HIV-1 and IL-1 beta regulate Fas ligand expression in human astrocytes through the NF-kappa B pathway

Reactive astrogliosis is a prominent pathological feature of HIV-1-associated dementia (HAD). We hypothesized that in HAD, astrocytes activated with proinflammatory stimuli such as IL-1beta express Fas ligand (FasL), a death protein. IL-1beta and HIV-1-activated astrocytes expressed FasL mRNA and protein. Luciferase reporter constructs showed that IL-1beta and HIV-1 upregulated FasL promoter activity (p<0.001). The NF-kappaB pathway was involved as shown by inhibition with SN50 and dominant negative IkappaBalpha mutants. Brain extracts from HAD patients had significantly elevated FasL levels compared to HIV-seropositive (p<0.001) and seronegative individuals (p<0.01). We propose that astrocyte expression of FasL may participate in neuronal injury in HAD.

Adenosine suppresses the response of neurons to gaba in the superficial laminae of the rat spinal dorsal horn

With the nystatin-perforated whole-cell patch-clamp recording technique, the modulatory effects of adenosine on GABA-activated whole-cell currents were investigated in neurons acutely dissociated from the superficial laminae (laminae I and II) of the rat spinal dorsal horn. The results showed that: (1) GABA acted on GABA(A) receptor and elicited inward Cl(-) currents (I(GABA)) at a holding potential (V(H)) of -40 mV; (2) adenosine suppressed GABA-induced Cl(-) current with affecting neither the reversal potential of I(GABA) nor the apparent affinity of GABA to its receptor; (3) N6-cyclo-hexyladenosine, a selective A(1) adenosine receptor agonist, mimicked the suppressing effect of adenosine on I(GABA), whereas 8-cyclopentyl-1,3-dipropylxanthine, a selective A(1) adenosine receptor antagonist, blocked the suppressing effect of adenosine; (4) chelerythrine, an inhibitor of protein kinase C, reduced the suppressing effect of adenosine on I(GABA); (5) pretreatment with 1,2-bis-(2-aminophenoxy) ethane-N,N,N',N'-tetraacetic acid tetrakis (acetoxy-methyl) ester, a Ca(2+) chelator, did not affect adenosine-induced suppression of I(GABA). The results indicate that: (1) the suppression of adenosine on I(GABA) is mediated by adenosine A(1) receptor and through a Ca(2+)-independent protein kinase C transduction pathway; (2) the interactions between adenosine and GABA might be involved in the modulation of nociceptive information transmission at spinal cord level.

Regulation of the glyoxalase pathway in human brain microvascular endothelium: effects of troglitazone and tertiary butylhydroperoxide

The glyoxalase system, comprised of glyoxalase-I and glyoxalase-II with glutathione as the cofactor, plays an important role in the detoxification of methylglyoxal and other alpha-oxo-aldehydes. Such aldehydes, which increase with hyperglycemia, give rise to advanced glycation end products. The objective of this research was to examine the glyoxalase system in human cerebromicrovascular cells. The hypothesis tested was that this pathway would be regulated by phase 2 enzyme inducers such as t-butylhydroquinone and modulated by the insulin-sensitizing drug troglitazone. Human cerebromicrovascular endothelial cells were cultured and exposed to varying concentrations of t-butylhydroquinone or troglitazone. The activity of glyoxylase-I in human endothelial cells was similar to the activity present in hepatocytes. The phase 2 enzyme inducer t-butylhydroquinone had no effect on the glyoxalase enzymes activities but significantly increased glutathione levels and glutathione reductase activity, indicating that phase 2 enzyme inducers might promote alpha-oxo-aldehyde scavenging. Troglitazone decreased the activities of glyoxalase-I and -II and decreased glyoxalase-I mRNA. Troglitazone had no effect on glutathione levels or on the activity of glutathione reductase or glutathione peroxidase. We conclude that phase 2 enzyme inducers may promote scavenging of alpha-oxoaldehydes in endothelial cells.

Roles of the PI-3K and MEK pathways in Ras-mediated chemoresistance in breast cancer cells

Activated Ras utilises several downstream pathways, including the mitogen-activated protein kinase (MAPK) kinase (MEK)/MAPK pathway and the phosphoinositide 3-kinase (PI-3k)/Akt pathway, to promote cell proliferation and to inhibit apoptosis. To investigate which pathway plays a major role in Ras-induced drug resistance to chemotherapeutic agents in breast cancer cells, we transfected MCF7 breast cancer cells with a constitutively active H-RasG12V and examined the toxicities of three commonly used breast cancer chemotherapeutic agents, paclitaxel, doxorubicin, and 5-fluorouracil in these cells under the conditions that PI-3K or MEK were selectively inhibited by their respective specific inhibitors or dominant negative expression vectors. We found that Ras-mediated drug resistance is well correlated with resistance to apoptosis induced by anticancer agents in MCF7 breast cancer cells. Although inhibition of MEK/MAPK or PI-3K/Akt can each enhance the cytotoxicity of paclitaxel, doxorubicin, or 5-fluorouracil, inhibition of the PI-3K/Akt pathway seems to have a greater effect than inhibition of the MEK/MAPK pathway in reversing Ras-mediated drug resistance. Our results indicate that the PI-3K pathway may play a more important role in receptor tyrosine kinase-mediated resistance to chemotherapy and suggest that PI-3K/Akt might be a critical target molecule for anticancer intervention in breast cancer.

[A review on phytoremediation of organic contaminants]

Plants can take up and accumulate most persistant chemicals such as PCBs and PAHs by roots. Some chemicals such as TNT, TCE, and most organic pesticides can be phytodegraded into polar metabolites, or assimilated to CO2 and water by some plants. On the other hand, more microorganisms in rhizosphere can enhance the degradation rate of organic contaminants in environment. The benefits and some issues on phytoremediation are also discussed.

Determination of in vivo oxygen uptake and carbon dioxide evolution rates from off-gas measurements under highly dynamic conditions

In vivo kinetics of Saccharomyces cerevisiae are studied, in a time window of 150 s, by analyzing the response of O(2) and CO(2) in the fermentor off-gas after perturbation of chemostat cultures by metabolite pulses. Here, a new mathematical method is presented for the estimation of the in vivo oxygen uptake rate (OUR) and carbon dioxide evolution rate (CER) directly from the off-gas data in such perturbation experiments. The mathematical construction allows effective elimination of delay and distortion in the off-gas measurement signal under highly dynamic conditions. A black box model for the fermentor off-gas system is first obtained by system identification, followed by the construction of an optimal linear filter, based on the identified off-gas model. The method is applied to glucose and ethanol pulses performed on chemostat cultures of S. cerevisiae. The estimated OUR is shown to be consistent with the independent dissolved oxygen measurement. The estimated in vivo OUR and CER provide valuable insights into the complex dynamic behavior of yeast and are essential for the establishment and validation of in vivo kinetic models of primary metabolism.

[Effects of amino acid-N and ammonium-N on wheat seedlings under sterile culture]

The dry weight, total N, and glutamate-oxaloacetate transaminase(GOT) and glutamate-pyruvate transaminase (GPT) activities in roots and leaves of wheat seedlings (Triticum aestivum) grown with ammonium sulfate or amino acids (glycine, glutamate or lysine) were studied under sterile sand culture. The results showed that both NH4(+)-N and amino acid-N could be absorbed by wheat. The total N of plant fed with NH4(+)-N was similar to that fed with amino acid-N. The dry weight of plants grown 30 days with glycine or glutamate was significantly higher than that of plants grown with NH4(+)-N or free N. The dry weight of ammonium treatment was similar to that of lysine treatment or free N. NH4(+)-N in concentration of 0.7 mmol.L-1 significantly increased GPT activity of roots, but had no significant effects on leaves or roots treated 6 h in concentration of 35.7 mmol.L-1. Different species or concentrations of amino acids had different abilities to increase the GOT or GPT activity in leaves or roots.

An automated computer system to support ultra high throughput SNP genotyping

Celera Genomics has constructed an automated computer system to support ultra high-throughput SNP genotyping that satisfies the increasing demand that disease association studies are placing on current genotyping facilities. This system consists of the seamless integration of target SNP selection, automated oligo design, in silico assay quality validation, laboratory management of samples, reagents and plates, automated allele calling, optional manual review of autocalls, regular status reports, and linkage disequilibrium analysis. Celera has proven the system by generating over 2.5 million genotypes from more than 10,000 SNPs, and is approaching the target capacity of over 10,000 genotypes per machine per hour using limited human intervention with state of the art laboratory hardware.

Phytoremediation of selenium-contaminated soils and waters: fundamentals and future prospects

Interest in selenium pollution and remediation technology has escalated during the past two decades. Although not known to be essential for plants, selenium is an essential micronutrient for humans and animals, having important benefits for their nutrition. At high concentrations, however, selenium becomes toxic to animals and humans. A major selenium controversy in the 1980s emerged in California at the Kesterson National Wildlife Refuge; hence, scientists, environmental regulators, politicians, and the general public in the United States became aware of selenium's potential as an environmental contaminant. Consequently, extensive research has been conducted in the western United States, and a vast amount of financial resources have been allocated to develop management strategies and remediation technologies for reducing the impact of naturally occurring selenium on the biological environment. A plant-based technology, defined as 'phytoremediation', has received increasing recognition as a low-cost, environmentally friendly approach for managing the toxic effects of selenium. Plants have the ability to absorb and sequester selenium and to convert inorganic selenium to volatile forms of organic compounds that are released harmlessly into the atmosphere. The present review summarizes recent research findings and information about strategies on using phytoremediation systems to detoxify selenium-contaminated soils and waters in natural and agricultural ecosystems.

Comparing the immunogenicity of hepatitis B virus S gene variants by DNA immunization

DNA immunization was used to compare the immunogenicity of hepatitis B virus S gene variants. Four recombinant plasmid DNAs containing the full-length virus genome with different S gene inserts were used to immunize BALB/c and C57/BL/6 mice. These inserts were cloned from 129L (residue 129, glutamine to leucine), 129H (residue 129, glutamine to histidine) 145R (residue 145, glycine to arginine) variants and the wild-type virus. The titer of hepatitis B virus core antibodies (anti-HBc) in immunized mice was used as the control for the efficiency of DNA immunization. Serum hepatitis B surface antibody (anti-HBs) titer and cytokines induced in splenocytes stimulated with hepatitis B surface antigen (HBsAg) were monitored as specific immune responses induced by different plasmid DNAs. 129L DNA induced significantly lower anti-HBs antibodies (IgG, IgG1, and IgG2a) and less interferon-gamma, compared to those in mice immunized with the 129H variant and the wild-type HBV DNA (p < 0.05). Computer modeling showed that a change from glutamine to leucine at 129 residue led to higher hydrophobicity and could result in decreased immunogenicity. Results indicate that DNA immunization can be used to compare the humoral and cellular immunogenicity among different HBV S variants.

Differential expression of thymus and activation regulated chemokine and its receptor CCR4 in nodal and cutaneous anaplastic large-cell lymphomas and Hodgkin's disease

Recent studies demonstrated that Hodgkin/Reed-Sternberg (H/RS) cells in Hodgkin's disease (HD) express thymus and activation-regulated chemokine (TARC), whereas reactive lymphocytes surrounding H/RS cells express its ligand, CC-chemokine receptor 4 (CCR4). Because in vitro studies showed that CCR4 expression is a marker for lymphocytes bearing a T-helper 2 (Th2) phenotype, it was suggested that expression of TARC is a new immune escape mechanism in HD. To find out whether this mechanism might also be operative in CD30+ malignant lymphomas other than HD, TARC and CCR4 expression was investigated by immunohistochemistry on paraffin and frozen-tissue sections of 39 nodal CD30+ anaplastic large cell lymphomas (ALCL), including 27 ALK-negative and 12 ALK-positive ALCL, 25 primary cutaneous CD30+ ALCL, including 11 patients with lymphomatoid papulosis, and 31 cases of HD. TARC was expressed by the neoplastic cells in 12/27 (44%) nodal ALK-negative ALCL and all cases of classic HD, but not in nodal ALK-positive ALCL (0/12) and only rarely in primary cutaneous CD30+ ALCL (3/25). In contrast, CCR4 was expressed by the neoplastic cells in 9/9 cutaneous CD30+ ALCL, and in 9/15 (60%) nodal ALK-negative ALCL, but only in 1/4 (25%) nodal ALK-positive ALCL and not by the H/RS cells in HD (0/8). Apart from three cases of HD showing 10 to 15% CCR4-positive lymphocytes surrounding TARC-positive H/RS cells, CCR4-positive reactive T cells were few (<5%) in all other cases studied. Our results demonstrate a differential expression of TARC and CCR4 in different types of CD30+ malignant lymphomas. The small number of CCR4-positive reactive T cells in most cases studied argues against an important role of TARC expression in the evasion of antitumor responses.

[Electrophoretic analysis of soluble antigens of a pathogenic isolate of Trichomonas vaginalis]

AIM

To analyze the parasite soluble antigens of a pathogenic isolate of Trichomonas vaginalis.

METHODS

The soluble antigens of a pathogenic isolate of T. vaginalis isolated from a patient suffered from trichomonad vaginitis was studied by means of SDS-PAGE followed by densitometric analysis and immunoblotting.

RESULTS

A total of 14 distinct protein bands was demonstrated using a 10% resolution gel concentration. Densitometrogram indicated that the soluble antigens with MWs of equal to and below 72 kDa accounted for 89.5% of the total volume with the dominant fractions of 48-51 kDa which accounted for 19.2%. Having MWs over 100 kDa accounted only for 7.4%, while the lowest M. W. fraction demonstrated was found to be at the site of 13 kDa. By immunoblotting, the specific anti-T. vaginalis antibodies raised in mice recognized a broad spectrum of molecular size range of these antigenic fraction. However, no immunological reaction was seen at the 86 kDa site.

CONCLUSION

The proteins of MWs 48-51 kDa possess a larger protein content and a higher immunological reactivity.

Relationship between compost stability and extractable organic carbon

Establishing a simple yet reliable compost stability test is essential for a better compost quality control and utilization efficiency. The objective of this study was to examine the relationship between extractable organic carbon (OC) and compost stability based on 18 compost samples from five composting facilities. The compost samples were extracted sequentially with water for 2 h [water(2h)] and 0.1 M NaOH for 2 and 24 h [NaOH(2h) and NaOH(24h), respectively]. The extractable OC was further separated into fulvic acid (FA) and humic acid (HA) fractions by adjusting the pH to <2. The mass specific absorbance (MSA) of OC in the six fractions was measured. Compost stability was estimated with a CO2 evolution method. The extractable OC concentration was influenced by the total volatile solids and decreased with curing time for compost with a high level of extractable OC. The OC levels in each fraction were significantly correlated (p < 0.05) to each other except for the water(2h)-extractable HA. In addition, all the FA and HA fractions except for water(2h)-extractable HA were highly (P < 0.01) and linearly correlated to CO2 evolution, but multiple regression showed that NaOH(24h)-extractable OC was insignificant for CO2 evolution. The relatively high slope of NaOH(2h)-extractable FA versus CO2 evolution suggests that this fraction may contribute the most to compost CO2 evolution. The water(2h)- and/or NaOH(2h)-extractable FA tests are recommended for measuring compost stability because of their high correlation with CO2 evolution. This estimation can be obtained through a simple photometric method covering a wide range of carbon concentrations up to 4,000 mg L(-1).

Partitioning and persistence of trichlorfon and chlorpyrifos in a creeping bentgrass putting green

Golf course putting greens typically receive high pesticide applications to meet high quality demands. Research on pesticide fate in turf ecosystems is important to better understand the potential impact of pesticide use on the environment and human health. This research was conducted to evaluate the environmental fate of two commonly used insecticides--trichlorfon (dimethyl 2,2,2-trichloro-1-hydroxyethylphosphonate) and chlorpyrifos (O,O-diethyl O-3,5,6-trichloro-2-pyridylphosphorothioate)--in a creeping bentgrass (Agrostis palustris Huds.) putting green under customary field management practices at the University of California-Riverside Turf Research Facility during 1996 and 1997. The two insecticides were chosen because of their difference in water solubility, persistence, adsorption, and vapor pressure. Volatilization, clipping removal, and soil residues of the insecticides were quantified and leaching was monitored using lysimeters installed in putting green plots. Results showed trichlorfon volatilization, clipping removal, and leaching loss was insignificant (in the range of 0.0001-0.06% of applied mass) both in 1996 and 1997. No significant difference in clipping removal of trichlorfon and chlorpyrifos was observed in both years (0.06 and 0.05% of applied mass for trichlorfon and 0.15 and 0.19% of applied mass for chlorpyrifos, respectively, in 1996 and 1997), but significantly lower cumulative leaching and lower soil concentration was observed in 1997 than in 1996. Volatilization loss of chlorpyrifos was not significantly different between 1996 (2.05%) and 1997 (2.71%). Volatilization loss of trichlorfon in 1996 (0.01%) was significantly higher than in 1997 (0.008%). This study demonstrated the fraction of applied insecticides leaving the turf putting greens was minimal.

Environmental fate of metalaxyl and chlorothalonil applied to a bentgrass putting green under southern California climatic conditions

Putting greens usually receive high inputs of fertilizers and pesticides to meet the high demand for visual quality and to overcome the stress from close mowing and traffic. In this study, two commonly used fungicides, metalaxyl (methyl N-(methoxyacetyl)-N-(2,6-xylyl)-DL-alaninate) and chlorothalonil (2,4,5,6-tetrachloro-1,3-benzenedicarbonitrile), were evaluated for their partitioning and persistence in a bentgrass (Agrostis palustris Huds) putting green under southern California climatic conditions. The putting green site was constructed according to the US Golf Association (USGA) specifications. Lysimeter assemblies installed at the center of each plot were used to monitor the leachate, flux chambers were used to measure volatilization, clippings were collected to determine the residues on grass, and soil cores were sampled to determine residues in the soil profile. Results showed that cumulative volatilization loss accounted for 0.10 and 0.02%, clipping removal 0.11 and 0.13%, and cumulative leaching 0.71 and 0.002% of the applied metalaxyl and chlorothalonil, respectively. The two fungicides were mainly found in the top 10 cm of the soil profile due to the high organic carbon content in the thatch and mat layers. The dissipation half-life was 1.4 days for metalaxyl and 4.9 days for chlorothalonil on grass, shorter than those found in agricultural fields. This study showed that, under normal turf management practices, the offsite transport of the parent fungicides was minimal. Future research should focus on investigating the fate and mobility of the metabolites of the fungicides.

The effects of collagen fragments on the extracellular matrix metabolism of bovine and human chondrocytes

Cartilage matrix degradation generates collagen type II fragments. The objective of this study is to explore the possibility that these collagen fragments may be part of an endogenous metabolic feedback. Initially, collagen fragments were extracted from normal or osteoarthritic cartilage, as part of a matrix fragment preparation. Later, collagen fragments were generated by digestion of bovine collagen type II with bacterial collagenase (col2f). These fragments were added to cultures of isolated chondrocytes (bovine and human) and cartilage explants (human). In a dose-dependent manner, col2f caused inhibition of cell attachment to collagen, inhibition of collagen synthesis, and induction of matrix degradation. In addition, when col2f were added to human cartilage explants, an induction of gelatinase activity was detected in the media. These data sets present first evidence that degradation products of collagen may be directly involved in the regulation of cartilage homeostasis.

Detection of tumor mutations in the presence of excess amounts of normal DNA

Mutations are important markers in the early detection of cancer. Clinical specimens such as bodily fluid samples often contain a small percentage of mutated cells in a large background of normal cells. Thus, assays to detect mutations leading to cancer need to be highly sensitive and specific. In addition, they should be possible to carry out in an automated and high-throughput manner to allow large-scale screening. Here we describe a screening method, termed PPEM (PNA-directed PCR, primer extension, MALDI-TOF), that addresses these needs more effectively than do existing methods. DNA samples are first amplified using peptide nucleic acid (PNA)-directed PCR clamping reactions in which mutated DNA is preferentially enriched. The PCR-amplified DNA fragments are then sequenced through primer extension to generate diagnostic products. Finally, mutations are identified using matrix-assisted laser-desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry. This method can detect as few as 3 copies of mutant alleles in the presence of a 10,000-fold excess of normal alleles in a robust and specific manner. In addition, the method can be adapted for simultaneous detection of multiple mutations and is amenable to high-throughput automation.

The expression of human alpha -like globin genes in transgenic mice mediated by bacterial artificial chromosome

After screening a bacterial artificial chromosome of human genomic DNA library with human HS-40, zeta-, alpha-, and theta-globin probes, a 110-kb clone bearing the whole human alpha-globin gene cluster was obtained and rare restriction endonuclease mapping was performed. The bacterial artificial chromosome DNA was isolated, and transgenic mice were generated. Three founders were detected from 35 newborn mice. The copy numbers were 1, 2, and 2, and the expression of human alpha-globin genes in various tissues at different developmental stages in the transgenic mice was assayed. The human alpha-globin mRNA can be detected in bone marrow, kidney, liver, brain, but not in muscle, testis, or thymus. The human zeta-globin genes were switched off, and the alpha-globin genes were switched at day 11.5 in mouse embryo, indicating that developmental stage-specific expression of the alpha-like globin genes was properly regulated. The human alpha-globin mRNA ranged between 17-68% of the endogenous mouse alpha-globin, suggesting that the expression of human alpha-globin genes is integration site-dependent in transgenic mice. The ratio of human alpha(2)- and alpha(1)-globin gene expression in adult transgenic mouse is about 2.5:1 similar to the expression in human.

Acquisition of a specific and potent PTP1B inhibitor from a novel combinatorial library and screening procedure

Protein-tyrosine phosphatases (PTPases) form a large family of enzymes that serve as key regulatory components in signal transduction pathways. Defective or inappropriate regulation of PTPase activity leads to aberrant tyrosine phosphorylation, which contributes to the development of many human diseases including cancers and diabetes. For example, recent gene knockout studies in mice identify PTP1B as a promising target for anti-diabetes/obesity drug discovery. Thus, there is intense interest in obtaining specific and potent PTPase inhibitors for biological studies and pharmacological development. However, given the highly conserved nature of the PTPase active site, it is unclear whether selectivity in PTPase inhibition can be achieved. We describe a combinatorial approach that is designed to target both the active site and a unique peripheral site in PTP1B. Compounds that can simultaneously associate with both sites are expected to exhibit enhanced affinity and specificity. We also describe a novel affinity-based high-throughput assay procedure that can be used for PTPase inhibitor screening. The combinatorial library/high-throughput screen protocols furnished a small molecule PTP1B inhibitor that is both potent (K(i) = 2.4 nm) and selective (little or no activity against a panel of phosphatases including Yersinia PTPase, SHP1, SHP2, LAR, HePTP, PTPalpha, CD45, VHR, MKP3, Cdc25A, Stp1, and PP2C). These results demonstrate that it is possible to acquire potent, yet highly selective inhibitors for individual members of the large PTPase family of enzymes.

Synthesis and structure-activity relationships of N-(1-benzylpiperidin-4-yl)arylacetamide analogues as potent sigma1 receptor ligands

A series of N-(1-benzylpiperidin-4-yl)arylacetamides were synthesized and evaluated for their binding properties for sigma1 and sigma2 receptors. In agreement with previously reported sigma1/sigma2 receptor binding data for N-(1-benzylpiperidin-4-yl)phenylacetamide, all of the N-(1-benzylpiperidin-4-yl)arylacetamide compounds reported below displayed higher affinity for sigma1 vs sigma2 receptors. Replacement of the phenyl ring of the phenylacetamide moiety with a thiophene, naphthyl, or indole aromatic ring had no significant effect on the sigma1 receptor affinity. Replacement of the phenyl ring with an imidazole or pyridyl aromatic ring resulted in a >60-fold loss in affinity for sigma1 receptors and no significant binding affinity for sigma2 receptors. Substitution on the aromatic ring of the benzyl group showed a similar or slightly decreased affinity for sigma1 receptors. Substitution on the aromatic rings of both the phenylacetamide moiety and the benzyl group with a halogen resulted in a similar affinity for sigma(1) receptors and a significantly increased affinity for sigma2 receptors. Comparative molecular field analysis revealed that electrostatic properties of the substituents in the phenylacetamide aromatic ring strongly influenced binding to sigma1 receptors. Compounds 1, 10, 18, 22, 37, and 40 showed the highest selectivity for sigma1 receptors with K(i) (sigma2) to K(i) (sigma(1)) ratios of 100, >92, >122, 77, 74, and 80, respectively. In agreement with previously reported results, the phenylacetamide analogues had no binding affinity for dopamine receptors (D2/D3).

Two-step transcriptional amplification as a method for imaging reporter gene expression using weak promoters

We are developing assays to image tissue-specific reporter gene expression in living mice by using optical methods and positron emission tomography. Approaches for imaging reporter gene expression depend on robust levels of mRNA and reporter protein. Attempts to image reporter gene expression driven by weak promoters are often hampered by the poor transcriptional activity of such promoters. Most tissue-specific promoters are weak relative to stronger but constitutively expressing viral promoters. In this study, we have validated methods to enhance the transcriptional activity of the prostate-specific antigen promoter for imaging by using a two-step transcriptional amplification (TSTA) system. We used the TSTA system to amplify expression of firefly luciferase (fl) and mutant herpes simplex virus type 1 thymidine kinase (HSV1-sr39tk) in a prostate cancer cell line (LNCaP). We demonstrate approximately 50-fold (fl) and approximately 12-fold (HSV1-sr39tk) enhancement by using the two-step approach. The TSTA system is observed to retain tissue selectivity. A cooled charge-coupled device optical imaging system was used to visualize the amplified fl expression in living mice implanted with LNCaP cells transfected ex vivo. These imaging experiments reveal a approximately 5-fold gain in imaging signal by using the TSTA system over the one-step system. The TSTA approach will be a valuable and generalizable tool to amplify and noninvasively image reporter gene expression in living animals by using tissue-specific promoters. The approaches validated should have important implications for study of gene therapy vectors, cell trafficking, transgenic models, as well as studying development of eukaryotic organisms.