Regulation of FRTL-5 thyroid cell growth by phosphatidylinositol (OH) 3 kinase-dependent Akt-mediated signaling

Thyroid. 2001 Apr;11(4):339-51. doi: 10.1089/10507250152039073.


Thyrotropin (TSH)-initiated cell cycle progression from G1 to S phase in FRTL-5 thyroid cells requires serum, insulin, or insulin-like growth factor 1 (IGF-1) and involves activation of 3-hydroxy-3-methylglutaryl-CoA reductase, geranylgeranylation of RhoA, p27Kip1 degradation, and activation of cyclin-dependent kinase (cdk) 2. In the present report, we show that the serine-threonine kinase Akt is an important mediator of insulin/IGF-1/serum effects on cell cycle progression in FRTL-5 thyroid cells. The phosphoinositol (OH) 3 kinase inhibitors, Wortmannin (WM) and Ly294002 (LY), block the ability of insulin/IGF-1 to reduce p27 expression, to induce expression of cyclins E, D1, and A as well as cdk 2 and 4, and to phosphorylate retinoblastoma protein. They also inhibit insulin/IGF-1-increased DNA synthesis and cell cycle entrance (S+G2/M). Insulin/IGF-1 rapidly induced activation of Aktl in a PI3 kinase-dependent manner, and increased Aktl RNA levels. Most importantly, FRTL-5 cells transfected with a constitutively active form of Aktl have higher basal rates of DNA synthesis and no longer require exogenous insulin/IGF-1 or serum for TSH-induced growth. In sum, Aktl appears to have an important role in insulin/IGF-1 regulation of FRTL-5 thyroid cell growth and cell cycle progression.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Cell Cycle
  • Cell Division
  • Cell Line
  • DNA / biosynthesis
  • Hydroxymethylglutaryl CoA Reductases / genetics
  • Insulin / pharmacology
  • Insulin-Like Growth Factor I / pharmacology
  • Phosphatidylinositol 3-Kinases / physiology*
  • Phosphorylation
  • Protein Serine-Threonine Kinases*
  • Proto-Oncogene Proteins / physiology*
  • Proto-Oncogene Proteins c-akt
  • Rats
  • Thyroid Gland / cytology*
  • Thyrotropin / pharmacology


  • Insulin
  • Proto-Oncogene Proteins
  • Insulin-Like Growth Factor I
  • Thyrotropin
  • DNA
  • Hydroxymethylglutaryl CoA Reductases
  • Akt1 protein, rat
  • Protein Serine-Threonine Kinases
  • Proto-Oncogene Proteins c-akt