Mechanisms underlying somatostatin receptor 2 down-regulation of vascular endothelial growth factor expression in response to hypoxia in mouse retinal explants.
Hypoxia is a trigger of VEGF expression, the primary cause of retinal pathologies characterized by neovascularization. During hypoxia, transcription factors such as STAT3 and HIF-1 promote the increase in VEGF expression. Octreotide, a somatostatin receptor 2 (sst(2) )-preferring agonist, reduces retinal VEGF expression and neovascularization. To investigate the intracellular pathways linking sst(2) activation to the inhibition of hypoxia-induced VEGF up-regulation, we used pharmacological approaches and siRNA in mouse retinal explants cultured in normoxia or hypoxia. In hypoxic explants in which STAT3 or HIF-1 was inhibited, we observed the existence of reciprocal interactions between STAT3 and HIF-1, which synergistically induced VEGF expression. Octreotide prevented hypoxia-induced activation of STAT3 and HIF-1, and the downstream increase in VEGF expression, as evaluated in hypoxic explants treated with pharmacological inhibitors of STAT3 or HIF-1 and in normoxic explants in which pharmacological activators of STAT3 or HIF-1 were used to mimic a hypoxia-like response. The effect of octreotide on STAT3 activation is in part indirect, through the blockade of VEGFR-2 phosphorylation. The effect of octreotide on STAT3, HIF-1, VEGFR-2, and VEGF required Src homology region 2 domain-containing phosphatase 1 (SHP-1). In hypoxic extracts, octreotide induced SHP-1 phosphorylation and activation, and inhibiting SHP-1 abolished the octreotide effect on STAT3, HIF-1, VEGFR-2, and VEGF. The central role of SHP-1 in the modulation of STAT3 and HIF-1 was confirmed in normoxic explants in which pharmacologically activated SHP-1 prevented the effect of STAT3 or HIF-1 activation. Immunohistochemical studies showed that under hypoxia sst(2) and VEGF are expressed by retinal vessels, thus indicating a possible direct effect of octreotide on VEGF-containing endothelial cells. These data clarify the mechanism by which octreotide prevents hypoxia-induced VEGF up-regulation and support the effectiveness of octreotide in treatment of oxygen-induced retinopathies. These results may have implications in designing therapies targeting STAT3 and/or HIF-1 aimed at preventing retinal neovascularization.
Mei S
，Cammalleri M
，Azara D
，Casini G
，Bagnoli P
，Dal Monte M
... -
《-》
Aspirin Affects Tumor Angiogenesis and Sensitizes Human Glioblastoma Endothelial Cells to Temozolomide, Bevacizumab, and Sunitinib, Impairing Vascular Endothelial Growth Factor-Related Signaling.
Glioblastoma (GBM) is the most common and fatal human brain tumor, with the worst prognosis. The aberrant microenvironment, enhanced by the activation of proangiogenic mediators such as hypoxia-inducible factor-1α (HIF-1α), vascular endothelial growth factor (VEGF), and their downstream effectors, sustain GBM malignancy. Proangiogenic signaling represents an attractive chemotherapeutic target. Recent evidence suggests a therapeutic benefit from aspirin (acetylsalicylic acid, or ASA) intake in reducing risk and cancer progression.
In the present study, human primary GBM-endothelial cells (ECs) were used to ascertain whether ASA could inhibit angiogenesis and improve cell sensitivity to drugs. The impact of ASA was observed by measuring cell viability, tube-like structure formation, migration, VEGF production, and proliferative, proangiogenic, and apoptotic modulators expression, such as HIF-1α/VEGF/vascular endothelial growth factor receptor/(VEGFR)-1/VEGFR-2, Ras/mitogen-activated protein kinase kinase/extracellular signal-regulated kinase, phosphoinositide 3-kinase/AKT signaling axis, and Bcl-2-associated X protein/B-cell lymphoma 2 (BCL-2) ratio. Furthermore, we evaluated the effect of ASA alone or in combination with temozolomide (TMZ), bevacizumab (BEV), and sunitinib (SUN).
Our data reported that ASA affected GBM-EC viability, tube-like structure formation, cell migration, and VEGF releasing in a dose-dependent manner and that combined treatments with TMZ, BEV, and SUN synergized to counteract proangiogenic cell ability. mRNA expression analysis displayed a marked effect of ASA in reducing VEGF, VEGFR-1, HIF-1α, RAS, mitogen-activated protein kinase kinase, AKT, and BCL-2, as well a combined anticancer effect of ASA together with TMZ, BEV, and SUN. Levels of HIF-1α, VEGFR-2, Bcl-2-associated X protein, and BCL-2 protein expression confirmed a positive trend.
ASA and antiangiogenic therapies showed synergetic anticancer efficacy in human primary GBM-ECs. Thus, the combination of conventional chemotherapy with ASA may offer a new strategy to counteract tumor malignancy.
Navone SE
，Guarnaccia L
，Cordiglieri C
，Crisà FM
，Caroli M
，Locatelli M
，Schisano L
，Rampini P
，Miozzo M
，La Verde N
，Riboni L
，Campanella R
，Marfia G
... -
《-》
ResearchGate
(全网免费下载)
钛学术
(全网免费下载)
