RESUMO
An epidemiological study showed that green tea consumption is associated with a reduced risk of hematopoietic malignancy. The major green tea polyphenol epigallocatechin3-O-gallate (EGCG) is reported to have anticancer effects. Chronic myeloid leukemia (CML) is a major hematopoietic malignancy characterized by expansion of myeloid cells. In the present study, we showed EGCG-induced acid sphingomyelinase (ASM) activation and lipid raft clustering in CML cells. The ASM inhibitor desipramine significantly reduced EGCG-induced cell death. Protein kinase Cδ is a wellknown kinase that plays an important role in ASM activation. We observed EGCG-induced phosphorylation of protein kinase Cδ at Ser664. Importantly, EGCG-induced ASM activation was significantly reduced by pretreatment of CML cells with the soluble guanylate cyclase inhibitor NS2028, suggesting that EGCG induced ASM activation through the cyclic guanosine monophosphate (cGMP)-dependent pathway. Indeed, pharmacological inhibition of a cGMP-negative regulator enhanced the anti-CML effect of EGCG. These results indicate that EGCG-induced cell death via the cGMP/ASM pathway in CML cells.
Assuntos
Anticarcinógenos/farmacologia , Catequina/análogos & derivados , Ativação Enzimática/efeitos dos fármacos , Leucemia Mielogênica Crônica BCR-ABL Positiva/patologia , Esfingomielina Fosfodiesterase/metabolismo , Western Blotting , Catequina/farmacologia , Linhagem Celular Tumoral , Humanos , Microdomínios da Membrana/efeitos dos fármacos , Chá/químicaRESUMO
We investigated the effects of extracts of Benifuuki (a tea cultivar that contains methylated catechins such as epigallocatechin-3-O-(3-O-methyl) gallate (EGCG3"Me)) in mice fed a high-fat/high-sucrose (HF/HS) diet. This tea cultivar was then compared with an extract of Yabukita (a popular tea cultivar that lacks methylated catechins). For 6 weeks, C57BL/6J mice were fed either HF/HS diet with or without tea extracts from tea cultivars, which contained almost identical ingredients except for methylated catechins (i.e., Yabukita (0.2% and 1%) or Benifuuki (0.2% and 1%) extract powders). Supplementation with Benifuuki 0.2% markedly lowered plasma levels of TG and NEFAs compared with mice supplemented with Yabukita 0.2%. The diet containing Benifuuki 1% decreased adipose tissue weights, liver TG, and expression of lipogenic genes in the liver. These results suggested that Benifuuki had much greater lipid-lowering effects than Yabukita. Taken together, these data suggest that methylated catechins direct the strong lipid-lowering activity of Benifuuki.
Assuntos
Catequina/uso terapêutico , Transtornos do Metabolismo dos Lipídeos/tratamento farmacológico , Transtornos do Metabolismo dos Lipídeos/prevenção & controle , Extratos Vegetais/uso terapêutico , Chá/química , Absorção , Tecido Adiposo/efeitos dos fármacos , Animais , Catequina/farmacologia , Colesterol/metabolismo , Dieta Hiperlipídica , Sacarose Alimentar , Ácidos Graxos não Esterificados/sangue , Comportamento Alimentar/efeitos dos fármacos , Metabolismo dos Lipídeos/efeitos dos fármacos , Metabolismo dos Lipídeos/genética , Transtornos do Metabolismo dos Lipídeos/sangue , Transtornos do Metabolismo dos Lipídeos/genética , Fígado/efeitos dos fármacos , Fígado/metabolismo , Masculino , Camundongos , Camundongos Endogâmicos C57BL , Análise de Sequência com Séries de Oligonucleotídeos , Fitoterapia , Extratos Vegetais/farmacologia , Triglicerídeos/sangueRESUMO
BACKGROUND: We previously identified the 67-kDa laminin receptor (67LR) as the cell-surface receptor conferring the major green tea polyphenol (-)-epigallocatechin-3-O-gallate (EGCG) responsiveness to cancer cells. However, the underlying mechanism for interaction between EGCG and 67LR remains unclear. In this study, we investigated the possible role of EGCG-67LR interaction responsible for its bioactivities. METHODOLOGY/PRINCIPAL FINDINGS: We synthesized various peptides deduced from the extracellular domain corresponding to the 102-295 region of human 67LR encoding a 295-amino acid. The neutralizing activity of these peptides toward EGCG cell-surface binding and inhibition of cancer cell growth were assayed. Both activities were inhibited by a peptide containing the 10-amino acid residues, IPCNNKGAHS, corresponding to residues 161-170. Furthermore, mass spectrometric analysis revealed the formation of a EGCG-LR161-170 peptide complex. A study of the amino acid deletion/replacement of the peptide LR161-170 indicated that the 10-amino acid length and two basic amino acids, K(166) and H(169), have a critical role in neutralizing EGCG's activities. Moreover, neutralizing activity against the anti-proliferation action of EGCG was observed in a recombinant protein of the extracellular domain of 67LR, and this effect was abrogated by a deletion of residues 161-170. These findings support that the 10 amino-acid sequence, IPCNNKGAHS, might be the functional domain responsible for the anti-cancer activity of EGCG. CONCLUSIONS/SIGNIFICANCE: Overall, our results highlight the nature of the EGCG-67LR interaction and provide novel structural insights into the understanding of 67LR-mediated functions of EGCG, and could aid in the development of potential anti-cancer compounds for chemopreventive or therapeutic uses that can mimic EGCG-67LR interactions.
Assuntos
Catequina/análogos & derivados , Polifenóis/metabolismo , Receptores de Laminina/química , Receptores de Laminina/metabolismo , Proteínas Ribossômicas/química , Proteínas Ribossômicas/metabolismo , Chá/química , Motivos de Aminoácidos , Sequência de Aminoácidos , Catequina/metabolismo , Catequina/farmacologia , Proliferação de Células/efeitos dos fármacos , Espaço Extracelular/metabolismo , Células Hep G2 , Humanos , Dados de Sequência Molecular , Polifenóis/farmacologia , Ligação Proteica , Estrutura Terciária de ProteínaRESUMO
EGCG [(-)-epigallocatechin-3-O-gallate], the major polyphenol of green tea, has cancer chemopreventive and chemotherapeutic activities. EGCG selectively inhibits cell growth and induces apoptosis in cancer cells without adversely affecting normal cells; however, the underlying molecular mechanism in vivo is unclear. In the present study, we show that EGCG-induced apoptotic activity is attributed to a lipid-raft clustering mediated through 67LR (67 kDa laminin receptor) that is significantly elevated in MM (multiple myeloma) cells relative to normal peripheral blood mononuclear cells, and that aSMase (acid sphingomyelinase) is critical for the lipid-raft clustering and the apoptotic cell death induced by EGCG. We also found that EGCG induces aSMase translocation to the plasma membrane and PKCδ (protein kinase Cδ) phosphorylation at Ser664, which was necessary for aSMase/ceramide signalling via 67LR. Additionally, orally administered EGCG activated PKCδ and aSMase in a murine MM xenograft model. These results elucidate a novel cell-death pathway triggered by EGCG for the specific killing of MM cells.