Isolation and characterization of the HC8 subunit gene of the human proteasome

Genetics of proteasome diseases

The proteasome is a large, multiple subunit complex that is capable of degrading most intracellular proteins. Polymorphisms in proteasome subunits are associated with cardiovascular diseases, diabetes, neurological diseases, and cancer. One polymorphism in the proteasome gene PSMA6 (-8C/G) is associated with three different diseases: type 2 diabetes, myocardial infarction, and coronary artery disease. One type of proteasome, the immunoproteasome, which contains inducible catalytic subunits, is adapted to generate peptides for antigen presentation. It has recently been shown that mutations and polymorphisms in the immunoproteasome catalytic subunit PSMB8 are associated with several inflammatory and autoinflammatory diseases including Nakajo-Nishimura syndrome, CANDLE syndrome, and intestinal M. tuberculosis infection. This comprehensive review describes the disease-related polymorphisms in proteasome genes associated with human diseases and the physiological modulation of proteasome function by these polymorphisms. Given the large number of subunits and the central importance of the proteasome in human physiology as well as the fast pace of detection of proteasome polymorphisms associated with human diseases, it is likely that other polymorphisms in proteasome genes associated with diseases will be detected in the near future. While disease-associated polymorphisms are now readily discovered, the challenge will be to use this genetic information for clinical benefit.

Analysis of gene expression during maturation of immature dendritic cells derived from peripheral blood monocytes

Dendritic cells (DCs) are the most important antigen-presenting cells. Many recent studies have compared the function of immature DCs (iDCs) and mature DCs (mDCs), but there have been few reports of the molecular changes that occur in DCs during maturation. Here, we report on differential gene expression in iDCs generated from peripheral blood monocytes compared with mDCs. Gene expression was evaluated using the differential display method after activation of iDCs with a low concentration of lipopolysaccharide (LPS) to induce maturation. Proteasome subunit alpha type 3 (PSMA3), transcription factor EC (TFEC) isoform and BTK region clone 2f10-rpi were transiently upregulated. Tryptophanyl-tRNA synthetase and CD63 antigen were upregulated for at least 24 h. Neuronal apoptosis inhibitory protein (NAIP) and transforming growth factor-beta-induced 68 kDa protein were downregulated. This is the first report of NAIP expression in human DCs. By comparing the expression of NAIP with that of other members of the inhibitor of apoptosis protein (IAP) family and the Bcl-2 family, only NAIP was found to be strongly expressed in iDCs before stimulation by LPS. PSMA3 was also induced in the DCs stimulated with immune complex. These findings might contribute to our understanding of DC maturation and the effectiveness of DC-based vaccines.

Exon/intron organisation of human proteasome PROS-27 K gene

The exon/intron structure of the human proteasome PROS-27 gene was established by means of partial sequencing of its genomic clones and comparison with the chromosome 14 sequences from the data bases. The gene contains seven exons spanning over 19kb. Introns of the gene contain numerous Alu type repeats, Mer 2 and LINE type repeats. Pattern of the repeats indicates conservatism of the sequence.

A degradation signal located in the C-terminus of p21WAF1/CIP1 is a binding site for the C8 alpha-subunit of the 20S proteasome

The cyclin-dependent kinase inhibitor p21WAF1/CIP1 is a key regulator of cell-cycle progression and its expression is tightly regulated at the level of transcription and by proteasome-dependent proteolysis. The turnover of p21WAF1/CIP1 by proteasomes does not always require the ubiquitylation of p21WAF1/CIP1 suggesting that there could be an alternative pathway into the proteasome. Here we show that the C8 alpha-subunit of the 20S proteasome interacts with the C-terminus of p21WAF1/CIP1 and mediates the degradation of p21WAF1/CIP1. A small deletion in this region that disrupts binding to C8 increased the half-life of p21WAF1/CIP1 expressed in vivo. In contrast a deletion that increased the affinity between C8 and p21WAF1/CIP1 significantly reduced the stability of the latter. These data suggest that interaction with a 20S proteasome alpha-subunit is a critical determinant of p21WAF1/CIP1 turn-over and show how non-ubiquitylated molecules might bypass the 19S regulator of the proteasome and become targeted directly to the 20S, core protease. Consistent with this, p21WAF1/CIP1 was degraded rapidly by purified 20S proteasomes in a manner that was dependent on the C8-interaction domain.

The mouse Psma1 gene coding for the alpha-type C2 proteasome subunit: structural and functional analysis, mapping, and colocalization with Pde3b on mouse chromosome 7

We have isolated and functionally characterized the mouse gene for the C2 subunit of the 20S proteasome. The gene contains 10 exons distributed over a region of 12 kb on the distal end of mouse chromosome 7. Its exon-intron structure differs from those of the other few known proteasome genes. Transfection assays revealed that 1.5 kb of 5' flanking sequence is active as promoter in cultured myoblasts. Deletion reporter constructs narrowed this presumptive promoter region to within 450 bp upstream of the translation initiation site. Several consensus motifs for transcription factor binding sites were identified in this upstream region of the gene. Psma1 was mapped to mouse chromosome 7 using the interspecific backcross DNA panels from The Jackson Laboratory. Additional mapping studies showed that the mouse genes Psma1 and Pde3b are closely linked, residing between cM 53 and 53.3 in a region syntenic to human chromosome 11p15. Our results extend the structural and functional analysis of genes encoding the 20S proteasome subunits and provide the basis for the study of their regulation.

CDNA cloning of p112, the largest regulatory subunit of the human 26s proteasome, and functional analysis of its yeast homologue, sen3p

The 26S proteasome is a large multisubunit protease complex, the largest regulatory subunit of which is a component named p112. Molecular cloning of cDNA encoding human p112 revealed a polypeptide predicted to have 953 amino acid residues and a molecular mass of 105,865. The human p112 gene was mapped to the q37.1-q37.2 region of chromosome 2. Computer analysis showed that p112 has strong similarity to the Saccharomyces cerevisiae Sen3p, which has been listed in a gene bank as a factor affecting tRNA splicing endonuclease. The SEN3 also was identified in a synthetic lethal screen with the nin1-1 mutant, a temperature-sensitive mutant of NIN1. NIN1 encodes p31, another regulatory subunit of the 26S proteasome, which is necessary for activation of Cdc28p kinase. Disruption of the SEN3 did not affect cell viability, but led to temperature-sensitive growth. The human p112 cDNA suppressed the growth defect at high temperature in a SEN3 disruptant, indicating that p112 is a functional homologue of the yeast Sen3p. Maintenance of SEN3 disruptant cells at the restrictive temperature resulted in a variety of cellular dysfunctions, including defects in proteolysis mediated by the ubiquitin pathway, in the N-end rule system, in the stress response upon cadmium exposure, and in nuclear protein transportation. The functional abnormality induced by SEN3 disruption differs considerably from various phenotypes shown by the nin1-1 mutation, suggesting that these two regulatory subunits of the 26S proteasome play distinct roles in the various processes mediated by the 26S proteasome.

Protein degradation and increased mRNAs encoding proteins of the ubiquitin-proteasome proteolytic pathway in BC3H1 myocytes require an interaction between glucocorticoids and acidification

In rats and humans, metabolic acidosis stimulates protein degradation and glucocorticoids have been implicated in this response. To evaluate the importance of glucocorticoids in stimulating proteolysis, we measured protein degradation in BC3H1 myocytes cultured in 12% serum. Acidification accelerated protein degradation but dexamethasone did not augment this response. To reduce the influence of glucocorticoids and other hormones and cytokines in 12% serum that could mediate proteolysis, we studied BC3H1 myocytes maintained in only 1% serum. Acidification of the medium or addition of dexamethasone at pH 7.4 did not significantly increase protein degradation, while acidification plus dexamethasone accelerated proteolysis. The steroid receptor antagonist RU 486 prevented this proteolytic response. Acidification of the medium with 1% serum did increase the mRNAs for ubiquitin and the C2 proteasome subunit, but when dexamethasone was added the mRNAs were increased significantly more. The steroid-receptor antagonist RU 486 suppressed this response to the addition of dexamethasone but the mRNAs remained at the levels measured in cells at pH 7.1 alone. Thus, acidification alone can increase the mRNAs of the ubiquitin-proteasome proteolytic pathway, but both acidosis and glucocorticoids are required to stimulate protein degradation. Since these changes occur without adding cytokines or other hormones, we conclude that the proteolytic response to acidification requires glucocorticoids.