Activation of phosphatidylcholine cycle enzymes in human epithelial ovarian cancer cells.
Altered phosphatidylcholine (PC) metabolism in epithelial ovarian cancer (EOC) could provide choline-based imaging approaches as powerful tools to improve diagnosis and identify new therapeutic targets. The increase in the major choline-containing metabolite phosphocholine (PCho) in EOC compared with normal and nontumoral immortalized counterparts (EONT) may derive from (a) enhanced choline transport and choline kinase (ChoK)-mediated phosphorylation, (b) increased PC-specific phospholipase C (PC-plc) activity, and (c) increased intracellular choline production by PC deacylation plus glycerophosphocholine-phosphodiesterase (GPC-pd) or by phospholipase D (pld)-mediated PC catabolism followed by choline phosphorylation. Biochemical, protein, and mRNA expression analyses showed that the most relevant changes in EOC cells were (a) 12-fold to 25-fold ChoK activation, consistent with higher protein content and increased ChoKalpha (but not ChoKbeta) mRNA expression levels; and (b) 5-fold to 17-fold PC-plc activation, consistent with higher, previously reported, protein expression. PC-plc inhibition by tricyclodecan-9-yl-potassium xanthate (D609) in OVCAR3 and SKOV3 cancer cells induced a 30% to 40% reduction of PCho content and blocked cell proliferation. More limited and variable sources of PCho could derive, in some EOC cells, from 2-fold to 4-fold activation of pld or GPC-pd. Phospholipase A2 activity and isoform expression levels were lower or unchanged in EOC compared with EONT cells. Increased ChoKalpha mRNA, as well as ChoK and PC-plc protein expression, were also detected in surgical specimens isolated from patients with EOC. Overall, we showed that the elevated PCho pool detected in EOC cells primarily resulted from upregulation/activation of ChoK and PC-plc involved in PC biosynthesis and degradation, respectively.
Iorio
Egidio
E
Department of Cell Biology and Neurosciences, Section of Molecular and Cellular Imaging, Istituto Superiore di Sanità, Rome, Italy.
Ricci
Alessandro
A
Bagnoli
Marina
M
Pisanu
Maria Elena
ME
Castellano
Giancarlo
G
Di Vito
Massimo
M
Venturini
Elisa
E
Glunde
Kristine
K
Bhujwalla
Zaver M
ZM
Mezzanzanica
Delia
D
Canevari
Silvana
S
Podo
Franca
F
D002797:Choline Kinase / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism; D004789:Enzyme Activation; D004847:Epithelial Cells / Q000473:pathology; D005260:Female; D006801:Humans; D026901:Membrane Transport Proteins / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism; D010051:Ovarian Neoplasms / Q000201:enzymology* / Q000235:genetics / Q000378:metabolism / Q000473:pathology; D010713:Phosphatidylcholines / Q000096:biosynthesis*; D010739:Phospholipase D / Q000378:metabolism; D010727:Phosphoric Diester Hydrolases / Q000378:metabolism; D010738:Type C Phospholipases / Q000378:metabolism
D026901:Membrane Transport Proteins; D010713:Phosphatidylcholines; C065637:choline transporter; D002797:Choline Kinase; D010727:Phosphoric Diester Hydrolases; D010738:Type C Phospholipases; C020677:glycerophosphocholine phosphodiesterase; C105598:phosphatidylcholine-specific phospholipase C; D010739:Phospholipase D