Site-directed mutagenesis of conserved Trp39 in Rhizomucor pusillus pepsin: possible role of Trp39 in maintaining Tyr75 in the correct orientation for maximizing catalytic activity

Replacement of Trp39 of Rhizomucor pusillus pepsin (RMPP) by Asn or Cys resulted in a marked decrease in the milk-clotting and proteolytic activities. Kinetic analysis with chromogenic synthetic oligopeptides as substrates revealed that the mutations caused marked changes in the kcat value, but only slight changes in the Km value. Similar enzymatic properties were observed in mutants of Tyr75, which was shown to have a role in enhancing the catalytic activity. Both Tyr75Asn and Trp39Asn mutants rapidly lost the activity at high temperatures due to autocatalytic digestion at two sites. The structures of several aspartic proteinases including RMPP, as revealed by X-ray crystallographic studies, showed that Trp39 occupies a position close to Tyr75 and the N delta atom of Trp39 within hydrogen-bonding distance of the hydroxyl side chain of Tyr75. These observations suggest that Trp39 plays a role in maintaining Tyr75 in the correct orientation in aspartic proteinases, including RMPP.

Detection of hepatitis C virus RNA using ligation-dependent polymerase chain reaction in formalin-fixed, paraffin-embedded liver tissues

Reverse transcription polymerase chain reaction (RT-PCR) has been used to detect hepatitis C virus (HCV) sequences in liver tissue. However, RT-PCR has a variable detection sensitivity, especially on routinely processed formalin-fixed, paraffin-embedded (FFPE) specimens. RNA-RNA and RNA-protein cross-links formed during formalin fixation is the major limiting factor preventing reverse trans criptase from extending the primers. To overcome this problem, we applied the ligation-dependent PCR (LD-PCR) for the detection of HCV RNA in FFPE liver tissue. This method uses two capture probes for RNA isolation and two hemiprobes for the subsequent PCR. Despite cross-links, the capture probes and the hemiprobes are able to form hybrids with HCV RNAs released from the FFPE tissue. The hybrids are isolated through binding of the capture probes to paramagnetic beads. The hemiprobes are then ligated by a T4 DNA ligase to form a full probe that serves as a template for the Taq DNA polymerase. A total of 22 FFPE liver specimens, 21 with hepatocellular carcinoma (HCC) and 1 with biliary cirrhosis secondary to bile duct atresia were selected for this study, of which 13 patients were HCV seropositive and 9 seronegative. HCV RNA was detectable by ID-PCR from all 13 HCV-seropositive HCCs and from 5 of 8 HCV-seronegative HCCs but not from the HCV-seronegative liver with biliary atresia. By contrast, RT-PCR detected HCV sequences in only 5 of the HCV-sero-positive and in 1 of the HCV-seronegative HCCs. To resolve the discordance between the LD-PCR and RT-PCR results, RT-PCR was performed on frozen liver tissue of the discrepant specimens, which confirmed the LD-PCR positive results. In conclusion, LD-PCR is a more sensitive method than RT-PCR for the detection of HCV sequences in routinely processed liver tissues. A high rate of HCV infection (86%) is found in HCC specimens, indicating a previously underestimated role of HCV in HCC pathogenesis.

Involvement of a residue at position 75 in the catalytic mechanism of a fungal aspartic proteinase, Rhizomucor pusillus pepsin. Replacement of tyrosine 75 on the flap by asparagine enhances catalytic efficiency

Residue 75 on the flap, a beta hairpin loop that partially covers the active site cleft, is tyrosine in most members of the aspartic proteinase family. Site-directed mutagenesis was carried out to investigate the functional role of this residue in Rhizomucor pusillus pepsin, an aspartic proteinase with high milk-clotting activity produced by the fungus Rhizomucor pusillus. A set of mutated enzymes with replacement of the amino acid at position 75 by 17 other amino acid residues except for His and Gly was constructed and their enzymatic properties were examined. Strong activity, higher than that of the wild-type enzyme, was found in the mutant with asparagine (Tyr75Asn), while weak but distinct activity was observed in Tyr75Phe. All the other mutants showed markedly decreased or negligible activity, less than 1/1000 of that of the wild-type enzyme. Kinetic analysis of Tyr75Asn using a chromogenic synthetic oligopeptide as a substrate revealed a marked increase in kcat with slight change in K(m), resulting in a 5.6-fold increase in kcat/K(m). When differential absorption spectra upon addition of pepstatin, a specific inhibitor for aspartic proteinase, were compared between the wild-type and mutant enzymes, the wild-type enzyme and Tyr75Asn, showing strong activity, had spectra with absorption maxima at 280, 287 and 293 nm, whereas the others, showing decreased or negligible activity, had spectra with only two maxima at 282 and 288 nm. This suggests a different mode of the inhibitor binding in the latter mutants. These observations suggest a crucial role of the residue at position 75 in enhancing the catalytic efficiency through affecting the mode of substrate-binding in the aspartic proteinases.

Novel, ligation-dependent PCR assay for detection of hepatitis C in serum

A simple, sensitive, and specific ligation-dependent PCR (LD-PCR) method for the detection of hepatitis C virus (HCV) RNA in serum is described. The assay uses two DNA capture probes for RNA isolation and two DNA hemiprobes for subsequent PCR. Each capture probe has a 3' sequence complementary to the conserved 5' untranslated region of HCV RNA and a biotin moiety at the 5' end capable of interacting with streptavidin-coated paramagnetic beads. Each hemiprobe contains a sequence complementary to the 5' untranslated region in juxtaposition to one another and a common sequence for PCR primer binding. In guanidinium thiocyanate solutions, the capture probes and the hemiprobes form a hybrid with their target, and the hybrid can be isolated from serum by the binding of the capture probes to the paramagnetic beads in the presence of a magnetic field. The hemiprobes can then be linked to each other by incubation with T4 DNA ligase to form a full probe that serves as a template for a PCR. When serial 10-fold dilutions of synthetic HCV RNA (10(7) to 10 molecules) were tested, there was a good correlation between the amount of PCR product and the initial number of RNA molecules, with a sensitivity of 100 HCV RNA molecules per reaction. Twenty-four specimens that had been tested by either a branched DNA probe (bDNA) assay (13 specimens) or a reverse transcription PCR (RT-PCR) assay (11 specimens) were also analyzed by LD-PCR. The results showed a good correlation among LD-PCR, RT-PCR, and the bDNA assay. However, both LD-PCR and RT-PCR were more sensitive than the bDNA assay when the HCV titer was low.

Transferrin receptor expression of the hyperplastic lesions of hepatocyte in experimental hepatocarcinogenesis

Transferrin receptor (TR) performs the major function of binding and internalizing its specific iron-loaded ligand, transferrin, and its expression is closely linked to the proliferation status of the cell. This study was undertaken to elucidate TR expression in the hyperplastic lesion of hepatocyte in chemically induced hepatic carcinogenesis. The resistant hepatocyte model was chosen for a rat model of carcinogenesis and Sprague-Dawley rats were divided into the following groups: the control groups of normal diet and iron-rich diet with or without hydroxyquinoline and the groups of carcinogen alone and carcinogen plus iron-rich diet with or without administration of hydroxyquinoline. Microscopic changes in the liver, expression of transferrin receptor and glucose-6-phosphatase were studied. The hepatocyte of the control group showed both cytoplasmic and membranous expression of TR. The liver of rats fed on high iron diet accumulated iron and the expression of TR was down regulated by intrahepatic iron accumulation. In the carcinogen administered group the resistant hepatocyte of hyperplastic lesion revealed strong membranous expression of TR and failed to accumulate iron in spite of high iron diet but in contrast the surrounding non-resistant hepatocyte expressed TR in both the membrane and cytoplasm and stored iron when fed on high iron diet. The strong membranous expression of TR is one of the characteristics of the resistant hepatocyte of hyperplastic lesion and it seems to be related to the inability to accumulate iron in spite of a high iron diet.

The effect of deferoxamine on the preneoplastic lesions in the chemically induced hepatocarcinogenesis

Iron is essential for the growth of all living cells. One of the most important intracellular roles of iron is the activation of ribonucleotide reductase, which is indispensible to the production of deoxyribonucleotide necessary for DNA synthesis. Deferoxamine (DFO) is an iron chelating agent and has been known to have an antiproliferative effect in various malignant cells including hepatocellular carcinoma and the effect seems to be related to depletion of iron. This study was undertaken to investigate the effect of DFO on preneoplastic lesions in chemically induced hepatocarcinogenesis. The resistant hepatocyte model was used and Sprague Dawley rats were divided into the following groups; I: normal control, II: carcinogen administered group, III: carcinogen and DFO administered group. Rats were sacrificed at 3 days, 1 week, 2 weeks, 3 weeks, 4 weeks and 8 weeks after partial hepatectomy (PH). DFO (50 mg/kg/day, I.P.) was daily injected from 3 weeks before administration of carcinogen to the time when rats were sacrificed. Hepatic iron content was higher in group II than in group III, especially at 3 days and 1 week after PH. Hyperplastic lesions of resistant hepatocytes were less well developed in group III than in group II. Bromodeoxyuridine labelling indices of oval cells and hyperplastic lesions of resistant hepatocytes were higher in group II than in group III except for rats examined at 3 days after PH. The results suggest that DFO has an antiproliferative effect on preneoplastic lesions in hepatocarcinogenesis and it might be related to reduction of the hepatic iron.

Dementia among the elderly in a rural Korean community

The age-specific prevalence of dementia, its sex difference, and the relative prevalence of important types of dementia were studied in the elderly people in a Korean rural community. A two-stage approach was employed, involving screening and clinical assessment. The prevalence among individuals aged 65 and over was found to be 10.8%, with rates of 7.2% in men and 14.5% in women. The dementia was of the Alzheimer type in 60.0% of cases, multi-infarct dementia in 12.0%, mixed dementia of Alzheimer type and multi-infarct in 10.7%, alcoholic dementia in 8.0%, and others and unclassifiable in 9.3%. The prevalence of dementia of the Alzheimer type was significantly higher in women and rapidly increased with age in both sexes. The prevalence of multi-infarct dementia was not related to sex or age. Alcoholic dementia was identified only in men. These findings indicate that the prevalence of dementia in rural Korea is similar to that reported in Western countries and that the prevalence of dementia of the Alzheimer type in rural Korea is greater than that of multi-infarct dementia.

Histopathological and immunohistochemical studies of polymorphic reticulosis

This study reviewed 65 cases of polymorphic reticulosis (PR) with respect to clinical and histopathologic bases, and immunohistochemical studies were done using MT1 and UCHL as T-cell markers, MB2 as a B-cell marker and alpha-1-antichymotrypsin as a histiocytic marker. The results obtained were as follows: 1. The male to female ratio was 2.4:1 and the mean age of patients was 44.5 years. The sites involved primarily were the nasal cavity, tonsil and pharynx and about one-fourth of the total cases showed extensive involvement of two anatomical sites at initial presentation. 2. Almost all cases showed characteristic histologic features similar to those of peripheral T-cell lymphoma and showed positive reaction to the T-cell marker. The above immunohistochemical findings suggest strongly that quite a significant portion of PR is in fact T-cell lymphoma.

Aberrant breast tissue of the perineum--a report on two cases

In this abstract we report on two cases of aberrant breast tissue of the perineum in a 41-year-old and a 42-year-old woman with the complaint of a slowly growing vulvar mass. The masses were not fixed, they were ovoid, rubbery firm and measured 3 x 2.5 and 4 x 3 cm in size. Microscopically, they revealed normal lobular architecture with focal papillomatosis in the former.

Infantile myofibromatosis

We report a case of infantile myofibromatosis in a male infant with involvement of the lungs and subcutaneous tissue. We studied our case by light microscopy, immunohistochemistry and electron microscopy. The results reveal that this entity is of a myofibroblastic nature. We reviewed 165 cases including our case. We believe this is the first report in Korea of infantile myofibromatosis with pulmonary involvement.

The dexamethasone suppression test and depressive symptoms in early and late withdrawal from alcohol

Results of the dexamethasone suppression test (DST) in 30 alcoholic patients tested on day 5 and again on day 25 after their last drink are presented. Nineteen patients (63%) failed to suppress cortisol on day 5; three (11%) failed to suppress cortisol on day 25. Depressive symptoms, measured by the Beck Depression Inventory, were significantly correlated with DST results; the lifetime diagnosis of depressive illness was not. The authors conclude that the DST is not useful in detecting primary affective disorders during the early phase of withdrawal from alcohol.