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Phosphatidylcholine-Specific Phospholipase C Activation in Epithelial Ovarian Cancer Cells

¹ Section of Molecular and Cellular Imaging, Department of Cell Biology and Neurosciences, Istituto Superiore di Sanità, Rome, Italy; ² Unit of Molecular Therapies, Department of Experimental Oncology and Laboratories, Fondazione IRCCS Istituto Nazionale dei Tumori, Milan, Italy; and ³ Department of Experimental Medicine, University of L'Aquila, L'Aquila, Italy

Requests for reprints: Franca Podo, Department of Cell Biology and Neurosciences, Istituto Superiore di Sanità, Viale Regina Elena 299, 00161 Rome, Italy. Phone: 39-06-49902686; Fax: 39-06-49387144; E-mail: franca.podo{at}iss.it or Silvana Canevari, Department of Experimental Oncology, Fondazione IRCCS Istituto Nazionale dei Tumori, Via Venezian 1, 20133 Milan, Italy. Phone: 39-02-23902567; Fax: 39-02-23903073; E-mail: silvana.canevari{at}istitutotumori.mi.it.

Key Words: ovarian cancer • choline metabolism • phospholipase C • confocal laser scanning microscopy • tumor progression

Elucidation of the mechanisms responsible for aberrant phosphatidylcholine (PC) metabolism in cancer cells may allow identification of novel biomarkers of tumor progression and design of new targeted anticancer therapies. We recently reported up-regulation of PC-specific phospholipases in epithelial ovarian cancer cells (EOC) compared with nontumoral (normal or immortalized) counterparts (EONT). In the present study, we focused, in the same cell systems, on levels, subcellular localization, and activity of PC-specific phospholipase C (PC-PLC), for which a key role in cell proliferation, differentiation, and apoptosis has been shown in several mammalian cells. A 66-kDa PC-PLC isoform, detected in nuclear and cytoplasmic compartments of both EOC and EONT cells, accumulated on the external plasma membrane of cancer cells only, where it colocalized with β1 integrin, in nonraft membrane domains. PC-PLC activity was 3-fold higher in total cell lysates and 5-fold higher in membrane-enriched fractions of EOC compared with EONT cells. Serum deprivation induced in EOC, but not in EONT, cells a 3-fold decrease in PC-PLC activity, associated with a 40% drop in S-phase fraction. The recovery of both variables to their original levels in serum-restimulated (or lysophosphatidic acid–restimulated) EOC cells was strongly delayed, for at least 24 h, in the presence of the PC-PLC inhibitor tricyclodecan-9-yl-potassium xanthate (D609). The S-phase of serum-restimulated EONT cells was not sensitive to D609. These findings warrant further investigations on the role of PC-PLC and on the effects of its inhibition on the pathways responsible for constitutive EOC cell stimulation and cell proliferation. [Cancer Res 2008;68(16):6541–9]