| dc.description.abstract | Endothelins (ETs) are a 21 amino acid (aa) peptide hormone that was known as a potent vasoconstrictor and pressor substance isolated from the culture supernatant of porcine aortic endothelial cells. Although the ETs have been also reported to potentiate the stimulatory effect of insulin-like growth factor (IGF)-I on the growth of prostate cancer cells, no reports are found whether ET-2 interacts with IGF-I in fat cells. Using 3T3-L1 preadipocytes, we found that ET-2 alone had no effect on cell growth, as indicated by changes in levels of cell number, BrdU incorporation, and cell viability. In the presence of IGF-I, ET-2 enhanced IGF-I-induced increases in both cell number and cell proliferation. When the ET-2 signaling pathway was examined, pretreatment with the specific inhibitors of endothelin receptors, ETAR antagonist (BQ610) but not ETBR antagonist (BQ788), prevented the enhancing effect of ET-2 on IGF-I-induced increases in both cell number and cell viability. Further Western blotting analysis showed that ET-2, IGF-I, and their combination tended to time-dependently stimulate phosphorylations of AKT, ERK, and STAT3 proteins. Interestingly, ET-2 at 1 h enhanced IGF-I-stimulated phosphorylation of STAT3, but not AKT or ERK1/2, proteins when compared to IGF-I alone. But, pretreatment with ET-2 at 15 and 30 min enhanced IGF-I-stimulated phosphorylation of AKT and ERK proteins. Moreover, pre-treatment with STAT3 inhibitor (AG490), ERK1/2 inhibitor (U0126), and PI3K/AKT inhibitor (wortmannin) prevented the stimulation of ET-2 and IGF-I in cell number and cell viability, respectively, as well as reducing the level of respective pSTAT3, pAKT, and pERK proteins. In conclusions, STAT3 and, to a lesser extent of AKT and ERK proteins are necessary for the synergistic effect of ET-2 and IGF-I on the growth of preadipocytes in an ETAR-dependent and ETBR-independent manner. | en_US |