Differences in specificities of anti-centromere sera for the monomeric and dimeric C-terminal peptides of human centoromere protein C

Anticentromere antibody-positive primary Sjögren's syndrome: Epitope analysis of a subset of anticentromere antibody-positive patients

OBJECTIVES

Anticentromere antibody (ACA) is generally considered to be a serological marker for systemic sclerosis (SSc). ACA-positive patients with primary Sjögren's syndrome (pSS) have also been reported. ACA often recognizes centromere proteins (CENPs): CENP-A, CENP-B, and CENP-C, and sometimes reacts to heterochromatin protein 1 (HP1)α. We compared the reactivity against six different epitopes for three ACA-positive clinical subgroups: 29 patients with pSS, 36 SSc patients with sicca symptoms, and 28 SSc patients without sicca symptoms.

METHODS

We utilized enzyme-linked immunosorbent assays (ELISAs) with recombinant proteins covering six different epitope regions of ACA (the amino terminus (Nt) of CENP-A, CENP-B, and CENP-C, the carboxyl terminus (Ct) of CENP-B and CENP-C, and HP1α).

RESULTS

The patients with pSS were found to have IgG-class autoantibodies against CENP-C-Nt and HP1α, and IgA-class autoantibodies against CENP-C-Ct with significantly higher frequencies than the SSc patients with or without sicca symptoms. The positive predictive value and the negative predictive value of the combination of these three autoantibodies for pSS were 73% and 82%, respectively, for pSS.

CONCLUSIONS

Based on the result that reactivities against CENP-C and HP1α in patients with pSS differ from those in patients with SSc, we propose ACA-positive pSS as a clinical subset of SS that is independent of SSc.

Diversity of humoral responses to the centromere proteins among HCV-related chronic liver disease, PBC and AIH patients

BACKGROUND

Anticentromere antibodies (ACAs) have been observed in patients with autoimmune hepatitis (AIH) and hepatitis C virus (HCV)-related chronic liver disease (CLD-C) as well as those with primary biliary cirrhosis (PBC). However, little is known about the differences in immune responses to the centromere proteins among these liver diseases.

OBJECTIVE

By synthesizing recombinant proteins consisting of the N- and C-termini of major centromere proteins, we investigated the humoral responses against them in each disease.

RESULTS

Eight of the 754 (1%) patients with CLD-C, 14 of the 57 (25%) patients with PBC and six of the 38 (16%) patients with AIH were seropositive for ACAs. There were no significant differences in ACA titers determined by an indirect immunofluorescent method among the groups of patients with CLD-C, PBC and AIH. However, the analysis of immunoreactivities against each recombinant protein revealed that the titers of IgG-subclass autoantibodies against the C-terminus of centromere protein (CENP)-B were significantly higher in the CLD-C patients than in the AIH patients. Likewise, the titers of IgM-subclass autoantibodies against the N-terminus of CENP-A were significantly higher in the PBC group than in the CLD-C group. The ACA-positive patients who developed liver cirrhosis had significantly higher titers of the IgA-subclass autoantibodies against the C-terminus of CENP-C than those who did not.

CONCLUSION

These findings suggest that immunoreactivities against the fragments of centromere proteins show distinct patterns among CLD-C, PBC and AIH and that the determination of immunoreactivities against the centromere proteins may be useful for the prediction of disease progression.

Evolution of functional diversity in the cupin superfamily

The cupin superfamily of proteins is among the most functionally diverse of any described to date. It was named on the basis of the conserved beta-barrel fold ('cupa' is the Latin term for a small barrel), and comprises both enzymatic and non-enzymatic members, which have either one or two cupin domains. Within the conserved tertiary structure, the variety of biochemical function is provided by minor variation of the residues in the active site and the identity of the bound metal ion. This review discusses the advantages of this particular scaffold and provides an evolutionary analysis of 18 different subclasses within the cupin superfamily.