RESUMO
Epigallocatechin gallate (EGCG) is the principal bioactive ingredient in green tea and has been reported to have many health benefits. EGCG influences multiple signal transduction pathways related to human diseases, including redox, inflammation, cell cycle, and cell adhesion pathways. However, the molecular mechanisms of these varying effects are unclear, limiting further development and utilization of EGCG as a pharmaceutical compound. Here, we examined the effect of EGCG on two representative transmembrane signaling receptors, integrinαIIbß3 and epidermal growth factor receptor (EGFR). We report that EGCG inhibits talin-induced integrin αIIbß3 activation, but it activates αIIbß3 in the absence of talin both in a purified system and in cells. This apparent paradox was explained by the fact that the activation state of αIIbß3 is tightly regulated by the topology of ß3 transmembrane domain (TMD); increases or decreases in TMD embedding can activate integrins. Talin increases the embedding of integrin ß3 TMD, resulting in integrin activation, whereas we observed here that EGCG decreases the embedding, thus opposing talin-induced integrin activation. In the absence of talin, EGCG decreases the TMD embedding, which can also disrupt the integrin α-ß TMD interaction, leading to integrin activation. EGCG exhibited similar paradoxical behavior in EGFR signaling. EGCG alters the topology of EGFR TMD and activates the receptor in the absence of EGF, but inhibits EGF-induced EGFR activation. Thus, this widely ingested polyphenol exhibits pleiotropic effects on transmembrane signaling by modifying the topology of TMDs.
Assuntos
Antioxidantes/metabolismo , Catequina/análogos & derivados , Receptores ErbB/metabolismo , Integrina beta3/metabolismo , Bicamadas Lipídicas/metabolismo , Modelos Moleculares , Transdução de Sinais , Substituição de Aminoácidos , Animais , Antioxidantes/química , Antioxidantes/uso terapêutico , Células CHO , Catequina/química , Catequina/metabolismo , Catequina/uso terapêutico , Cricetulus , Suplementos Nutricionais , Dimerização , Receptores ErbB/agonistas , Receptores ErbB/química , Receptores ErbB/genética , Humanos , Integrina alfa2/química , Integrina alfa2/genética , Integrina alfa2/metabolismo , Integrina beta3/química , Integrina beta3/genética , Ligantes , Bicamadas Lipídicas/química , Mutação , Fragmentos de Peptídeos/antagonistas & inibidores , Fragmentos de Peptídeos/química , Fragmentos de Peptídeos/metabolismo , Complexo Glicoproteico GPIIb-IIIa de Plaquetas/agonistas , Complexo Glicoproteico GPIIb-IIIa de Plaquetas/química , Complexo Glicoproteico GPIIb-IIIa de Plaquetas/genética , Complexo Glicoproteico GPIIb-IIIa de Plaquetas/metabolismo , Domínios e Motivos de Interação entre Proteínas , Proteínas Recombinantes de Fusão/química , Proteínas Recombinantes de Fusão/metabolismo , Talina/antagonistas & inibidores , Talina/química , Talina/metabolismoRESUMO
Cancer metastasis is a highly coordinated and dynamic multistep process in which cancer cells interact with a variety of host cells. Morphological studies have documented the association of circulating tumor cells with host platelets, where a surface coating of platelets protects tumor cells from mechanical trauma and the immune system. Cantharidin is an active constituent of mylabris, a traditional Chinese medicine. Cantharidin and norcantharidin are potent protein phosphatase 2A (PP2A) inhibitors that exhibit in vitro and in vivo antitumor activity against several types of cancer, including breast cancer. We investigated whether cantharidin and norcantharidin could repress the ability of MCF-7 breast cancer cells to adhere to platelets. Using MTT, clone formation, apoptosis, adhesion and wound-healing assays, we found that cantharidin and norcantharidin induced apoptosis and repressed MCF-7 cell growth, adhesion and migration. Moreover, we developed a flow cytometry-based analysis of tumor cell adhesion to platelets. We proved that cantharidin and norcantharidin repressed MCF-7 cell adhesion to platelets through downregulation of α2 integrin, an adhesion molecule present on the surface of cancer cells. The repression of α2 integrin expression was found to be executed through the protein kinase C pathway, the activation of which could have been due to PP2A inhibition.
Assuntos
Plaquetas/metabolismo , Neoplasias da Mama/tratamento farmacológico , Compostos Bicíclicos Heterocíclicos com Pontes/farmacologia , Cantaridina/farmacologia , Integrina alfa2/química , Adesividade Plaquetária/efeitos dos fármacos , Proteína Quinase C/metabolismo , Apoptose/efeitos dos fármacos , Plaquetas/efeitos dos fármacos , Western Blotting , Neoplasias da Mama/metabolismo , Neoplasias da Mama/patologia , Adesão Celular/efeitos dos fármacos , Proliferação de Células/efeitos dos fármacos , Regulação para Baixo , Inibidores Enzimáticos/farmacologia , Feminino , Citometria de Fluxo , Humanos , Integrina alfa2/genética , Integrina alfa2/metabolismo , Células MCF-7 , Proteína Quinase C/genética , RNA Mensageiro/genética , RNA Interferente Pequeno/genética , Reação em Cadeia da Polimerase em Tempo Real , Reação em Cadeia da Polimerase Via Transcriptase Reversa , Fator de Transcrição RelA/antagonistas & inibidores , Fator de Transcrição RelA/genética , Fator de Transcrição RelA/metabolismo , Cicatrização/efeitos dos fármacosRESUMO
BACKGROUND: Integrins influence tumourigenesis, tumor progression and development of metastases. The impact of polymorphisms in integrin genes on relapse-free survival (RFS) and overall survival (OS) for 433 Caucasian patients with colorectal cancer was analysed in this retrospective study. PATIENTS AND METHODS: A Cox regression model including integrin genotype, age, grading, tumour size, number of lymph nodes examined, number of metastatic lymph nodes, stage and application of fluorouracil-based adjuvant chemotherapy was used to estimate their effect. RESULTS: After a median follow-up of 41 months for RFS and 55 months for OS, no significant correlation between the ITGA2 1648A allele (RFS p=0.618, OS p=0.604), the ITGA2 807T allele (RFS p=0.603, OS p=0.807) and the ITGB3 176C allele (RFS p=0.719, OS p=0.261) and survival was detectable. CONCLUSION: The investigated integrin polymorphisms are not associated with RFS or OS in colorectal cancer patients.
Assuntos
Neoplasias Colorretais/genética , Integrina alfa2/genética , Integrina beta3/genética , Recidiva Local de Neoplasia/genética , Polimorfismo de Nucleotídeo Único/genética , Antimetabólitos Antineoplásicos/uso terapêutico , Quimioterapia Adjuvante , Neoplasias Colorretais/mortalidade , DNA de Neoplasias/genética , Feminino , Fluoruracila/uso terapêutico , Seguimentos , Humanos , Masculino , Pessoa de Meia-Idade , Recidiva Local de Neoplasia/mortalidade , Reação em Cadeia da Polimerase , Prognóstico , Estudos Retrospectivos , Taxa de SobrevidaRESUMO
Recent studies have shown opposing effects of n-6 and n-3 fatty acids on the development of cancer and suggest a role for the ratio of n-6 to n-3 fatty acids in the control of cancer. However, whether an alteration in the n-6/n-3 fatty acid ratio of cancer cells affects their invasive potential has not been well investigated. We recently developed a genetic approach to modify the n-6/n-3 ratio by expression of the Caenorhabditis elegans fat-1 gene encoding an n-3 desaturase that converts n-6 to n-3 fatty acids in mammalian cells. The objective of this study was to examine the effect of alteration in the n-6/n-3 fatty acid ratio on the invasive potential of human lung cancer A549 cells. Adenovirus-mediated gene transfer of the n-3 desaturase resulted in a marked reduction of the n-6/n-3 fatty acid ratio, particularly the ratio of arachidonic acid to eicosapentaenic acid. Cell adhesion assay showed that the cells expressing fat-1 gene had a delayed adhesion and retarded colonization. Matrigel assay for invasion potential indicated a 2-fold reduction of cell migration in the fat-1 transgenic cells when compared with the control cells. An increased apoptosis was also observed in the fat-1 transgenic cells. Microarray and quantitative polymerase chain reaction revealed a downregulation of several adhesion/invasion-related genes (MMP-1, integrin-alpha2 and nm23-H4) in the fat-1 transgenic cells. These results demonstrate that a decreased n-6/n-3 fatty acid ratio reduces the invasion potential of human lung cancer cells by probably downregulating the cell adhesion/invasion-related molecules, suggesting a role for the ratio of n-6 to n-3 fatty acids in the prevention and treatment of cancer.