Translocation of Fas by LPA prevents ovarian cancer cells from anti-Fas-induced apoptosis.
OBJECTIVE
Alterations in the expression of Fas have been demonstrated in various cancers as a mechanism for tumor cells to escape from immune surveillance. In this study, we observed the effect of lysophosphatidic acid (LPA) on Fas expression and function in ovarian cancer cells.


METHODS
Ovarian cancer cell lines were incubated with or without LPA and Fas cell surface presentations were detected by flow cytometry. Anti-Fas IgM was added for induction and analysis of apoptosis by flow cytometry. Cell lysis and subcellular fractions were probed for protein expression by Western blot. Cells were also stained with human anti-Fas Ab, followed with Rhodamine red-X-conjugated goat anti-mouse IgG, and immunofluorescence images were acquired on a Nikon digital camera.


RESULTS
Following treatment with LPA, ovarian cancer cells showed significant rapid reduction of Fas presentation on the cell surface. LPA protected ovarian cancer cells from anti-Fas-induced apoptosis. Cell lysis and subcellular fractionations proved that LPA treatment induced a translocation of Fas receptors, along with phosphorylated ezrin, from the membrane anchored to the actin cytoskeleton, to the cytosol. Translocation of the Fas receptor reduced Fas concentration in the membrane and may inhibit its clustering and internalization during early apoptosis induced by anti-Fas. DISC staining proved that LPA inhibited Fas receptor aggregation and caspase-8 activation at the membrane, which further inhibited caspase-3 and 7 activation in the cytosol.


CONCLUSIONS
Our studies suggest that LPA induces translocation of Fas from the cell membrane to the cytosol, which may provide a mechanism by which ovarian cancer cells evade FasL-bearing immune cells.
Meng
Yuru
Y
Department of Obstetrics and Gynecology, New York University School of Medicine, New York, NY 10016, USA.
Kang
Shijun
S
So
John
J
Reierstad
Scott
S
Fishman
David A
DA
D017209:Apoptosis / Q000187:drug effects* / Q000502:physiology; D020169:Caspases / Q000378:metabolism; D002462:Cell Membrane / Q000378:metabolism; D002465:Cell Movement / Q000502:physiology; D003600:Cytosol / Q000378:metabolism; D015536:Down-Regulation / Q000187:drug effects; D004789:Enzyme Activation; D053222:Fas Ligand Protein; D005260:Female; D006801:Humans; D007075:Immunoglobulin M / Q000276:immunology / Q000494:pharmacology; D008246:Lysophospholipids / Q000494:pharmacology*; D008562:Membrane Glycoproteins / Q000276:immunology / Q000378:metabolism / Q000502:physiology; D009361:Neoplasm Invasiveness; D010051:Ovarian Neoplasms / Q000188:drug therapy* / Q000276:immunology / Q000378:metabolism* / Q000473:pathology; D019014:fas Receptor / Q000276:immunology / Q000378:metabolism* / Q000502:physiology
C505661:FASLG protein, human; D053222:Fas Ligand Protein; C505658:Fasl protein, mouse; D007075:Immunoglobulin M; D008246:Lysophospholipids; D008562:Membrane Glycoproteins; D019014:fas Receptor; D020169:Caspases; C032881:lysophosphatidic acid