OBJECTIVE: To investigate the effect of overexpression of glycosylphosphatidyl-inositol-specific phospholipase D (GPI-PLD) on the biological character of hepatocellular carcinoma cell line HepG2. METHODS: The GPI-PLD gene eukaryon expression vector pcDNA3.1(+)/ GPI-PLD was transiently transfected into HepG2 cell by lipid-media transfection. The untransfected HepG2 and HepG2 transfected with pcDNA3.1(+) were used as controls. After screening with G418, the single clone was obtained. The expression level of GPI-PLD mRNA in HepG2 was identified by reverse transcription polymerase chain reaction (RT-PCR). GPI-PLD activities were analyzed quantitatively by triton-X-114 partition with GPI anchored placental alkaline phosphatase (PLAP) as a substrate. Cell count was used to detect the proliferation of the 3 groups, and complement dependent cytotoxicity (CDC) effects were observed by the staining of trypan blue. Apoptosis cells were analyzed by flow cytometry. Carcinoembryonic antigen (CEA)was detected by enzyme linked immunosorbent assay (ELISA). RESULTS: Compared with HepG2 and pcDNA3.1(+)/HepG2 cell, the levels of GPI-PLD activities and its mRNA from pcDNA3.1(+)/GPI-PLD/HepG2 were increased with almost 2 to 5 times,respectively. The GPI anchored PLAP and CEA released into the medium by GPI-PLD, and the rate of CDC killing on the cells were significantly increased. However, the proliferative capacity was obviously decreased, and the typical apoptosis cells were presented in positive clones and its apoptosis rates were increased significantly. CONCLUSION The stable cell line with overexpression of GPI-PLD has been constructed. The overexpression of GPI-PLD in these cells increases the sensitivity of these cells to CDC killing and impairs the proliferative capacity of cells, and promotes the apoptosis.
Apoptosis ; genetics ; Carcinoma, Hepatocellular ; genetics ; pathology ; Complement Activation ; genetics ; Cytotoxicity, Immunologic ; genetics ; Eukaryotic Cells ; metabolism ; Genetic Vectors ; genetics ; metabolism ; Humans ; Liver Neoplasms ; genetics ; pathology ; Phospholipase D ; biosynthesis ; genetics ; RNA, Messenger ; biosynthesis ; genetics ; Transfection ; Tumor Cells, Cultured ; Up-Regulation

Growth factor-stimulated phospholipase D (PLD) catalyzes the hydrolysis of phosphatidylcholine (PC), generating phosphatidic acid (PA) which may act as a second messenger during cell proliferation and survival. Therefore, PLD is believed to play an important role in tumorigenesis. In this study, a potential mechanism for PLD-mediated tumorigenesis was explored. Ectopic expression of PLD1 or PLD2 in human glioma U87 cells increased the expression of hypoxia-inducible factor-1alpha (HIF-1alpha) protein. PLD-induced HIF-1 activation led to the secretion of vascular endothelial growth factor (VEGF), a HIF-1 target gene involved in tumorigenesis. PLD induction of HIF-1alpha was significantly attenuated by 1-butanol which blocks PA production by PLD, and PA per se was able to elevate HIF-1alpha protein level. Inhibition of mTOR, a PA-responsive kinase, reduced the levels of HIF-1alpha and VEGF in PLD-overexpressed cells. Epidermal growth factor activated PLD and increased the levels of HIF-1alpha and VEGF in U87 cells. A specific PLD inhibitor abolished expression of HIF-1alpha and secretion of VEGF. PLD may utilize HIF-1-VEGF pathway for PLD-mediated tumor cell proliferation and survival.
Cell Line, Tumor ; Epidermal Growth Factor/metabolism ; Gene Expression Regulation, Neoplastic ; Glioma/genetics/*metabolism ; Humans ; Hypoxia-Inducible Factor 1, alpha Subunit/genetics/metabolism ; Phosphatidic Acids/*metabolism ; Phospholipase D/genetics/*metabolism ; *Signal Transduction ; Transfection ; Vascular Endothelial Growth Factor A/*metabolism

Phospholipase Ds (PLDs) exist in many plants. PLDs catalyse the hydrolysis of phospholipids (e.g. phosphatidylcholine) in cell membrane into phosphatidic acid (PA) and polar free heads (e.g. choline). Two PLD members from rice, OsPLD3 and OsPLD4, were studied by reverse genetics approaches. The results showed that the promoters of OsPLD3 and OsPLD4 could drive the expression of the reporter gene in various tissues of the rice flower organs at different levels. The expression of both genes was induced by wounding and methyl jasmonate (MeJA), but with different intensity at different time intervals. No prominent phenotypes were observed by RNA interference with the gene-specific artificial miRNAs or over-expression of the target genes in rice plants, implying the functional redundancy among different members of the rice PLD family.
Acetates ; pharmacology ; Base Sequence ; Cyclopentanes ; pharmacology ; Flowers ; genetics ; metabolism ; Genes, Plant ; genetics ; Genes, Reporter ; genetics ; Molecular Sequence Data ; Oryza ; enzymology ; genetics ; Oxylipins ; pharmacology ; Phospholipase D ; genetics ; metabolism ; Promoter Regions, Genetic ; genetics

The pathogenesis and pathophysiology of Acanthamoeba infections remain incompletely understood. Phos-pholipases are known to cleave phospholipids, suggesting their possible involvement in the host cell plasma membrane disruption leading to host cell penetration and lysis. The aims of the present study were to determine phospholipase activities in Acanthamoeba and to determine their roles in the pathogenesis of Acanthamoeba. Using an encephalitis isolate (T1 genotype), a keratitis isolate (T4 genotype), and an environmental isolate (T7 genotype), we demonstrated that Acanthamoeba exhibited phospholipase A2 (PLA2) and phospholipase D (PLD) activities in a spectrophotometry-based assay. Interestingly, the encephalitis isolates of Acanthamoeba exhibited higher phospholipase activities as compared with the keratitis isolates, but the environmental isolates exhibited the highest phospholipase activities. Moreover, Acanthamoeba isolates exhibited higher PLD activities compared with the PLA2. Acanthamoeba exhibited optimal phospholipase activities at 37degrees C and at neutral pH indicating their physiological relevance. The functional role of phospholipases was determined by in vitro assays using human brain microvascular endothelial cells (HBMEC), which constitute the blood-brain barrier. We observed that a PLD-specific inhibitor, i.e., compound 48/80, partially inhibited Acanthamoeba encephalitis isolate cytotoxicity of the host cells, while PLA2-specific inhibitor, i.e., cytidine 5'-diphosphocholine, had no effect on parasite-mediated HBMEC cytotoxicity. Overall, the T7 exhibited higher phospholipase activities as compared to the T4. In contract, the T7 exhibited minimal binding to, or cytotoxicity of, HBMEC.
Acanthamoeba/*enzymology/genetics/*isolation & purification/physiology ; Cell Adhesion ; Cells, Cultured ; Endothelial Cells/parasitology ; Humans ; Keratitis/*parasitology ; Phospholipase D/genetics/*metabolism ; Phospholipases A2/genetics/*metabolism ; Protozoan Proteins/genetics/*metabolism ; Soil/*parasitology

This study was purposed to investigate the expression and significance of glycosylphosphatidylinositol-specific phospholipase D (GPI-PLD) in bone marrow mononuclear cells (BMMNC) isolated from patients with acute myeloid leukemia (AML), GPI-PLD activity in BMMNC isolated from 78 patients with AML and 15 normal persons was measured by using GPI-anchored placental alkaline phosphatase (PLAP) as a substrate and Triton X-114 phase partitioning. The GPI-PLD mRNA expression was measured by semi-quantitive reverse transcription-polymerase chain reaction (RT-PCR). The results showed that the mRNA expression level and activity of GPI-PLD in BMMNC from de novo AML patients were 1.86 +/- 0.32 and 46.96 +/- 7.15% respectively; the mRNA expression level and activity of GPI-PLD in BMMNC from completely remission and refractory or relapsed patients were 1.26 +/- 0.29, 33.36 +/- 5.13%and 1.79 +/- 0.19, 44.31 +/- 7.22%, while those in BMMNC from normal controls were 1.27 +/- 0.23, 35.38 +/- 5.15% respectively. The mRNA expression level and activity of GPI-PLD in de novo and refractory or relapsed patients were obviously higher than those in normal controls with significant difference (p < 0.01), while the comparison between remitted patients and normal controls showed no statistical difference (p > 0.05). It is concluded that the expression level of GPI-PLD mRNA coincides with GPI-PLD activity. The mRNA expression and activity of GPI-PLD in de novo and refractory or relapsed patients are obviously higher than those in normal controls. It is worthy of further exploring whether GPI-PLD plays a certain role in process of leukemia pathogenesis.
Adolescent ; Adult ; Bone Marrow Cells ; cytology ; metabolism ; Case-Control Studies ; Child ; Female ; Humans ; Leukemia, Myeloid, Acute ; metabolism ; pathology ; Male ; Middle Aged ; Phospholipase D ; genetics ; metabolism ; RNA, Messenger ; genetics ; Young Adult

Ceramide, a product of sphingomyelin hydrolysis, is now recognized as an intracellular lipid messenger, which mediates the effects of extracellular agents on cellular growth, differentiation and apoptosis. Recently, ceramide has been implicated in the regulation of phospholipase D (PLD). In this study, we examined the effects of ceramide on the activity and mRNA level of PLD during apoptotic process in FRTL-5 thyroid cells. C2-ceramide (N-acetyl sphingosine) induced apoptosis in FRTL-5 thyroid cells. Fluorescent staining showed that ceramide induced the typical features of apoptosis including condensed or fragmented nuclei. DNA fragmentation was also observed by agarose gel electrophoresis. Flow cytometric cell cycle analysis showed more clearly that ceramide induced apoptotic cell death in FRTL-5 thyroid cells. The treatment of FRTL-5 thyroid cells with thyroid-stimulating hormone (TSH) resulted in an increased PLD activity in a dose- and time-dependent manner. However, the TSH-induced increase in PLD activity was down-regulated within 2 h after ceramide treatment. Furthermore, the levels of PLD mRNA were found to be decreased throughout apoptotic process as inferred by reverse transcription-polymerase chain reaction. However, the decreases in PLD mRNA levels were not correlated with those in PLD activities after ceramide treatment. Taken together, these data suggest that ceramide inhibits the PLD activity in an early apoptotic phase and down-regulation of the levels of PLD mRNA may be implicated in apoptotic process in FRTL-5 thyroid cells.
Animal ; Apoptosis/drug effects* ; Cells, Cultured ; DNA Fragmentation ; Enzyme Activation/drug effects ; Flow Cytometry ; Gene Expression Regulation, Enzymologic/drug effects ; Phospholipase D/metabolism* ; Phospholipase D/genetics ; RNA, Messenger/genetics ; Rats ; Rats, Inbred Strains ; Sphingosine/pharmacology ; Sphingosine/analogs & derivatives* ; Thyroid Gland/enzymology ; Thyroid Gland/drug effects* ; Thyrotropin/pharmacology

In spite of the importance of phospholipase D (PLD) in cell proliferation and tumorigenesis, little is known about the molecules regulating PLD expression. Thus, identification of small molecules inhibiting PLD expression would be an important advance for PLD-mediated physiology. We examined one such here, denoted "Triptolide", which was identified in a chemical screen for inhibitors of PLD expression using cell assay system based on measurement of PLD promoter activity. Triptolide significantly suppressed the expression of both PLD1 and PLD2 with sub-microM potency in MDA-MB-231 breast cancer cells as analyzed by promoter assay and RT-PCR. Moreover, triptolide abolished the protein level of PLD in a time and dose-dependent manner. Triptolide-induced PLD1 downregulation was also observed in all the cancer cells examined, suggesting a general phenomenon detected in various cancer cells. Decrease of PLD expression by triptolide suppressed both basal and PMA-induced PLD activity. In addition, triptolide inhibited activation of NFkappaB which increased PLD1 expression. Ultimately, downregulation of PLD by triptolide inhibited proliferation of breast cancer cells. Taken together, we demonstrate that triptolide suppresses the expression of PLD via inhibition of NFkappaB activation and then decreases cell proliferation.
Antineoplastic Agents, Alkylating/*pharmacology ; Breast Neoplasms/drug therapy/enzymology ; Cell Line, Tumor ; Cell Proliferation/drug effects ; Diterpenes/*pharmacology ; Epoxy Compounds/pharmacology ; Female ; Gene Expression Regulation, Neoplastic/*drug effects ; Humans ; NF-kappa B/genetics/metabolism ; Phenanthrenes/*pharmacology ; Phospholipase D/*genetics/metabolism

Autophagy is a conserved lysosomal self-digestion process used for the breakdown of long-lived proteins and damaged organelles, and it is associated with a number of pathological processes, including cancer. Phospholipase D (PLD) isozymes are dysregulated in various cancers. Recently, we reported that PLD1 is a new regulator of autophagy and is a potential target for cancer therapy. Here, we investigated whether PLD2 is involved in the regulation of autophagy. A PLD2-specific inhibitor and siRNA directed against PLD2 were used to treat HT29 and HCT116 colorectal cancer cells, and both inhibition and genetic knockdown of PLD2 in these cells significantly induced autophagy, as demonstrated by the visualization of light chain 3 (LC3) puncta and autophagic vacuoles as well as by determining the LC3-II protein level. Furthermore, PLD2 inhibition promoted autophagic flux via the canonical Atg5-, Atg7- and AMPK-Ulk1-mediated pathways. Taken together, these results suggest that PLD2 might have a role in autophagy and that its inhibition might provide a new therapeutic basis for targeting autophagy.
Autophagy/*drug effects ; Cell Line, Tumor ; Colorectal Neoplasms/enzymology/*genetics/*therapy ; Genetic Therapy ; HCT116 Cells ; Humans ; Phospholipase D/*antagonists & inhibitors/*genetics/metabolism ; Quinolines/*pharmacology ; *RNA Interference ; RNA, Small Interfering/genetics/pharmacology ; Signal Transduction/drug effects ; Spiro Compounds/*pharmacology

Endocytosis is differentially regulated by hypoxia-inducible factor-1alpha (HIF-1alpha) and phospholipase D (PLD). However, the relationship between HIF-1alpha and PLD in endocytosis is unknown. HIF-1alpha is degraded through the prolyl hydroxylase (PHD)/von Hippel-Lindau (VHL) ubiquitination pathway in an oxygen-dependent manner. Here, we show that PLD1 recovers the decrease in epidermal growth factor receptor (EGFR) endocytosis induced by HIF-1alpha independent of lipase activity via the Rab5-mediated endosome fusion pathway. EGF-induced interaction of PLD1 with HIF-1alpha, PHD and VHL may contribute to EGFR endocytosis. The pleckstrin homology domain (PH) of PLD1 itself promotes degradation of HIF-1alpha, then accelerates EGFR endocytosis via upregulation of rabaptin-5 and suppresses tumor progression. These findings reveal a novel role of the PLD1-PH domain as a positive regulator of endocytosis and provide a link between PLD1 and HIF-1alpha in the EGFR endocytosis pathway.
Animals ; Blood Proteins/chemistry/*metabolism ; Endocytosis ; Female ; HEK293 Cells ; HT29 Cells ; Humans ; Hypoxia-Inducible Factor 1, alpha Subunit/metabolism ; Mice, Nude ; Neoplasms/genetics/metabolism/pathology ; Phospholipase D/chemistry/*metabolism ; Phosphoproteins/chemistry/*metabolism ; Protein Structure, Tertiary ; Receptor, Epidermal Growth Factor/*metabolism ; Signal Transduction ; *Up-Regulation ; Vesicular Transport Proteins/*genetics/metabolism ; rab5 GTP-Binding Proteins/*metabolism

Rebamipide a gastroprotective drug, is clinically used for the treatment of gastric ulcers and gastritis, but its actions on gastric cancer are not clearly understood. Phospholipase D (PLD) is overexpressed in various types of cancer tissues and has been implicated as a critical factor in inflammation and carcinogenesis. However, whether rebamipide is involved in the regulation of PLD in gastric cancer cells is not known. In this study, we showed that rebamipide significantly suppressed the expression of both PLD1 and PLD2 at a transcriptional level in AGS and MKN-1 gastric cancer cells. Downregulation of PLD expression by rebamipide inhibited its enzymatic activity. In addition, rebamipide inhibited the transactivation of nuclear factor kappa B (NFkappaB), which increased PLD1 expression. Rebamipide or PLD knockdown significantly suppressed the expression of genes involved in inflammation and proliferation and inhibited the proliferation of gastric cancer cells. In conclusion, rebamipide-induced downregulation of PLD may contribute to the inhibition of inflammation and proliferation in gastric cancer.
Alanine/*analogs & derivatives/pharmacology ; Cell Line, Tumor ; Cell Proliferation/drug effects ; Down-Regulation/*drug effects ; Gene Expression Regulation, Neoplastic/*drug effects ; Humans ; Inflammation/*enzymology/genetics/pathology ; Isoenzymes/genetics/metabolism ; NF-kappa B/metabolism ; Phospholipase D/*genetics/metabolism ; Promoter Regions, Genetic/genetics ; Quinolones/*pharmacology ; Stomach Neoplasms/*enzymology/genetics/*pathology ; Transcription, Genetic/drug effects