Thyroid hormones regulate DNA-synthesis and cell-cycle proteins by activation of PKCalpha and p42/44 MAPK in chick embryo hepatocytes.
The molecular mechanism by which thyroid hormones exert their effects on cell growth is still unknown. In this study, we used chick embryo hepatocytes at different stages of development as a model to investigate the effect of the two thyroid hormones, T3 and T4, and of their metabolite T2, on the control of cell proliferation. We observed that T2 provokes increase of DNA-synthesis as well as T3 and T4, independently of developmental stage. We found that this stimulatory effect on the S phase is reverted by specific inhibitors of protein kinase C (PKC) and p42/44 mitogen-activated protein kinase (p42/44 MAPK), Ro 31-8220 or PD 98059. Furthermore, the treatment with thyroid hormones induces the activation of PKCalpha and p42/44 MAPK, suggesting their role as possible downstream mediators of cell response mediated by thyroid hormones. The increase of DNA-synthesis is well correlated with the increased levels of cyclin D1 and cdk4 that control the G1 phase, and also with the activities of cell-cycle proteins involved in the G1 to S phase progression, such as cyclin E/A-cdk2 complexes. Interestingly, the activity of cyclin-cdk2 complexes is strongly repressed in the presence of PKC and p42/44 MAPK inhibitors. In conclusion, we demonstrated that the thyroid hormones could modulate different signaling pathways that are able to control cell-cycle progression, mainly during G1/S transition.
Alisi
A
A
Department of Cellular and Developmental Biology, University La Sapienza, Roma, Italy.
Spagnuolo
S
S
Napoletano
S
S
Spaziani
A
A
Leoni
S
S
D000818:Animals; D018797:Cell Cycle Proteins / Q000187:drug effects* / Q000378:metabolism; D002455:Cell Division / Q000187:drug effects / Q000502:physiology; D002478:Cells, Cultured; D002642:Chick Embryo; D004261:DNA Replication / Q000187:drug effects* / Q000502:physiology; D004789:Enzyme Activation / Q000187:drug effects / Q000502:physiology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005434:Flow Cytometry; D022781:Hepatocytes / Q000187:drug effects* / Q000378:metabolism; D015151:Immunoblotting; D047468:Immunoprecipitation; D019950:Mitogen-Activated Protein Kinase 1 / Q000187:drug effects / Q000378:metabolism; D048052:Mitogen-Activated Protein Kinase 3 / Q000187:drug effects / Q000378:metabolism; D020928:Mitogen-Activated Protein Kinases / Q000187:drug effects* / Q000378:metabolism; D011493:Protein Kinase C / Q000187:drug effects* / Q000378:metabolism; D051571:Protein Kinase C-alpha; D015398:Signal Transduction; D013963:Thyroid Hormones / Q000378:metabolism / Q000494:pharmacology*; D013974:Thyroxine / Q000378:metabolism / Q000494:pharmacology; D014284:Triiodothyronine / Q000494:pharmacology
D018797:Cell Cycle Proteins; D004791:Enzyme Inhibitors; D013963:Thyroid Hormones; D014284:Triiodothyronine; D011493:Protein Kinase C; D051571:Protein Kinase C-alpha; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases; D013974:Thyroxine