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Recent studies have demonstrated that arachidonic acid (AA) may serve as an important signal that blocks cell proliferation of certain neoplastic cells. The current study was conducted to determine whether disruption of AA homeostasis influences breast cancer cell proliferation and death. Initial experiments revealed that inhibition of AA remodeling through membrane phospholipids by inhibitors of the enzyme, coenzyme A-independent transacylase (CoA-IT), attenuates the proliferation of the estrogen receptor-negative, MDA-MB-231, and estrogen receptor-positive, MCF-7 breast cancer cell lines. This growth inhibition was accompanied by a marked accumulation of AA in both free fatty acid and triglyceride forms, a marker of intracellular AA stress within mammalian cells. Cell cycle synchronization experiments revealed that the CoA-IT inhibitor, SB-98625, blocked MDA-MB-231 cell replication in early to mid G1 phase. Time-lapse video microscopy, used to observe the changes in cell morphology associated with apoptosis, indicated that SB-98625 treatment induced early rounding and occasional blebbing but not late apoptotic events, blistering, and lysis. The cyclooxygenase inhibitors, NS-398 and indomethacin, were found to be less potent blockers of cell proliferation and poor inducers of cellular AA accumulation than CoA-IT inhibitors in these breast cancer cell lines. Finally, AA provided exogenously blocked the proliferation of MCF-7 cells, and this effect could be attenuated in MCF-7 cells overexpressing the glutathione peroxidase gene, GSHPx-1. Taken together, these experiments suggest that disruption of AA remodeling in a manner that increases intracellular AA may represent a novel therapeutic strategy to reduce cancer cell proliferation and that an oxidized AA metabolite is likely to mediate this effect.

1-O-Alkyl-2-O-acetyl-sn-glycero-3-phosphocholine (AAGPC) triggered the release of [3H]arachidonate but not [14C]stearate from cellular phospholipids in cytochalasin B-treated rabbit polymorphonuclear leukocytes. Concentrations of AAGPC up to 20 nM caused a dose-dependent release and subsequent metabolism of the released [3H]arachidonic acid. Most of the release of the [3H]arachidonate had taken place within the first 2 min of stimulation. Phosphatidylinositol and phosphatidylcholine served as the sources of [3H]arachidonate with about 50% of the label coming from each pool. Challenge of cytochalasin B-treated polymorphonuclear leukocytes with AAPGC led to the production of [3H]hydroxyeicosatetraenoic acids and [3H]dihydroxyeicosatetraenoic acids. No significant production of [3H]prostaglandins or [3H]thromboxanes was detected. AAGPC also caused a dose-dependent degranulation of cytochalasin B-treated rabbit polymorphonuclear leukocytes as shown by the release of beta-glucuronidase and lysozyme. Both the AAGPC-stimulated production of arachidonate metabolites and the degranulation response were blocked by eicosatetraynoic acid and non-dihydroguaiaretic acid at similar inhibitor concentrations. These findings suggest the bioactions of AAGPC on polymorphonuclear leukocytes may be mediated by the release of arachidonic acid and the production of mono- and dihydroxyeicosatetraenoic acids.

Dual radiolabel incorporation of [3H]arachidonic acid and [14C]palmitate or [14C]stearate by human neutrophils was employed to study both the release and metabolism of arachidonic acid. Results indicate the involvement of a phospholipase A2 mechanism causing [3H]arachidonate release from membrane phospholipid. Phosphatidylinositol and phosphatidylcholine were the sources of [3H]arachidonate; about twice as much radiolabeled phosphatidylinositol was degraded as phosphatidylcholine. Challenge of neutrophils with opsonized zymosan and calcium ionophores caused the release of [3H]arachidonate; however, ionophores but not opsonized zymosan led to the production of [3H]hydroxyicosatetraenoic acid and [3H]dihydroxyicosatetraenoic acid. These products were preferentially released by neutrophils into the extracellular milieu in contrast with free [3H]arachidonate which remained cell associated. One-third of the [3H]hydroxyicosatetraenoic acid but not [3H]dihydroxyicosatetraenoic acid was reincorporated into cellular lipid, primarily phospholipid. No significant production of [3H]prostaglandin or [3H]thromboxane was detected. In contrast to zymosan and ionophore, phorbol myristate acetate, another potent stimulant of neutrophil oxidative metabolism and degranulation, did not release [3H]arachidonate.

1-O-Alkyl-2-O-acetyl-sn-glycero-3-phosphocholine (AAGPC) triggered the release of [3H]arachidonate but not [14C]stearate from cellular phospholipids in cytochalasin B-treated rabbit polymorphonuclear leukocytes. Concentrations of AAGPC up to 20 nM caused a dose-dependent release and subsequent metabolism of the released [3H]arachidonic acid. Most of the release of the [3H]arachidonate had taken place within the first 2 min of stimulation. Phosphatidylinositol and phosphatidylcholine served as the sources of [3H]arachidonate with about 50% of the label coming from each pool. Challenge of cytochalasin B-treated polymorphonuclear leukocytes with AAPGC led to the production of [3H]hydroxyeicosatetraenoic acids and [3H]dihydroxyeicosatetraenoic acids. No significant production of [3H]prostaglandins or [3H]thromboxanes was detected. AAGPC also caused a dose-dependent degranulation of cytochalasin B-treated rabbit polymorphonuclear leukocytes as shown by the release of beta-glucuronidase and lysozyme. Both the AAGPC-stimulated production of arachidonate metabolites and the degranulation response were blocked by eicosatetraynoic acid and non-dihydroguaiaretic acid at similar inhibitor concentrations. These findings suggest the bioactions of AAGPC on polymorphonuclear leukocytes may be mediated by the release of arachidonic acid and the production of mono- and dihydroxyeicosatetraenoic acids.

Dual radiolabel incorporation of [3H]arachidonic acid and [14C]palmitate or [14C]stearate by human neutrophils was employed to study both the release and metabolism of arachidonic acid. Results indicate the involvement of a phospholipase A2 mechanism causing [3H]arachidonate release from membrane phospholipid. Phosphatidylinositol and phosphatidylcholine were the sources of [3H]arachidonate; about twice as much radiolabeled phosphatidylinositol was degraded as phosphatidylcholine. Challenge of neutrophils with opsonized zymosan and calcium ionophores caused the release of [3H]arachidonate; however, ionophores but not opsonized zymosan led to the production of [3H]hydroxyicosatetraenoic acid and [3H]dihydroxyicosatetraenoic acid. These products were preferentially released by neutrophils into the extracellular milieu in contrast with free [3H]arachidonate which remained cell associated. One-third of the [3H]hydroxyicosatetraenoic acid but not [3H]dihydroxyicosatetraenoic acid was reincorporated into cellular lipid, primarily phospholipid. No significant production of [3H]prostaglandin or [3H]thromboxane was detected. In contrast to zymosan and ionophore, phorbol myristate acetate, another potent stimulant of neutrophil oxidative metabolism and degranulation, did not release [3H]arachidonate.

The purpose of this investigation was to determine whether cells transformed by herpes simplex virus type 2 (HSV-2) can be stimulated to synthesize prostaglandins (PG). Stimulation was determined by measuring the release of PG into overlay fluids from cell monolayers prelabeled with [3H]arachidonic acid. Results showed that Ca2+ ionophore A-23187 markedly stimulated arachidonic acid release starting 30 min after treatment of HSV-2-transformed and nontransformed rat embryo fibroblast cells. However, only HSV-2-transformed cells were stimulated in production of PG. HSV-2-transformed, nontumorigenic, rat embryo fibroblast, line G, clone 2.0 cells synthesize nearly equal amounts of prostaglandin E2 (PGE2) and prostaglandin F2 alpha, while tumor (rat fibrosarcoma) cells synthesize primarily PGE2. Stimulation of PGE2 synthesis by Ca2+ ionophore A-23187 or 12-O-tetradecanoyl-phorbol-13-acetate decreased as rat fibrosarcoma cells were serially passaged in tissue culture. At low passage of parental rat fibrosarcoma cells, four distinct morphological clonal cell lines were isolated, which varied markedly in their capacity to be stimulated in PG synthesis by 12-O-tetradecanoyl-phorbol-13-acetate. There was correlation between the capacity of clone 1 cells to be stimulated in PGE2 synthesis by serum alone and capacity of the tumors produced by the clone 1 cells to metastasize to the lungs of syngeneic tumor-bearing rats. In summary, cell transformation by HSV-2 appears to be essential for stimulation of PG synthesis in cells. The capacity to be stimulated in arachidonic acid metabolism and PG synthesis may be important in the process of carcinogenesis by a putative human cancer virus.