Prognostic significance of thyroglobulin antibody epitopes in differentiated thyroid cancer.

CONTEXT: Thyroglobulin antibodies (TgAbs) are surrogate markers of disease recurrence or persistence in differentiated thyroid cancer (DTC). However, the prognostic significance of TgAb heterogeneity in DTC has not been investigated. OBJECTIVE: To evaluate the relationship between TgAb epitope specificities and clinical outcomes in DTC patients. DESIGN: We studied 61 TgAb-positive patients with DTC, post-thyroidectomy and remnant ablation (7 males, 54 females; age-range 16-80 years, median follow-up duration 8.9 years). TgAb epitope reactivities were mapped using a panel of 10 thyroglobulin (Tg) monoclonal antibodies delineating six antigenic Tg clusters in competitive ELISA studies. Sera from 45 patients with Hashimoto's thyroiditis (HT) and 22 TgAb-positive healthy subjects served as autoimmune and healthy controls. Tg was measured by immunoradiometric assay (IRMA), electrochemiluminescence immunoassay (ECLIA), and RIA, while TgAbs was measured by ELISA and ECLIA methods. RESULTS: Samples from 26 DTC patients showed TgAb epitope restriction similar to HT patients, while 35 patients exhibited nonspecific reactivity comparable to healthy controls. DTC patients with epitope restriction had higher rates of recurrent/persistent disease (81% vs 17%, P < .001), higher median TgAb concentration (887.0 vs 82.0 kIU/L; P < .001), and a higher prevalence of thyroid lymphocytic infiltration (71.4% vs 26.8%; P < .001) compared to patients with nonspecific reactivity. Samples with epitope restriction also had a lower median Tg-IRMA/RIA ratio (3.0% vs 36.0%; P < .001) denoting greater degrees of Tg assay interference. CONCLUSIONS: TgAb epitope restriction is associated with a less favorable prognosis than nonspecific reactivity in DTC patients. TgAb epitope specificities may have prognostic value in DTC.

Functional domains of yeast plasmid-encoded Rep proteins.

Both of the Saccharomyces cerevisiae 2 microm circle-encoded Rep1 and Rep2 proteins are required for efficient distribution of the plasmid to daughter cells during cellular division. In this study two-hybrid and in vitro protein interaction assays demonstrate that the first 129 amino acids of Rep1 are sufficient for self-association and for interaction with Rep2. Deletion of the first 76 amino acids of Rep1 abolished the Rep1-Rep2 interaction but still allowed some self-association, suggesting that different but overlapping domains specify these interactions. Amino- or carboxy-terminally truncated Rep1 fusion proteins were unable to complement defective segregation of a 2 microm-based stability vector with rep1 deleted, supporting the idea of the requirement of Rep protein interaction for plasmid segregation but indicating a separate required function for the carboxy-terminal portion of Rep1. The results of in vitro baiting assays suggest that Rep2 contains two nonoverlapping domains, both of which are capable of mediating Rep2 self-association. The amino-terminal domain interacts with Rep1, while the carboxy-terminal domain was shown by Southwestern analysis to have DNA-binding activity. The overlapping Rep1 and Rep2 interaction domains in Rep1, and the ability of Rep2 to interact with Rep1, Rep2, and DNA, suggest a model in which the Rep proteins polymerize along the 2 microm circle plasmid stability locus, forming a structure that mediates plasmid segregation. In this model, competition between Rep1 and Rep2 for association with Rep1 determines the formation or disassembly of the segregation complex.