Epidermal growth factor (EGF) receptor (EGFR) emerges as an essential molecule for the regulating of osteoblast cellular functions. In the current study, we explored the effect of epiregulin, a new EGFR ligand, on osteoblast functions in vitro, and studied the underlying mechanisms. We found that epiregulin-induced EGFR activation in both primary osteoblasts and osteoblast-like MC3T3-E1 cells. Meanwhile, epiregulin activated AKT-mammalian target of rapamycin (mTOR) and Erk-mitogen-activated protein kinase (MAPK) signalings in cultured osteoblasts, which were blocked by EGFR inhibitor AG1478 or monoclonal antibody against EGFR (anti-EGFR). Further, in primary and MC3T3-E1 osteoblasts, epiregulin promoted cell proliferation and increased alkaline phosphatase activity, while inhibiting dexamethasone (Dex)-induced cell death. Such effects by epiregulin were largely inhibited by AG1478 or anti-EGFR. Notably, AKT-mTOR inhibitors, but not Erk inhibitors, alleviated epiregulin-induced above pleiotropic functions in osteoblasts. Meanwhile, siRNA depletion of Sin1, a key component of mTOR complex 2 (mTORC2), also suppressed epiregulin-exerted effects in MC3T3-E1 cells. Together, these results suggest that epiregulin-induced pleiotropic functions in cultured osteoblasts are mediated through EGFR-AKT-mTOR signalings.
Epiregulin EGFR AKT/mTOR signalings Osteoblasts
Epidermal growth factor
Mammalian target of rapamycin
Ribosomal S6 kinase 1
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This work was generously supported by Grants from the National Natural Science Foundation of China.
Conflict of interests
The authors declare that they have no competing interests.
Supplementary Fig. 1. MC3T3-E1 osteoblasts were pre-incubated with PD-98059 (1 μM) or U0126 (1 μM) for 1 h, followed by epiregulin (50 ng/ml) stimulation for 24 h, cell proliferation (cell counting assay, A) and ALP activity (B) were analyzed. For detecting cell death, above cells were co-incubated with Dex (1 μM, 24 h), trypan blue staining assay was performed (C). (EPS 695 kb)
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