alpha 1-Antitrypsin nullGranite Falls, a nonexpressing alpha 1-antitrypsin gene associated with a frameshift to stop mutation in a coding exon

alpha 1-Antitrypsin (alpha 1-AT) deficiency is a hereditary disorder associated with serum alpha 1-AT levels less than 35% of normal. There are two categories of alpha 1-AT genes that cause this state: the deficient alleles, in which alpha 1-AT is present in serum but in low levels, and the null alleles, in which no alpha 1-AT in serum can be attributed to the gene. The present study defines the molecular basis for the alpha 1-AT gene nullGranite Falls, identified and cloned from genomic DNA of an individual with severe alpha 1-AT deficiency and emphysema resulting from the heterozygous inheritance of the nullGranite Falls and Z alpha 1-AT genes. Sequencing of the 5'-flanking region, all five coding exons, and all exon-intron junctions of nullGranite Falls demonstrated it was identical with the common normal M1(Ala213) alpha 1-AT gene, except for two bases: a single deletion in the codon for amino acid Tyr160 of the mature protein and a single base substitution 168 base pairs 5' to exon I. Although no role for the promoter region mutation could be assigned, the coding exon deletion [Tyr(TAC)----(TA-)] resulted in a frameshift causing a stop coding to be formed approximately 44% from the N terminus of the precursor protein. Using oligonucleotide probes to evaluate the family of the index case demonstrated the deletion----frameshift/stop mutation was inherited in an autosomal co-dominant fashion. Thus, although the molecular basis for alpha 1-AT deficiency of the alpha 1-AT null haplotype such as nullGranite Falls is very different from the molecular basis of the more common deficient haplotypes such as Z, the phenotypic consequences of the two genes are similar; i.e. severe alpha 1-AT deficiency and an association of a high risk for the development of emphysema.     

Identification of DNA polymorphisms associated with the V type alpha1-antitrypsin gene

alpha1-Antitrypsin (alpha1-AT) is a highly polymorphic protein. The V allele of alpha1-AT has been shown to be associated with focal glomerulosclerosis (FGS) in Negroid and mixed race South African patients. To identify mutations and polymorphisms in the gene for the V allele of alpha1-AT in five South African patients with FGS nephrotic syndrome DNA sequence analysis and restriction fragment length polymorphisms of the coding exons were carried out. Four of the patients were heterozygous for the BstEII RFLP in exon III [M1(Val213)(Ala213)] and one patient was a M1(Ala213) homozygote. The mutation for the V allele was identified in exon II as Gly-148 (GGG)-->Arg (AGG) and in all patients was associated with a silent mutation at position 158 (AAC-->AAT). The patient who was homozygous for (Ala213) also had a silent mutation at position 256 in exon III (GAT-->GAC) which was not present in any of the other four patients. Although the V allele of alpha1-AT is not associated with severe plasma deficiency, it may be in linkage disequilibrium with other genes on chromosome 14 that predispose to FGS. Furthermore, the associated silent mutation at position 158 and the Ala213 polymorphism are of interest, as these could represent an evolutionary intermediate between the M1(Ala213) and M1(Val213) subtypes.     

Cell-specific involvement of HNF-1beta in alpha(1)-antitrypsin gene expression in human respiratory epithelial cells

The synergistic action of hepatocyte nuclear factor (HNF)-1alpha and HNF-4 plays an important role in expression of the alpha(1)-antitrypsin (alpha(1)-AT) gene in human hepatic and intestinal epithelial cells. Recent studies have indicated that the alpha(1)-AT gene is also expressed in human pulmonary alveolar epithelial cells, a potentially important local site of the lung antiprotease defense. In this study, we examined the possibility that alpha(1)-AT gene expression in a human pulmonary epithelial cell line H441 was also directed by the synergistic action of HNF-1alpha and HNF-4 and/or by the action of HNF-3, which has been shown to play a dominant role in gene expression in H441 cells. The results show that alpha(1)-AT gene expression in H441 cells is predominantly driven by HNF-1beta, even though HNF-1beta has no effect on alpha(1)-AT gene expression in human hepatic Hep G2 and human intestinal epithelial Caco-2 cell lines. Expression of alpha(1)-AT and HNF-1beta was also demonstrated in primary cultures of human respiratory epithelial cells. HNF-4 has no effect on alpha(1)-AT gene expression in H441 cells, even when it is cotransfected with HNF-1beta or HNF-1alpha. HNF-3 by itself has little effect on alpha(1)-AT gene expression in H441, Hep G2, or Caco-2 cells but tends to have an upregulating effect when cotransfected with HNF-1 in Hep G2 and Caco-2 cells. These results indicate the unique involvement of HNF-1beta in alpha(1)-AT gene expression in a cell line and primary cultures derived from human respiratory epithelium.     

Molecular analysis of the gene of the alpha 1-antitrypsin deficiency variant, Mnichinan.

Mnichinan, a variant of alpha 1-antitrypsin (alpha 1-AT) was detected in a Japanese individual with serum alpha 1-AT deficiency (18 mg/dl), associated with aggregated alpha 1-AT molecules in the hepatocytes. Cloning and sequencing of the 10,627-bp-long region containing the Mnichinan gene and the normal M1(Val213) alpha 1-AT gene revealed all five exons of the Mnichinan gene to be identical with the M1(Val213) alpha 1-AT gene, except for two changes: a TTC trinucleotide deletion in the codon for amino acid Phe52 and a G-A substitution, by which the normal Gly148 (GGG) became Arg148 (AGG). Dot blot analysis of the polymerase chain-reaction-amplified DNA derived from the proband and other family members showed both mutations to be associated with an alpha 1-AT deficiency phenotype. Ninety-eight alpha 1-AT alleles were all negative for both changes. Comparison of the region, except for five exons between the Mnichinan and M1(Val213) genes, demonstrated one base difference in the 5' flanking region and 14 base changes in the introns. All exon-intron junctions were identical, and base changes in the 5' flanking region did not seem significant. The G-A substitution in codon 148 of the Mnichinan gene could not be responsible for the alpha 1-AT deficiency phenotype because Arg- and not Gly- was located at the corresponding position of the protein C inhibitor belonging to the serine protease inhibitor superfamily. The deletion of Phe52 may cause the newly synthesized alpha 1-AT protein to aggregate, resulting in alpha 1-AT deficiency. Comparison of the alpha 1-AT gene sequences available indicated that the C-T substitution at the CpG dinucleotide has an important role in generation of variants and nucleotide changes in the noncoding regions of the alpha 1-AT gene.     

Secretory expression of human alpha1 -antitrypsin in Saccharomyces cerevisiae using galactose as a gratuitous inducer

Human alpha1 -antitrypsin (alpha1-AT) was expressed and secreted in Saccharomyces cerevisiae carrying the gal1 and reg1-501 mutations under the control of GAL10 promoter. Increasing galactose from 0 to 0.5 g/l increased the extracellular concentration of alpha1-AT, though the secretion efficiency was decreased. The final titre of alpha1-AT secreted and the secretion efficiency were 17.9 mu g/ml and 24.8% respectively, with 0.5 g galactose/l. © Rapid Science Ltd. 1998     

A frameshift mutation results in a truncated alpha 1-antitrypsin that is retained within the rough endoplasmic reticulum

The major physiological role of the serine protease inhibitor alpha 1-antitrypsin (alpha 1-AT) is to protect elastic fibers in the lung from excessive hydrolysis by neutrophil elastase. Genetic deficiency of alpha 1-AT predisposes individuals toward the development of emphysema. We have cloned and characterized a mutant alpha 1-AT gene from an individual exhibiting a total absence of immunoreactive alpha 1-AT in serum. Nucleotide sequence analysis of this "null" allele has demonstrated a TC dinucleotide deletion within the codon for Leu318 in exon IV. This frame-shift mutation results in the generation of a premature termination codon at residue 334, which is upstream of the active inhibitory site. To determine the biochemical basis of the null phenotype, the mutant and normal genes were transferred into mouse hepatoma cells for expression analysis. Pulse-chase experiments demonstrated that the mutant gene is expressed into a truncated protein of 45 kDa, which is retained within the rough endoplasmic reticulum. The complete lack of secretion of the truncated protein is consistent with the absence of immunoreactive alpha 1-AT in the patient's serum. In addition, a G to A transition was identified in exon II of the mutant gene, changing the codon for Arg101 to His101. Finally, an A to C transversion was identified in exon V changing the codon for Glu376 to Asp376. Since the latter conservative amino acid substitution has previously been identified in the common PiM2 variant, the frame-shift mutation might have occurred on a PiM2 background chromosome. Using the birthplace of this index case, this mutant alpha 1-AT allele has been designated "nullHong Kong."     

Role of human neutrophil peptides in lung inflammation associated with alpha1-antitrypsin deficiency

Individuals with alpha(1)-antitrypsin (alpha(1)-AT) deficiency are at risk for early-onset destructive lung disease as a result of insufficient lower respiratory tract alpha(1)-AT and an increased burden of neutrophil products such as elastase. Human neutrophil peptides (HNP), the most abundant protein component of neutrophil azurophilic granules, represent another potential inflammatory component in lung disease characterized by increased numbers of activated or deteriorating neutrophils. The purpose of this study was to determine the role of HNP in lower respiratory tract inflammation and destruction occuring in alpha(1)-AT deficiency. alpha(1)-AT-deficient individuals (n = 33) and healthy control subjects (n = 21) were evaluated by bronchoalveolar lavage. HNP concentrations were significantly higher in alpha(1)-AT-deficient individuals (1,976 +/- 692 vs. 29 +/- 12 nM, P < 0.0001), and levels correlated with markers of neutrophil-mediated lung inflammation. In vitro, HNP produced a dose-dependent cytotoxic effect on alveolar macrophages and stimulated production of the potent neutrophil chemoattractants leukotriene B(4) and interleukin-8 by alveolar macrophages, with a 6- to 10-fold increase in chemoattractant production over negative control cultures (P < 0.05). A synergistic effect was noted between HNP and neutrophil elastase with regard to leukotriene B(4) production. Importantly, the proinflammatory effects of HNP were blocked by alpha(1)-AT. HNP likely play an important role in amplifying and maintaining neutrophil-mediated inflammation in the lungs.     

Inhibition of neutrophil superoxide production by human plasma alpha 1-antitrypsin.

We report here that human plasma alpha 1-antitrypsin (alpha 1-AT) inhibited human neutrophil O2.- release elicited by a variety of stimulants. In comparison, the inhibitory capacities of two serine protease inhibitors, L-1-tosylamide 2-phenylethyl chloromethyl ketone (TPCK) and soybean trypsin inhibitor (SBTI), and the human recombinant alpha 1-AT mutant, alpha 1-AT-Arg358 were in the order: alpha 1-AT = TPCK much greater than alpha 1-AT-Arg358 greater than SBTI when cells were stimulated with concanavalin A plus cytochalasin E. These data suggest that, in human inflammatory fluids containing relatively high concentrations of alpha 1-AT (such as rheumatoid arthritis synovial fluid), (i) alpha 1-AT may down-regulate the inflammatory process by inhibiting the neutrophil respiratory burst and (ii) serpin oxidation by neutrophil-released reactive oxygen species is unlikely to occur.     

Grp78, Grp94, and Grp170 interact with alpha1-antitrypsin mutants that are retained in the endoplasmic reticulum

In alpha1-antitrypsin (alpha1-AT) deficiency, a mutant form of alpha1-AT polymerizes in the endoplasmic reticulum (ER) of liver cells resulting in chronic hepatitis and hepatocellular carcinoma by a gain of toxic function mechanism. Although some aspects of the cellular response to mutant alpha1-AT Z have been partially characterized, including the involvement of several proteasomal and nonproteasomal mechanisms for disposal, other parts of the cellular response pathways, particularly the chaperones with which it interacts and the signal transduction pathways that are activated, are still not completely elucidated. The alpha1-AT Z molecule is known to interact with calnexin, but, according to one study, it does not interact with Grp78. To carry out a systematic search for the chaperones with which alpha1-AT Z interacts in the ER, we used chemical cross-linking of several different genetically engineered cell systems. Mutant alpha1-AT Z was cross-linked with Grp78, Grp94, calnexin, Grp170, UDP-glucose glycoprotein:glucosyltransferase, and two unknown proteins of approximately 110-130 kDa. Sequential immunoprecipitation/immunoblot analysis and coimmunoprecipitation techniques demonstrated each of these interactions without chemical cross-linking. The same chaperones were found to interact with two nonpolymerogenic alpha1-AT mutants that are retained in the ER, indicating that these interactions are not specific for the alpha1-AT Z mutant. Moreover, sucrose density gradient centrifugation studies suggest that approximately 85% of alpha1-AT Z exists in heterogeneous soluble complexes with multiple chaperones and approximately 15% in extremely large polymers/aggregates devoid of chaperones. Agents that perturb the synthesis and/or activity of ER chaperones such as tunicamycin and calcium ionophore A23187, have different effects on the solubility and degradation of alpha1-AT Z as well as on its residual secretion.     

An approach for producing transgenic cloned cows by nuclear transfer of cells transfected with human alpha 1-antitrypsin gene

In an attempt to produce transgenic cloned cows secreting alpha 1-antitrypsin (alpha1-AT) protein into milk, bovine cumulus cells were transfected with a plasmid containing an alpha1-AT gene and green fluorescent protein (GFP) reporter gene using Fugene 6 as a lipid carrier. The GFP-expressing cells were selected and transferred into enucleated bovine oocytes. Couplets were fused, chemically activated and cultured. Developmental competence was monitored and the number of inner cell mass (ICM) and trophectoderm (TE) cells in blastocysts were counted after differential staining. The percentage of blastocysts was lower (P < 0.05) in transgenic cloned embryos compared to non-transgenic cloned embryos (23% versus 35%). No difference in the numbers of ICM and TE cells between the two groups of embryos was observed. One or two GFP-expressing blastocysts were transferred into the uterus of each recipient cow. Out of 49 recipient cows, three pregnancies were detected by non-return estrus and rectal palpation. However, the pregnancies failed to maintain to term; two fetuses were aborted at Day 60 and 150, respectively, and one fetus at Day 240. The genomic DNA from the aborted fetus was amplified by polymerase chain reaction (PCR) to investigate integration of the transgene in the fetus. The expected PCR product was sequenced and was identical to the sequence of alpha1-AT transgene. In conclusion, the present study demonstrated that developmental competence of cloned embryos derived from transgenic donor cells was lower than embryos derived from non-transfected donor cells. Although we failed to obtain a viable transgenic cloned calf, integration of alpha1-AT gene into the fetus presents the possibility of producing transgenic cloned cows by somatic cell nuclear transfer.     

A naturally occurring nonpolymerogenic mutant of alpha 1-antitrypsin characterized by prolonged retention in the endoplasmic reticulum.

The classical form of alpha 1-antitrypsin (alpha 1-AT) deficiency is associated with a mutant alpha 1-ATZ molecule that polymerizes in the endoplasmic reticulum (ER) of liver cells. A subgroup of individuals homozygous for the protease inhibitor (PI) Z allele develop chronic liver injury and are predisposed to hepatocellular carcinoma. In this study we evaluated the primary structure of alpha 1-AT in a family in which three affected members had severe liver disease associated with alpha 1-AT deficiency. We discovered that one sibling was a compound heterozygote with one PI Z allele and a second allele, the PI Z + saar allele, bearing the mutation that characterizes alpha 1-ATZ as well as the mutation that characterizes alpha 1-AT Saarbrucken (alpha 1-AT saar). The mutation in PI saar introduces a premature termination codon resulting in an alpha 1-AT protein truncated for 19 amino acids at its carboxyl terminus. Studies of a second sib with severe liver disease and other living family members did not reveal the presence of the alpha 1-AT saar mutation and therefore do not substantiate a role for this mutation in the liver disease phenotype of this family. However, studies of alpha 1-AT saar and alpha 1-ATZ + saar expressed in heterologous cells show that there is prolonged intracellular retention of these mutants even though they do not have polymerogenic properties. These results therefore have important implications for further understanding the fate of mutant alpha 1-AT molecules, the mechanism of ER retention, and the pathogenesis of liver injury in alpha 1-AT deficiency.     

Serum levels of alpha-1-antitrypsin in individuals with different Pi M subtypes

Individuals with heterozygous Pi M subtypes were found to have higher serum levels of alpha 1-antitrypsin (alpha 1-AT) than homozygotes. The alpha 1-AT levels in heterozygotes showed a unimodal distribution. Among homozygotes, a tendency towards a bimodal distribution was found. The mechanism behind this difference is not known. The result can apparently not be explained as the result of a hitherto undiscovered deficiency gene.