Induction of lymphocyte apoptosis by tumor cell secretion of FasL-bearing microvesicles.
The hypothesis that FasL expression by tumor cells may impair the in vivo efficacy of antitumor immune responses, through a mechanism known as 'Fas tumor counterattack,' has been recently questioned, becoming the object of an intense debate based on conflicting results. Here we definitely show that FasL is indeed detectable in the cytoplasm of melanoma cells and its expression is confined to multivesicular bodies that contain melanosomes. In these structures FasL colocalizes with both melanosomal (i.e., gp100) and lysosomal (i.e., CD63) antigens. Isolated melanosomes express FasL, as detected by Western blot and cytofluorimetry, and they can exert Fas-mediated apoptosis in Jurkat cells. We additionally show that melanosome-containing multivesicular bodies degranulate extracellularly and release FasL-bearing microvesicles, that coexpress both gp100 and CD63 and retain their functional activity in triggering Fas-dependent apoptosis of lymphoid cells. Hence our data provide evidence for a novel mechanism potentially operating in Fas tumor counterattack through the secretion of subcellular particles expressing functional FasL. Such vesicles may form a sort of front line hindering lymphocytes and other immunocompetent cells from entering neoplastic lesions and exert their antitumor activity.
Andreola
Giovanna
G
Unit of Immunotherapy of Human Tumors, Istituto Nazionale dei Tumori, Milan 20133, Italy.
Rivoltini
Licia
L
Castelli
Chiara
C
Huber
Veronica
V
Perego
Paola
P
Deho
Paola
P
Squarcina
Paola
P
Accornero
Paola
P
Lozupone
Francesco
F
Lugini
Luana
L
Stringaro
Annarita
A
Molinari
Agnese
A
Arancia
Giuseppe
G
Gentile
Massimo
M
Parmiani
Giorgio
G
Fais
Stefano
S
D017209:Apoptosis; D015153:Blotting, Western; D017077:Culture Media, Conditioned; D005089:Exocytosis; D053222:Fas Ligand Protein; D006801:Humans; D007150:Immunohistochemistry; D007425:Intracellular Membranes / Q000378:metabolism; D019169:Jurkat Cells; D008214:Lymphocytes / Q000166:cytology* / Q000276:immunology; D008545:Melanoma / Q000276:immunology / Q000378:metabolism* / Q000473:pathology*; D020460:Melanosomes / Q000378:metabolism*; D008562:Membrane Glycoproteins / Q000276:immunology / Q000378:metabolism*; D008854:Microscopy, Electron; D022142:Secretory Vesicles / Q000276:immunology / Q000378:metabolism*; D014407:Tumor Cells, Cultured
D017077:Culture Media, Conditioned; C505661:FASLG protein, human; D053222:Fas Ligand Protein; D008562:Membrane Glycoproteins