Ultrastructural observations of the anterior chamber angle tissues in congenital glaucoma

Eighteen trabeculectomy specimens of congenital glaucoma were examined by light and transmission electron microscopy. The results showed that the primary anomalies in congenital glaucoma included the developmental defects of trabecular meshwork, excessive collagen fibrils in the trabecular matrix, shifting forward of ciliary muscle fibres and persistent mesenchymal tissues in the anterior-chamber angle. The authors also pointed out the importance of the secondary lesions of the trabecular meshwork in the pathogenesis of congenital glaucoma.

A nonstationary Poisson point process describes the sequence of action potentials over long time scales in lateral-superior-olive auditory neurons

The behavior of lateral-superior-olive (LSO) auditory neurons over large time scales was investigated. Of particular interest was the determination as to whether LSO neurons exhibit the same type of fractal behavior as that observed in primary VIII-nerve auditory neurons. It has been suggested that this fractal behavior, apparent on long time scales, may play a role in optimally coding natural sounds. We found that a nonfractal model, the nonstationary dead-time-modified Poisson point process (DTMP), describes the LSO firing patterns well for time scales greater than a few tens of milliseconds, a region where the specific details of refractoriness are unimportant. The rate is given by the sum of two decaying exponential functions. The process is completely specified by the initial values and time constants of the two exponentials and by the dead-time relation. Specific measures of the firing patterns investigated were the interspike-interval (ISI) histogram, the Fano-factor time curve (FFC), and the serial count correlation coefficient (SCC) with the number of action potentials in successive counting times serving as the random variable. For all the data sets we examined, the latter portion of the recording was well approximated by a single exponential rate function since the initial exponential portion rapidly decreases to a negligible value. Analytical expressions available for the statistics of a DTMP with a single exponential rate function can therefore be used for this portion of the data. Good agreement was obtained among the analytical results, the computer simulation, and the experimental data on time scales where the details of refractoriness are insignificant.(ABSTRACT TRUNCATED AT 250 WORDS)

[Presenile dementia with marked recent memory disturbance--in relation to hippocampal dementia]

Two cases of presenile dementia with marked recent memory disturbance were reported. Patient 1 is a 54-year-old woman. She noticed forgetfulness at the age of 51 years. Neurological examination at aged 52 revealed marked recent memory disturbance, but examination by WAIS (Wechsler Adult Intelligence Scale) showed good results (verbal IQ 106, performance IQ 104, total IQ 106). There was neither disorientation in place nor character change. Cranial CT scan and MRI revealed the absence of brain atrophy. About 3 years after the onset of the disease, the degree of dementia is slight and disorientation in place does not appear. Patient 2 is a 67-year-old man. He noticed forgetfulness at the age of 63 years. Neurological examination at aged 66 revealed marked recent memory disturbance, but examination by WAIS-R showed moderate results (verbal IQ 89, performance IQ 87, total IQ 88). There was neither disorientation in place nor character change. Cranial CT scan and MRI revealed slight dilatation of the inferior horns of the lateral ventricle and slight cortical atrophy. About 4 years after the onset of the disease, the degree of dementia was slight and disorientation in place did not appear. We can not rule out the possibility that our cases belong to Alzheimer's disease, but the clinical course of our cases is peculiar. In the relation of responsible lesion in pure amnestic syndrome, hippocampal dementia, and simple senile dementia, our cases are interesting and important.

Role for DNA methylation in genomic imprinting

The paternal and maternal genomes are not equivalent and both are required for mammalian development. The difference between the parental genomes is believed to be due to gamete-specific differential modification, a process known as genomic imprinting. The study of transgene methylation has shown that methylation patterns can be inherited in a parent-of-origin-specific manner, suggesting that DNA methylation may play a role in genomic imprinting. The functional significance of DNA methylation in genomic imprinting was strengthened by the recent finding that CpG islands (or sites) in three imprinted genes, H19, insulin-like growth factor 2 (Igf-2), and Igf-2 receptor (Igf-2r), are differentially methylated depending on their parental origin. We have examined the expression of these three imprinted genes in mutant mice that are deficient in DNA methyltransferase activity. We report here that expression of all three genes was affected in mutant embryos: the normally silent paternal allele of the H19 gene was activated, whereas the normally active paternal allele of the Igf-2 gene and the active maternal allele of the Igf-2r gene were repressed. Our results demonstrate that a normal level of DNA methylation is required for controlling differential expression of the paternal and maternal alleles of imprinted genes.

[Effects of replenishing kidney herbs on estrogen and 1,25-dihydroxyvitamin D3 of dexamethasone-induced rats model with osteoporosis]

Estrogen and 1,25-(OH)2-D3 change in rats with osteoporosis induced by dexamethasone (DXM) was observed. The calcium and replenishing Kidney Herbs (RKH) was used in treating osteoporosis. The results shown: The level of estrogen and 1,25-(OH)2-D3 in rats with osteoporosis was lower than that of the normal. Calcium and RKH were effective in treating osteoporosis and they could recover the level of estrogen and 1,25-(OH)2-D3 to normal state, the effect of RKH was better than that of calcium. There was positive correlation between the level of estrogen and 1,25-(OH)2-D3. The treatment of RKH might be an optimal method for osteoporotic treatment.

[Pathologic classification of 435 primary orbital tumors]

This paper analysed the pathologic classification of 435 primary orbital tumors, which were mainly divided into eight types, including 83 cases (19.1%) of cystic lesions, 64 cases (14.7%) of vasculogenic lesions, 50 cases (11.5%) of mesenchymal tumors, 73 cases (16.8%) of lacrimal gland epithelial lesions, 54 cases (12.4%) of neural tissue tumors, 55 cases (12.6%) of lymphocytic lesions, 16 cases (3.7%) of histiocytic lesions and 40 cases (9.2%) of idiopathic orbital pseudotumor. The clinicopathologic characteristics of the common orbital tumors were also discussed.

Inter-tryptophan distances in rat cellular retinol binding protein II by solid-state NMR

Structural constraints for the tryptophans in rat cellular retinol binding protein II (CRBP II) have been obtained by rotational-echo double-resonance (REDOR) solid-state NMR. CRBP II was labeled with L-[6-19F]tryptophan and L-[2-13C]tryptophan. The 13C-19F dipolar coupling was determined for various possible tryptophan geometries. The allowed distance between the closest two of the four tryptophans in CRBP II was obtained for each geometry. The minimum possible distance between these two tryptophans in CRBP II is 7 A, and the maximum possible distance is 11 A.

Differential binding of retinol analogs to two homologous cellular retinol-binding proteins

A comparative study of the interactions of rat cellular retinol-binding protein (CRBP) and cellular retinol-binding protein II (CRBP II) with a number of synthetic phenyl-substituted analogs of all-trans-retinol was performed using fluorescence and nuclear magnetic resonance analysis. These studies indicate that CRBP II is more sensitive to modifications of the ring moiety than CRBP. Removal of the two methyl substituents on the ring which are ortho to the polyene chain abolishes binding to CRBP II. Conformational analysis of the ligands indicates that these two methyl groups influence the planarity of the ligand. The identification of monospecific ligands may prove useful for studying the physiological roles of these two proteins.

Normal development and growth of mice carrying a targeted disruption of the alpha 1 retinoic acid receptor gene

Three unlinked genes encode receptors for retinoic acid (RAR alpha, -beta, and -gamma). Each gene expresses two major protein isoforms differing in the amino terminal A domain by alternative promoter use, fused to common exons encoding most of the receptor protein. The two RAR alpha transcripts (RAR alpha 1 and -alpha 2) are differentially expressed and evolutionarily conserved, as are the RAR beta and -gamma transcripts, suggesting that each isoform may have specific functions in the development of animals. To address the biological function of the alpha 1 receptor, we have disrupted the portion of the RAR alpha gene encoding this isoform by homologous recombination in mouse embryonic stem cells. Surprisingly, offspring homozygous for this mutation were viable and showed no apparently altered phenotype. RNA analysis confirmed that the RAR alpha 1 transcript was absent in homozygous tissues, and no evidence for a compensatory increase of RAR alpha 2 or of another RAR gene was obtained to account for the vitality of the mutant animals. These results clearly demonstrate that loss of RAR alpha 1 function does not disrupt embryonic development and argue for combinatorial or overlapping functions among the RAR isoforms.

Ligand-protein electrostatic interactions govern the specificity of retinol- and fatty acid-binding proteins

Cellular retinol-binding protein II (CRBP-II) and intestinal fatty acid-binding protein (I-FABP) are both expressed in small intestinal enterocytes and exhibit 31% sequence identity. I-FABP binds a single molecule of long-chain fatty acid and forms an ion-pair electrostatic interaction between the cationic side chain of arginine-106 and the anionic fatty acid carboxyl group. In contrast, CRBP-II binds all-trans-retinol or -retinal and contains a glutamine residue in the corresponding position, residue 109. We have characterized and compared the interactions of fatty acids and retinoids with I-FABP, CRBP-II, and two reciprocal mutant proteins. The mutants were designated CRBP-II(Q109R), where glutamine-109 was replaced by arginine, and I-FABP(R106Q), where arginine-106 was replaced by glutamine. As monitored by titration calorimetry and carbon-13 NMR spectroscopy, the fatty acid-binding properties of CRBP-II(Q109R) were found to be essentially identical to those of wild-type I-FABP. Both proteins bound 1 molecule of fatty acid with identical affinities (Kd = 0.2 microM). The enthalpic contribution to the total free energy of binding was large for both proteins: 66% and 87%, respectively. In addition, the carboxyl groups of fatty acids bound to both proteins were solvent-inaccessible. There was little or no change in the ionization state of the bound fatty acid over a wide pH range, as monitored by the chemical shift of the fatty acid carboxyl 13C resonance. Furthermore, the binding of fatty acid to both proteins was accompanied by a selective perturbation of the guanidino 13C resonance of a single arginine residue.(ABSTRACT TRUNCATED AT 250 WORDS)

Use of a recombinant 170-kilodalton surface antigen of Entamoeba histolytica for serodiagnosis of amebiasis and identification of immunodominant domains of the native molecule

We expressed the gene that encodes one of the major surface antigens of Entamoeba histolytica, the 170-kDa protein (1,270 amino acids), as a glutathione S-transferase fusion protein containing amino acids 1 to 1202 (lacking the putative transmembrane and cytoplasmic regions) and as separate fusion proteins containing each of three major domains of the 170-kDa molecule. Lysates from bacteria induced to express one of these proteins were used as the target antigens in a Western blot (immunoblot) analysis to determine whether a recombinant 170-kDa antigen could serve as the basis for a serologic test used to detect invasive amebiasis and whether there are differences in humoral immunogenicity among the three major domains of the 170-kDa antigen. Among patients with invasive amebiasis from three major areas where the disease is endemic and two sites in the United States, 54 (90%) of 60 had antibodies to the recombinant 170-kDa protein. Among 37 patients from regions where the disease is endemic and 20 patients from the United States without amebic disease, 1 (2%) of 57 had antibodies to the recombinant 170-kDa protein. We found significant differences in seroreactivity to each of three major domains of the molecule among patients seropositive for the complete construct, ranging from 100% seroreactivity with the fusion protein containing the domain designated cysteine rich and 89% seropositivity with the fusion protein incorporating a portion of the region designated cysteine poor to only 9% seropositivity for the fusion protein containing the pseudorepeat domain. Our study indicates that a serologic test based on the recombinant 170-kDA antigen could serve as a highly sensitive and specific test for acute invasive amebiasis.

The role of newer antibiotics in gastroenterology

The past decade has seen the introduction of a number of new potent antimicrobial agents, including broad-spectrum beta-lactam compounds such as the ureidopenicillins, third-generation cephalosporins, carbapenems, and monobactams; combinations of penicillins with inhibitors of beta-lactamase; and the quinolones. Most of these agents have excellent activity against enteric gram-negative rods and some are active against anaerobic organisms, the two bacterial groups most likely to be encountered in gastrointestinal infections. Despite the potency and wide spectrum of many of these new agents, there are currently relatively few clinical situations in which any of the newer antimicrobials are the first-line agents for therapy or prophylaxis of gastrointestinal diseases. Reluctance to use these agents as first-line therapy is based on concerns about the selection and spread of resistant organisms, superinfection syndromes, and the high cost of many of the newer agents. Specific clinical settings in which these agents may be given preference are as follows: 1. use of a third-generation cephalosporin (cefotaxime or ceftriaxone) in the treatment of spontaneous bacterial peritonitis. 2. use of broad-spectrum beta-lactam compounds to provide gram-negative coverage in patients who should not receive aminoglycosides 3. use of a third-generation cephalosporin (ceftriaxone) in the treatment of central nervous system relapses of Whipple's disease 4. use of quinolones for the empiric treatment of suspected bacterial diarrhea in patients sufficiently ill to require empiric initiation of antibiotics. 5. use of quinolones for the treatment of chronic carriers of Salmonella typhi 6. use of norfloxacin for prophylaxis against SBP. As further experience with these new antimicrobial agents is obtained and as more bacteria develop resistance to current first-line agents, there can be little doubt that these new antibiotics will play an increasing role in the prevention and treatment of gastrointestinal disease.

Targeted mutation of the DNA methyltransferase gene results in embryonic lethality

Gene targeting in embryonic stem (ES) cells has been used to mutate the murine DNA methyltransferase gene. ES cell lines homozygous for the mutation were generated by consecutive targeting of both wild-type alleles; the mutant cells were viable and showed no obvious abnormalities with respect to growth rate or morphology, and had only trace levels of DNA methyltransferase activity. A quantitative end-labeling assay showed that the level of m5C in the DNA of homozygous mutant cells was about one-third that of wild-type cells, and Southern blot analysis after cleavage of the DNA with a methylation-sensitive restriction endonuclease revealed substantial demethylation of endogenous retroviral DNA. The mutation was introduced into the germline of mice and found to cause a recessive lethal phenotype. Homozygous embryos were stunted, delayed in development, and did not survive past mid-gestation. The DNA of homozygous embryos showed a reduction of the level of m5C similar to that of homozygous ES cells. These results indicate that while a 3-fold reduction in levels of genomic m5C has no detectable effect on the viability or proliferation of ES cells in culture, a similar reduction of DNA methylation in embryos causes abnormal development and embryonic lethality.

Targeted mutation of the gene encoding the low affinity NGF receptor p75 leads to deficits in the peripheral sensory nervous system

We have generated mice carrying a mutation of the gene encoding the low affinity NGF receptor p75NGFR by targeted mutation in embryonic stem cells. Mice homozygous for the mutation were viable and fertile. Immunohistochemical analyses of the footpad skin of mutant mice revealed markedly decreased sensory innervation by calcitonin gene-related peptide- and substance P-immunoreactive fibers. The defective innervation was correlated with loss of heat sensitivity and associated with the development of ulcers in the distal extremities. Complicated by secondary bacterial infection, the ulcers progressed to toenail and hair loss. Crossing a human transgene encoding p75NGFR into the mutant animals rescued the absent heat sensitivity and the occurrence of skin ulcers and increased the density of neuropeptide-immunoreactive sensory innervation of footpad skin. The mutation in the gene encoding p75NGFR did not decrease the size of sympathetic ganglia or the density of sympathetic innervation of the iris or salivary gland. Our results suggest that p75NGFR has an important role in the development and function of sensory neurons.

Fluorescence studies of rat cellular retinol binding protein II produced in Escherichia coli: an analysis of four tryptophan substitution mutants

Rat intestinal cellular retinol binding protein II (CRBP II) is an abundant 134-residue protein that binds all-trans-retinol which contains 4 tryptophans in positions 9, 89, 107, and 110. Our ability to express CRBP II in Escherichia coli and to construct individual tryptophan substitution mutants by site-directed mutagenesis has provided a useful model system for studying the fluorescence of a multi-tryptophan protein. Each of the four mutant proteins binds all-trans-retinol with high affinity, although their affinities are less than that of the wild-type protein. Steady-state and time-resolved fluorescence analyses of these proteins indicate that W107 is at the hydrophobic binding site, W110 is in a polar environment, and the remaining two tryptophans are in a hydrophobic environment. Time-resolved fluorescence study indicates that excited-state energy transfer occurs from the hydrophobic tryptophans to W110. The Stern-Volmer analysis with acrylamide of these proteins reveals that static quenching occurs in the W9F mutant protein while others do not. The fluorescence of rat intestinal fatty acid binding protein (I-FABP), a related protein of known X-ray structure, was also studied for comparison. The results of these findings, coupled with those derived from NMR studies and molecular graphics, suggest that CRBP II undergoes minor structural changes in all of the mutant proteins. Since these effects may be cumulative on the protein structure and function, any conclusions derived from higher mutants in this family of proteins must be treated with caution.

Isolation and partial characterization of a surface glycoconjugate of Entamoeba histolytica

To study surface molecules of Entamoeba histolytica we produced monoclonal antibodies from mice immunized with lysates from the pathogenic amebic strain HM1:IMSS, and screened them for the ability to inhibit E. histolytica adhesion. One monoclonal antibody, CC 8.6, was a potent inhibitor of amebic adhesion to a Chinese hamster ovary cell line, and was capable of inhibiting HM1:IMSS mediated cytotoxicity by 50%. We found that monoclonal antibody CC 8.6 bound to an amebic glycoconjugate. The glycoconjugate is present only in E. histolytica and not in other Entamoeba sp. It migrates as a polydisperse band on SDS-PAGE, and can be metabolically radiolabeled with [14C]glucose, [32P]phosphate, and [3H]palmitate. The glycoconjugate can be purified by hydrophobic interaction chromatography on octyl-Sepharose; enzymatic hydrolysis with phosphatidylinositol-specific phospholipase C alters the hydrophobic properties of the molecule. HPLC analysis of [14C]glucose-labeled glycoconjugate saccharides revealed that approximately 82% of the incorporated label was in glucose and 12% in galactose. Our studies demonstrate that one of the immunogenic surface molecules of E. histolytica is a phosphorylated, lipid-containing, glycoconjugate, and that antibodies to this antigen may have the potential to protect against E. histolytica adhesion and cytotoxicity.

Alteration of the binding specificity of cellular retinol-binding protein II by site-directed mutagenesis

Rat cellular retinol-binding protein II (CRBP II) is an abundant 134-residue intestinal protein that binds all-trans-retinol and all-trans-retinal. It belongs to a family of homologous, 15-kDa cytoplasmic proteins that bind hydrophobic ligands in a noncovalent fashion. These binding proteins include a number of proteins that bind long chain fatty acids. X-ray analyses of the structure of two family members, rat intestinal fatty acid-binding protein and bovine myelin P2 protein, indicate that they have a high degree of conformational similarity and that the carboxylate group of their bound fatty acid interacts with a delta-guanidium group of at least 1 of 2 "buried" arginine residues. These 2 Arg residues are conserved in other family members that bind long chain fatty acids and in cellular retinoic acid-binding protein, but are replaced by Gln109 and Gln129 in CRBP II. We have genetically engineered two amino acid substitutions in CRBP II: 1) Gln109 to Arg and 2) Gln129 to Arg. The purified Escherichia coli-derived CRBP II mutant proteins were analyzed by fluorescence and nuclear magnetic resonance spectroscopy. Both mutants exhibit markedly decreased binding of all-trans-retinol and all-trans-retinaldehyde, but no increased binding of all-trans-retinoic acid. Arg substitution for Gln109 but not for Gln129 produces a dramatic increase in palmitate binding activity. Analysis of the endogenous fatty acids associated with the purified E. coli-derived proteins revealed that E. coli-derived intestinal fatty acid binding protein and the Arg109 CRBP II mutant are complexed with endogenous fatty acids in a qualitatively and quantitatively similar manner. These results provide evidence that this internal Arg may play an important role in the binding of long chain fatty acids by members of this protein family.

Serodiagnosis of invasive amebiasis using a recombinant Entamoeba histolytica protein

One hundred eight serum samples from 106 patients were examined by Western blot analysis for the presence of antibodies to a recombinant fusion protein containing the sequence of the newly described serine-rich Entamoeba histolytica protein (SREHP). Among patients with invasive amebiasis from Durban, Republic of South Africa; San Diego, Calif; Mexico City, Mexico; and St Louis, Mo, 53 (82%) of 65 had antibodies to SREHP. In contrast, only one patient (2%) of 43 without acute invasive amebiasis had antibodies to SREHP. The predictive value of a positive test for anti-SREHP antibodies in the detection of acute invasive amebiasis was most marked when analyzed in the patients from Durban, where 11 (92%) of 12 patients who were seropositive for SREHP had acute invasive amebiasis vs 17 (65%) of 26 patients who had a positive serologic diagnosis as determined by agar gel diffusion. The use of a serologic test based on the recombinant SREHP fusion protein may be a useful adjunct to the diagnosis of acute invasive amebiasis in endemic regions.

Pulmonary surfactant will secure free airflow through a narrow tube

Well functioning pulmonary surfactant is necessary to ensure alveolar stability. It is proposed that surfactant is also required to keep the finest cylindrical airways open, thereby securing an unrestricted flow of air to and from the alveoli. If the surfactant is inadequate in quality or quality there is a risk that liquid will accumulate in the most marrow section of the airway and form a blocking column. To study that possibility special glass capillaries were used. The glass capillaries were heated and extended to make a short section very narrow. In the lumen of that section a minute volume (1 microliter) of liquid was deposited, which formed a blocking column. When pressure was raised on one side of the column, it forced the liquid to move away from the narrow section. Pressure dropped to zero as air could pass, and if the liquid column consisted of calf lung surfactant extract (CLSE), pressure remained at zero because a new liquid column did not form. If, on the other hand, the liquid column consisted of saline solution it would repeatedly reform as soon as it had been pressed out of the capillary's narrow section. The same occurred if the CLSE suspension forming the liquid column was very dilute or contained inhibiting proteins. These observations did not require that the capillary consisted of the material glass; they were also noted when the narrow tube was outlined by epithelium.

Isolation of a strain-specific Entamoeba histolytica cDNA clone

Entamoeba histolytica is an intestinal parasite causing significant morbidity and mortality worldwide. More tools are needed to understand the epidemiology and molecular pathogenesis of amebiasis. A cDNA library was constructed by using poly(A)+ RNA isolated from an axenic strain of E. histolytica, HM1:IMSS, which expresses a pathogenic isoenzyme pattern (zymodeme). Differential screening of the library yielded a strain-specific 3' polyadenylated cDNA clone, C2, possessing nine 26-nucleotide tandem repeats. RNA and DNA transfer blot analysis of four axenic strains of E. histolytica possessing the same pathogenic zymodeme revealed that the gene is present and expressed in pathogenic E. histolytica HM1:IMSS and 200:NIH but is not present in pathogenic strains HK-9 and Rahman. In addition, Southern blot analysis using the C2 clone showed heterogeneity of genomic organization between HM1:IMSS and 200:NIH. DNA dot blot hybridization analysis demonstrated that cDNA clone C2 was also able to distinguish axenically cultured E. histolytica strains possessing pathogenic zymodemes from those possessing nonpathogenic zymodemes and could detect as few as 100 amebic trophozoites. We conclude that C2 is a strain-specific E. histolytica cDNA clone that, in conjunction with other E. histolytica-specific probes, could serve as a useful epidemiologic tool.

Fluorine nuclear magnetic resonance analysis of the ligand binding properties of two homologous rat cellular retinol-binding proteins expressed in Escherichia coli

Comparative 19F NMR studies were performed on rat cellular retinol-binding protein (CRBP) and cellular retinol-binding protein II (CRBPII) to better understand their role in intracellular retinol metabolism within the polarized absorptive epithelial cells (enterocytes) of the intestine. Efficient incorporation of 6-fluorotryptophan (6-FTrp) into these homologous proteins was achieved by growing a tryptophan auxotroph of Escherichia coli, harboring prokaryotic expression vectors with either a full-length rat CRBPII or CRBP cDNA on defined medium supplemented with the analog. It is possible to easily distinguish resonances corresponding to 6-FTrp-apoCRBP, 6-FTrp-CRBP-retinol (or retinal), 6-FTrp-apoCRBPII, and 6-FTrp-CRBPII-retinol (or retinal). We were thus able to use 19F NMR spectroscopy to monitor transfer of all-trans-retinol and all-trans-retinal between CRBPII and CRBP in vitro. Retinol complexed to CRBPII is readily transferred to CRBP, whereas retinol complexed to CRBP is not readily transferred to CRBPII. We estimated that the Kd for CRBP-retinol is approximately 100-fold less than the Kd for CRBPII-retinol. Transfer of all-trans-retinal occurs readily from CRBPII to CRBP and from CRBP to CRBPII. Results from competitive binding studies with retinol and retinal indicated that there is a much larger difference between the affinities of CRBP for retinol and retinal than between the affinities of CRBPII for these two ligands. However, the differences in binding specificities reflect differences in how the two proteins interact with retinol, rather than with retinal. 19F NMR analysis of recombinant isotopically labeled proteins represents a sensitive new and useful method for monitoring retinoid flux between the CRBPs in vitro.

19F nuclear magnetic resonance studies of 6-fluorotryptophan-substituted rat cellular retinol binding protein II produced in Escherichia coli. An analysis of four tryptophan substitution mutants and their interactions with all-trans-retinol

Rat cellular retinol binding protein (CRBP II) is a 134-amino acid intracellular protein synthesized in the polarized absorptive cells of the intestine. We have previously used 19F nuclear magnetic resonance (NMR) spectroscopy to survey the structural effects of ligand binding on the apoprotein. For these studies, all 4 Trp residues of rat CRBP II were efficiently labeled with 6-fluorotryptophan (6-F-Trp) by inducing its expression in a tryptophan auxotroph of Escherichia coli. Resonances corresponding to 2 of its Trp residues underwent large downfield shifts upon binding of all-trans-retinol and retinal, while resonances corresponding to the other 2 Trp residues underwent only minor perturbations in chemical shifts. To identify which Trp residues undergo changes in their environment upon ligand binding, we have constructed four CRBP II mutants where Trp9, Trp89, Trp107, or Trp110 have been replaced by another hydrophobic amino acid. By comparing the 19F NMR spectrum of each 6-F-Trp-labeled mutant with that of wild type 6-F-Trp CRBP II, we demonstrate that the 19F resonance corresponding to Trp107 undergoes the largest change in chemical shift upon ligand binding (2.0 ppm downfield). This is consistent with the position of this residue predicted from molecular modeling studies. The 19F resonance corresponding to Trp9 also undergoes a downfield change in chemical shift of 0.5 ppm associated with retinol binding even though it is predicted to be removed from the ligand binding site. By contrast, the resonances assigned to Trp89 and Trp110 undergo only minor perturbations in chemical shifts. These results have allowed us to identify residue-specific probes for evaluating the interactions of all-trans-retinol (and other retinoids) with this intracellular binding protein.

Cloning and expression of a membrane antigen of Entamoeba histolytica possessing multiple tandem repeats

Entamoeba histolytica causes amebic dysentery and amebic liver abscess, major causes of morbidity and mortality worldwide. We have used differential hybridization screening to isolate an E. histolytica-specific cDNA clone. The cDNA was found to encode a serine-rich E. histolytica protein (SREHP) containing multiple tandem repeats. The structural motif of SREHP resembles some of the repetitive antigens of malarial species, especially the circumsporozoite proteins. A recombinant trpE fusion protein containing the tandem repeats of SREHP was recognized by immune serum from a patient with amebiasis, demonstrating that SREHP is a naturally immunogenic protein. An antiserum raised against the recombinant fusion protein specifically bound to two distinct bands with apparent molecular masses of 46 and 52 kDa in a crude preparation of E. histolytica trophozoite membranes. This antiserum also inhibited E. histolytica trophozoite adhesion to Chinese hamster ovary cells in vitro. The ability to isolate E. histolytica-specific genes, and to express those genes in Escherichia coli, may be important in studying the molecular basis of E. histolytica pathogenesis and for the future development of vaccines.

Cardiac involvement in systemic lupus erythematosus detected by echocardiography

Cardiac involvement in patients with systemic lupus erythematosus (SLE) was assessed by full echocardiography and continuous wave Doppler in 50 consecutive patients and 50 age- and sex-matched control subjects in a prospective, blinded study. The left ventricular ejection fraction was decreased in patients compared to control subjects (61 +/- 9 vs 68 +/- 7%, p less than 0.001), whereas interventricular septum (12 +/- 3 vs 9 +/- 1 mm, p less than 0.001), and posterior wall dimension (9 +/- 2 vs 8 +/- 1 mm, p less than 0.001), left ventricular mass (186 +/- 54 vs 130 +/- 32 g, p less than 0.001) and mitral valve Doppler A:E ratio (0.8 +/- 0.2 vs 0.7 +/- 0.1, p less than 0.01) were increased. Pericardial effusion was detected in 27 patients and 5 control subjects, and valvular regurgitation was more frequent in the patients (aortic 2 vs 0; mitral 23 vs 5, p less than 0.001; tricuspid 34 vs 22, p less than 0.01 and pulmonary 28 vs 17, p less than 0.05). Mitral or aortic regurgitation was more common in patients with active SLE (60 vs 40%, difference not significant) but was not related to the duration of SLE (r = 0.02), duration of prednisone therapy (r = -0.13) or current dosage of prednisone (r = 0.01). This study demonstrates that pericardial effusion, valvular regurgitation and myocardial abnormalities are frequently present in patients with SLE.

Germ-line transmission of a disrupted beta 2-microglobulin gene produced by homologous recombination in embryonic stem cells

Major histocompatibility complex (MHC) class I molecules are integral membrane proteins present on virtually all vertebrate cells and consist of a heterodimer between the highly polymorphic alpha-chain and the beta 2-microglobulin (beta 2-m) protein of relative molecular mass 12,000 (ref. 1). These cell-surface molecules play a pivotal part in the recognition of antigens, the cytotoxic response of T cells, and the induction of self tolerance. It is possible, however, that the function of MHC class I molecules is not restricted to the immune system, but extends to a wide variety of biological reactions including cell-cell interactions. For example, MHC class I molecules seem to be associated with various cell-surface proteins, including the receptors for insulin, epidermal growth factor, luteinizing hormone and the beta-adrenergic receptor. In mice, class I molecules are secreted in the urine and act as highly specific olfactory cues which influence mating preference. The beta 2-m protein has also been identified as the smaller component of the Fc receptor in neonatal intestinal cells, and it has been suggested that the protein induces collagenase in fibroblasts. Cells lacking beta 2-m are deficient in the expression of MHC class I molecules, indicating that the association with beta 2-m is crucial for the transport of MHC class I molecules to the cell surface. The most direct means of unravelling the many biological functions of beta 2-m is to create a mutant mouse with a defective beta 2-m gene. We have now used the technique of homologous recombination to disrupt the beta 2-m gene. We report here that introduction of a targeting vector into embryonic stem cells resulted in beta 2-m gene disruption with high frequency. Chimaeric mice derived from blastocysts injected with mutant embryonic stem cell clones transmit the mutant allele to their offspring.

Nuclear magnetic resonance studies of 6-fluorotryptophan-substituted rat cellular retinol-binding protein II produced in Escherichia coli. Analysis of the apoprotein and the holoprotein containing bound all-trans-retinol and all-trans-retinal

Rat cellular retinol-binding protein II (CRBP II) is a 15.6-kDa intestinal protein which binds all-trans-retinol and all-trans-retinal but not all-trans-retinoic acid. We have previously analyzed the interaction of Escherichia coli-derived rat apoCRBP II with several retinoids using fluorescence spectroscopic techniques. Interpretation of these experiments is complicated, because the protein has 4 tryptophan residues. To further investigate ligand-protein interactions, we have utilized 19F nuclear magnetic resonance (NMR) spectroscopy of CRBP II labeled at its 4 tryptophan residues with 6-fluorotryptophan. Efficient incorporation of 6-fluorotryptophan (93%) was achieved by growing a tryptophan auxotroph of E. coli harboring a prokaryotic expression vector with a full-length rat CRBP II cDNA on defined medium supplemented with the analog. Comparison of the 19F NMR spectra of 6-fluorotryptophan-substituted CRBP II with and without bound all-trans-retinol revealed that resonances corresponding to 2 tryptophan residues (designated WA and WB) undergo large downfield changes in chemical shifts (2.0 and 0.5 ppm, respectively) associated with ligand binding. In contrast, 19F resonances corresponding to two other tryptophan residues (WC and WD) undergo only minor perturbations in chemical shifts. The 19F NMR spectra of 6-fluorotryptophan-substituted CRBP II complexed with all-trans-retinal and all-trans-retinol were very similar, suggesting that the interactions of these two ligands with the protein are similar. Molecular model building, based on the crystalline structures of two homologous proteins was used to predict the positions of the 4 tryptophan residues of CRBP II and to make tentative resonance assignments. The fact that ligand binding produced residue-specific changes in the chemical shifts of resonances in CRBP II suggests that NMR analysis of isotopically labeled retinoid-binding proteins expressed in E. coli will provide an alternate, albeit it complementary, approach to fluorescence spectroscopy for examining the structural consequences of their association with ligand.

An unusual case of systemic lupus erythematosus with isolated hypoglossal nerve palsy, fulminant acute pneumonitis, and pulmonary amyloidosis

A 53 year old Chinese man with systemic lupus erythematosus (SLE) had an isolated 12th nerve palsy and acute pneumonitis. He died of respiratory failure despite intensive treatment. A limited necropsy was performed, and amyloid deposits were identified in both lung and kidney tissue. This case is highly unusual because (a) to our knowledge an isolated hypoglossal nerve palsy associated with active SLE has never been reported; (b) only one of nine reported cases of amyloidosis in patients with SLE had amyloid deposits in the lung.

Chinese hamster ovary cells deficient in N-acetylglucosaminyltransferase I activity are resistant to Entamoeba histolytica-mediated cytotoxicity

To study the relationship between carbohydrate-specific amebic cytoadherence and ameba-mediated cytotoxicity, we measured Entamoeba histolytica trophozoite-mediated cytolysis directed against a panel of four Chinese hamster ovary (CHO) cell lines that have defined alterations in their glycosylation patterns. We recently measured amebic trophozoite adherence to this panel of CHO cells and showed that trophozoites bind variant cells (RICR 15B), which are deficient in Asn-linked N-acetyllactosamine units, at 12% of the level observed for wild-type cells (E. Li, A. Becker, and S. L. Stanley, J. Exp. Med 167:1725-1730, 1988). Using a 51Cr release assay to measure trophozoite-mediated cytolysis, we demonstrate in this study that RICR 15B cells are less susceptible to trophozoite-mediated cytolysis than are wild-type cells. In addition, we found that N-acetyllactosamine, which inhibits trophozoite adherence to CHO cells, also inhibited trophozoite-mediated cytolysis of wild-type cells. These studies indicate that surface carbohydrates on target cells can influence susceptibility to ameba-mediated cytotoxicity. This panel of CHO cells provides a useful model system for investigating the role of glycoconjugates in mediating amebic interactions with mammalian cells.

Comparison of the ligand binding properties of two homologous rat apocellular retinol-binding proteins expressed in Escherichia coli

Cellular retinol-binding protein (CRBP) and cellular retinol-binding protein II (CRBP II) are 132-residue cytosolic proteins which have 56% amino acid sequence identity and bind all-trans-retinol as their endogenous ligand. They belong to a family of cytoplasmic proteins which have evolved to bind distinct hydrophobic ligands. Their patterns of tissue-specific and developmental regulation are distinct. We have compared the ligand binding properties of rat apo-CRBP and apo-CRBP II that have been expressed in Escherichia coli. Several observations indicate that the E. coli-derived apoproteins are structurally similar to the native rat proteins: they co-migrate on isoelectric focusing gels; and when complexed with all-trans-retinol, their absorption and excitation/emission spectra are nearly identical to those of the authentic rat holoproteins. Comparative lifetime and acrylamide quenching studies suggest that there are differences in the conformations of apo-CRBP and apo-CRBP II. The interaction of E. coli-derived apo-CRBP and apo-CRBP II with a variety of retinoids was analyzed using spectroscopic techniques. Both apoproteins formed high affinity complexes with all-trans-retinol (K'd approximately 10 nM). In direct binding assays, all-trans-retinal bound to both apoproteins (K'd approximately 50 nM for CRBP; K'd approximately 90 nM for CRBP II). However, all-trans-retinal could displace all-trans-retinol bound to CRBP II but not to CRBP. These observations suggests that there is a specific yet distinct interaction between these two proteins and all-trans-retinal. Apo-CRBP and apo-CRBP II did not demonstrate significant binding to either retinoic acid or methyl retinoate, an uncharged derivative of all-trans-retinoic acid. This indicates that the carboxymethyl group of methyl retinoate cannot be sterically accommodated in their binding pockets and that failure to bind retinoic acid probably is not simply due to the negative charge of its C-15 carboxylate group. Finally, neither all-trans-retinol nor retinoic acid bound to E. coli-derived rat intestinal fatty acid-binding protein, a homologous protein whose tertiary structure is known. Together, the data suggest that these three family members have acquired unique functional capabilities.

Use of Chinese hamster ovary cells with altered glycosylation patterns to define the carbohydrate specificity of Entamoeba histolytica adhesion

We compared the adherence of E. histolytica trophozoites with a panel of lectin-resistant CHO mutants with altered glycosylation patterns. Our results coupled with data from saccharide inhibition studies indicate that terminal N-acetyllactosamine units on Asn-linked complex type oligosaccharides provide the major determinants on the cellular receptor for E. histolytica adhesion.

Antigen induced rheumatoid factors: characteristics of monoclonal rheumatoid factors produced after protein and carbohydrate immunization

We generated a panel of monoclonal rheumatoid factors (MRF) from BALB/c mice immunized with ovalbumin, dextran or group-A-carbohydrate. Individual MRF were analyzed in terms of their binding to the four isotypes of murine IgG, isotypes of human IgG, and rabbit IgG, the idiotypes they express, and the VH gene families they employ. We found that antigen induced rheumatoid factors could be divided into three different families based on their isotypic specificity for murine IgG: an IgG1 binding family, and IgG3 binding family, and a family of MRF that bound all four murine isotypes. Rheumatoid factors belonging to all three families were isolated from mice immunized with carbohydrate antigens. The rheumatoid factors isolated from protein immunized mice all belonged to the IgG1 binding family. We were able to define two cross-reactive idiotypes among MRF, one expressed by a subgroup of the IgG1 binding family, and a second cross-reactive idiotype expressed by some members of the pan-binding family. We determined VH gene use in five of six MRF belonging to the IgG1 binding family and four of four members of the pan-binding family. Four of the IgG1 binding rheumatoid factors and three of the pan-binding rheumatoid factors utilize the J558 VH gene family. Rheumatoid factors produced after carbohydrate antigen immunization, as compared with those generated by protein immunization, are diverse in their isotypic specificity, and show a greater ability to bind heterologous IgG.

Crystallization of rat cellular retinol binding protein II. Preliminary X-ray data obtained from the apoprotein expressed in Escherichia coli

Rat cellular retinol-binding protein II (CRBP II) is a member of a family of cytoplasmic proteins which bind hydrophobic ligands. CRBP II is thought to participate in the intestinal absorption and intracellular metabolism of retinoids. We have previously described the crystallization of a homologous rat intestinal fatty acid-binding protein (I-FABP) isolated from Escherichia coli containing a suitably constructed prokaryotic expression vector (Sacchettini, J. C., Meininger, T. A., Lowe, J. B., Gordon, J. I., and Banaszak, L. J., J. Biol. Chem. 262, 5428-5430). We have now efficiently expressed rat CRBP II in E. coli. The E. coli-derived protein, which does not contain any bound retinoid, has been purified and crystals grown from solutions of polyethylene glycol 4000. Crystals of apo-CRBP II are triclinic, space group P1, a = 36.8 A, b = 64.0 A, c = 30.4 A; alpha = 92.8 degrees, beta = 113.5 degrees, gamma = 90.1 degrees. Each unit cell contains two molecules of the 134-residue apoprotein. X-ray diffraction data suggest that the unit cell parameters of crystalline apo-CRBP II resemble those of I-FABP. Comparison of the tertiary structures of E. coli-derived rat I-FABP and CRBP II should provide insights about how these proteins evolved to bind different hydrophobic ligands.

Characterization of rat cellular retinol-binding protein II expressed in Escherichia coli

Rat cellular retinol-binding protein II (CRBP II) is a small (15.6 kDa) intracellular protein that binds all-trans-retinol. In the adult rat, expression of the CRBP II gene is essentially limited to the small intestinal lining cells (enterocytes), suggesting that CRBP II may be uniquely adapted for intestinal metabolism of newly absorbed retinol. Functional and structural analysis of this protein has been hampered by difficulties in freeing rat intestinal CRBP II from its ligand without denaturation. To circumvent this problem, we have obtained efficient expression of rat apoCRBP II in Escherichia coli. The purified E. coli-derived apoprotein, when complexed with all-trans-retinol, demonstrates fluorescence excitation-emission spectra and absorption spectra indistinguishable from that of CRBP II-retinol isolated from rat intestine. Quantitative ligand binding studies were performed by monitoring either the fluorescence of bound retinol or the quenching of protein fluorescence. They revealed that E. coli-derived CRBP II binds retinol tightly (the apparent dissociation constant is estimated to be 10(-7)-10(-8) M), with a stoichiometry of 1:1. Fluorescence quenching studies used acrylamide as a probe for the exposure of the 4 tryptophan residues to solvent. The results indicate that although there is heterogeneity in the exposure of these 4 tryptophan residues to solvent, they are situated in a relatively nonpolar environment. These studies suggest that E. coli-derived apoCRBP II will serve as a useful model for studying retinol-protein interactions.

Comparison of the tissue-specific expression and developmental regulation of two closely linked rodent genes encoding cytosolic retinol-binding proteins

Cellular retinol-binding protein (CRBP) and cellular retinol-binding protein II (CRBP II) are two highly homologous cytoplasmic proteins that bind all-trans-retinol. We have recently demonstrated that the mouse genes encoding CRBP and CRBP II are closely linked on chromosome 9 and that both human genes are located on chromosome 3 (Demmer, L.A., Birkenmeier, E.H., Sweetser, D.A., Levin, M.S., Zollman, S., Sparkes, R.S., Mohandas, T., Lusis, A.J., and Gordon, J.I. (1987) J. Biol. Chem. 262, 2458-2467). We have now used RNA blot hybridization analysis to assess the degree to which these genes are coordinately expressed in fetal, suckling, weaning, and adult rat tissues. Both genes exhibit different developmental patterns of expression in liver, intestine, lung, kidney, testes, and placenta. In the intestine, CRBP mRNA was detected during the 16th day of gestation--prior to the development of a well-differentiated absorptive epithelium--and remained essentially unchanged throughout the peri- and postpartum periods. By contrast, the pattern of intestinal CRBP II mRNA accumulation closely parallels the times of first appearance, and subsequent proliferation, of the intestinal absorptive columnar epithelium, supporting the hypothesis that CRBP II is involved in the intestinal uptake or intracellular trafficking of this hydrophobic vitamin. In the fetal liver, both genes were expressed by gestational day 16. Whereas the concentration of hepatic CRBP mRNA increased markedly during the suckling and early weaning periods, CRBP II mRNA levels fell abruptly immediately after birth. These peripartum changes were not paralleled by remarkable alterations in the steady state levels of hepatic retinol. Marked changes in the expression of CRBP in the liver and of CRBP II in the intestine were also documented in pregnant and lactating female rats. These differences in CRBP/CRBP II gene expression strongly suggest that their proteins serve different physiological functions. The peripartum liver may provide a useful model for dissecting the relative roles played by these homologous proteins in retinoid metabolism as well as the factors which modulate activation and repression their genes.

Rat cellular retinol-binding protein II: use of a cloned cDNA to define its primary structure, tissue-specific expression, and developmental regulation

The primary structure of rat cellular retinol-binding protein (CRBP) II has been determined from a cloned cDNA. Alignment of this 134-amino acid, 15,580-Da polypeptide with rat CRBP revealed that 75 of 133 comparable residues are identical. Both proteins contain four tryptophan residues, which occupy identical relative positions in the two primary structures, providing a structural explanation for their similar fluorescence spectra when complexed to retinol. Two of the three cysteines in each single-chain protein are comparably positioned. Both polypeptides contain reactive thiol groups, but the rate of disruption of CRBP II-retinol complexes by p-chloromercuribenzoate is greater than that of CRBP-retinol. The small intestine contains the highest concentrations of CRBP II mRNA in adult rats. CRBP II mRNA is first detectable in intestinal RNA during the 19th day of gestation, a time that corresponds to the appearance of an absorptive columnar epithelium. Unlike in intestine, a dramatic fall in liver CRBP II mRNA concentration occurs immediately after birth. The CRBP II gene remains quiescent in the liver during subsequent postnatal development. These data suggest that ligand-protein interactions may be somewhat different for the two rat CRBPs. They also support the concept that CRBP II plays a role in the intestinal absorption or esterification of retinol and suggest that changes in hepatic metabolism of vitamin A occur during development.