Thyroid hormones regulate DNA‐synthesis and cell‐cycle proteins by activation of PKCα and p42/44 MAPK in chick embryo hepatocytes

Abstract

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.

Genistein prevents thyroid hormone‐dependent tail regression of Rana catesbeiana tadpoles by targetting protein kinase C and thyroid hormone receptor α

“…Since tyrosine phosphorylation is important for PKC activity (Tapia et al, 2002;Pula et al, 2005), these data suggest that the inhibition of T 3 -induced tail regression may be through alteration of tyrosine kinase signaling. This is consistent with the observations that T 3 or T 4 enhances kinase activity of PKC in the chick embryo (Alisi et al, 2004) and that the PKC inhibitor, H7, inhibits T 3 (Fig. 8A) or T 4 -induced tadpole tail regression (Petcoff and Platt, 1992;Phillips and Platt, 1994).…”

“…The pathways involved include those mediated by tyrosine kinases (Di Fulvio et al, 2000;Utoh et al, 2003;Martinez and Gomes, 2005), protein kinase C (PKC) (Petcoff and Platt, 1992;Phillips and Platt, 1994;Wagner et al, 2001;Alisi et al, 2004), mitogen-activated protein kinase (MAPK)/extracellular signal-regulated kinase (ERK) (Lin et al, 1997(Lin et al, , 1998(Lin et al, , 1999aDavis et al, 2000;Bergh et al, 2005), cyclin-dependent kinases (Barrera-Hernandez et al, 1999;Nguyen et al, 2003;Skirrow, 2003;Skirrow and Helbing, 2007), and phosphatidylinositol-3 kinase (PI3K) (Lei et al, 2004;Cao et al, 2005;. However, the precise target substrates, the location of phosphorylation sites, their integration into the TH signaling pathway, and functional roles in specific tissues remain to be elucidated.…”

Thyroid hormone stimulation of extracellular signal-regulated kinase and cell proliferation in human osteoblast-like cells is initiated at integrin αVβ3

“…These findings are consistent with previous studies in HeLa cells, CV-1 monkey fibroblasts and chick embryo hepatocytes that have demonstrated the ability of thyroid hormones to activate the MAPK signalling cascade and promote the phosphorylation of ERK within 5-20 min after treatment (Lin et al 1999, Alisi et al 2004, Bergh et al 2005. We used concentrations of T 3 and T 4 that were reported previously to produce the maximal ERK activation response in other cell types.…”

“…However, these studies were performed in rat osteoblast cell lines and used only T 3 (and not T 4 ) at a very high concentration of 100 nM for 30 min. Thus, there may be species differences in response, or as reported previously (Lin et al 1999, Alisi et al 2004, Bergh et al 2005, thyroid hormone effects on ERK activation are rapid and transient with activation returning to control levels by 30 min.…”

“…This was also the case when cells were treated with the specific MEK inhibitor, U0126, and might suggest that molecular mechanisms other than those initiated at the integrin a V b 3 receptor exist for T 4 action at the cell surface as proposed by Davis et al (2005). In other cell types, activation of the integrin a V b 3 receptor is reported to activate the MAPK pathway via protein kinase C (PKC; Alisi et al 2004) and we have preliminary data using a specific PKC inhibitor (data not shown) that would suggest that this is also the case in osteoblast cells.…”