TY - JOUR
T1 - Thyroid-stimulating hormone rapidly stimulates inositol polyphosphate formation in FRTL-5 thyrocytes without activating phosphoinositidase C
AU - Singh, Jatinder
AU - Hunt, Philip
AU - Eggo, Margaret C.
AU - Sheppard, Michael C.
AU - Kirk, Christopher J.
AU - Michell, Robert H.
PY - 1996/5/15
Y1 - 1996/5/15
N2 - The thyroid-stimulating hormone (TSH) receptor is widely regarded as one of a limited number of G-protein-coupled receptors that activate both adenylate cyclase and phosphoinositidase C (PIC) via G-proteins, but the existing experimental evidence for TSH-stimulated PtdIns(4,5)P2 hydrolysis remains inconclusive. We have compared the effects of TSH and of ATP (acting via P2-purinergic receptors) on the inositol lipids and polyphosphates of [2-3H]inositol-labelled FRTL-5 rat thyroid cells. ATP initiated a rapid decrease in 3H-labelled PtdIns4P and PtdIns(4,5)P2, whereas TSH did not. Stimulation with ATP and, less consistently, with noradrenaline (acting via α-adrenergic receptors) provoked rapid formation of Ins(1,4,5)P3, Ins(1,3,4,5)P4, Ins(1,3,4)P3 and Ins(1,4)P2, confirming activation of PtdIns(4,5)P2 hydrolysis. No concentration of TSH provoked detectable accumulation of Ins(1,4,5)P3 or Ins(1,4)P2 during the first few minutes of stimulation. However, an InsP3 [with the chromatographic properties of Ins(1,3,4)P3] and two InsP4 isomers [neither of which was Ins(1,3,4,5)P4] accumulated quickly in TSH-stimulated cells. ATP immediately provoked a large increase in intracellular calcium concentration ([Ca2+](i)) in Indo 1-AM-loaded cells. TSH provoked a small and delayed [Ca2+](i) elevation in only some experiments. We therefore confirm that activation of P2-purinergic receptors and α1-adrenergic receptors provokes PIC activation, an accumulation of Ins(1,4,5)P3 and its metabolites and rapid [Ca2+](i) mobilization in FRTL-5 cells. By contrast, TSH provokes no rapid PIC-catalysed PtdIns(4,5)P2 hydrolysis or immediate [Ca2+](i) mobilization. These results fail to support the widespread view that the TSH receptor of FRTL-5 cells signals, in part, through PIC activation. Our results suggest that TSH activates another, still undefined, mechanism that causes accumulation of an InsP3 and two isomers of InsP4.
AB - The thyroid-stimulating hormone (TSH) receptor is widely regarded as one of a limited number of G-protein-coupled receptors that activate both adenylate cyclase and phosphoinositidase C (PIC) via G-proteins, but the existing experimental evidence for TSH-stimulated PtdIns(4,5)P2 hydrolysis remains inconclusive. We have compared the effects of TSH and of ATP (acting via P2-purinergic receptors) on the inositol lipids and polyphosphates of [2-3H]inositol-labelled FRTL-5 rat thyroid cells. ATP initiated a rapid decrease in 3H-labelled PtdIns4P and PtdIns(4,5)P2, whereas TSH did not. Stimulation with ATP and, less consistently, with noradrenaline (acting via α-adrenergic receptors) provoked rapid formation of Ins(1,4,5)P3, Ins(1,3,4,5)P4, Ins(1,3,4)P3 and Ins(1,4)P2, confirming activation of PtdIns(4,5)P2 hydrolysis. No concentration of TSH provoked detectable accumulation of Ins(1,4,5)P3 or Ins(1,4)P2 during the first few minutes of stimulation. However, an InsP3 [with the chromatographic properties of Ins(1,3,4)P3] and two InsP4 isomers [neither of which was Ins(1,3,4,5)P4] accumulated quickly in TSH-stimulated cells. ATP immediately provoked a large increase in intracellular calcium concentration ([Ca2+](i)) in Indo 1-AM-loaded cells. TSH provoked a small and delayed [Ca2+](i) elevation in only some experiments. We therefore confirm that activation of P2-purinergic receptors and α1-adrenergic receptors provokes PIC activation, an accumulation of Ins(1,4,5)P3 and its metabolites and rapid [Ca2+](i) mobilization in FRTL-5 cells. By contrast, TSH provokes no rapid PIC-catalysed PtdIns(4,5)P2 hydrolysis or immediate [Ca2+](i) mobilization. These results fail to support the widespread view that the TSH receptor of FRTL-5 cells signals, in part, through PIC activation. Our results suggest that TSH activates another, still undefined, mechanism that causes accumulation of an InsP3 and two isomers of InsP4.
UR - http://www.scopus.com/inward/record.url?scp=0029891632&partnerID=8YFLogxK
U2 - 10.1042/bj3160175
DO - 10.1042/bj3160175
M3 - Article
C2 - 8645202
AN - SCOPUS:0029891632
SN - 0264-6021
VL - 316
SP - 175
EP - 182
JO - Biochemical Journal
JF - Biochemical Journal
IS - 1
ER -