Repeatedly passed FRTL-5 rat thyroid cells can develop insulin and insulin-like growth factor-I-sensitive cyclooxygenase and prostaglandin E2 isomerase-like activities together with altered basal and thyrotropin-responsive thymidine incorporation into DNA.
Repeatedly passed or aged rat FRTL-5 thyroid cells develop a high level of basal [3H]thymidine incorporation into DNA and a reduced response to TSH in medium containing 5% serum and insulin (5H medium). The basal [3H]thymidine incorporation into DNA of aged cells can exceed the TSH-induced increase in earlier passages of the same cell line (fresh cells) and the TSH response decreases from more than 10-fold above basal in fresh cells to less than 2-fold in aged cells. This change is not associated with a loss of the diploid karyotype, a change in basal cAMP levels, or a change in dependence on TSH for cell growth. Attenuation of the TSH response in the [3H]thymidine incorporation assay is more evident than the reduced effect of TSH on cAMP levels or iodide transport; moreover, the TSH effect on cAMP levels does not correlate with that on [3H] thymidine incorporation as a function of hormone concentration. The high basal activity in [3H]thymidine incorporation into DNA in aged cells is due to an increased responsiveness to insulin, insulin-like growth factor-I (IGF-I), or serum. Thus, removal of serum and insulin from the medium eliminates the high basal [3H]thymidine incorporation into DNA, and this activity is restored by insulin or IGF-I in a concentration-dependent manner. The increased responsiveness of aged cells to insulin or IGF-I is inhibited by indomethacin or hydrocortisone and is associated with insulin or IGF-I, but not TSH, stimulation of cyclooxygenase and prostaglandin E2 (PGE2) isomerase-like activity. Fresh cells, in contrast, require TSH plus insulin or IGF-I to increase these activities. Increased responsiveness of cyclooxygenase activity to insulin or IGF-I in aged cells reflects at least in part an increase in cyclooxygenase mRNA levels. We suggest that insulin/IGF-I stimulation of PGE2 production leads to the high basal thymidine incorporation into DNA in aged cells maintained in TSH-depleted (5H) medium; the reduced stimulation by TSH of cAMP content or iodide uptake may reflect PG inhibition (negative feedback regulation) of cAMP production.
Bellur
S
S
Section on Cell Regulation, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, Maryland 20892.
Tahara
K
K
Saji
M
M
Grollman
E F
EF
Kohn
L D
LD
D000818:Animals; D001483:Base Sequence; D001769:Blood; D002455:Cell Division; D002460:Cell Line; D002470:Cell Survival; D000242:Cyclic AMP / Q000378:metabolism; D004247:DNA / Q000096:biosynthesis*; D006854:Hydrocortisone / Q000494:pharmacology; D007213:Indomethacin / Q000494:pharmacology; D007328:Insulin / Q000494:pharmacology; D007334:Insulin-Like Growth Factor I / Q000494:pharmacology; D019746:Intramolecular Oxidoreductases; D007454:Iodides / Q000378:metabolism; D007535:Isomerases / Q000378:metabolism*; D008969:Molecular Sequence Data; D000071876:Prostaglandin-E Synthases; D011451:Prostaglandin-Endoperoxide Synthases / Q000235:genetics / Q000378:metabolism*; D051381:Rats; D013961:Thyroid Gland / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D013972:Thyrotropin / Q000494:pharmacology*
D007328:Insulin; D007454:Iodides; D007334:Insulin-Like Growth Factor I; D013972:Thyrotropin; D004247:DNA; D000242:Cyclic AMP; D011451:Prostaglandin-Endoperoxide Synthases; D007535:Isomerases; D019746:Intramolecular Oxidoreductases; D000071876:Prostaglandin-E Synthases; D006854:Hydrocortisone; D007213:Indomethacin