Endothelin (ET)-1 regulates adipogenesis and the endocrine activity of fat cells. However, relatively little is known about the ET-1 signaling pathway in preadipocyte growth. We used 3T3-L1 preadipocytes to investigate the signaling pathways involved in ET-1 modulation of preadipocyte proliferation. As indicated by an increased number of cells and greater incorporation of bromodeoxyuridine (BrdU), the stimulation of preadipocyte growth by ET-1 depends on concentration and timing. The concentration of ET-1 that increased preadipocyte number by 51-67% was ~100 nM for ~24-48 h of treatment. ET-1 signaling time dependently stimulated phosphorylation of ERK, c-JUN, STAT3, AMPK, and PKCα/βII proteins but not AKT, JNK, or p38 MAPK. Treatment with an ETAR antagonist, such as BQ610, but not ETBR antagonist BQ788, blocked the ET-1-induced increase in cell proliferation and phosphorylated levels of ERK, c-JUN, STAT3, AMPK, and PKCα/βII proteins. In addition, pretreatment with specific inhibitors of ERK1/2 (U0126), JNK (SP600125), JAK2/STAT3 (AG490), AMPK (compound C), or PKC (Ro318220) prevented the ET-1-induced increase in cell proliferation and reduced the ET-1-stimulated phosphorylation of ERK1/2, c-JUN, STAT3, AMPK, and PKCα/β. Moreover, the SphK antagonist suppressed ET-1-induced cell proliferation and ERK, c-JUN, STAT3, AMPK, and PKC phosphorylation, and the SMase2 antagonist suppressed ET-1-induced cell proliferation. However, neither the p38 MAPK antagonist nor the CerS inhibitor altered the effect of ET-1. The results indicate that ETAR, JAK2/STAT3, ERK1/2, JNK/c-JUN, AMPK, PKC, SphK, and SMase2, but not ETBR, p38 MAPK, or CerS, are necessary for the ET-1 stimulation of preadipocyte proliferation.
Keywords: AMP-activated protein kinase; mitogen-activated protein kinase; protein kinase C; signal transducer and activator of transcription; sphingosine kinase.