Suppressive effects on simian virus 40-induced oncogenesis of several immunosuppressive agents and hormonal modifications applied during the latent period.

The long latent period required for tumor induction with Simian virus 40 (SV40) in the subcutis of hamsters can be used to investigate whether host factor(s) participate in oncogenesis. Several treatments were applied during this period, and the results were compared with those of the same treatment applied in another series of experiments, homologous SV40 tumor grafting in hamsters. The results obtained were as follows: (a) the latent period for SV40 tumor induction in the female was shorter than that in the male; tumor development was delayed significantly by oophorectomy but was little affected by orchiectomy. Tumor development was markedly delayed in animals of both sexes by estrone given at birth but was accelerated by testosterone given in the adult male; (b) by each of these hormonal modifications, growth of transplanted SV40 tumors was influenced in a different way from that of tumor induction; (c) immunosuppressive treatments, such as thymectomy, administration of antilymphocyte sera, cyclophosphamide, or cortisone acetate delayed and decreased tumor development when applied in the latent period, and the degree or pattern of this effect varied from one procedure to another, depending on the sex and age of the animals; (d) in contrast, tumor growth was markedly accelerated in thymectomized or cortisone-treated hosts irrespective of sex. The different and almost reverse effect of the same procedure in the two phases of tumorigenesis may indicate two discriminating mechanisms operating in the host during these phases. This different effect may be due to virtual absence of any "mature" neoplastic cell in the latent period, except for a few weeks before the appearance of a palpable tumor. These results suggest that the long period of latency may be spent to complete SV40-induced neoplastic conversion of cells, receiving some help by host factors.

A new tumor-associated antigen useful for serodiagnosis of hepatocellular carcinoma, defined by monoclonal antibody KM-2.

After immunization of mice with the human hepatocellular carcinoma (HCC) cell line PLC/PRF/5, we produced monoclonal antibody KM-2, which allowed us to characterize a new HCC-associated antigen (KM-2 antigen) and to develop a sandwich-type radioimmunoassay. The KM-2 antigen was strongly expressed on the cell surface of HCC cell lines. Immunofluorescence staining of frozen sections of different tissues and tumors confirmed its specific expression on the cell surface of a group of HCC. The antigen was also detected in the bile canaliculi of normal liver. Its biochemical characterization revealed a high molecular weight (M(r) approximately 900,000) glycoprotein with an N-linked carbohydrate chain close to the peptide epitope recognized by the KM-2 monoclonal antibody. By the radioimmunoassay for the KM-2 antigen, the antigen was detected in sera of 72 (47%) of 154 patients with HCC and 3 (3%) of 102 patients with liver cirrhosis; it was not detected in 96 patients with chronic hepatitis or in 100 healthy control individuals. The positive rate of KM-2 antigen (72 of 154, 47%) was significantly (P less than 0.01) higher than that (51 of 154, 33%) of alpha-fetoprotein (AFP) when the cut-off level of AFP was taken as the widely accepted 400 ng/ml. No significant correlation was recognized between serum levels of the KM-2 antigen and AFP (r = 0.15; P greater than 0.05). In addition, among 103 patients with HCC whose AFP levels were less than 400 ng/ml, 31 (30%) were positive for the KM-2 antigen. Determination of the serum KM-2 antigen would be useful for the serodiagnosis of patients with HCC, particularly in cases with normal or low AFP levels.

Cloning and characterization of a novel RNA-binding protein SRL300 with RS domains.

AT-rich element binding factor 1 (ATBF1) mRNA encodes a transcription factor implicated in neuronal differentiation. A cDNA for the protein that can bind the 5'-noncoding sequence of the ATBF1 mRNA was cloned. The deduced protein, termed SRL300, contains a unique RNA-binding region, two large RS domains and many phosphorylation sites. SRL300 protein was detected in both human and rat cells.

Cloning and characterization of the rat p130, a member of the retinoblastoma gene family.

A cDNA clone encoding rat p130, a member of the retinoblastoma (Rb) gene family, was isolated based on the sequence homology of the E1A-binding domain. The 4.87 kb cDNA contained an 1135-amino acid open reading frame with high homologies to the human and mouse p130 and a partial homology to the pRb protein. p130 showed difference in distribution of potential phosphorylation sites from pRb in the N-terminal and the B pocket regions. p130 mRNA was detected in most rat tissues. The p130 gene was mapped to rat chromosome 19p11-13 by fluorescence in situ hybridization.

Characterization of rat and human steroid sulfatases.

Rat and human steroid sulfatases were purified from liver and placenta, respectively, by the same procedure. The rat and human enzymes were solubilized with Triton X-100, and purified by immunoaffinity chromatography with a monoclonal antibody showing high binding activities to both the enzymes. They were further purified by high-pressure anion-exchange chromatography to compare their structural and catalytic properties. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis showed that both enzymes had a molecular weight of 62,000. The enzymes had similar amino acid compositions and amino-terminal amino acid sequences. Significant differences of the optimum pH, Michaelis constant and maximum velocity were observed between these enzymes. The optimum pH of each enzyme varied from 6.0 to 8.0, depending on substrates and with or without Triton X-100. In detergent-free media, steroid sulfates competitively inhibited the ability of these enzymes to hydrolyze 4-nitrophenyl sulfate. In media containing Triton X-100, on the other hand, the inhibition types of the steroid sulfates on the hydrolyzing activities of the rat and human enzymes were noncompetitive- and mixed-types, respectively.

CALNUC (nucleobindin) is localized in the Golgi apparatus in insect cells.

A mouse monoclonal antibody 12B1 was raised against Golgi fractions from Sf21 insect cells and selected as Golgi-specific by immunostaining of the cells. The antigen was purified from the cells by immunoaffinity chromatography with the monoclonal antibody, and its N-terminal and internal amino acid sequences were determined. Based on the partial amino acid sequences, cDNA encoding the antigen protein was cloned and sequenced. The amino acid sequence deduced from the cDNA nucleotide sequence showed a homology to those of CALNUC family proteins, CALNUC (or nucleobindin, a calcium-binding Golgi protein with DNA-binding activity) and protein NEFA (a cell surface protein with DNA-binding, EF-hand, and acidic domains). The insect protein had two EF-hand loops at the same sites as the mammalian CALNUC family proteins, but had no leucine zipper which the mammalian homologues commonly have. An electron microscopic immunoperoxidase study demonstrated that the insect protein was localized in the cis-Golgi cisternae and cis-Golgi networks. Since this localization is identical to that of mammalian CALNUC, the insect protein was considered to be a homologue of CALNUC rather than that of NEFA. Assays involving proteinase K digestion, sodium carbonate extraction and Triton X-114 extraction revealed that the insect CALNUC-like protein was a soluble protein tightly associated with the luminal surface of Golgi membranes as reported for mammalian CALNUC. The insect protein was also shown to have calcium-binding activity as does mammalian CALNUC. These data verify that the insect protein is CALNUC. The existence of CALNUC in insect cells suggests that CALNUC is an essential calcium-binding Golgi protein in a wide range of the animal kingdom. A phylogenetic tree analysis, however, suggested that NEFA was derived from CALNUC long after the segregation of a mammalian ancestor from an insect ancestor.

Thyroxine (T4) release from thyroglobulin and its T4-containing peptide by thyroid thiol proteases.

Two thiol proteases, TP-1 and TP-2, were purified 500- and 400-fold, respectively, from hog thyroid lysosomal extracts and examined for their activities as releasers of T4 1) from hog thyroglobulin, 2) a fragment (mol wt, approximately 15,000) prepared therefrom, and 3) a T4-containing peptide (19 amino acid residues) derived from the fragment, by measuring the liberation of free T4 with reversed phase HPLC. TP-1 released 8%, 55%, and 95% of the bound T4 present in thyroglobulin, the fragment, and the peptide, respectively, after incubation for 8 h. TP-2, on the other hand, released only 2% of the bound T4 in thyroglobulin and liberated no T4 from the fragment and the peptide. The release of T4 from thyroglobulin by the action of TP-1 was increased approximately 2-fold by the addition of TP-2. This synergistic effect suggested that TP-1 can release T4 from thyroglobulin much more efficiently after the protein has been partially degraded by the action of TP-2, which has only a poor T4-releasing activity. It also suggested that the T4-releasing activity of TP-1 markedly increases as the size of protein substrate is decreased. The amino acid composition of the T4-containing peptide was identical with that previously isolated from bovine thyroglobulin, and this peptide sequence has been shown to be derived from the NH2-terminal portion of the thyroglobulin. This suggests that TP-1 can release T4 at least from the NH2-terminal region of thyroglobulin.

Calcium release from porcine thyroid microsomes by phosphatidylinositol 4,5-bisphosphate and inositol 1,4,5-trisphosphate.

We have demonstrated Ca2+ mobilization induced by inositol compounds from intracellular stores of isolated porcine thyroid cells that were permeabilized with saponin and from fractionated thyroid microsomes that were preloaded with Ca2+. In the presence of saponin and antimycin A, a mitochondrial inhibitor, the Ca2+ concentration in the cell suspension decreased after the addition of ATP; the addition of inositol 1,4,5-trisphosphate (IP3) elicited transient elevations in Ca2+. The half-effective concentration (EC50) of IP3 was about 1 microM. TSH, acetylcholine, and norepinephrine had no effect on the Ca2+ movement, but phosphatidylinositol 4,5-bisphosphate (PIP2) induced a similar Ca2+ release (EC50 = 3 microM). PIP2-induced release decreased as the Mg2+ concentration was raised. After the release induced by a maximal amount of IP3, PIP2 could induce a further Ca2+ release. We also measured Ca2+ efflux from fractionated microsomes preloaded with 45Ca2+ by ATP-dependent transport. IP3 induced a small efflux of 45Ca2+, but PIP2 was much more effective at low Mg2+ concentrations. More than half of the loaded 45Ca2+ was released by 10 microM PIP2 within 30 sec, and the EC50 was 0.7 microM. These results suggest that Ca2+ mobilization from the microsomes mediated by inositol compounds participates in the regulation of thyroid cell functions.

Partial purification and characterization of two thiol proteases from hog thyroid lysosomes.

Two proteases were purified from lysosomal supernatants of hog thyroids. The first step of the purification by diethylaminoethyl cellulose chromatography separated the two proteases, which were shown to have quite similar properties with respect to 2-mercaptoethanol requirement and pH optima for benzoyl-L-arginine-2-naphthylamide (BANA) hydrolytic activity, and inhibition by sulfhydryl inhibitors. One of the proteases, designated as thiol protease-1 (TP-1), was further purified by gel filtration (Sephacryl S-200) and vigorously hydrolyzed BANA but not casein. BANA hydrolytic activity of TP-1 was 50% inhibited by 10(-5) M leupeptin and by 10(-7) M L-trans-epoxysuccinyl-leucylamido(4-amino)butane. A highly purified preparation of the other protease, designated as thiol protease-2 (TP-2), was obtained after gel filtration on Sephacryl S-200 and carboxymethyl cellulose chromatography. In contrast to TP-1, TP-2 exhibited high hydrolytic activity against both casein and BANA, and was more sensitive to leupeptin and L-trans-epoxysuccinyl-leucylamido(4-amino)butane, the concentrations for 50% inhibition being 10(-7) and 10(-8) M, respectively. Electrophoresis and chromatofocusing revealed that the two proteases had different isoelectric points. TP-1 could bind to concanavalin A Sepharose and hydrolyzed L-arginine-2-naphthylamide but not carbobenzoxy-L-arginyl-L-arginine methylcoumarylamide whereas TP-2 did not bind to concanavalin A Sepharose and hydrolyzed carbobenzoxy-L-arginyl-L-arginine methylcoumarylamide but not L-arginine-2-naphthylamide. These results suggested that TP-1 and TP-2 had properties similar to those of the liver lysosomal thiol proteases, cathepsins H and B, respectively.

Active calcium transport by porcine thyroid microsomes.

Microsomal fractions prepared from porcine thyroid glands by differential centrifugations and sucrose density gradient centrifugation showed an ATP-dependent Ca2+ uptake. Electron microscopy and the study of marker enzyme activities suggested that the fractions consisted mainly of endoplasmic reticulum. The amount of transported Ca2+ increased four times in the presence of 20 mM oxalate owing to the precipitation of calcium oxalate, which was detected inside the microsomal vesicles by electron microscopy. Ca2+ was released rapidly when the calcium ionophore, A-23187, was added. The Ca2+ concentration for the half-maximal activation of Ca2+ transport was about 1 microM. These results indicate that Ca2+ is translocated into the lumen of microsomes against a concentration gradient in a manner of the active transport. The microsomes showed Ca2+-dependent ATPase activity and were phosphorylated by the reaction with [gamma-32P]ATP in a similar Ca2+ dependence to that of transport rate. A 105-kDa phosphoprotein was identified by dodecyl sulfate polyacrylamide gel electrophoresis and was found to be sensitive to hydroxylamine. These properties of the phosphoprotein were the same as those of Ca2+ pump ATPase in the endoplasmic reticulum of other cells. These results suggest that the cytosolic Ca2+ is maintained at low levels by the microsomal uptake of Ca2+ by the action of the ATP-dependent Ca2+ pump or active transport system.

Characterization of human thyroid peroxidase purified by monoclonal antibody-assisted chromatography.

A murine monoclonal antibody (mAb) to human thyroid peroxidase (TPO) was produced and used for purification of the enzyme. This report describes studies done to characterize the mAb and the purified human TPO. The mAb bound to human TPO at a molar ratio of 1:2 or 1:1 and to human thyroid microsomes with a dissociation constant of 1.2 nM. The mAb had no effect on TPO activity to catalyze guaiacol oxidation. As immunoglobulin G, the mAb consisted of a light chain (kappa) of 26 kilodaltons (kDa) and a heavy chain (gamma 1) of 53 kDa; its pI value was 5.9. Using an mAb immunoaffinity column, 85% of TPO activity was recovered from an ammonium sulfate precipitate of a human thyroid microsomal preparation solubilized with deoxycholate. The purified TPO had a specific activity of 164 guaiacol U/mg protein and an A413 nm/A280 nm ratio of 0.26. The enzyme showed bands only at 107 and 100 kDa on sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Purified TPO was very stable at alkaline pH, and its ability to catalyze iodide oxidation and tyrosine iodination was increased to the same extent as its ability to catalyze guaiacol oxidation. For comparison with a conventional method, the immunoaffinity-purified TPO was trypsinized and rechromatographed on the immunoaffinity column. The trypsinized enzyme had a specific activity of 336 U/mg and an A413 nm/A280nm ratio of 0.65. The absorption spectrum of the enzyme suggested that the prosthetic group of human TPO is protoheme IX. These results indicate the value of the immunoaffinity procedure for human TPO purification. The major advantages of this purification procedure are not only high yield and speed, but also recovery of intact enzyme.

Detection of autoantibodies to thyroid peroxidase in autoimmune thyroid diseases by micro-ELISA and immunoblotting.

Serum autoantibodies to thyroid peroxidase (TPO) in patients with thyroid autoimmune diseases were studied by micro-ELISA and immunoblotting. Twenty-four patients, 15 with Graves' disease and 9 with Hashimoto's thyroiditis, whose serum titers were greater than 3200 on the microsomal hemagglutination test (except for 1 patient with a titer of 800) had autoantibodies to TPO. Both immunoglobulin G and M classes of autoantibodies were detected, with the former being more prominent. When TPO and thyroid microsomes were used as a target in a competitive binding inhibition test, the results suggested that TPO was a major thyroid microsomal antigen. On the other hand, immunoblotting analysis showed 3-4 bands in the 45-60K region stained by patients' sera in addition to human TPO with mol wt of 100K and 107K; only the latter 2 bands stained with antiporcine TPO antibody. In the majority of sera, TPO bands were clearer than others, although some sera showed the clearest band with a mol wt of 55K. These results indicate that patients with autoimmune thyroid disease often have autoantibodies to TPO that can be detected by micro-ELISA and immunoblotting, and that TPO is a major component of the thyroid microsomal antigen.

Cloning and characterization of rat p27Kip1, a cyclin-dependent kinase inhibitor.

Cyclin-dependent kinase (Cdk) inhibitors play significant roles in the cell cycle control of various biological phenomena. To characterize the role of Cdk inhibitors in rat cells, we isolated a cDNA encoding rat p27Kip1, a 27-kDa Cdk inhibitor. The 1.04-kb cDNA of rat p27 contained an open reading frame of 197 amino acids that shared high homology with mammalian p27 and significant homology with mammalian p21Cip1 and p57Kip2. p27 mRNA was detected in most rat tissues and cell lines. The levels of p27 protein expression were similar in rat cell lines transformed by E1A and in normal cells. Rat p27 was able to interact with Cdk 2/4 and cyclin A/D in rat cells, but the amounts of rat p27 in Cdk2 complexes were different between transformed cells and normal cells. Thus, the formation of stable complexes of rat p27 may be modulated by E1A. Rat p27 protein could inhibit the increased Cdk2-associated kinase activity in transformed rat cells.

Nucleotide sequence of the cDNA encoding mouse thyroid peroxidase.

The nucleotide (nt) sequence of the cDNA encoding mouse thyroid peroxidase (TPO) has been determined. The TPO cDNA is 3281 nt long and its open reading frame encodes a protein composed of 914 amino acids (aa), including a putative initiation Met. The mouse TPO cDNA shows 75.3, 70.8, and 93.5% homology in the coding nt sequence with human, porcine, and rat TPO cDNAs, respectively. In the aa sequence, mouse TPO shows 73.4, 68.4, and 93.9% homology with human, porcine, and rat TPOs, respectively. Specifically, the aa sequence surrounding the proximal His residue, probably essential for TPO activity, is well conserved among these four organisms.

cDNA-directed expression of human thyroid peroxidase.

A human thyroid peroxidase cDNA, hTPO-1 [(1987) Proc. Natl. Acad. Sci. USA 84, 5555-5559], was expressed in human Hep G2 cells using a vaccinia virus cDNA-expression system. When examined by immunoblot analysis, the level of hTPO-1 protein expression reached a maximum approx. 24 h after infection and remained at a similar level up to 72 h post-infection. The expressed protein was enzymatically active as measured by guaiacol oxidation. Monoclonal antibody-assisted immunoaffinity column chromatography was used for partial purification of vaccinia-expressed hTPO-1, resulting in more than 300-fold higher specific activity and a measurable difference spectrum of the hTPO-1 (Fe3+)-CN complex.

Resonance Raman characterization of hog thyroid peroxidase. An SERRS study.

Resonance Raman (RR) spectra of hog thyroid peroxidase (TPO) were observed for the first time and compared with those of lactoperoxidase (LPO) and horseradish peroxidase (HRP). Since TPO purified by monoclonal antibody-assisted immunoaffinity chromatography was strongly fluorescent, the surface enhancement technique using Ag colloid adsorption was used for the oxidized form, but ordinary RR spectra could be obtained for the reduced form. The RR spectra of TPO were distinct from those of HRP in both the oxidized and reduced states and indicated the presence of six-coordinated iron-protoporphyrin.

A Japanese family with high density lipoprotein deficiency.

Two siblings with marked reduction of plasma high density lipoprotein (HDL) were found in a Japanese family. Their plasma cholesterol levels were very low (30-60 mg/dl), especially in the HDL fraction (0-1 mg/dl). The concentration of apolipoprotein (Apo) A-I in their plasma was 2-3 mg/dl and that of Apo A-II was 1.5-2.0 mg/dl, determined by means of a single radial immunodiffusion technique. An ultracentrifugally separated HDL fraction contained two different populations of lipoprotein particles, as shown by electron microscopy; a small particle with a diameter of 50-70 A and a relatively large particle at 200 A. Plasma lecithin: cholesterol acyltransferase activity was substantially retained in both cases. Hepatosplenomegaly was present and liver biopsy revealed lipid deposition in reticuloendothelial cells, although the tonsils were apparently normal. No severe atherosclerotic lesions were noticed. The results from these two cases were consistent with the characteristic features of homozygotes of familial HDL deficiency (Tangier disease). HDL cholesterol levels were relatively low in the parents and two children from one patient, which is consistent with the heterozygote state. Two other cases in the kindred were also found to have relatively low HDL cholesterol levels, besides these 4 cases of obligate heterozygotes. Apo A-I and Apo A-II levels in the plasma of the obligate heterozygotes, however, were within the normal range. Plasma low density lipoprotein in the patients moved faster in polyacrylamide gel electrophoresis than those of normal subjects, as did those in the heterozygotes.

High-density-lipoprotein-independent killing of Trypanosoma brucei by human serum.

The cattle pathogen Trypanosoma brucei brucei is morphologically indistinguishable from the human pathogens T.b. rhodesiense and T.b. gambiense. However, unlike the human pathogens, T.b. brucei is lysed by normal human serum (NHS). The trypanolytic factor in NHS co-purifies with high-density lipoproteins (HDL), but its precise nature is unknown. Using a new fluorescence-based viability assay to assess T.b. brucei killing, we find that the HDL-deficient sera from two patients with Tangier disease are as trypanolytic as NHS. Fractionation of the Tangier sera by density ultracentrifugation revealed that the activity resides only in lipoprotein-depleted fractions. Tangier and NHS were also subjected to molecular sieving chromatography, and the activity profiles were identical. Lytic fractions to T. brucei (but not to T. rhodesiense) appeared under two distinct peaks of 100-600 kDa and > 1000 kDa. Neither peak coincided with the position of the major serum lipoproteins, as determined by cholesterol titrations. The high-molecular-mass peak did not contain the HDL-associated apolipoprotein-A1. Further, we did not find that purified apolipoproteins A1 or J are lytic for the trypanosomes. We conclude that the killing of T. brucei by human serum can be independent of HDL.

A monoclonal antibody to rat liver arylsulfatase C and its application in immunohistochemistry.

We purified arylsulfatase C from rat liver microsomes and prepared a monoclonal antibody (P42C2) to the purified enzyme. By SDS-PAGE and immunoblotting analysis using P42C2, the molecular weight of the purified enzyme and of the enzyme in liver and kidney microsomes were estimated at 62,000 daltons. P42C2 caused little inhibition of arylsulfatase C activity, and was bound only slightly to liver microsomes. Localization of arylsulfatase C was studied at the light and electron microscopic level by the indirect immunoperoxidase method using P42C2. In rat liver, arylsulfatase C was detected mainly in the hepatocytes, and less frequently in endothelial cells, Kupffer's cells, and Ito's cells. In rat kidney, strong staining was observed in the straight portions of the proximal tubules. The podocytes, interstitial cells, endothelial cells, and epithelial cells of Henle's thin limbs were stained faintly. By electron microscopy, arylsulfatase C was found localized on the membranes of the endoplasmic reticulum and nuclear envelopes in these cells. These immunohistochemical findings agree with the localization demonstrated by an enzyme-histochemical method which we had previously developed.

Epitopic difference among rat thyroglobulins.

Epitopes on thyroglobulin (Tg) were examined using mouse monoclonal antibodies (mAbs). Two out of 6 mAbs indicated a remarkable difference in binding to three rat Tgs. Namely, they bound to one Tg as well as immunized Tg but could not bind to another at all. They could hardly bind to the third Tg. Another mAb was similar, to some extent, in binding to three rat Tgs as described above, although three other mAbs bound almost equally to three rat Tgs. Since competitive binding inhibition by Tgs supported the result of the binding study, the epitopic difference on rat Tgs was confirmed. Furthermore, competitive binding inhibition by unlabeled mAbs revealed that six mAbs recognized different epitopes individually. Therefore, there were at least two unique epitopes located on one rat Tg but not located on another. The relation between unique epitopes and thyroiditis in the rats used in the present study is also discussed.