RESUMEN
Targets that could improve the treatment of brain tumors remain important to define. This study of a transformation-associated isoform of alpha2-macroglobulin (A2M*) and its interaction with the low-density lipoprotein receptor-related protein-1 (LRP1) suggests a new mechanism for abrogating the malignant potential of astrocytoma cells. LRP1 bound A2M* found to be associated with an inhibition of tumor cell proliferation, migration, invasion, spheroid formation, and anchorage-independent growth. Transcriptional studies implicated effects on the Wnt/beta-catenin signaling pathway. Notably, LRP1 antibodies could phenocopy the effects of A2M*. Our findings suggest a pathway of tumor suppression in astrocytoma that might be tractable to therapeutic exploitation.
Asunto(s)
Astrocitoma/metabolismo , Proteína Asociada a Proteínas Relacionadas con Receptor de LDL/metabolismo , Transducción de Señal/fisiología , alfa-Macroglobulinas/metabolismo , beta Catenina/metabolismo , Western Blotting , Adhesión Celular/fisiología , Línea Celular Tumoral , Movimiento Celular/fisiología , Proliferación Celular , Expresión Génica , Humanos , InmunohistoquímicaRESUMEN
BACKGROUND: Glyoxalases (Glo1 and Glo2) are involved in the glycolytic pathway by detoxifying the reactive methylglyoxal (MGO) into D-lactate in a two-step reaction using glutathione (GSH) as cofactor. Inhibitors of glyoxalases are considered as anti-inflammatory and anti-carcinogenic agents. The recent finding that various polyphenols modulate Glo1 activity has prompted us to assess curcumin's potency as an Glo1 inhibitor. METHODOLOGY/PRINCIPAL FINDINGS: Cultures of whole blood cells and tumor cell lines (PC-3, JIM-1, MDA-MD 231 and 1321N1) were set up to investigate the effect of selected polyphenols, including curcumin, on the LPS-induced cytokine production (cytometric bead-based array), cell proliferation (WST-1 assay), cytosolic Glo1 and Glo2 enzymatic activity, apoptosis/necrosis (annexin V-FITC/propidium iodide staining; flow cytometric analysis) as well as GSH and ATP content. Results of enzyme kinetics revealed that curcumin, compared to the polyphenols quercetin, myricetin, kaempferol, luteolin and rutin, elicited a stronger competitive inhibitory effect on Glo1 (K(i) = 5.1+/-1.4 microM). Applying a whole blood assay, IC(50) values of pro-inflammatory cytokine release (TNF-alpha, IL-6, IL-8, IL-1beta) were found to be positively correlated with the K(i)-values of the aforementioned polyphenols. Moreover, whereas curcumin was found to hamper the growth of breast cancer (JIMT-1, MDA-MB-231), prostate cancer PC-3 and brain astrocytoma 1321N1 cells, no effect on growth or vitality of human primary hepatocytes was elucidated. Curcumin decreased D-lactate release by tumor cells, another clue for inhibition of intracellular Glo1. CONCLUSIONS/SIGNIFICANCE: The results described herein provide new insights into curcumin's biological activities as they indicate that inhibition of Glo1 by curcumin may result in non-tolerable levels of MGO and GSH, which, in turn, modulate various metabolic cellular pathways including depletion of cellular ATP and GSH content. This may account for curcumin's potency as an anti-inflammatory and anti-tumor agent. The findings support the use of curcumin as a potential therapeutic agent.
Asunto(s)
Antiinflamatorios/farmacología , Antineoplásicos Fitogénicos/farmacología , Curcumina/farmacología , Lactoilglutatión Liasa/antagonistas & inhibidores , Células Sanguíneas/efectos de los fármacos , Células Sanguíneas/metabolismo , Proliferación Celular/efectos de los fármacos , Supervivencia Celular/efectos de los fármacos , Células Cultivadas , Evaluación Preclínica de Medicamentos , Inhibidores Enzimáticos/farmacología , Flavonoides/farmacología , Humanos , Interleucina-1beta/metabolismo , L-Lactato Deshidrogenasa/metabolismo , Lipopolisacáridos/farmacología , Modelos Biológicos , Neoplasias/patología , Fenoles/farmacología , Polifenoles , Especificidad por SustratoRESUMEN
Esters of alpha-oxo-carbonic acids such as ethyl pyruvate (EP) have been demonstrated to exert inhibitory effects on the production of anti-inflammatory cytokines. So far, there is no information about effects, if any, of ethyl lactate (EL), an obviously inactive analogue of EP, on inflammatory immune responses. In the present study, we provide evidence that the anti-inflammatory action of alpha-oxo-carbonic acid esters is mediated by inhibition of glyoxalases (Glo), cytosolic enzymes that catalyse the conversion of alpha-oxo-aldehydes such as methylglyoxal (MGO) into the corresponding alpha-hydroxy acids using glutathione as a cofactor. In vitro enzyme activity measurements revealed the inhibition of human Glo1 by alpha-oxo-carbonic acid esters, whilst alpha-hydroxy-carbonic acid esters such as EL were not inhibitory. In contrast, both EP and EL were shown to suppress the Lipopolysaccharide (LPS)-induced production of pro-inflammatory cytokines such as tumor necrosis factor-alpha, interleukin (IL)-1beta, IL-6 and IL-8 from human immunocompetent cells, and modulated the expression of the immune receptors HLA-DR, CD14 and CD91 on human monocytes. Here, we show a crossing link between glyoxalases and the immune system. The results described herein introduce glyoxalases as a possible target for therapeutic approaches of immune suppression.