[Realization of a new segmental bioelectrical impedance method for assessing body composition: correlation analysis of human body parameters]

The method of segmental bioelectrical impedance analysis for assessing body composition requires measurement of segmental lengths and cross-sectional areas; thus its complexity is increased. This paper reports the correlation analysis of human body parameters and the linear regressions for predicting segmental parameters by use of gender, height and weight. Accordingly, segmental impedance analysis is simplified.

NF-kappaB signaling pathway governs TRAIL gene expression and human T-cell leukemia virus-I Tax-induced T-cell death

The Tax oncoprotein encoded by human T-cell leukemia virus induces both T-cell activation and apoptosis. The mechanism by which Tax induces apoptosis has remained unclear. Using genetically manipulated T-cell lines, we demonstrate that Tax-induced T-cell death is dependent on NF-kappaB signaling. Tax fails to induce apoptosis in T cells lacking IkappaB kinase gamma (IKKgamma), an essential component of the NF-kappaB signaling pathway. This defect was rescued when the mutant cells were reconstituted with exogenous IKKgamma. We further demonstrate that the Tax-induced T-cell death is mediated by TNF (tumor necrosis factor)-related apoptosis-inducing ligand (TRAIL), because this event can be effectively inhibited by a TRAIL-blocking antibody. Consistent with this functional aspect, Tax stimulates the expression of TRAIL mRNA. Finally, we provide genetic evidence demonstrating that the NF-kappaB signaling pathway is essential for TRAIL gene induction by both Tax and T-cell activation signals. These studies reveal a novel function of the NF-kappaB signaling pathway and suggest a key mechanism by which Tax induces T-cell death.

[Effects of quinacrine on gut-origin bacteria/endotoxin translocation in rats with gut ischemia/reperfusion injury]

OBJECTIVE

To explore the influence of quinacrine, which is an inhibitor of phospholipase A2, on gut-origin bacteria/endotoxin translocation in rats with gut ischemia/reperfusion injury.

METHODS

Forty-two Wistar rats were randomly divided into normal control (C, n = 6), gut ischemia/reperfusion injury control (IC, n = 12), quinacrine use at 3 hours after the injury(3 h, n = 12), and quinacrine use at 12 hours after the injury (12 h, n = 12) groups. The contents of blood endotoxin and TNF alpha in venae cavae and portal vein were measured in all groups. At the same time, tissue samples from mesenteric lymph nodes, liver, lungs and kidneys were harvested for bacterial culture.

RESULTS

Plasma contents of endotoxin and TNF alpha were lowered in both quinacrine treatment groups (P < 0.01). The incidence of bacterial/endotoxin translocation was decreased by quinacrine use in mesenteric lymph nodes, lungs, liver and kidneys after the injury (P < 0.05 approximately 0.01).

CONCLUSION

Early application of quinacrine in Wistar rats inflicted by gut ischemia reperfusion injury could obviously lower bacterial/endotoxin translocation and ameliorate the release of pro-inflammatory mediators and cytokines, thus attenuating injury to remote organs.

Activation by IKKalpha of a second, evolutionary conserved, NF-kappa B signaling pathway

In mammals, the canonical nuclear factor kappaB (NF-kappaB) signaling pathway activated in response to infections is based on degradation of IkappaB inhibitors. This pathway depends on the IkappaB kinase (IKK), which contains two catalytic subunits, IKKalpha and IKKbeta. IKKbeta is essential for inducible IkappaB phosphorylation and degradation, whereas IKKalpha is not. Here we show that IKKalpha is required for B cell maturation, formation of secondary lymphoid organs, increased expression of certain NF-kappaB target genes, and processing of the NF-kappaB2 (p100) precursor. IKKalpha preferentially phosphorylates NF-kappaB2, and this activity requires its phosphorylation by upstream kinases, one of which may be NF-kappaB-inducing kinase (NIK). IKKalpha is therefore a pivotal component of a second NF-kappaB activation pathway based on regulated NF-kappaB2 processing rather than IkappaB degradation.

[The effects of gut -- origin lipopolysaccharide translocation on the apoptosis of lymphocytes in scalded rats]

OBJECTIVE

To investigate the relationship between lymphocyte apoptosis in spleen and mesenteric lymph nodes (MLNs) and gut -- origin lipopolysaccharide (LPS) translocation after severe scalding in rats.

METHODS

Wistar rats inflicted 30% TBSA III degree scalding were employed as the model. Serum LPS levels in portal vein and vena cava were determined by limulus amebocyte lysate (LAL) test. Apoptotic lymphocytes in paraffin -- embedded spleen and MLNs sections were detected with TdT -- mediated and dUTP nick end labeling (TUNEL) and peroxidase (POD) staining. The images were taken by cooldccd camera system, and the count and optical density (OD) value of apoptotic lymphocytes were analyzed with software Spot and Imagine proplus 4.10a (IPP4.10a).

RESULTS

Serum LPS levels in portal vein and vena cava increased sharply in rats postburn (P < 0.01) and reached a peak value at 6 postburn hour (PBH). LPS level in portal vein was higher than that in vena cava (P < 0.01) in the period of 3 to 48 PBHs. The results of TUNEL -- POD staining and the count of apoptotic lymphocytes showed that the apoptotic cells were few in normal MLNs, but increased obviously postburn (P < 0.01), especially at 3 PBH. On the contrary, apoptotic lymphocytes were concentrated in spleen cortex before injury and decreased obviously postburn (P < 0.01), though a slight recovery was found after 24 PBH. Optical density of apoptotic lymphocytes was significantly reduced in spleen at 24 PBH, But the OD value of apoptotic lymphocytes in MLNs increased significantly within 48 PBHs when compared with that before injury (P < 0.01).

CONCLUSION

Gut -- origin endotoxemia in rat could occur in early postburn period. The LPS translocation might induce lymphocyte apoptosis in MLNs. The decreased apoptotic lymphocytes in spleen implied abnormal immune function in spleen.

Synthesis of substituted 5[H]phenanthridin-6-ones as potent poly(ADP-ribose)polymerase-1 (PARP1) inhibitors

1-, 2-, 3-, 4-, 8-, or 10-Substituted 5(H)phenanthridin-6-ones were synthesized and found to be potent PARP1 inhibitors. Among the 28 compounds prepared, some showed not only low IC(50) values (compound 1b, 10 nM) but also desirable water solubility characteristics. These properties, which are superior to the common PARP1 inhibitors such as benzamides and isoquinolin-1-ones, are essential for potential therapeutic usage. The variety of compounds allows SAR analysis of favored substituents and substituted positions on 5(H)phenanthridin-6-one ring.

Determination of the spin polarization of half-metallic CrO(2) by point contact Andreev reflection

Andreev reflection at a Pb/CrO(2) point contact has been used to determine the spin polarization of single-crystal CrO(2) films made by chemical vapor deposition. The spin polarization is found to be 0.96 +/- 0.01, which confirms that CrO(2) is a half-metallic ferromagnet, as theoretically predicted.

Visualizing pneumococcal infections in the lungs of live mice using bioluminescent Streptococcus pneumoniae transformed with a novel gram-positive lux transposon

Animal studies with Streptococcus pneumoniae have provided valuable models for drug development. In order to monitor long-term pneumococcal infections noninvasively in living mice, a novel gram-positive lux transposon cassette, Tn4001 luxABCDE Km(r), that allows random integration of lux genes onto the bacterial chromosome was constructed. The cassette was designed so that the luxABCDE and kanamycin resistance genes were linked to form a single promoterless operon. Bioluminescence and kanamycin resistance only occur in a bacterial cell if this operon has transposed downstream of a promoter on the bacterium's chromosome. S. pneumoniae D39 was transformed with plasmid pAUL-A Tn4001 luxABCDE Km(r), and a number of highly bioluminescent colonies were recovered. Genomic DNA from the brightest D39 strain was used to transform a number of clinical S. pneumoniae isolates, and several of these strains were tested in animal models, including a pneumococcal lung infection model. Strong bioluminescent signals were seen in the lungs of the animals containing these pneumococci, allowing the course and antibiotic treatment of the infections to be readily monitored in real time in the living animals. Recovery of the bacteria from the animals showed that the bioluminescent signal corresponded to the number of CFU and that the lux construct was highly stable even after several days in vivo. We believe that this lux transposon will greatly expand the ability to evaluate drug efficacy against gram-positive bacteria in living animals using bioluminescence.

Calreticulin functions as a molecular chaperone for the β-amyloid precursor protein 1 1Abbreviations used: Aβ, β-amyloid peptide; AD, Alzheimer’s disease; APP, β-amyloid precursor protein; CHAPS, 3-[(3-Cholamidopropyl)-dimethylammonio]-1-propanesulfonate; Crt, calreticulin; DMEM, Dulbecco’s Modified Eagle Medium; DMJ, deoxymannojirimycin; DTSSP, 3,3′-Dithio bis (sulfosuccinimidylpropionate); ECL, Enhanced Chemiluminescence; ER, endoplasmic reticulum; FBS, fetal bovine serum; HRP, horseradish peroxidase; kDa, kiloDaltons; MES, 2-(N-Morpholino) ethane sulfonic acid; NRS, normal rabbit serum; PBS, PBS; PMSF, phenymethylsulfonyl fluoride; PVDF, polyvinylidene fluoride

Processing of the beta-amyloid precursor protein (APP) in the endoplasmic reticulum and the Golgi apparatus may be critical in generating the beta-amyloid molecules linked to the pathogenesis of Alzheimer's disease. Since chaperone molecules such as calreticulin (Crt) have been shown to be important in the maturation of many glycoproteins, we investigated the interaction between Crt and APP. We show that APP binds transiently to Crt in a manner that is pH, divalent cation, and N-linked glycosylation-dependent. Both immature APP (containing only N-linked sugars) and mature APP (containing both N-linked and O-linked sugars) bind to Crt. Both proteins are part of a complex that appears to be large enough to accommodate other proteins as well. However, while most of the immature form is associated with the complexes, very little of the mature form is. The interaction between APP and Crt is likely to be of physiological significance with respect to APP maturation since Crt is involved in quality control of nascent glycoproteins in the secretory pathway.

[Prognostic influence of parapharyngeal space involvement in nasopharyngeal carcinoma]

OBJECTIVE

To explore the prognostic influence of parapharyngeal space involvement in nasopharyngeal carcinoma (NPC).

METHODS

From Jan. 1987 to Dec. 1994, 197 previously untreated NPC patients were examined by CT scan. The prognostic factors ware evaluated by univariate and multivariate analyses on SPSS 8.0 software.

RESULTS

The actual survival rate, disease-free survival rate and local failure-free rate were negatively affected by the presence of parapharyngeal space involvement (P = 0.0115, P = 0.0035, P = 0.0367). The 5-year actual survival rate, disease-free survival rate and local failure-free rate in patients without tumor invasion to parapharyngeal space was 87.9%, 88.0% and 96.9%, respectively. The survival rate in patients with tumor invasion to prestyloid space was 75.0%, 71.2% and 93.7%, respectively. That in patients with tumor invasion to poststyloid space was 60.5%, 57.7% and 86.8%, respectively. The 5-year distant metastasis-free survival rate was 88.1% in patients without poststyloid involvement as compared to 73.8% in those with poststyloid involvement.

CONCLUSION

The survival and local tumor control are affected by parapharyngeal space involvement. Distant metastasis is more likely to occur when the tumor growth involves poststyloid space.

Inhibition of the HIV-1 rev–RRE complex formation by unfused aromatic cations

RNA viruses cause a wide range of human diseases. Development of new agents to target such viruses is an active area of research. Towards this goal, a series of diphenylfuran cations as potential inhibitors of the Rev-RRE complex have been designed and synthesized. Analysis of the interaction of the diphenylfurans with RRE and TAR RNA model systems by gel shift assays indicates that they exhibit both sequence and structure-dependent binding modes. Our results show a strong interaction between the diphenylfuran ring system and RRE bases, while the TAR interactions are much weaker with the compounds that are the best inhibitors of Rev-RRE.

Effect of benzene, toluene, xylene on the semen quality and the function of accessory gonad of exposed workers

The effects on semen and the function of accessory gonad of workers after short and long term exposure to benzene, toluene, and xylene were examined. The semen and blood of 24 married workers exposed to benzene, toluene, and xylene were collected. Routine sperm characteristic, acrosin activity, and Lactate dehydrogenase C4 (LDH-C4) relative activity were detected. The results showed that benzene, toluene, and xylene were found in the blood and semen of some ex-workers at workplaces where the air concentration of benzene, toluene, and xylene exceeded the maximum allowable concentration (MAC). No such solvents were detected in the blood and semen of workers of the control group. The sperm vitality and sperm motility decreased in the exposed workers. The mean acrosin activity, gamma-GT activity and LDH-C4 relative activity in the exposed workers were lower, and fructose concentration was higher than those in the control. There were negative correlations between sperm vitality, sperm activity, acrosin activity, or LDH-C4 relative activity and working history. These results suggest that the mixture of these solvents could affect the sperm and the function of accessory gonad. This might be one reason of the abnormal pregnancy outcome among the wives of workers exposed to benzene, toluene, and xylene.

[42 years' experience on the prevention and treatment of systemic infection after severe burn]

OBJECTIVE

To summarize the experience of the management of 329 patients with major burn accompanied by severe systemic infection during the past 42 years, so as to help improve the treatment standard.

METHODS

One thousand and one hundred twenty seven cases with major burns (TBSA > 50%) were admitted to our hospital during the past 42 years. The incidence of postburn systemic infection and change in the mortality were analyzed in terms of 3 periods, i.e. 1958 to 1980, 1981 to 1990 and 1991 to 2000.

RESULTS

Postburn systemic infection developed in 329 out of 1127 cases with the morbidity of 29.4%. The incidences of the infection were 48.5%, 29.3% and 13.1% in the 3 periods, consecutively, with significant differences between them (P < 0.01 similar 0.05). During the 3 periods of past 42 years, the overall cure rate and cure rates in patients with different TBSA increased gradually, especially in those with TBSA Larger than 70%.

CONCLUSION

The management of pastburn systemic infection was satisfactorily achieved by early comprehensive clinical measures such as immediate fluid resuscitation, early feeding, appropriate application of antibiotics and early escharectomy en masse, etc. which were established on the basis of experimental results.

[An experimental study on the release of endotoxin from gram negative bacteria induced by antibiotics]

OBJECTIVE

To explore the characteristics and possible mechanism of LPS released from Gram negative bacteria induced by antibiotics, so as to improve clinical management of endotoxemia and sepsis.

METHODS

Cultures containing PA103 subtype of Pseudomonas aeruginosa (PA) and E coli 25922 subtype of E coli were treated with four kinds of antibiotics as Imipenam (IMP), ceftazidime (CTZ), amikacin (AMN) and pefloxacine (PFX) in four concentrations of 0.5, 1, 5 and 10 MIC for 8 hours. The changes in the bacterial quantity and morphology and the supernatant levels of free LPS of the culture media were observed at different time points.

RESULTS

All the four kinds of antibiotics could kill the tested bacteria in similar degree, but lead to the different types of morphological changes of the bacteria. In detail, IMP could convert the bacteria into spherical shape, while CTZ and PFX made the bacteria to filamentous shape. But AMN could induce lysis of bacterial thallus. Under same condition, the ability of different kinds and concentrations of antibiotics to induce LPS release ranked as CTZ > PFX > IMP > AMN, 0.5MIC > 1MIC > 5MIC > 10MIC. Along with the prolongation of the action time, the LPS release increased. Furthermore, PA103 released less endotoxin than E. coli after the action of antibiotics.

CONCLUSION

All of the four antibiotics, i,e, IMP, CTZ, AMN and PFX could induce PA103 and E coli 25922 to release different levels of LPS, which was related to bacterial morphological changes. The LPS release from the bacteria was correlated to the antibiotics applied, concentrations, action time and the bacterial features. Antibiotics with less ability of inducing LPS release were recommended for clinical management of the sepsis and/or septic shock caused by Gram negative bacteria.

[Study of noninvasive intracranial pressure monitoring by bioelectric impedance method]

The changes of intracranial components and corresponding brain impedance were analyzed while intracranial pressure was increasing, and the relation of intracranial pressure pulse wave and brain impedance pulse wave were discussed. A theory of noninvasive intracranial pressure monitoring by bioelectric impedance was put forward. The result of primary experiment suggested that the theory be feasible.

Engineering new bone tissue in vitro on highly porous poly(alpha-hydroxyl acids)/hydroxyapatite composite scaffolds

Engineering new bone tissue with cells and a synthetic extracellular matrix (scaffolding) represents a new approach for the regeneration of mineralized tissues compared with the transplantation of bone (autografts or allografts). In the present work, highly porous poly(L-lactic acid) (PLLA) and PLLA/hydroxyapatite (HAP) composite scaffolds were prepared with a thermally induced phase separation technique. The scaffolds were seeded with osteoblastic cells and cultured in vitro. In the pure PLLA scaffolds, the osteoblasts attached primarily on the outer surface of the polymer. In contrast, the osteoblasts penetrated deep into the PLLA/HAP scaffolds and were uniformly distributed. The osteoblast survival percentage in the PLLA/HAP scaffolds was superior to that in the PLLA scaffolds. The osteoblasts proliferated in both types of the scaffolds, but the cell number was always higher in the PLLA/HAP composite scaffolds during 6 weeks of in vitro cultivation. Bone-specific markers (mRNAs encoding bone sialoprotein and osteocalcin) were expressed more abundantly in the PLLA/HAP composite scaffolds than in the PLLA scaffolds. The new tissue increased continuously in the PLLA/HAP composite scaffolds, whereas new tissue formed only near the surface of pure PLLA scaffolds. These results demonstrate that HAP imparts osteoconductivity and the highly porous PLLA/HAP composite scaffolds are superior to pure PLLA scaffolds for bone tissue engineering.

NF-kappaB-inducing kinase regulates the processing of NF-kappaB2 p100

Processing of the nf(kappa)b2 gene product p100 to generate p52 is an important step in NF-kappaB regulation. We show that this step is negatively regulated by a processing-inhibitory domain (PID) within p100 and positively regulated by the NF-kappaB-inducing kinase (NIK). While the PID suppresses the constitutive processing of p100, NIK induces p100 processing by stimulating site-specific phosphorylation and ubiquitination of this precursor protein. Further, a natural mutation of the gene encoding NIK in alymphoplasia (aly) mice cripples the function of NIK in p100 processing, causing a severe defect in p52 production. These data suggest that NIK is a specific kinase regulating p100 processing and explain why the aly and nf(kappa)b2 knockout mice exhibit similar immune deficiencies.

A novel proton-dependent nucleoside transporter, CeCNT3, from Caenorhabditis elegans

In this study, we describe the cloning and characterization of a proton-dependent, broadly selective nucleoside transporter from Caenorhabditis elegans. Recently, we constructed a broadly selective nucleoside transporter which accepts both purine and pyrimidine nucleosides. Based on these studies, we hypothesized that CNTs with novel substrate selectivities exist in nature and that a CNT homolog in the C. elegans genomic database may function as a broadly selective nucleoside transporter. We cloned the cDNA for this transporter, termed CeCNT3 because of its broad selectivity, using polymerase chain reaction-based methods. CeCNT3 is predicted to have 575 amino acid residues (63.4 kDa) with 11 to 14 putative transmembrane domains and exhibits approximately 30% identity to members of the mammalian CNT family. This transporter exhibits a novel substrate selectivity, transporting a wide range of purine and pyrimidine nucleosides (inosine, guanosine, adenosine, uridine, and thymidine) but not cytidine. The apparent Km values for inosine and thymidine are 15.2 +/- 5.3 microM and 11.0 +/- 2.4 microM, respectively. Kinetic studies demonstrate that purine and pyrimidine nucleosides share a common recognition site in the transporter. In contrast to all known members of the mammalian CNT family, CeCNT3-mediated transport of nucleosides is proton-, but not sodium-, dependent. Mutation of tyrosine 332 in CeCNT3 decreased both the maximum uptake rate and apparent Km of thymidine, suggesting that this residue is in the domain of nucleoside recognition and translocation. The broad nucleoside specificity of CeCNT3 may be explained by this and other residues that restrict purine and pyrimidine nucleoside uptake and that discriminate among pyrimidine nucleosides.

[Study on the pharmacokinetics of Imipenem cilastatin in burn patients during the acute phase]

OBJECTIVE

To investigate the pharmacokinetic characteristics of Imipenem/cilastatin in burn patients during the acute phase.

METHODS

Imipenem concentrations in the plasma, blister and, interstitial fluids and urine of 6 burn patients (P group) were determined during the acute phase by high performance liquid chromatography after the first initial dose. Pharmacokinetic parameters were thus produced and statistically analyzed by program package STAT 5. Ten healthy volunteers served as control group (C group).

RESULTS

Compared to those in control group, pharmacokinetic parameters of Imipenem exhibited evident difference, such as prolonged half-life [(1.56 plus minus 0.55) h vs (1.06 plus minus 0.24) h] and enlarged distributing volume (16.16 plus minus 4.26) vs (13.96 plus minus 7.10). Imipenem could be detected in the blister and interstitial fluids of burn patients 1 hr after the initial dose. Renal clearance of Imipenem was positively correlated to creatinine clearance (r = 0.5834).

CONCLUSION

The intervals between doses should better be prolonged when loaded-dosage of Imipenem was administered in burn patients during the acute phase. Imipenem could penetrate II and III degree burn wound when given in the acute phase. Attention should be paid to renal function when Imipenem was given.

A novel Rb- and p300-binding protein inhibits transactivation by MyoD

The retinoblastoma protein (Rb) regulates both the cell cycle and tissue-specific transcription, by modulating the activity of factors that associate with its A-B and C pockets. In skeletal muscle, Rb has been reported to regulate irreversible cell cycle exit and muscle-specific transcription. To identify factors interacting with Rb in muscle cells, we utilized the yeast two-hybrid system, using the A-B and C pockets of Rb as bait. A novel protein we have designated E1A-like inhibitor of differentiation 1 (EID-1), was the predominant Rb-binding clone isolated. It is preferentially expressed in adult cardiac and skeletal muscle and encodes a 187-amino-acid protein, with a classic Rb-binding motif (LXCXE) in its C terminus. Overexpression of EID-1 in skeletal muscle inhibited tissue-specific transcription. Repression of skeletal muscle-restricted genes was mediated by a block to transactivation by MyoD independent of G(1) exit and, surprisingly, was potentiated by a mutation that prevents EID-1 binding to Rb. Inhibition of MyoD may be explained by EID-1's ability to bind and inhibit p300's histone acetylase activity, an essential MyoD coactivator. Thus, EID-1 binds both Rb and p300 and is a novel repressor of MyoD function.

Domain-specific interaction with the I kappa B kinase (IKK)regulatory subunit IKK gamma is an essential step in tax-mediated activation of IKK

The human T-cell leukemia virus type 1 Tax oncoprotein deregulates the NF-kappa B signaling pathway by persistently stimulating a key signal transducer, the I kappa B kinase (IKK). Tax physically associates with the IKK regulatory subunit, IKK gamma, although the underlying biochemical mechanism and functional significance remain unclear. We show that the Tax-IKK gamma interaction requires two homologous leucine zipper domains located within IKK gamma. These leucine zipper domains are unique for the presence of a conserved upstream region that is essential for Tax binding. Site-directed mutagenesis analysis revealed that a leucine-repeat region of Tax is important for IKK gamma binding. Interestingly, all the Tax mutants defective in IKK gamma binding failed to engage the IKK complex or stimulate IKK activity, and these functional defects can be rescued by fusing the Tax mutants to IKK gamma. These results provide mechanistic insights into how Tax specifically targets and functionally activates the cellular kinase IKK.

Activation of I-kappaB kinase by the HTLV type 1 Tax protein: mechanistic insights into the adaptor function of IKKgamma

The Tax protein encoded by human T cell leukemia virus type 1 (HTLV-1) induces constitutive nuclear expression of the transcription factor NF-kappaB, causing aberrant expression of a large array of cellular genes. Tax activates NF-kappaB by stimulating the activity of the I-kappaB kinase (IKK), which in turn leads to phosphorylation and degradation of the NF-kappaB inhibitor I-kappaBalpha. In normal T cells, IKK activation occurs transiently on cellular stimulation through the T cell receptor (TCR) and the CD28 costimulatory molecule. However, this inducible kinase is constitutively activated in Tax-expressing and HTLV-1-infected T cells, which contributes to the deregulated nuclear expression of NF-kappaB. As a genetic approach to dissect the pathways mediating IKK activation by Tax and T cell activation signals, somatic cell mutagenesis was performed to isolate signaling-defective mutant Jurkat T cell lines. One of the mutant cell lines was shown to have a defect in NF-kappaB activation by both T cell mitogens and Tax. Interestingly, this mutant cell line lacks expression of the IKK regulatory protein, IKKgamma. Expression of exogenous IKKgamma in the mutant cells restored NF-kappaB activation, thus confirming the essential role of this regulatory factor in IKK activation by the cellular and viral stimuli. Mechanistic studies have shown that Tax physically interacts with IKKgamma via specific domains, including two homologous leucine zipper motifs present in IKKgamma. The Tax/IKKgamma interaction serves to recruit Tax to the IKK catalytic subunits, IKKalpha and IKKbeta, and this recruitment appears to be an essential mechanism by which Tax stimulates the activity of IKK.

Activation of IKKalpha and IKKbeta through their fusion with HTLV-I tax protein

Human T-cell leukemia virus type I (HTLV-I) Tax protein persistently stimulates the activity of IkappaB kinase (IKK), resulting in constitutive activation of the transcription factor NF-kappaB. Tax activation of IKK requires physical interaction of this viral protein with the IKK regulatory subunit, IKKgamma. The Tax/IKKgamma interaction allows Tax to engage the IKK catalytic subunits, IKKalpha and IKKbeta, although it remains unclear whether this linker function of IKKgamma is sufficient for supporting the Tax-specific IKK activation. To address this question, we have examined the sequences of IKKgamma required for modulating the Tax/IKK signaling. We demonstrate that when fused to Tax, a small N-terminal fragment of IKKgamma, containing its minimal IKKalpha/beta-binding domain, is sufficient for bringing Tax to and activating the IKK catalytic subunits. Disruption of the IKKalpha/beta-binding activity of this domain abolishes its function in modulating the Tax/IKK signaling. We further demonstrate that direct fusion of Tax to IKKalpha and IKKbeta leads to activation of these kinases. These findings suggest that the IKKgamma-directed Tax/IKK association serves as a molecular trigger for IKK activation.

Stressing-out DNA? The contribution of serine-phosphodiester interactions in catalysis by uracil DNA glycosylase

The DNA repair enzyme uracil DNA glycosylase (UDG) pinches the phosphodiester backbone of damaged DNA using the hydroxyl side chains of a conserved trio of serine residues, resulting in flipping of the deoxyuridine from the DNA helix into the enzyme active site. We have investigated the energetic role of these serine-phosphodiester interactions using the complementary approaches of crystallography, directed mutagenesis, and stereospecific phosphorothioate substitutions. A new crystal structure of UDG bound to 5'-HO-dUAAp-3' (which lacks the 5' phosphodiester group that interacts with the Ser88 pinching finger) shows that the glycosidic bond of dU has been cleaved, and that the enzyme has undergone the same specific clamping motion that brings key active site groups into position as previously observed in the structures of human UDG bound to large duplex DNA substrates. From this structure, it may be concluded that glycosidic bond cleavage and the induced fit conformational change in UDG can occur without the 5' pinching interaction. The S88A, S189A, and S192G "pinching" mutations exhibit 360-, 80-, and 21-fold damaging effects on k(cat)/K(m), respectively, while the S88A/S189A double mutant exhibits an 8200-fold damaging effect. A free energy analysis of the combined effects of nonbridging phosphorothioate substitution and mutation at these positions reveals the presence of a modest amount of strain energy between the compressed 5' and 3' phosphodiester groups flanking the bound uridine. Overall, these results indicate a role for these serine-phosphodiester interactions in uracil flipping and preorganization of the sugar ring into a reactive conformation. However, in contrast to a recent proposal [Parikh, S. S., et al. (2000) Proc Natl. Acad. Sci. 94, 5083], there is no evidence that conformational strain of the glycosidic bond induced by serine pinching plays a major role in the 10(12)-fold rate enhancement brought about by UDG.