Antibody-induced modulation of TSH receptor post-translational processing

Abstract

The post-translational processing of the TSH receptor (TSHR) includes intra-molecular cleavage with the loss of a 50 amino acid ectodomain region and the formation of two subunits (a and b), followed by likely a subunit shedding. TSHR antibodies (TSHR-Abs), which are directed at the ectodomain, may influence thyroid function by stimulating or inhibiting TSHR signaling or may bind without any such influence (the neutral group of antibodies). When we examined the characteristics of a series of monoclonal TSHR-Abs, we found that many were able to inhibit receptor cleavage and enhance TSHR expression. This was especially apparent with the neutral type of TSHR-Abs directed to the cleaved region of the ectodomain (aa 316-366). Indeed, such inhibition appeared to be epitope dependent with TSHR-Abs directed to regions after residues 335-354 showing no such activity. We propose that this aberrant process, whereby TSHR-Abs influence antigen processing, is a novel mechanism for the maintenance and exacerbation of autoimmune thyroid disease.

Delineating the autoimmune mechanisms in Graves’ disease

“…After many years of studying serum IgG from patients with GD, the most precise delineation of the characteristics of TSHR-Abs has resulted from the analysis of monoclonal antibodies to the TSHR derived from patients with GD or from rodents immunized with the TSHR [29–31]. Three varieties of TSHR-Ab are present in most patients with GD; stimulating, blocking and neutral antibodies (Fig.…”

TSH Receptor Cleavage Into Subunits and Shedding of the A-Subunit; A Molecular and Clinical Perspective

“…As mentioned above (Section VIII.C.4), neutral hamster mAbs were observed to inhibit TSHR cleavage into subunits, as detected by the flow cytometric, dual mAb approach (80). Remarkably, rather than being neutral, these TSHR mAbs were reported to possess unusual and unexpected functions, namely the ability to signal via multiple pathways not utilized by TSH and not involving Gs␣ (33).…”

“…Some monoclonal TSHR antibodies derived from hamsters vaccinated with adenovirus expressing the human TSH holoreceptor neither activate the receptor via the dominant Gs␣/cAMP pathway nor compete for TSH binding (79,80). These "neutral" antibodies were observed to inhibit TSHR cleavage into subunits (33) using the flow cytometric, dual mAb approach (80).…”

“…These "neutral" antibodies were observed to inhibit TSHR cleavage into subunits (33) using the flow cytometric, dual mAb approach (80). Unlike previously recognized pathogenic TSHR autoantibodies (both human and mouse), most of these hamster neutral antibodies recognize linear epitopes (synthetic peptides) within the C-peptide region deleted by intramolecular cleavage of the single-chain TSHR on the cell surface (79, 80), a logical location for an inhibitor of TSHR intramolecular cleavage into subunits.…”

Growth stimulating antibody, as another predisposing factor of Graves’ disease (GD): analysis using monoclonal TSH receptor antibodies derived from patients with GD

“…Previously, Sande et al reported differences in the kinetics of intracellular cAMP [29] and inositol-1,4,5-triphosphate production [30] when TSHR was stimulated with TSH or TRAb. Although the mechanisms of these effects have not been elucidated, we consider that differences of TSHR reactions such as multimerization [31] or post-translational processing [32] against TSH or TRAb stimulation might participate in those phenomenon. In the future, it is necessary to clarify the detailed mechanisms responsible for such TSHR conformational changes and their relationships with thyrocyte function.…”