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At least 1,765 records · Page 98Linked to original sources
PubMed2000

Second-look laparotomy after modified posterior exenteration: patterns of persistence and recurrence in patients with stage III and stage IV ovarian cancer.

OBJECTIVE: The purpose of this study was to determine patterns of persistence and recurrence in patients with advanced ovarian cancer (stage IIIC and stage IV) after modified posterior exenteration. STUDY DESIGN: Retrospective chart review was used to determine patterns of persistence and recurrence of disease in patients undergoing modified posterior exenteration. From January 1, 1987, to September 15, 1998, 151 of 212 (71.2%) patients undergoing modified posterior exenteration in addition to other cytoreductive surgical procedures for stage IIIC and stage IV ovarian cancer underwent second-look laparotomy. The average age of the patients was 60.3 years (range, 20.3-86.3). A total of 207 of the 212 (97.6%) had grade 2 or 3 disease. Papillary serous carcinoma (113/212; 53.3%) and adenocarcinoma (75/212; 35.4%) were the most frequent cell types encountered. After initial cytoreductive surgery, minimal disease (<5 mm) was present in 206 of the 212 (96.2%) patients with 153 of 212 (72.2%) having no visible residual disease. There were 4 (1.9%) postoperative deaths. In 13 patients (6.1%) progressive disease was noted. Second-look laparotomy was not undertaken in 61 of the 212 (28%) patients. Fluid for cytologic testing was obtained from all four intra-abdominal quadrants, and biopsies of previously noted sites of disease were performed, in addition to random biopsies of diaphragmatic peritoneum, colonic gutters, and pelvic peritoneum. If present, the retroperitoneal lymph nodes were resected; biopsy specimens of these sites were obtained if there was no evidence of intraperitoneal disease. RESULTS: Findings at second-look laparotomy were negative for cancer in 85 of 151 (56.3%) and positive for cancer in 66 of 151 (43.7%). Only 8 of 151 (5.3%) patients had persistent disease in the pelvis. In the remainder (58/151; 38.4%) disease was found either in the upper abdomen or in the bowel mesentery. Recurrence was documented in the upper abdomen only (71/212; 33.5%), upper abdomen and pelvis (18/212; 8.5%), multiple sites excluding the pelvis (22/212; 10.4%), pelvis only (2/212; 0. 9%), chest alone (5/212; 2.4%), head alone (4/212; 1.9%), or groin alone (2/212; 0.9%). Median survival in the overall group was 51.1 months, with estimated 5- and 10-year survival rates of 44.2% and 32. 9%, respectively. CONCLUSIONS: Modified posterior exenteration is an effective surgical means of eliminating pelvic disease in patients with advanced ovarian cancer. Results of second-look laparotomy confirmed that only 8 of 151 (5.3%) had persistent disease in the pelvis.

Adult↗
PubMed2000

Prospective study of modified condylotomy for treatment of nonreducing disk displacement.

OBJECTIVE: This study was performed to provide an objective assessment of the outcome of modified condylotomy for treatment of the painful temporomandibular joint with nonreducing disk displacement (Wilkes late stage III, IV, V). STUDY DESIGN: A prospective study of 31 consecutive patients (43 joints) was conducted. All patients had nonreducing disk displacement verified by means of disk imaging. Independent evaluations were performed to assess pain, dysfunction, and progression of disease. The examinations were performed before modified condylotomy and at intervals up to 1 year after the operation. Eighteen patients (26 joints) completed the required examinations. Patient-based assessments were completed for pain and diet on 15 of these 18 patients (23 joints) 3 years after the operation. RESULTS: Visual analog scale (VAS) scores (mean +/- SE) for pain improved from 7.4 +/- 0.4 before modified condylotomy to 2.4 +/- 0.5 1 year later (P <. 001). Joints with degenerative joint disease (Wilkes stage IV, V) had less satisfactory pain relief compared with stage III joints (3. 6 +/- 0.9 vs 1.1 +/- 0.4, P =.05) and an 11-fold higher risk (P <. 04) for serious residual pain (VAS score >4). Dietary restrictions improved from a mean VAS score of 5.3 +/- 0.7 before the operation to 7.7 +/- 0.5 1 year later (P =.02). Minor differences between mean VAS scores at 1 (2.1 +/- 0.5) and 3 (2.1 +/- 0.5) years for pain, and 1 (7.4 +/- 0.6) and 3 (8.1 +/- 0.6) years for diet, were not significant. Mean maximal interincisal opening was 36.7 +/- 2.0 mm before the operation, and this improved to 40.1 +/- 2.0 mm 1 year later (P <.02). Mean contralateral movement was 8.3 +/- 0.5 mm before the operation and 8.4 +/- 0.6 mm 1 year after the operation (P >.05). None of the 12 Wilkes late III joints progressed to Wilkes IV or V, and none of the 14 Wilkes IV, V joints showed evidence of further bone resorption. The rate for reoperation was 4%. Minor complications occurred in 5 patients and were resolved in all but 1 a year later. When these outcomes were judged by 7 American Association of Oral and Maxillofacial Surgeons assessment indices for internal derangement, the mean rate of favorable outcome was 87%. CONCLUSION: Modified condylotomy is a safe and effective operation for treating pain and diminished function of temporomandibular joints with nonreducing disk displacement. It also seems to be an effective treatment for slowing further progression of the internal derangement and associated pathologic conditions.

Adult↗
PubMed2001

A modified technique for measurement of nasal transepithelial potential difference in infants.

OBJECTIVE: To establish a method for measuring nasal transepithelial potential difference (PD) in infants. STUDY DESIGN: A modified infant method (smaller catheter size, reduced flow rates, and shorter protocol time) was compared with an established adult nasal PD method in 10 adult volunteers (4 with cystic fibrosis [CF]). Nasal PD was measured in 13 infants with a possible diagnosis of CF. RESULTS: Recordings were similar for the established and the modified methods in adult volunteers. An amiloride concentration of 10(-4) mol/L was necessary for full inhibition of amiloride-sensitive sodium ion (Na(+)) transport. Of the 13 infants, 2 had PD values suggestive of CF (mean baseline PD, -50.1 mV and -31.4 mV; maximum baseline PD, -61 mV and -49 mV; change in PD after perfusion with zero chloride solution with isoprenaline and amiloride [DeltazeroCl(-)/Iso], -1 mV and +3.5 mV), and 11 had normal values (mean +/- SEM baseline PD, -13.2 +/- 1.0 mV; maximum baseline PD, -21.4 +/- 2.0; DeltazeroCl(-)/Iso, -15.3 +/- 1.9 mV). These results correlated with subsequent sweat test data, mutation analysis, and clinical outcome. CONCLUSION: Nasal PD measured with this modified method is comparable to that measured with an established adult method. The measurements were well tolerated in 13 infants and discriminated bioelectric profiles characteristic of normal and CF respiratory epithelium. This study supports the use of this modified nasal PD technique as a diagnostic test for CF in newborn infants.

Adult↗
PubMed1975

A kinetic approach to defining the role of chemically modifiable residues at the active sites of enzymes.

Initial velocity studies can be used to define the function of chemically modifiable residues in the active site of a multisubstrate enzyme. Since the method relies on measuring biological activity, it has the advantage that it can be used with small amounts of relatively impure enzyme, but requires that modified enzyme molecules have some residual catalytic activity. The kinetic analysis of the modified enzyme can be carried out in the presence of some unmodified enzyme molecules. Consideration of examples of single- and multisubstrate enzymic reactions shows that interpretation of changes in apparent Km and apparent V values following chemical modification, in terms of effects on substrate binding or catalysis or both, requires a detailed knowledge of the kinetic reaction sequence. In the case of multisubstrate enzymes, it is necessary to ensure that, during the kinetic investigation, the concentrations of the non-varied substrates remain at near-saturating levels. For this reason, and because modification may induce changes in the rate-limiting step, a full kinetic analysis of the modified enzyme is advisable.

Amino Acids↗
PubMed2003

Small ubiquitin-related modifier-1 modification mediates resolution of CREB-dependent responses to hypoxia.

Phosphorylation-dependent ubiquitination combined with proteasomal degradation of transcriptional regulators is a recently appreciated mechanism for control of a number of inflammatory genes. Far less is known about the counterregulatory mechanisms that repress transcriptional activity in these pathways during resolution. Here, we investigated the transient nature of hypoxia-induced tumor necrosis factor (TNF)alpha in T84 cells, a process we have previously shown to involve phosphorylation-dependent degradation of the cAMP-response element-binding protein (CREB). Initial studies indicate hypoxia-induced TNFalpha to be a transient event, the resolution of which is associated with the appearance of a higher molecular weight modified form of CREB. Gene array analysis of mRNA derived from hypoxic cells identified a time-dependent induction of small ubiquitin-related modifier (SUMO)-1 mRNA. In prolonged hypoxia, CREB is posttranslationally modified by SUMO-1. Furthermore, SUMO-1 overexpression stabilizes CREB in hypoxia and enhances CREB-dependent reporter gene activity. Site-directed mutagenesis of lysine residues K285 and K304 identifies them as SUMO acceptors in vivo and in vitro. Mutation of K304 also results in loss of CREB nuclear localization, implying a role for SUMO-1 modification at this site in the subcellular localization of CREB. Thus, in prolonged hypoxia, CREB is modified by association with SUMO-1. Furthermore, we hypothesize that such an event stabilizes and promotes nuclear localization of CREB and thus complements an endogenous resolution phase for hypoxia-induced inflammatory processes.

Amino Acid Motifs↗
PubMed1980

Arrest and metastasis of blood-borne tumor cells are modified by fusion of plasma membrane vesicles from highly metastatic cells.

B16 mouse melanoma sublines in culture spontaneously shed intact plasma membrane vesicles. These vesicles can be fused with the plasma membrane of cells from homologous and heterologous B16 sublines by using polyethylene glycol and phytohemagglutinin-P. Fusion of vesicles from a highly metastatic subline (F10) that localizes exclusively in the lung with cells from a poorly metastatic subline (F1) significantly increased the ability of F1 cells to become arrested in the lung and form metastases in this organ. In contrast, fusion of F1 vesicles with F10 cells did not alter the ability of vesicle-modified cells to localize in the lung or form lung metastases. F10 vesicle-modified F1 cells reverted to their original arrest behavior and metastatic capacity after removal of F10 vesicle components from the plasma membrane. The changes in the arrest and metastatic behavior of F10 vesicle-modified F1 cells were highly highly specific. Vesicles from other B16 sublines that are poorly metastatic and show limited localization in the lung (F1, FLLr, and F10Lr) did not modify the arrest behavior and metastatic capacity of FU cells. These results suggest that the differences in the abilities of the F1 and F10 sublines to localize in the lung are determined by differences in cell surface properties.

Animals↗
PubMed1982

Antibodies elicited against cis-diamminedichloroplatinum(II)-modified DNA are specific for cis-diamminedichloroplatinum(II)-DNA adducts formed in vivo and in vitro.

Rabbit antiserum elicited against calf thymus DNA modified to 4.4% (Pt drug/nucleotide ratio = 0.044) with the antitumor drug cis-diamminedichloroplatinum(II) (cis-DDP) contains antibodies specific for the Pt-modified DNA immunogen as well as for Pt-DNA adducts formed in both cultured mouse leukemia L1210 cells and in L1210 cells from the ascites fluid of tumor-bearing mice exposed to cis-DDP. Pt-modified DNA was electrostatically complexed to methylated bovine serum albumin and injected into rabbits. Early bleedings of the derived antiserum were used to establish a competitive enzyme-linked immunosorbent assay (ELISA), which demonstrated specificity for the Pt-modified DNA but not for DNA or the Pt drug alone. In the ELISA, 50% inhibition occurred at a concentration of 0.5 nM Pt (on DNA) as determined by atomic absorption spectroscopy. This value corresponds to a lower limit of detectability of one adduct in 10(7) nucleotides, with 50 micrograms of sample DNA added per microtiter well. DNA isolated from cultured mouse L1210 cells exposed to increasing doses of the Pt drug was found by ELISA to contain from 0.2 to 10.0 fmol of Pt adduct per microgram of DNA. These levels remained stable for up to 4 hr after a 1-hr drug treatment, during which time DNA interstrand crosslinks developed. Thus, the antiserum appears not to be specific for DNA interstrand crosslinks. DNAs from L1210 cells exposed to trans-diamminedichloroplatinum(II) and L-phenylalanine mustard were not recognized in the ELISA. DNA prepared from the ascites cells of mice bearing the L1210 tumor 5 hr after injection of cis-DDP was found to contain about 2 fmol of Pt per microgram of DNA. This work establishes that cis-DDP-DNA adducts prepared in vitro are relevant to the in vivo binding of the Pt drug to its biological target, DNA, and opens new avenues for studying the mechanism of action of the Pt anticancer drugs.

Animals↗
PubMed1982

Specificity of receptor-mediated recognition of malondialdehyde-modified low density lipoproteins.

Blood-borne human monocytes and macrophages derived from human monocytes in vitro express an active low density lipoprotein (LDL) receptor and an active receptor for negatively charged proteins, the scavenger receptor. When less than 15% of the lysine residues of human LDL were modified by malondialdehyde while the lipoprotein was in solution, recognition and uptake of the modified lipoprotein occurred via the LDL receptor. Further modification resulted in threshold recognition and uptake by the scavenger receptor with concomitant loss of recognition by the LDL receptor. The rate of degradation via the LDL receptor pathway was inversely related to the degree of modification whereas that mediated by the scavenger receptor was independent of the extent of incorporation of malondialdehyde once threshold recognition was achieved. In contrast to the interaction of LDL with malondialdehyde in solution, modification of less than 15% of the lysine residues of LDL adsorbed to heparin-Sepharose resulted in recognition and uptake by the scavenger receptor. The scavenger receptor-mediated uptake of malondialdehyde-modified LDL may be dependent on formation of recognition sites involving specific modified lysine residues or changes in the conformation of LDL induced by neutralization of specific lysine residues of the apoB polypeptides or both.

Apolipoproteins↗
PubMed1986

An evolutionary reduction principle for genetic modifiers.

The joint evolution of major genes under viability selection and a modifier locus that controls recombination between the major genes, mutation at the major gene, or migration between two demes is studied. The modifying locus is selectively neutral and may have an arbitrary number of alleles. For each case a class of polymorphic equilibria exists in which the frequencies of the modifying alleles are those computed by assuming that the recombination, mutation, or migration rates were viabilities and in which the major and modifier loci are not statistically associated. These are called viability-analogous Hardy-Weinberg (VAHW) equilibria. A new allele introduced near these equilibria will enter the population if its marginal average rate of recombination, mutation, or migration (whichever applies) is less than the population average prior to its introduction. Stability properties of these VAHW equilibria are also reported.

Biological Evolution↗
PubMed1991

Epithelial-mesenchymal transformation of embryonic cardiac endothelial cells is inhibited by a modified antisense oligodeoxynucleotide to transforming growth factor beta 3.

During early cardiac development, the progenitor cells of the heart valves and membranous septa undergo an epithelial-mesenchymal transformation. Previous studies have shown that this transformation depends on the activity of a transforming growth factor beta (TGF beta) molecule produced by the heart. In the present study, we have used modified antisense oligodeoxynucleotides generated to nonconserved regions of TGF beta 1, -2, -3, and -4 to examine the possible roles of these members in this transformation. A phosphoramidate-modified oligonucleotide complementary to TGF beta 3 mRNA was capable of inhibiting normal epithelial-mesenchymal transformation by 80%. Unmodified oligonucleotides to TGF beta 3, modified oligonucleotides to TGF beta 1, -2, and -4, and two modified control oligonucleotides were unable to inhibit the transformation. These data demonstrate that a specific member of the TGF beta family, TGF beta 3, is essential for the epithelial-mesenchymal cell transformation.

Animals↗
PubMed1998

Epitopes close to the apolipoprotein B low density lipoprotein receptor-binding site are modified by advanced glycation end products.

Advanced glycation end products (AGEs) are thought to contribute to the abnormal lipoprotein profiles and increased risk of cardiovascular disease of patients with diabetes and renal failure, in part by preventing apolipoprotein B (apoB)-mediated cellular uptake of low density lipoproteins (LDL) by LDL receptors (LDLr). It has been proposed that AGE modification at one site in apoB, almost 1,800 residues from the putative apoB LDLr-binding domain, may be sufficient to induce an apoB conformational change that prevents binding to the LDLr. To further explore this hypothesis, we used 29 anti-human apoB mAbs to identify other potential sites on apoB that may be modified by in vitro advanced glycation of LDL. Glycation of LDL caused a time-dependent decrease in its ability to bind to the LDLr and in the immunoreactivity of six distinct apoB epitopes, including two that flank the apoB LDLr-binding domain. ApoB appears to be modified at multiple sites by these criteria, as the loss of glycation-sensitive epitopes was detected on both native glycated LDL and denatured, delipidated glycated apoB. Moreover, residues directly within the putative apoB LDLr-binding site are not apparently modified in glycated LDL. We propose that the inability of LDL modified by AGEs to bind to the LDLr is caused by modification of residues adjacent to the putative LDLr-binding site that were undetected by previous immunochemical studies. AGE modification either eliminates the direct participation of the residues in LDLr binding or indirectly alters the conformation of the apoB LDLr-binding site.

Antibodies, Monoclonal↗
PubMed1999

A normal beta-globin allele as a modifier gene ameliorating the severity of alpha-thalassemia in mice.

Thalassemia is a heritable human anemia caused by a variety of mutations that affect expression of the alpha- or the beta-chain of hemoglobin. The expressivity of the phenotype is likely to be influenced by unlinked modifying genes. Indeed, by using a mouse model of alpha-thalassemia, we find that its phenotype is strongly influenced by the genetic background in which the alpha-thalassemia mutation resides [129(sv/ev)/129(sv/ev) (severe) or 129(sv/ev)/C57BL/6 (mild)]. Linkage mapping indicates that the modifying gene is very tightly linked to the beta-globin locus (Lod score = 13.3). Furthermore, the severity of the phenotype correlates with the size of beta-chain-containing inclusion bodies that accumulate in red blood cells and likely accelerate their destruction. The beta-major globin chains encoded by the two strains differ by three amino acids, one of which is a glycine-to-cysteine substitution at position 13. The Cys-13 should be available for interchain disulfide bridging and consequent aggregation between excess beta-chains. This normal polymorphic variation between murine beta-globin chains could account for the modifying action of the unlinked beta-globin locus. Here, the variation in severity of the phenotype would not depend on a change in the ratio between alpha- and beta-chains but on the chemical nature of the normal beta-chain, which is in excess. This work also indicates that modifying genes can be normal variants that-absent an apparent physiologic rationale-may be difficult to identify on the basis of structure alone.

Alleles↗
PubMed1996

Reconstitution of barley photosystem I with modified PSI-C allows identification of domains interacting with PSI-D and PSI-A/B.

The PSI-C subunit of photosystem I shows similarity to soluble 2[4Fe-4S] ferredoxins. Alignment analysis clearly shows that PSI-C contains an 8-residue internal loop and a 15-residue C-terminal extension that are absent in the ferredoxins. The remaining residues in PSI-C are likely to be folded in a way similar to the soluble 2[4Fe-4S] ferredoxins. Two modified PSI-C subunits lacking either the 8-residue loop or 10 residues of the C terminus were expressed in Escherichia coli and used to reconstitute a barley P700-FX core prepared to specifically lack PSI-C, PSI-D, and PSI-E. As shown by EPR spectroscopy, the modified proteins carry two [4Fe-4S] clusters with characteristics similar to those of native PSI-C. Western blot analysis of the reconstituted photosystem I complexes showed that the modified PSI-C proteins bind to the P700-FX core. Flash photolysis revealed that in photosystem I complexes reconstituted in the presence of PSI-D with the C-terminally deleted PSI-C, the FA/FB back-reaction was less efficiently restored than with wild-type PSI-C. The loop-deleted PSI-C was even less efficient. We attribute these differences to altered binding properties of the modified proteins. Comparison of reconstitutions performed in the presence and absence of PSI-D shows that the loop-deleted PSI-C is unable to bind without PSI-D, whereas the C-terminally deleted PSI-C binds only weakly with PSI-D. These results imply that the internal loop of PSI-C interacts with the PSI-A/B heterodimer and that the C terminus of PSI-C interacts with PSI-D.

Amino Acid Sequence↗
PubMed1997

Identification of sulfhydryl-modified cysteine residues in the ligand binding pocket of retinoic acid receptor beta.

The diverse biological functions of retinoic acid (RA) are mediated through retinoic acid receptors (RARs) and retinoid X receptors. RARs contain a high affinity binding site for RA which is sensitive to treatment with sulfhydryl modification reagents. In an attempt to identify which Cys residues are important for this loss of binding, we created three site-specific RARbeta mutants: C228A, C258A, and C267A. The affinity for RA of all three mutant receptors was in the range of that of the wild type protein, suggesting that none of these Cys residues are critical for RA binding. Rather, these modified Cys residue(s) function to sterically hinder RA binding; however, the modified Cys residues critical for the inhibition of binding differ depending on the reagent employed. Only modification of Cys228 is necessary to inhibit RA binding when RARbeta is modified by reagents which transfer large bulky groups while both Cys228 and Cys267 must be modified when a small functional group is transferred. These data suggest that both Cys228 and Cys267 but not Cys258 lie in the ligand binding pocket of RARbeta. However, Cys228 lies closer to the opening of the RARbeta ligand binding pocket whereas Cys267 lies more deeply buried.

Binding Sites↗
PubMed1999

Structural and kinetic studies of a cisplatin-modified DNA icosamer binding to HMG1 domain B.

The high mobility group (HMG) domain is a DNA-binding motif found in the non-histone chromosomal proteins, HMG1 and HMG2, and some transcription factors. Experimental evidence has demonstrated that HMG-domain proteins can play a role in sensitizing cells to the anticancer drug cisplatin. Fluorescence resonance energy transfer (FRET) experiments were performed in the present study to investigate structural changes that accompany complex formation between the HMG domain B of HMG1 and a cisplatin-modified, 20-base pair double-stranded DNA probe containing fluorescein and rhodamine tethered at its two ends. The binding affinity of HMG1 domain B for the cisplatin-modified DNA probe was investigated in fluorescence titration experiments, and a value of 60 +/- 30 nM was determined for the dissociation constant. Single photon counting methods were employed to measure the fluorescence lifetime of the fluorescein donor in the presence and absence of HMG1 domain B. These FRET experiments revealed a distance change that was used to estimate a bend angle of 80-95 degrees for the cisplatin-modified DNA upon protein binding. Stopped-flow fluorescence spectroscopic experiments afforded kinetic parameters for HMG1 domain B binding to the cisplatin-modified DNA probe, with kon = 1.1 +/- 0.1 x 10(9) M-1 s-1 and koff = 30 +/- 4 s-1.

Base Sequence↗
PubMed1999

Engineering of the myosin-ibeta nucleotide-binding pocket to create selective sensitivity to N(6)-modified ADP analogs.

Distinguishing the cellular functions carried out by enzymes of highly similar structure would be simplified by the availability of isozyme-selective inhibitors. To determine roles played by individual members of the large myosin superfamily, we designed a mutation in myosin's nucleotide-binding pocket that permits binding of adenine nucleotides modified with bulky N(6) substituents. Introduction of this mutation, Y61G in rat myosin-Ibeta, did not alter the enzyme's affinity for ATP or actin and actually increased its ATPase activity and actin-translocation rate. We also synthesized several N(6)-modified ADP analogs that should bind to and inhibit mutant, but not wild-type, myosin molecules. Several of these N(6)-modified ADP analogs were more than 40-fold more potent at inhibiting ATP hydrolysis by Y61G than wild-type myosin-Ibeta; in doing so, these analogs locked Y61G myosin-Ibeta tightly to actin. N(6)-(2-methylbutyl) ADP abolished actin filament motility mediated by Y61G, but not wild-type, myosin-Ibeta. Furthermore, a small fraction of inhibited Y61G molecules was sufficient to block filament motility mediated by mixtures of wild-type and Y61G myosin-Ibeta. Introduction of Y61G myosin-Ibeta molecules into a cell should permit selective inhibition by N(6)-modified ADP analogs of cellular processes dependent on myosin-Ibeta.

Actins↗
PubMed2002

Structure and dynamics of thioguanine-modified duplex DNA.

Mercaptopurine and thioguanine, two of the most widely used antileukemic agents, exert their cytotoxic, therapeutic effects by being incorporated into DNA as deoxy-6-thioguanosine. However, the molecular mechanism(s) by which incorporation of these thiopurines into DNA translates into cytotoxicity is unknown. The solution structure of thioguanine-modified duplex DNA presented here shows that the effects of the modification on DNA structure were subtle and localized to the modified base pair. Specifically, thioguanine existed in the keto form, formed weakened Watson-Crick hydrogen bonds with cytosine and caused a modest approximately 10 degrees opening of the modified base pair toward the major groove. In contrast, thioguanine significantly altered base pair dynamics, causing an approximately 80-fold decrease in the base pair lifetime with cytosine compared with normal guanine. This perturbation was consistent with the approximately 6 degrees C decrease in DNA melting temperature of the modified oligonucleotide, the 1.13 ppm upfield shift of the thioguanine imino proton resonance, and the large increase in the exchange rate of the thioguanine imino proton with water. Our studies provide new mechanistic insight into the effects of thioguanine incorporation into DNA at the level of DNA structure and dynamics, provide explanations for the effects of thioguanine incorporation on the activity of DNA-processing enzymes, and provide a molecular basis for the specific recognition of thioguanine-substituted sites by proteins. These combined effects likely cooperate to produce the cellular responses that underlie the therapeutic effects of thiopurines.

Antimetabolites, Antineoplastic↗
PubMed2002

Scavenger receptors class A-I/II and CD36 are the principal receptors responsible for the uptake of modified low density lipoprotein leading to lipid loading in macrophages.

Modification of low density lipoprotein (LDL) can result in the avid uptake of these lipoproteins via a family of macrophage transmembrane proteins referred to as scavenger receptors (SRs). The genetic inactivation of either of two SR family members, SR-A or CD36, has been shown previously to reduce oxidized LDL uptake in vitro and atherosclerotic lesions in mice. Several other SRs are reported to bind modified LDL, but their contribution to macrophage lipid accumulation is uncertain. We generated mice lacking both SR-A and CD36 to determine their combined impact on macrophage lipid uptake and to assess the contribution of other SRs to this process. We show that SR-A and CD36 account for 75-90% of degradation of LDL modified by acetylation or oxidation. Cholesteryl ester derived from modified lipoproteins fails to accumulate in macrophages taken from the double null mice, as assessed by histochemistry and gas chromatography-mass spectrometry. These results demonstrate that SR-A and CD36 are responsible for the preponderance of modified LDL uptake in macrophages and that other scavenger receptors do not compensate for their absence.

Animals↗