Sp100 nuclear antigen is an interferon stimulated

antigen In immunology, an antigen (Ag) is a molecule or molecular structure or any foreign particulate matter or a pollen grain that can bind to a specific antibody or T-cell receptor. The presence of antigens in the body may trigger an immune respons ...

found in the cell nuclei of many human and higher animal cells. Autoantibodies directed against Sp100 are often found in patients with primary biliary cirrhosis. Histologically Sp100 'dots' regions of the cell nucleus. Viral infection and

mitogens A mitogen is a small bioactive protein or peptide that induces a cell to begin cell division, or enhances the rate of division (mitosis). Mitogenesis is the induction (triggering) of mitosis, typically via a mitogen. The mechanism of action of a ...

affect the expression of the Sp100 autoantigen. Cells grown in the presence of interferons (α, β, and γ) revealed an increase both in size and number of the Sp100 protein-containing nuclear dots and increase the protein concentration. This raises "the question whether

cytokine Cytokines are a broad and loose category of small proteins (~5–25 kDa) important in cell signaling. Cytokines are peptides and cannot cross the lipid bilayer of cells to enter the cytoplasm. Cytokines have been shown to be involved in autocrin ...

-mediated increase of Sp100 protein expression plays a role in induction of anti-Sp100 autoantibodies."

Sp100 and nuclear dots

Two proteins, Sp100 and promyelocytic leukemia ( PML) factor are localized to punctate domains in the nucleus ( nuclear dots or nuclear bodies). These domains (few to 20) were found to form a donut shaped structure when cells were starved of amino acids. In particular, depravation of cystine results in most pronounced changes. Two other proteins, PIC1/

SUMO-1 Small ubiquitin-related modifier 1 is a protein that in humans is encoded by the ''SUMO1'' gene. Function This gene encodes a protein that is a member of the SUMO (small ubiquitin-like modifier) protein family. It is a ubiquitin-like protein a ...

, that also interact with

nuclear pore A nuclear pore is a part of a large complex of proteins, known as a nuclear pore complex that spans the nuclear envelope, which is the double membrane surrounding the eukaryotic cell nucleus. There are approximately 1,000 nuclear pore complexe ...

complex factors also interact with these two proteins. In addition Sp100 interacts with a chromatin binding protein, HP1 alpha.

Sp100 splicoforms

Some Sp100 variants contain a domain similar to two interferon-inducible nuclear phosphoproteins, suppressin and DEAF1. This defines a novel protein motif, the HNPP-box. Another class of variants has

high mobility group High-Mobility Group or HMG is a group of chromosomal proteins that are involved in the regulation of DNA-dependent processes such as transcription, replication, recombination, and DNA repair. Families The HMG proteins are subdivided into 3 supe ...

1 (HMG1) protein sequence as a domain. Both major classes of Sp100 splice variant proteins localize in part to nuclear dots/PML bodies and other nuclear domains.

References

{{Autoantigens Autoantigens