatus to encompass populations morphologically convergent with S. kasneri and restrict the ranges of the already threatened S. kasneri and S. gronovii even further. The paraphyly of S. gronovii and the placement of each clade as sister to clades of species bearing two digits on the hind limbs suggests that digit loss has occurred at least twice in this group.

Synthesis of Purine Derivatives as Scaffolds for a Diversity of Biological Activities

The purine ring is undoubtedly among the most ubiquitous of all the heterocyclic compounds. This arises not only from the universal occurrence of adenine and guanine in DNA and RNA and of additional modified derivatives in the various tRNAs but also from the subsidiary uses of the ring system in a great number of biochemical systems. The development of new methods for metal-mediated coupling with aryl or heteroaryl halide substrates has expanded the range of synthetically accessible arylpurine derivatives. Aryl boronic acids have proved to be extremely available reagents for metal-mediated C-C and C-N coupling reactions. Coupling reactions resulting in C-C bond formation are catalyzed by palladium and nickel catalysts at positions C2, C6 and C8. The reactivity at C6 position has been demonstrated using fluoro-, chloro-, bromo-, iodo-, sulfanyl, sulfonyl, sulfonyloxy- and azole-substrates. The ease of obtaining the activated purine substrates is an important factor when selecting appropriate coupling conditions. Copper-mediated N-arylations occur at positions N7 and N9. These methods are also applicable using solid-supported purine substrates and provide convenient access to structurally unique derivatives with applications in drug discovery. Continuing advances in this field can be expected to result through improved mechanistic understanding and the development of new catalysts and ligands. Keywords: Alkyl-purine derivatives, aryl-purine derivatives, cross-coupling, ferrocene-modified purines, fluorinated compounds, microwave, nucleosides, solid-phase synthesis, antiparasitic agents, cyclin-dependent kinase inhibitors, 5-alkylamino-4-amino-6-arylthiopyrimidine, cyclohexyl nucleosides, 9-Phenyl-9H-purin-6-amines, 5-amino-1-phenyl-1H-imidazole-4-carbonitriles, methyl ethyl ketone, perfluoroalkylation reaction, Tetrabutylammonium triphenyldifluorosilicate, imidazolium-carbene ligand, Phosphonated azaheterocycles, C6-phosphonated purine nucleosides, 2-Amino-6-(1,2,4-triazol-4-yl)purine, Disubstituted Purines, tetrabutylammonium nitrate, trifluoroacetic anhydride, 2,6-Dichloropurine, tributyltin chloride, trimethylsilyl chloride, hexamethyldisilazane, anhydrous acetonitrile, 1,2-dichloroethane, dihydrodiazepinopurine, Mycobacterium avium, N,N-dimethylacetamide, TETRASUBSTITUTED PURINES, diaminopyrimidine

309 Sentinel node biopsy in “high risk” DCIS patients

The major barrier to the physical characterization and structure determination of membrane proteins is low protein yield and/or low functionality in recombinant expression. The enteric bacterium Escherichia coli is the most widely employed organism for producing recombinant proteins. Beside several advantages of this expression host, one major drawback is that the protein of interest does not always adopt its native conformation and may end up in large insoluble aggregates. We describe a robust strategy to increase the likelihood of overexpressing membrane proteins in a functional state. The method involves fusion in tandem of green fluorescent protein and the erythromycin resistance protein (23S ribosomal RNA adenine N-6 methyltransferase, ErmC) to the C-terminus of a target membrane protein. The fluorescence of green fluorescent protein is used to report the folding state of the target protein, whereas ErmC is used to select for increased expression. By gradually increasing the erythromycin concentration of the medium and testing different membrane protein targets, we obtained a number of evolved strains of which four (NG2, NG3, NG5 and NG6) were characterized and their genome was fully sequenced. Strikingly, each of the strains carried a mutation in the hns gene, whose product is involved in genome organization and transcriptional silencing. The degree of expression of (membrane) proteins correlates with the severity of the hns mutation, but cells in which hns was deleted showed an intermediate expression performance. We propose that (partial) removal of the transcriptional silencing mechanism changes the levels of proteins essential for the functional overexpression of membrane proteins.

Effect of aminoglycoside antibiotics on the conformation of the unpaired loop adenine of avian leucosis virus RNA as revealed using 2-aminopurine fluorescence

The fluorescent properties of 2-aminopurine (2-AP) incorporated in an RNA sequence are used to study the structural dynamics and local changes of the retroviral RNA structure. Using 2-AP, the conformational states of the unpaired loop adenine in avian leucosis virus RNA were studied upon its interaction with aminoglycoside antibiotics. The intensity of 2-AP fluorescence in the monomeric RNA hairpin was higher than in both RNA dimers. The intensity of fluorescence in the extended dimer was significantly lower than in the kissing loop dimer. The finding was be explained by the fact that stacking contacts in the extended dimer produce a more compact loop structure than in the kissing loop dimer. When the binding of aminogycoside antibiotics with the kissing loop dimer RNA was analyzed, only tobramycin increased the intensity of 2-AP fluorescence almost threefold. The results showed that 2-AP fluorescence is suitable for detecting local changes in complexes of retroviral RNA with ligands.

Metal-ion binding and metal-ion induced folding of the adenine-sensing riboswitch aptamer domain

Divalent cations are important in the folding and stabilization of complex RNA structures. The adenine-sensing riboswitch controls the expression of mRNAs for proteins involved in purine metabolism by directly sensing intracellular adenine levels. Adenine binds with high affinity and specificity to the ligand binding or aptamer domain of the adenine-sensing riboswitch. The X-ray structure of this domain in complex with adenine revealed an intricate RNA-fold consisting of a three-helix junction stabilized by long-range base-pairing interactions and identified five binding sites for hexahydrated Mg2+-ions. Furthermore, a role for Mg2+-ions in the ligand-induced folding of this RNA was suggested. Here, we describe the interaction of divalent cations with the RNA–adenine complex in solution as studied by high-resolution NMR spectroscopy. Paramagnetic line broadening, chemical shift mapping and intermolecular nuclear Overhauser effects (NOEs) indicate the presence of at least three binding sites for divalent cations. Two of them are similar to those in the X-ray structure. The third site, which is important for the folding of this RNA, has not been observed previously. The ligand-free state of the RNA is conformationally heterogeneous and contains base-pairing patterns detrimental to ligand binding in the absence of Mg2+, but becomes partially pre-organized for ligand binding in the presence of Mg2+. Compared to the highly similar guanine-sensing riboswitch, the folding pathway for the adenine-sensing riboswitch aptamer domain is more complex and the influence of Mg2+ is more pronounced.

Alterations in Mitochondrial and Apoptosis‐regulating Gene Expression in Photodynamic Therapy‐resistant Variants of HT29 Colon Carcinoma Cells¶

ABSTRACTPhotodynamic therapy (PDT) is a novel cancer therapy inducing irreversible photodamage to tumor tissue via photosensitizer‐mediated oxidative cytotoxicity. The cellular and molecular responses associated with PDT are only partially understood. We have reported previously the generation of several photosensitizer‐specific PDT‐resistant cell variants of HT29 human colon adenocarcinoma cells by selecting cells from sequential PDT treatment using different photosensitizers. In this report, we describe the use of messenger RNA (mRNA) differential display to identify genes that were differentially expressed in the parental HT29 cells compared with their resistant variants. In comparison with parental HT29 cells, mRNA expression was increased in the PDT‐resistant cell variants for BNIP3, estrogen receptor‐binding fragmentassociated gene 9, Myh‐1c, cytoplasmic dynein light chain 1, small membrane protein I and differential dependent protein. In contrast, expression in the PDT‐resistant variants was downregulated for NNX3, human HepG2 3′region Mbol complementary DNA, glutamate dehydrogenase, hepatomaderived growth factor and the mitochondrial genes coding for 16S ribosomal RNA (rRNA) and nicotinamide adenine dinucleotide (NADH) dehydrogenase subunit 4. The reduction for mitochondrial 16S rRNA in the PDT‐resistant variants was confirmed by Northern blotting, and the elevated expression of the proapoptotic BNIP3 in the PDT‐resistant variants was confirmed by Northern and Western blotting analysis. We also examined the expression of some additional apoptosis‐regulating genes using Western blotting. We show an increased expression of Bcl‐2 and heat shock protein 27 and a downregulation of Bax in the PDT‐resistant variants. In addition, the mutant p53 levels in the parental HT29 cells were reduced substantially in the PDT‐resistant variants. We suggest that the altered expression in several mitochondria1 and apoptosisregulating genes contributes to PDT resistance.

Alterations in mitochondrial and apoptosis regulating gene expression in photodynamic therapy resistant variants of HT29 colon carcinoma cells

Photodynamic therapy (PDT) is a novel cancer therapy inducing irreversible photodamage to tumor tissue via photosensitizer-mediated oxidative cytotoxicity. The cellular and molecular responses associated with PDT are only partially understood. We have reported previously the generation of several photosensitizer-specific PDT-resistant cell variants of HT29 human colon adenocarcinoma cells by selecting cells from sequential PDT treatment using different photosensitizers. In this report, we describe the use of messenger RNA (mRNA) differential display to identify genes that were differentially expressed in the parental HT29 cells compared with their resistant variants. In comparison with parental HT29 cells, mRNA expression was increased in the PDT-resistant cell variants for BNIP3, estrogen receptor-binding fragment-associated gene 9, Myh-1c, cytoplasmic dynein light chain 1, small membrane protein I and differential dependent protein. In contrast, expression in the PDT-resistant variants was downregulated for NNX3, human HepG2 3' region Mbol complementary DNA, glutamate dehydrogenase, hepatoma-derived growth factor and the mitochondrial genes coding for 16S ribosomal RNA (rRNA) and nicotinamide adenine dinucleotide (NADH) dehydrogenase subunit 4. The reduction for mitochondrial 16S rRNA in the PDT-resistant variants was confirmed by Northern blotting, and the elevated expression of the proapoptotic BNIP3 in the PDT-resistant variants was confirmed by Northern and Western blotting analysis. We also examined the expression of some additional apoptosis-regulating genes using Western blotting. We show an increased expression of Bcl-2 and heat shock protein 27 and a downregulation of Bax in the PDT-resistant variants. In addition, the mutant p53 levels in the parental HT29 cells were reduced substantially in the PDT-resistant variants. We suggest that the altered expression in several mitochondrial and apoptosis-regulating genes contributes to PDT resistance.