Biomedical subjects

A Maffei

Publications and source records attributed to A Maffei.

33 records · Page 2Linked to original sources

PubMed1992

DNA polymorphisms in the 5'-flanking region of the HLA-DQA1 gene.

The HLA-DQA1 gene exhibits haplotype-specific restriction fragment polymorphisms due to DNA rearrangements. We found that some of these polymorphisms extend into the 5' flanking region of the gene and are distinct from other HLA-DQA1 related DNA polymorphisms so far reported. Sequencing of genomic DNA subclones derived from the 5' flanking region of HLA-DQA1 showed the presence, in a DR4 haplotype, of two repetitive elements of the Alu family, oriented in opposite directions and bracketing an approximately 3 kilobase region immediately adjacent to the promoter of the gene. When DNAs extracted from several cell lines were analyzed by genomic hybridization using single-copy probes relative to these intervening sequences, polymorphisms were observed. No structural alterations of the gene immediately outside the DNA portion delimited by the two Alu elements were observed, thus suggesting that polymorphisms of the 5' end of HLA-DQA1 may be limited to the intervening region between the two Alu repeats. The latter includes upstream regulatory elements controlling the expression of the genes. The possibility that the structure of the DNA in this region may influence the regulation of HLA-DQA1 gene expression in different haplotypes is discussed.

Base Sequence↗

PubMed1990

Effect of the AIR-1 locus on the activation of an enhancerless HLA-DQA1 promoter.

Studies on the regulation of a major histocompatibility complex (MHC) class II gene, HLA-DQA1, in Ia-positive cells (Raji, a human B-lymphoma cell line) and in isogenic Ia-negative cells (RJ2.2.5, a mutant of Raji altered at the AIR-1 locus) are reported. As previously found, AIR-1 is required in its entirety for the activity of an enhancer factor, the absence of which abolishes transcription of MHC class II genes. In this paper, we show that HLA-DQA1 gene expression can be directed by an enhancerless promoter. The fact that this promoter is inactive in the RJ2.2.5 mutant suggests that the trans-acting element determined by the AIR-1 locus is not only an enhancer factor as previously described, but also acts at the MHC class II promoter level.

Base Sequence↗

PubMed1989

Transcriptional and post-transcriptional regulation of human MHC class II genes require the synthesis of short-lived proteins.

We have studied the stability of protein factors which control the intracellular levels of human MHC class II genes in B cells. We report that human MHC class II gene transcription and mRNA stability require the synthesis of short-lived proteins which undergo rapid intracellular turnover. We found, in fact, that the amount of MHC class II mRNA produced by human B lymphoma or B lymphoblastoid cell lines abruptly decreased upon cultivation of cells in the presence of cycloheximide, a potent inhibitor of protein synthesis. Measurements of the rate of mRNA transcription in nuclei isolated from treated cells indicated that a cycloheximide-sensitive activator protein is needed to allow MHC class II mRNA transcription initiation. Likewise, comparison of mRNA turnover rate in cells treated with actinomycin D, an inhibitor of RNA synthesis, and in cycloheximide-treated cells shows that a post-transcriptional factor is required to stabilized human MHC class II mRNA by a factor of 8- to 10-fold in B cells. These results indicate that, along with the trans- and cis-acting factors required for transcriptional control, a series of signals must exist in B cells which implement a post-transcriptional level of regulation of MHC class II gene expression in B cells.

Cell Line↗

PubMed1989

Transcriptional control of MHC class II gene expression during differentiation from B cells to plasma cells.

In this study we investigated the molecular mechanisms responsible for the extinction of the constitutive MHC class II gene expression of human B cells on somatic cell hybridization with murine plasmocytoma cells. We found that this event is due to trans-acting suppressor functions of mouse origin pre-existing in the plasmocytoma cells and acting at transcriptional level. Transcription of the entire family of human class II genes is suppressed, including genes as DO beta for which a distinct regulation of expression in B cells had been previously demonstrated. Suppression appears specific for class II genes because in the hybrids expression of MHC class I genes of mouse is unaffected and of human only partially reduced. Interestingly, also murine invariant chain gene is expressed in both parental plasmocytoma and hybrid cells although at reduced amounts as compared to a murine class II positive B cell line. The class II negative phenotype of hybrid cells and parental plasmocytoma cells is highly stable and unaffected by treatment with protein synthesis inhibitors, suggesting that the transcriptional suppressor function is not mediated by rapid, labile turning-over proteins. Possible mechanisms responsible for transcriptional regulation of MHC class II gene expression during terminal differentiation of B cells to plasma cells are discussed.

B-Lymphocytes↗

PubMed1988

Molecular genotyping of the HLA-DQ alpha gene region.

Restriction fragment analysis has been applied to genomic DNA extracted from human tumor cell lines. Polymorphic restriction fragments encompassing the HLA-DQ alpha gene were observed upon digestion with Bgl II, Eco RI, and Hind III. Analysis of these polymorphic fragments (or allogenotopes) showed that for each restriction enzyme a series of three differently sized allogenotopes existed. Clusters of cosegregating allogenotopes belonging to the different allelic series defined three different allogenotypes. Each allogenotype exhibited a distinctive restriction map generated by digestion with five restriction enzymes. Comparison of these restriction maps showed that generation of the polymorphisms observed at the HLA-DQ alpha region in these sets of cell lines is not caused by a single event. In some B- and T-lymphoma cell lines a fourth allogenotype was found. The restriction site map of genomic DNA from these cell lines suggested that the latter distribution of restriction enzyme sites was most probably generated by recombination between two of the previously observed allogenotypes at a crossover site(s) adjacent to the HLA-DQ alpha gene.

Alleles↗

PubMed1988

Heterogeneity of lymphokine-activated killer (LAK) populations at the clonal level: both NK and CD3+, CD4-, CD8- clones efficiently mediate tumor cell killing.

To investigate at the clonal level the phenotypic and functional properties of interleukin 2 (IL-2) activated killer cells (LAK), recombinant IL-2 activated peripheral blood lymphocytes were cultured under limiting conditions. Among 56 clones that lysed P815 in the presence of phytohemagglutinin (PHA) (22% of total proliferating microcultures) 36 clones lysed also the natural killer (NK)-sensitive K562 and the NK-resistant Hu126 glioma cell lines and one clone lysed only the K562 cell line. Several LAK clones were further assayed for both phenotype and functional activity. Of 22 clones, 10 were CD3-, CD4-, CD8-, and expressed the CD16 marker of NK cells; only one clone had the conventional phenotype of cytolytic T cells (CD3+, CD4-, CD8+), while 11 clones were CD3+, CD4-, CD8- and did not express alpha/beta heterodimer of T-cell antigen receptor as identified by WT31 monoclonal antibody. Only one of the latter clones was CD16+. Endogenous production of IL-2 after stimulation with PHA and phorbol myristate acetate was positive in 3/9 CD3- and in 8/8 CD3+, CD4-, CD8- clones. CD3- mediated strong antibody-dependent cellular cytotoxicity, a function exerted also by some CD3+, CD4-, CD8- T-cell clones to a lower extent. CD3+, CD4-, CD8- T-cell clones lysed different major histocompatibility complex unrelated tumor targets; moreover, this lytic activity seems to be CD3 dependent.

Antibody-Dependent Cell Cytotoxicity↗

PubMed1988

Active suppression of major histocompatibility complex class II gene expression during differentiation from B cells to plasma cells.

Constitutive expression of major histocompatibility complex class II genes is acquired very early in B-cell ontogeny and is maintained up to the B-cell blast stage. Terminal differentiation in plasma cells is, however, accompanied by a loss of class II gene expression. In B cells this gene system is under the control of several loci encoding transacting factors with activator function, one of which, the aIr-1 gene product, operates across species barriers. In this report human class II gene expression is shown to be extinguished in somatic cell hybrids between the human class II-positive B-cell line Raji and the mouse class II-negative plasmacytoma cell line P3-U1. Since all murine chromosomes are retained in these hybrids and no preferential segregation of a specific human chromosome is observed, the results are compatible with the presence of suppressor factors of mouse origin, operating across species barriers and inhibiting class II gene expression. Suppression seems to act at the level of transcription or accumulation of class II-specific mRNA, since no human, and very few murine, class II transcripts are detectable in the hybrids.

Animals↗

PubMed1987

Distinct mechanisms regulate MHC class II gene expression in B cells and macrophages.

In a previous series of studies, we had shown that the constitutive Ia expression in an immunoselected Ia-human B cell variant, RJ 2.2.5, could be restored by somatic cell hybridization with mouse B cells. These experiments allowed us to show the existence of a transacting activator factor(s) operating across species barriers and encoded by the aIr-1 locus located on mouse chromosome 16. The aim of the present study was to investigate whether the B cell constitutive Ia expression and the inducible Ia expression, as seen in macrophages treated with IFN-gamma, are controlled by similar intracellular factors. To this purpose, we constructed an interspecies somatic cell hybrid between the human Ia-RJ 2.2.5 B cells and the mouse Ia-P388 D1 macrophage cells. These murine cells transiently express Ia antigens when incubated with IFN-gamma. Our results show that RJ 2.2.5 X P388 D1 cell hybrids do not express either human or mouse class II gene products. Treatment with human recombinant IFN-gamma did not modify the MHC phenotype of either the hybrid cells or the human parental cells. On the other hand, treatment of the hybrid cells with murine recombinant IFN-gamma resulted in de novo expression of mouse Ia mRNA and corresponding cell surface antigens without, however, reinduction of the human class II-positive phenotype. Furthermore, treatment with the mouse lymphokine significantly increased the levels of human HLA class I mRNA and corresponding cell surface antigens in the hybrid cells, further reinforcing the notion of the existence of non-species-specific secondary mediators generated after receptor-ligand interaction in the IFN-gamma system. Together, these results indicate that in macrophages, the intracellular events taking place after binding of IFN-gamma with its own receptor and leading to the expression of a class II-positive phenotype do not operate via an activation of the aIr-1 locus and/or its products. Thus, at least in our experimental system, we can firmly establish a first, relevant distinction between constitutive and inducible class II gene expression. This difference, dictated by the specific differentiation program of each cell type, may be relevant for the understanding of the function of class II gene products.

Animals↗

PubMed1986

aIr-1, a newly found locus on mouse chromosome 16 encoding a trans-acting activator factor for MHC class II gene expression.

RJ 2.2.5 is a human B cell line that has lost the capacity to express MHC class II genes. The human class II-positive phenotype is restored in somatic cell hybrids between RJ 2.2.5 and mouse spleen cells. By karyotype and molecular studies of an informative family of hybrids we have now shown that the reexpression of human class II gene products, as well as the maintenance of the mouse class II-positive phenotype, correlates with the presence of mouse chromosome 16. Thus, the existence on this mouse chromosome of a newly found locus, designated by us aIr-1, that determines a trans-acting activator function for class II gene expression, is established. Possible implications of this finding are discussed.

Animals↗

PubMed1984

Polymorphism of rat seminal vesicle secretory proteins: characterization of svp-1 and svp-2 and their identification with the major secretory proteins IV and V.

The proteins secreted by the rat seminal vesicle can be separated into five denaturing conditions. Two polymorphic proteins, svp-1 and svp-2, also present in the mouse, are produced by the seminal vesicle as well, but the procedure used for their identification makes it impossible to ascertain whether they correspond to any of the major fractions mentioned above. We show here that, on the basis of molecular weight measurements and of amino acid composition determinations, svp-1 and RSV-V are indeed the same protein. We also show that svp-2 is strictly related to another major secretory protein, RSV-IV, whose amino acid composition is almost identical, but for a few amino acid residues, to that of svp-2. We thus conclude that the latter protein is a variant of RSV-IV that can be expressed only in rats homozygous for a given allele at the svp-2 locus. This paper thus brings together published information on the genetics of the loci coding for svp-1 and for svp-2 and on the molecular biology of RSV-IV and RSV-V and of their corresponding gene.

Amino Acids↗

PubMed1973