RESUMO
Water influx through aquaporin-1 (AQP-1) has been linked to the ability of different cell types to migrate, and therefore plays an important part in processes like metastasis and angiogenesis. Since the erythroid growth factor erythropoietin (Epo) is now recognized as an angiogenesis promoter, we investigated the participation of AQP-1 as a downstream effector of this cytokine in the migration of endothelial cells. Inhibition of AQP-1 with either mercury ions (Hg2+) or a specific siRNA led to an impaired migration of EA.hy926 endothelial cells exposed to Epo (wound-healing assays). Epo also induced the expression of AQP-1 at mRNA and protein levels, an effect which was dependent on the influx of extracellular calcium through L-type calcium channels as well as TRPC3 channels. The relationship between Epo and AQP-1 was further confirmed at shorter exposure times, as the cytokine was unable to trigger calcium influxes in cells where AQP-1 had previously been knocked down. Moreover, Epo promoted changes in the subcellular localization of AQP-1 as well as rearrangements in the actin cytoskeleton, which are consistent with a migratory phenotype. Worthy of note, carbamylated erythropoietin (cEpo), the non-erythropoietic and non-promigratory derivative of Epo, was incapable of AQP-1 modulation. The therapeutical implications of aquaporin targeting in angiogenesis-related diseases highlight the importance of the present results in the context of the relationship between AQP-1 and Epo.
Assuntos
Aquaporina 1/fisiologia , Movimento Celular/efeitos dos fármacos , Eritropoetina/farmacologia , Células Endoteliais da Veia Umbilical Humana/efeitos dos fármacos , Células Endoteliais da Veia Umbilical Humana/fisiologia , Células A549 , Aquaporina 1/antagonistas & inibidores , Movimento Celular/genética , Células Cultivadas , Eritropoetina/fisiologia , Humanos , RNA Interferente Pequeno/farmacologia , Cicatrização/efeitos dos fármacos , Cicatrização/genéticaRESUMO
Many patients under therapy with recombinant human erythropoietin (rhuEPO) show resistance to the treatment, an effect likely associated with the accumulation of tissue factors, especially in renal and cardiovascular diseases. Hyperhomocysteinemia due to high serum levels of homocysteine has been suggested among the risk factors in those pathologies. Its main effect is the N-homocysteinylation of proteins due to the interaction between the highly reactive homocysteine thiolactone (HTL) and lysine residues. The aim of this study was to evaluate the effect of N-homocysteinylation on the erythropoietic and antiapoptotic abilities of EPO, which can be a consequence of structural changes in the modified protein. We found that both cellular functions were altered in the presence of HTL-EPO. A decreased net positive charge of HTL-EPO was detected by capillary zone electrophoresis, while analysis of polyacrylamide gel electropherograms suggested formation of aggregates. Far-UV spectra, obtained by Circular Dichroism Spectroscopy, indicated a switch of the protein's secondary structure from α-helix to ß-sheet structures. Results of Congo red and Thioflavin T assays confirm the formation of repetitive ß-sheet structures, which may account for aggregates. Accordingly, Dynamic Light Scattering analysis showed a markedly larger radius of the HTL-EPO structures, supporting the formation of soluble oligomers. These structural changes might interfere with the conformational adaptations necessary for efficient ligand-receptor interaction, thus affecting the proliferative and antiapoptotic functions of EPO. The present findings may contribute to explain the resistance exhibited by patients with cardio-renal syndrome to treatment with rhuEPO, as a consequence of structural modifications due to protein N-homocysteinylation.
Assuntos
Apoptose , Proliferação de Células , Eritropoetina/química , Homocisteína/análogos & derivados , Lisina/química , Processamento de Proteína Pós-Traducional , Estrutura Secundária de Proteína , Células Cultivadas , Eritropoetina/metabolismo , Homocisteína/química , Humanos , Megacariócitos/metabolismo , Megacariócitos/patologia , Ligação ProteicaRESUMO
Calcium (Ca2+) plays an important role in angiogenesis, as it activates the cell migration machinery. Different proangiogenic factors have been demonstrated to induce transient Ca2+ increases in endothelial cells. This has raised interest in the contribution of Ca2+ channels to cell migration, and in a possible use of channel-blocking compounds in angiogenesis-related pathologies. We have investigated the ability of erythropoietin (Epo), a cytokine recently involved in angiogenesis, to induce Ca2+ influx through different types of membrane channels in EA.hy926 endothelial cells. The voltage-dependent Ca2+ channel antagonists amlodipine and diltiazem inhibited an Epo-triggered transient rise in intracellular Ca2+, similarly to a specific inhibitor (Pyr3) and a blocking antibody against the transient potential calcium channel 3 (TRPC3). Unlike diltiazem, amlodipine and the TRPC3 inhibitors prevented the stimulating action of Epo in cell migration and in vitro angiogenesis assays. Amlodipine was also able to inhibit an increase in endothelial cell migration induced by Epo in an inflammatory environment generated with TNF-α. These results support the participation of Ca2+ entry through voltage-dependent and transient potential channels in Epo-driven endothelial cell migration, highlighting the antiangiogenic activity of amlodipine.