Effects of thyroid hormone on sex hormone-binding globulin gene expression in human cells.
We have used a human hepatoblastoma cell line to establish a model system for thyroid hormone (T3) action in human cells. HepG2 cells were grown for 3 days in Dulbecco's Modified Eagle's Medium containing fetal calf serum and were maintained in serum-free medium for experimental manipulations. [125I]T3 incubated with cells was bound by newly secreted protein and degraded. After 24-h exposure to HepG2 cells in Dulbecco's Modified Eagle's Medium, only 35-40% of the radioactivity was recovered as authentic T3. Degradation of hormone was neither time nor concentration dependent, and occurred to a greater degree in the absence of cells, suggesting an interaction between the hormone and the plastic culture dish. After 4 days, in the absence of fetal calf serum and considering hormone binding and degradation, the concentration of free T3 available to cells was approximately 15% of that added initially. Sex hormone-binding globulin (SHBG) was secreted by HepG2 cells in the absence of T3 and was specifically stimulated by the addition of T3. After 4 days, maximum stimulation occurred with added T3 concentrations of 10(-8) M or greater, and half-maximal stimulation of SHBG secretion was observed at about 3 x 10(-11) M free T3. No significant changes in total secreted protein or cellular DNA content were observed under similar conditions. Northern analysis of RNA extracted from HepG2 cells revealed a SHBG mRNA of 2 kilobases, which was stimulated in a dose-responsive manner by T3. No stimulation of corticosteroid-binding globulin mRNA was seen. Stimulation of the SHBG gene in HepG2 cells may be a useful model for investigation of T3 action in human cells.
Raggatt
L E
LE
Ewen Downie Metabolic Unit, Alfred Hospital, Melbourne, Victoria, Australia.
Blok
R B
RB
Hamblin
P S
PS
Barlow
J W
JW
D015152:Blotting, Northern; D015870:Gene Expression / Q000187:drug effects; D006801:Humans; D007457:Iodine Radioisotopes; D012738:Sex Hormone-Binding Globulin / Q000235:genetics*; D014284:Triiodothyronine / Q000378:metabolism / Q000494:pharmacology*; D014407:Tumor Cells, Cultured
D007457:Iodine Radioisotopes; D012738:Sex Hormone-Binding Globulin; D014284:Triiodothyronine