Multi-modal expression of apolipoprotein (a) gene in vivo

The apolipoprotein (a) [apo(a)] gene encodes a protein component of lipoprotein (a) [Lp(a)] whose plasma levels vary among individuals. To study the implications of Lp(a), we examined plasma Lp(a) levels and molecular weights of apo(a) in patients with cerebrovascular disease (CVD) or diabetes mellitus (DN). Mean Lp(a) concentrations were higher in the CVD cases with atherothrombotic brain infarction than in those with brain hemorrhage and lacunar infarction. Lp(a) levels were lower in the DM cases on diet therapy alone than in those treated with insulin or oral hypoglycemic agents. These results suggest that Lp(a) is thrombogenic and atherogenic, and that insulin may modulate Lp(a) levels. We subclassified the apo(a) gene into four types (A-D) by polymorphisms in the 5'-flanking region. We also measured plasma Lp(a) concentrations and examined expression of the gene by an in vitro assay. Homozygotes of type C had higher Lp(a) levels than those of type D, and the relative expression of type C was higher than that of type D in vitro. Lp(a) levels, however, varied even within the same 5'-allele having similar apo(a) isoforms. Thus, Lp(a) concentrations are genetically determined and may be modified by some hormones and cytokines. When we examined transcript levels for apo(a) by RT-PCR in various normal tissues, apo(a) was strongly expressed in liver while not in thyroid or leukocytes. Small amounts of apo(a) transcript were observed in all other organs and tissues. Apo(a) in these tissues may also play a role in inframmation, tissue remodeling, cell migration, and other physiological functions.

Multiple novel transcripts for apolipoprotein(a)-related gene II generated by alternative splicing in tissue- and cell type-specific manners

Various Kringle 4 (K4) sequences were identified in human genomic clones and genomic DNAs amplified by PCR. These K4s were homologous to those found in the apo(a) gene and thus termed apo(a)-related genes (ARGs). The same sequences were obtained when human peripheral leukocytes were analyzed by reverse transcription-PCR in order to study the expression mode of the ARGs. It was of note that multiple transcripts with three optional exons for an ARG (ARGII) were detected in leukocytes, indicating that they were generated by alternative splicing. All these transcripts possessed the first half of the second K4 sequence, which had been reported to be skipped. The variant products of ARGII are expected to contain an additional region of either 44, 66, or 100 unique amino acids at the C-terminus of a single K4 unit. When normal human tissues and cultured tumor cells were analyzed, the multiple ARGII transcripts were detected at varying levels. The presence of the cellular state-specific alternative splicing machinery may provide not only redundancy but also diversity in the structure/function of ARGII.

Plasma lipoprotein(a) levels are high in patients with central retinal artery occlusion

High plasma lipoprotein(a) (Lp[a]) concentration is an independent risk factor for atherosclerosis and thrombosis. To study the implications of Lp(a) in central retinal artery occlusion (CRAO), we examined Lp(a) levels and molecular weights (MWs) of apolipoprotein(a) (apo(a)). Mean Lp(a) concentration was significantly higher in the cases with CRAO than in the controls. Lp(a) levels higher than 30 mg/dl were also more frequent in the CRAO cases than in the controls. Lp(a) concentrations correlated significantly with low-MW isoforms of apo(a). Impaired fibrinolysis and atherogenesis induced by Lp(a) may play a role in the pathophysiology of CRAO. Since high Lp(a) levels were reported in CRVO by other investigators, patients with central retinal vein occlusion (CRVO) were also examined for Lp(a). Although Lp(a) levels were higher in the CRVO cases than in the controls, the difference was not significant. Therefore, high Lp(a) levels may not be associated with venous thrombosis and/or embolism.

Apolipoprotein(a) and thrombosis: molecular and genetic bases of hyper-lipoprotein(a)-emia

The apolipoprotein(a) [APO(a)] gene encodes a protein component of lipoprotein(a) [LP(a)], whose plasma levels vary among individuals. To study the implications of LP(a), we examined plasma LP(a) levels and molecular weights of APO(a) in patients with cerebrovascular disease (CVD) or diabetes mellitus (DM). Mean LP(a) concentrations were higher in the CVD patients with atherothrombotic brain infarction than in those with brain hemorrhage and lacunar infarction. LP(a) levels were lower in the DM cases on diet therapy alone than in those treated with insulin or oral hypoglycemic agents. These results suggest that LP(a) is thrombogenic and atherogenic and that insulin may modulate LP(a) levels. We subclassified the APO(a) gene into four types (A to D) by polymorphisms in the 5'-flanking region. We also measured plasma LP(a) concentrations and examined expression of the gene by an in vitro assay. Homozygotes of type C had higher LP(a) levels than those of type D, and the relative expression of type C was higher than that of type D in vitro. Thus, LP(a) concentrations are genetically determined, and hyper-LP(a)-nemia is related to atherosclerosis and thrombosis.

A founder effect is proposed for factor XIII B subunit deficiency caused by the insertion of triplet AAC in exon III encoding the second Sushi domain

We previously concluded that genetic defects in the B subunit of factor XIII were the basis for former Type I deficiency (i.e. factor XIII B subunit deficiency). When we examined an Italian patient with the disease at the DNA level, restriction digestion and sequencing analyses of amplified DNAs revealed that the proband and her family members possessed an AAC insertion within the codon for Tyr-80 in exon III in the gene for the B subunit. a nucleotide polymorphism (A-G) in its 3'-noncoding region in exon XII, and a short tandem repeat polymorphism of (TTTA9, in the 3'-flanking region. These mutations and 3'-polymorphisms were also identified in another Italian family reported in a previous study (10). suggesting that a founder effect is responsible for factor XIII B subunit deficiency in Italians.

The gene for human protein Z is localized to chromosome 13 at band q34 and is coded by eight regular exons and one alternative exon

Human protein Z is a vitamin K-dependent plasma glycoprotein, deficiency of which leads to a mild bleeding tendency. Protein Z appears to assist hemostasis by binding thrombin and promoting its association with phospholipid vesicles. In this study, to characterize the gene for protein Z, its organization and structure were determined by a combination of PCR amplification of leukocyte DNA and isolation of phage clones from a human genomic library. The gene spanned about 14 kb and consisted of 9 exons including one alternative exon. It was of note that the gene organization was essentially identical to that of other vitamin K-dependent proteins, such as factors VII, IX, and X and protein C. The nucleotides in introns at exon/intron boundaries for eight regular exons were the consensus GT-AG sequences. In contrast, the sequence at an optional exon/intron junction was found to be GC rather than GT. The extra exon inserts a unique peptide consisting of 22 amino acids in the prepro-leader sequence. A similar situation was previously observed in factor VII, but not in other vitamin K-dependent plasma proteins. We also assigned the gene for protein Z to chromosome 13 by PCR amplification of genomic DNAs from human/hamster cell hybrids. Fluorescence in situ hybridization, employing a genomic clone coding for human protein Z, further localized the gene to band q34, where the genes of three other vitamin K-dependent proteins are clustered. These genes may have evolved via duplication of an ancestral gene at this locus.

Arg260-Cys mutation in severe factor XIII deficiency: conformational change of the A subunit is predicted by molecular modelling and mechanics

To explore the implications of the structure/ function relationships in factor XIII. a patient with severe A subunit deficiency was examined at the DNA and RNA levels. Nucleotide sequence analysis of the patient's DNA amplified by PCR revealed that the patient had a replacement of C by T in the codon for Arg260. RT-PCR analysis demonstrated that only one kind of mRNA coding for the Arg260-Cys mutation was expressed in the patient at a normal level. Another possible defective allele of the A subunit gene with a G-A polymorphism was not expressed (null allele). The substitution of Arg260 by Cys located on the interface of two A subunits would preclude the reciprocal ionic interaction (salt bridge) between Arg260 and Asp404. Molecular modelling and, for the first time, molecular mechanics calculated that Cys260 changed the local conformation of the A subunit and reduced the electrostatic interaction between two monomers, suggesting destabilization of the molecule's dimer.

Molecular mechanisms of type II factor XIII deficiency: novel Gly562-Arg mutation and C-terminal truncation of the A subunit cause factor XIII deficiency as characterized in a mammalian expression system

To explore the biological and clinical implications of the structure/function relationships in factor XIII, mutations in two patients with type II deficiency were identified and characterized in a mammalian expression system. Nucleotide sequence analysis of the A subunit gene showed that case no. 1 had a deletion of 4 bp (AATT) in exon XI and that, in case no. 2, Gly562 (GGG) had been replaced by Arg(AGG). The deletion in case no. 1 leads to a premature termination at codon 464. Restriction digestion of amplified DNAs confirmed that both cases were homozygous for their respective mutations. Reverse transcription-polymerase chain reaction analysis demonstrated that the level of mRNA was greatly reduced in case no. 1, whereas the level of mutant mRNA expressed in case no. 2 was normal. Molecular modeling calculated that Arg562 changed the conformation of the A subunit, suggesting misfolding and/or destabilization of the molecule. To determine how these mutations impaired synthesis of the A subunit, recombinant A subunits bearing the mutations were expressed in mammalian cells. Pulse-chase experiments showed that the mutants were synthesized normally but disappeared rapidly, whereas the wild-type remained. These results indicate that both mutant proteins with an altered conformation become prone to rapid degradation, resulting in factor XIII deficiency in these patients.

Novel deletion and insertion mutations cause splicing defects, leading to severe reduction in mRNA levels of the A subunit in severe factor XIII deficiency

In order to explore molecular mechanisms for factor XIII deficiency, a patient (Nagoya I) was examined at the DNA and RNA levels. Nucleotide sequence analysis of the patient's DNA amplified by PCR revealed that he had a 20 bp deletion at the boundary of exon I/intron A, and an insertion of T in the invariant GT dinucleotide at the splicing donor site of exon IV/intron D. The presence of these heterozygous mutations was confirmed by restriction digestion of the amplified fragments of the proband and his parents. RT-PCR analysis demonstrated that only one kind of mRNA without exon IV was detected in Nagoya I, although its level was greatly reduced to less than 5% of normal. The other detective allele of the A subunit gene containing the 20 bp deletion was not detected. Thus, both mutations impaired normal processing of mRNA for the A subunit, resulting in his severe factor XIII deficiency.

Possible roles of transglutaminases in Alzheimer's disease

The localizations of two transglutaminases [factor XIIIa and tissue transglutaminase (tTG)] and their mRNAs were examined in human brain tissues from neurologically normal and Alzheimer disease (AD) cases, using immunohistochemical and in situ hybridization methods. In all cases, meningeal macrophages and ependymal macrophage/microglia were positive for factor XIIIa. The mRNA encoding factor XIIIa was detected in macrophages and microglia. As reported previously, intense staining with the antibody to factor XIIIa of a subset of microglia was seen in the parietal cortex in AD brains. Few or no microglia were found associated with classical senile plaques. In contrast, many labeled microglia were associated with primitive plaques. Further-more, most of these cells were mainly seen in the subpial cortical layer but were very rare in the hippocampus. On the other hand, few factor-XIIIa-positive microglia were found in the parietal cortices from non-neurological cases, but moderate numbers were found in their hippocampal tissues. TG and its mRNA were localized in astrocytes in all the cases. In AD, a few neurofibrillary tangles were positive to tTG. These results suggest that the subsets of microglia which express factor XIIIa may play some roles in the early phase of AD pathology.

Electron microscopic examination of Aedes albopictus clone C6/36 cells infected with dengue virus 2 at elevated incubation temperature

Morphological changes such as loss of cytoplasm, membrane destruction and vacuolar swelling in Aedes albopictus clone C6/36 cells infected with dengue virus 2 (DV-2) New Guinea B strain and incubated at 28 degrees C and 37 degrees C, were observed under electron microscope. Both infected and uninfected cells showed significant damage at 37 degrees C in contrast to normal appearance at 28 degrees C. A higher number of virus particles were observed in the cytoplasm at 37 degrees C than at 28 degrees C.

Presence of two plasminogen alleles in normal populations

When we compared nucleotide sequences of the 5'-flanking regions for plasminogen genes from 11 individuals, six substitutions were identified even among normal subjects. A new haplotype (termed allele II) was screened by PCR-RFLP analysis among 54 Japanese and 58 Caucasian normal subjects. The frequency of allele II was 0.787 in the Japanese and 0.560 in the Caucasians, indicating that the ratio of alleles differs between populations. Examination of 118 cases with dysplasminogenemia revealed that the Ala601-Thr mutation was present on allele I in most cases. This mutation was also associated with allele II in one-fourth of all cases, suggesting possible recombination within the plasminogen gene. Interestingly, we previously demonstrated that the expression activity of allele II was about 1.8 fold that of allele I in vitro.

Ala601-Thr type dysplasminogenaemia genetically diagnosed in patients with retinochoroidal vascular disorders

Dysplasminogenaemia has been reported in patients with retinochoroidal vascular disorders. The precise genetic defects of these cases, however, remain unclear because of the limitations of conventional diagnostic techniques. In this study, three patients with these diseases were investigated at the DNA level for the first time to define the molecular bases of these disorders. Polymerase chain reaction-restriction fragment length polymorphism analysis revealed that all three cases carried the same Ala601-Thr mutation. This defect may also play a role in the pathogenesis of circulation disorders in small local vessels because of reduced fibrinolytic activity due to decreased functional plasminogen levels.

Lipoprotein(a) concentration and molecular weight of apolipoprotein(a) in patients with cerebrovascular disease and diabetes mellitus

Plasma lipoprotein(a) [Lp(a)] concentrations are genetically determined, and hyper-Lp(a)-emia is an independent risk factor for atherosclerosis and thrombosis. To study the implications of Lp(a) in cerebrovascular disease (CVD) and diabetes mellitus (DM), we examined plasma Lp(a) levels and molecular weights of apolipoprotein(a) [apo(a)] in 118 patients with CVD, and 125 cases with DM. Although mean Lp(a) concentrations were higher in those cases with atherothrombotic brain infarction than in those with brain hemorrhage and lacunar infarction, the difference was not statistically significant. Lp(a) levels were significantly higher in the DM cases treated with insulin and in those treated with oral hypoglycemic agents than in those on diet therapy alone, suggesting that insulin and oral agents modulate apo(a) expression. Lp(a) concentrations correlated significantly with the low-molecular-weight isoforms of apo(a) in all CVD and DM groups.

Binding of cationic alpha-helical peptides to plasmid DNA and their gene transfer abilities into cells

Polycationic reagents such as cationic lipids and poly-L-lysine are widely used for gene transfer into cells in vitro and show promise as vectors for in vivo gene therapy applications as nonviral gene transfer techniques. We have developed a novel transfection method using cationic amphiphilic alpha-helical oligopeptides with repeated sequences. Oligopeptide has the advantages of being easily designed and modified because of its simple structure. In this study, we synthesized five kinds of peptides of which the total chain length and the width of the hydrophobic region were changed. The binding of the peptides to plasmid DNA was evaluated by agarose gel electrophoresis. It was found that the long and/or hydrophobic peptides can strongly bind to the DNA. The formation of large aggregates with a 0.5-5-microm diameter, which consisted of the long peptides and the DNA, was observed by electron microscopy. The transfection abilities of the peptides were determined by the expression of luciferase from its cDNA in COS-7 cells. The long peptides showed high transfection abilities. As a result, it could be said that the transfection ability of these peptides was parallel to their ability to form aggregates with DNA. Furthermore, the transfection ability was increased by the addition of chloroquine in the transfection procedure. This result indicated that the internalization of the peptide-DNA aggregates would be mediated by the endocytosis pathway.

Plasma lipoprotein(a) levels and expression of the apolipoprotein(a) gene are dependent on the nucleotide polymorphisms in its 5'-flanking region

The apolipoprotein(a) (apo[a]) gene encodes a protein component of lipoprotein(a) [Lp(a)] whose plasma levels vary widely among individuals. Hyper-Lp(a)-emia constitutes a risk factor for thromboembolic disease. We previously subclassified the apo(a) gene into four allelic types (A-D) by polymorphisms in the 5'-flanking region. To elucidate whether these polymorphisms affect the expression of apo(a), we measured plasma Lp(a) concentrations in vivo by ELISA and examined expression of the gene by an in vitro assay using its 5'-flanking region. Homozygotes of type C had significantly higher Lp(a) levels than those of type D. The relative expression of type C was also about three times higher than that of type D, which was consistent with the in vivo results. Deletion analysis revealed that the substitution of C by T (+93) led to negative regulation in expression of the gene, while the change of G to A (+121) led to positive regulation. These results indicate that the polymorphisms in the 5'-flanking region of the apo(a) gene affect the efficiency of its expression and, in part, play a role in regulating plasma Lp(a) levels.

Characterization of the 5'-flanking regions of plasminogen-related genes A and B

We examined the promoter activity of two homologous plasminogen-related genes (PRGA and PRGB) employing HepG2 cells. The 5'-flanking regions of these genes were sequenced first, then inserted into the upstream region of the CAT gene in an expression vector. CAT assays revealed that the promoter activity of PRGA was 3-fold that of plasminogen, while the activity of PRGB was 5-fold. Deletion analysis of these genes demonstrated that a region between -283 and +153 bp relative to the transcription initiation site was essential for their expression, and that there were regions with either negative or positive effects on expression farther upstream.

Expression and induction by IL-6 of the normal and variant genes for human plasminogen

We examined the promoter activity of the gene for human plasminogen (PLG) employing its 1.1 kb fragment of the 5'-flanking region inserted in front of a reporter gene. Deletion analysis revealed that a region surrounding the transcription start site was essential for the PLG expression. Since the PLG gene has three sequences for the interleukin-6 (IL-6) responsive element, we examined the effect of IL-6 on the PLG expression. IL-6 stimulation of PLG resulted in a 2.5-fold increase in its transcription. This is also true for the PLG gene of a case with dysplasminogenemia. Although the patient's gene had six mutations in the 5'-flanking region, its promoter activity was 1.8-fold that of normal PLG.

The normal and abnormal genes of the a and b subunits in coagulation factor XIII

Factor XIII consists of two catalytic a and two noncatalytic b subunits. The gene for the a subunit is located on chromosome 6, the gene for the b subunit on chromosome 1. Both genes have been characterized. There are several different allelic forms of the a subunit in the normal population and some microheterogeneity for the b subunit. Most patients with congenital factor XIII deficiency lack the a subunit in plasma; few patients appear to have a complete lack of the b subunit. The genes from patients with factor XIII deficiencies were obtained and examined. Based on these analyses a new genetic classification for factor XIII deficiency is proposed: a deficiency of the a subunit (formerly termed type II), a deficiency of the b subunit (formerly known as type I), and a possible combined deficiency of both a and b subunits.

Genetic diagnosis of dysplasminogenemia: detection of an Ala601-Thr mutation in 118 out of 125 families and identification of a new Asp676-Asn mutation

Dysplasminogenemia (plasminogen abnormality) is frequently found in association with thrombosis. Two types of mutation, Ala601-Thr and Val355-Phe, have already been identified; the precise genetic defects of most of these patients, however, remain unknown. In this study, we examined the genetic DNAs of two unrelated cases by single-strand conformational polymorphism and nucleotide sequencing analysis. A new mutation, designated as Asp676-Asn, has been identified in these cases. This mutation leads to the loss of a negatively-charged residue and the creation of a potential carbohydrate attachment site, which may impair the enzymatic properties of plasminogen. As many as 158 individuals with dysplasminogenemia were analyzed by a combination of in vitro amplification and restriction digestion. Among 125 unrelated families, the Ala601-Thr mutation accounted for about 94% of cases. The Val355-Phe mutation was found in four unrelated families, indicating that it is a recurring mutation and is not very rare.

Expression and release of the a and b subunits for human coagulation factor XIII in baby hamster kidney (BHK) cells

The a subunit of coagulation factor XIII lacks a hydrophobic signal sequence for secretion from cells, while the b subunit has a typical signal sequence. To determine whether the a subunit can be synthesized and released, expression vectors containing the cDNA for either subunit were transfected into baby hamster kidney (BHK) cells. Western blotting analysis and gel filtration chromatography demonstrated that the recombinant a and b subunits (rXIIIa and rXIIIb) had the same molecular weights and subunit structures (a2, b2, and a2b2) as the native molecules. rXIIIa was enzymatically active when activated by thrombin. Most rXIIIb was secreted as measured by ELISA, while most rXIIIa was detected in the cytosol by subcellular fractionation. Co-expression with rXIIIb in the same cells did not promote the release of rXIIIa. Treatment of the cells with brefeldin A, a potent inhibitor of protein transportation, blocked the secretion of rXIIIb, although it had no effect on the release of rXIIIa. Several drugs and heat stress induced the release of rXIIIa, which correlated directly with that of cytoplasmic lactate dehydrogenase. These results suggest that the a subunit is released from cells as a consequence of cell injury, which is independent of the classical secretory pathway.

Type I factor XIII deficiency is caused by a genetic defect of its b subunit: insertion of triplet AAC in exon III leads to premature termination in the second Sushi domain

Factor XIII deficiency has been classified into two categories: type I deficiency, characterized by the lack of both the a and b subunits; and type II deficiency, characterized by the lack of the a subunit alone. To clarify the genetic bases of these diseases, previously reported cases of the type I deficiency were examined at the DNA level. DNA sequence analysis showed that a nucleotide triplet (AAC) was inserted within the codon for Tyr-80 in exon III of the gene for a female proband's b subunit, resulting in the creation of a stop codon. Restriction digestion of amplified DNAs confirmed that the proband and her sister were homozygotes, and their family members were heterozygotes of this mutant allele. A truncated protein composed of 79 amino acids could be synthesized by these homozygotes; however, such a protein would not be secreted or it would degrade quickly, because there were normal amounts of the mutant mRNA, but no b subunit was detected in these patients. The a subunit deficiency of these patients must be a secondary to the b subunit deficiency, as their gene for the a subunit was intact, and the a subunit in their platelets was present within normal levels.

Rapid killing of human neutrophils by the potent activator phorbol 12-myristate 13-acetate (PMA) accompanied by changes different from typical apoptosis or necrosis

To elucidate the relationship between activation of neutrophils and their subsequent death, the effect of phorbol 12-myristate 13-acetate (PMA), a potent activator of neutrophils, was examined. PMA-treated neutrophils showed morphological changes quite different from those of typical apoptosis or necrosis. After fusion of the lobate nucleus, nuclear contents of chromatin uniformly decreased in compactness and soon after the nuclear envelope was broken. Even at this stage, cytoplasmic organelles did not undergo degeneration. Membrane permeability began increasing at 3 h of incubation with PMA, subsequent to nuclear change. Conventional agarose gel electrophoresis and pulsed field gel electrophoresis of DNA from PMA-treated neutrophils revealed no DNA degradation products smaller than 300 kbp. PKC inhibitors, staurosporine and H-7, prevented cytotoxicity by PMA. Furthermore, antioxidants, thiourea, dimethylthiourea, pyrrolidinethiocarbamate, and N-acetyl-L-cysteine, but not superoxide dismutase, were also active in preventing PMA cytotoxicity, suggesting that cell suicide resulting from PMA treatment is due to oxygen radicals, especially the hydroxyl radical. A certain population of neutrophils phagocytosing opsonized zymosan also showed changes similar to those observed in PMA-treated cells.