title: Thyrotropin stimulates the generation of inositol 1,4,5-trisphosphate in human thyroid cells.
abstract: BACKGROUND
  Dual activation by TSH of the phospholipase C and cAMP cascades has been reported in human thyroid cells. In contrast, Singh et al. reported convincing data in FRTL-5 thyrocytes arguing against such an effect in this model. Their data in FRTL-5 cells indicated no increase in inositol 1,4,5-trisphosphate [Ins(1,4,5)P3] in response to TSH. Therefore, the authors questioned results previously obtained on human cells by cruder methodology.
  
  
  OBJECTIVE
  We investigated the formation of inositol phosphates by HPLC techniques in human thyroid slices to separate the inositol phosphate isomers.
  
  
  RESULTS
  Ins(1,4,5)P3, inositol 1,3,4-trisphosphate, and inositol 1,3,4,5-tetrakisphosphate were increased after TSH stimulation. The effect of TSH in human thyroid cells was reproduced by recombinant TSH and prevented by antibodies blocking the TSH receptor. Thyroid-stimulating antibodies at concentrations eliciting a cAMP response equivalent to TSH failed to stimulate inositol phosphate generation.
  
  
  CONCLUSIONS
  TSH, but not thyroid-stimulating antibodies, activates both cAMP and the phospholipase C cascade in human thyroid as now demonstrated by an increase in Ins(1,4,5)P3 and its inositol phosphate metabolites. Therefore, this effect cannot be extrapolated to the FRTL-5 cell line. The apparent discrepancy may be due to a difference between species (human vs. rat) or to the loss of the fresh tissue properties in a cell line. The dual effect of TSH in human cells, through cAMP on secretion of thyroid hormones and through the diacylglycerol, Ins(1,4,5)P3 Ca2+ pathway on thyroid hormone synthesis, implies the possible separation of these effects in thyroid disease.
authors.affiliation: Institute of Interdisciplinary Research, Campus Erasme Building C, 808 Route de Lennik, 1070 Brussels, Belgium.
authors.forename: Jacqueline
authors.initials: J
authors.lastname: Van Sande
authors.forename: Didier
authors.initials: D
authors.lastname: Dequanter
authors.forename: Philippe
authors.initials: P
authors.lastname: Lothaire
authors.forename: Claude
authors.initials: C
authors.lastname: Massart
authors.forename: Jacques E
authors.initials: JE
authors.lastname: Dumont
authors.forename: Christophe
authors.initials: C
authors.lastname: Erneux
mesh_terms: D000818:Animals; D016466:CHO Cells; D002417:Cattle; D006224:Cricetinae; D006801:Humans; D066298:In Vitro Techniques; D015544:Inositol 1,4,5-Trisphosphate / Q000378:metabolism*; D007295:Inositol Phosphates / Q000378:metabolism; D011989:Receptors, Thyrotropin / Q000235:genetics / Q000378:metabolism; D011994:Recombinant Proteins / Q000494:pharmacology; D013961:Thyroid Gland / Q000187:drug effects / Q000378:metabolism*; D013972:Thyrotropin / Q000494:pharmacology*; D014162:Transfection
chemical_list: D007295:Inositol Phosphates; D011989:Receptors, Thyrotropin; D011994:Recombinant Proteins; D015544:Inositol 1,4,5-Trisphosphate; D013972:Thyrotropin