sphingosine-kinase and epigallocatechin-gallate

Topics: Antineoplastic Agents; Catechin; Cell Line, Tumor; Cell Survival; Drug Synergism; Enzyme Inhibitors; Gene Expression; Humans; Leukemia; Phosphotransferases (Alcohol Group Acceptor)

Activation of acid sphingomyelinase (ASM) leads to ceramide accumulation and induces apoptotic cell death in cancer cells. In the present study, we demonstrate that the activation of ASM by targeting cancer-overexpressed 67-kDa laminin receptors (67LR) induces lipid raft disruption and inhibits receptor tyrosine kinase (RTK) activation in multiple myeloma cells. Sphingosine kinase 1 (SphK1), a negative regulator of ceramide accumulation with antiapoptotic effects, was markedly elevated in multiple myeloma cells. The silencing of SphK1 potentiated the apoptotic effects of the green tea polyphenol epigallocatechin-3-O-gallate (EGCG), an activator of ASM through 67LR. Furthermore, the SphK1 inhibitor safingol synergistically sensitized EGCG-induced proapoptotic cell death and tumor suppression in multiple myeloma cells by promoting the prevention of RTK phosphorylation and activation of death-associated protein kinase 1 (DAPK1). We propose that targeting 67LR/ASM and SphK1 may represent a novel therapeutic strategy against multiple myeloma.

Topics: Animals; Antineoplastic Agents; Apoptosis; Catechin; Cell Line, Tumor; Death-Associated Protein Kinases; Drug Synergism; Enzyme Activation; Female; Humans; Membrane Microdomains; Mice, Inbred BALB C; Multiple Myeloma; Phosphotransferases (Alcohol Group Acceptor); Receptor Protein-Tyrosine Kinases; Signal Transduction; Sphingomyelin Phosphodiesterase; Sphingosine; Xenograft Model Antitumor Assays

ENOX2 (tNOX), a tumor-associated cell surface ubiquinol (NADH) oxidase, functions as an alternative terminal oxidase for plasma membrane electron transport. Ubiquitous in all cancer cell lines studied thus far, ENOX2 expression correlates with the abnormal growth and division associated with the malignant phenotype. ENOX2 has been proposed as the cellular target for various quinone site inhibitors that demonstrate anticancer activity such as the green tea constituent epigallocatechin-3-gallate (EGCg) and the isoflavone phenoxodiol (PXD). Here we present a possible mechanism that explains how these substances result in apoptosis in cancer cells by ENOX2-mediated alterations of cytosolic amounts of NAD(+) and NADH. When ENOX2 is inhibited, plasma membrane electron transport is diminished, and cytosolic NADH accumulates. We show in HeLa cells that NADH levels modulate the activities of two pivotal enzymes of sphingolipid metabolism: sphingosine kinase 1 (SK1) and neutral sphingomyelinase (nSMase). Their respective products sphingosine 1-phosphate (S1P) and ceramide (Cer) are key determinants of cell fate. S1P promotes cell survival and Cer promotes apoptosis. Using plasma membranes isolated from cervical adenocarcinoma (HeLa) cells as well as purified proteins of both bacterial and human origin, we demonstrate that NADH inhibits SK1 and stimulates nSMase, while NAD(+) inhibits nSMase and has no effect on SK1. Additionally, intact HeLa cells treated with ENOX2 inhibitors exhibit an increase in Cer and a decrease in S1P. Treatments that stimulate cytosolic NADH production potentiate the antiproliferative effects of ENOX2 inhibitors while those that attenuate NADH production or stimulate plasma membrane electron transport confer a survival advantage.

Topics: Anticarcinogenic Agents; Apoptosis; Catechin; Cell Line; Cell Line, Tumor; Cell Membrane; Cell Proliferation; Cell Survival; Ceramides; Chromatography, Thin Layer; Cytosol; Dose-Response Relationship, Drug; HeLa Cells; Humans; Isoflavones; Lysophospholipids; Multienzyme Complexes; NAD; NADH, NADPH Oxidoreductases; Phosphotransferases (Alcohol Group Acceptor); Sphingolipids; Sphingomyelin Phosphodiesterase; Sphingosine