CALR Antibody

Background:

Calreticulin is a multifunctional protein that acts as amajor Ca(2+)-binding (storage) protein in the lumen of theendoplasmic reticulum. It is also found in the nucleus, suggestingthat it may have a role in transcription regulation. Calreticulinbinds to the synthetic peptide KLGFFKR, which is almost identicalto an amino acid sequence in the DNA-binding domain of thesuperfamily of nuclear receptors. Calreticulin binds to antibodiesin certain sera of systemic lupus and Sjogren patients whichcontain anti-Ro/SSA antibodies, it is highly conserved amongspecies, and it is located in the endoplasmic and sarcoplasmicreticulum where it may bind calcium. The amino terminus ofcalreticulin interacts with the DNA-binding domain of theglucocorticoid receptor and prevents the receptor from binding toits specific glucocorticoid response element. Calreticulin caninhibit the binding of androgen receptor to its hormone-responsiveDNA element and can inhibit androgen receptor and retinoic acidreceptor transcriptional activities in vivo, as well as retinoicacid-induced neuronal differentiation. Thus, calreticulin can actas an important modulator of the regulation of gene transcriptionby nuclear hormone receptors. Systemic lupus erythematosus isassociated with increased autoantibody titers against calreticulinbut calreticulin is not a Ro/SS-A antigen. Earlier papers referredto calreticulin as an Ro/SS-A antigen but this was later disproven.Increased autoantibody titer against human calreticulin is found ininfants with complete congenital heart block of both the IgG andIgM classes.