A recent article suggested that polycystins control mTOR activity by inhibiting ERK.19 We have
previously shown that PKA-mediated phosphorylation of pERK1/2 is increased in cystic cholangiocytes, and this correlates with increased secretion of VEGF and response to VEGFR2 stimulation.7 To better understand the relationships between mTOR activation and PKA-mediated phosphorylation of ERK in cystic cholangiocytes, we measured the phosphorylation of P70S6K, a kinase activated by mTOR, after inhibition of PKA with protein kinase A inhibitor 14-22 amide (PKI; 1 μM, n = 3) and after inhibition of the ERK pathway with the mitogen signal-regulated kinase (MEK) inhibitor KPT-330 U1026 (10 μM). As shown in Fig. 6, phosphorylation of P70S6K was increased in Selleck Ipilimumab Pkd2KO cholangiocytes and was inhibited by PKI and by U1026, and this suggests that the PKA/ERK pathway activates mTOR.19 Conversely, to determine if mTOR affects ERK1/2 activity, we studied pERK1/2 expression
after administration of IGF1 with or without rapamycin or the VEGFR2 inhibitor SU5416. As shown in Fig. 7, IGF1-induced ERK1/2 phosphorylation was significantly inhibited by treatment with rapamycin (5 μM) and also by the VEGFR2 inhibitor SU5416 (the pERK/ERK ratio in control Pkd2KO cells was 1.21 ± 0.4 versus 2.1 ± 0.4 after IGF1 administration, P < 0.05). The pERK/ERK ratio was reduced to 1.34 ± 0.5 after IGF1 and rapamycin (P < 0.05, n = 5) and to 1.34 ± 0.5 after IGF1 and SU5416 (P < 0.05, n = 5). As shown in Supporting Fig. 5, SU5416 had no inhibitory effects on IGFR-1; therefore, these findings suggest that mTOR does not directly activate pERK1/2, but rather the increased secretion
of VEGF caused by IGF1 via the mTOR pathway activates the MEK/ERK1/2 pathway downstream of VEGFR2. The progressive growth of liver cysts can cause significant morbidity 上海皓元 in patients with ADPKD.1 Understanding the mechanisms by which liver cysts become larger may lead to novel treatment paradigms. Liver cysts are not connected to the biliary tree, and their growth is dependent on the autocrine effect of cytokines and growth factors produced by the cystic epithelium. Among these factors, VEGF and IGF1, along with their cognate receptors, are expressed by cystic cholangiocytes and are capable of autocrine stimulation of the liver cyst epithelium.5, 6 In this study, using mice with conditional inactivation of PC2, we have demonstrated that mTOR plays a central role in cyst growth. Furthermore, we have shown that IGF1 and VEGF signaling are linked through the PI3K/AKT/mTOR pathway, that there is significant crosstalk between mTOR and ERK1/2, and that the mTOR inhibitor rapamycin reduces the growth of liver cysts in vivo through the repression of VEGF secretion, with reduced cell proliferation and increased apoptosis. m-TOR is a signaling molecule that integrates a broad spectrum of signals, including growth factors.