Endocrine Abstracts

Does Iodide Modulate The Biological Outcome of Activating Thyrotropin Receptor Mutations?
Dr. F. Al-Khafaji and Dr. M. Ludgate
Hyperthyroidism is caused by pathogenic activation of the thyrotropin receptor (TSHR) either by the thyroid stimulating antibodies of Graves' disease (GD) or activating TSHR mutations. These produce nodular goitre or familial hyperthyroidism. The pathogenic mechanism predominating varies according to the iodide intake, with nodular goitre accounting for most hyperthyroidism in iodine deficient regions and vice versa.
The aim of the present study was to investigate whether iodide modulates the biological outcome of activating TSHR mutations.
Pools of FRTL-5 cells stably expressing 3 different activating TSHR mutations, Del 613-621,M453V and L629F, were cultured in the presence and absence of TSH and in varying concentrations of NaI and compared with control FRTL-5 cells (Neo). We have investigated cell proliferation by direct cell counting, applied flow cytometry for cell cycle analysis and used western blots to examine signal transduction.
In the presence of TSH, the population doubling (PD) time for Neo and activating TSHR mutant expressing FRTL-5 cells is similar (18+/- 1.5 hours). The addition of 10-50 mM NaI reduced proliferation and increased the PD of all 4 FRTL-5 cell types to 28+/- 2 hours. In the absence of TSH, PD Neo is ~ 66 hours, PD Del613-621 is ~ 61 hours, Pd L629F is ~ 47 hours and PD M453V is ~ 35 hours. The different growth rates were confirmed by cell cycle analysis in which only a few cells were in the G2/S phase in Neo and Del (8%/8% G2, 4%/8% S respectively), yet M453V had 26% in S and 6% in G2 phase. Preliminary western blot experiments indicate that phospho-CREB was upregulated and phospho-MAPK down regulated by 50mM NaI.
The growth promoting effects of activating TSHR mutations were inhibited by moderate doses of iodide. This can be due either to reduced proliferation, increased apoptosis or a combination of both.