nuclear autoantigen Sp-100; nuclear dot-associated Sp100 protein; speckled 100 kDa; Lysp100b (SP100)

Function

• may play a role in the control of gene expression
• phosphorylated
• sumoylated; sumoylation depends on a functional nuclear localization signal but is not necessary for nuclear import or nuclear body targeting
• homodimer
• splice variants heterodimerize
• interacts with members of the HP1 family of nonhistone chromosomal proteins, such as CBX5 & CBX3 via the PxVxL motif
• interacts with Epstein-Barr virus EBNA-LP

Structure

• the HSR domain is important for the nuclear body targeting as well as for the dimerization
• contains one Pro-Xaa-Val-Xaa-Leu (PxVxL) motif, which is required for interaction with chromoshadow domains; this motif requires additional residues -7, -6, +4 & +5 of the central Val which contact the chromoshadow domain
• contains 2 HMG box DNA-binding domains
• contains 1 HSR domain
• contains 1 SAND domain

Compartment

• nucleus
• found in the nuclear body
• subnuclear localization may be modulated by
  • interferon
  • cell cycle

Alternative splicing

named isoforms=5

Expression

• widely expressed
• Sp100-B is expressed only in spleen, tonsil, thymus, mature B-cell line & some T-cell line, but not in brain, liver, muscle or non-lymphoid cell lines
• induced by interferon

Pathology

• this antigen is recognized by autoantibodies from patients with primary biliary cirrhosis (PBC)

Laboratory

• SP100 antibody in serum
  • SP100 IgG in serum

Notes

• the major isoform Sp100-A, has a calculated MW of 54 kD, but exhibits aberrant electrophoretic mobilities, with an apparent MW of 100 kD

More general terms

• nuclear protein
• antigen
• phosphoprotein

Component of

• PML NB complex

Database

• UniProt: http://www.uniprot.org/uniprot/P23497.html
• Entrez gene: http://www.ncbi.nlm.nih.gov/sites/entrez?db=gene&cmd=Retrieve&dopt=Graphics&list_uids=6672
• Kegg: http://www.genome.jp/dbget-bin/www_bget?hsa:6672
• OMIM: https://mirror.omim.org/entry/604585