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Blood, 1 January 2007, Vol. 109, No. 1, pp. 203-211.
Prepublished online as a Blood First Edition Paper on September 25, 2006; DOI 10.1182/blood-2006-06-025882.
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IMMUNOBIOLOGY
IgA Fc receptor I signals apoptosis through the FcR ITAM and affects tumor growth
Yutaka Kanamaru1,3,
Houda Tamouza1,3,
Séverine Pfirsch1,3,
Delphine El Mehdi2,3,
Claudine Guérin-Marchand1,3,
Marina Pretolani2,3,
Ulrich Blank1,3, and
Renato C. Monteiro1,3,
1 Institut National de la Santé et de la Recherche Médicale (INSERM) U699, Paris, France;
2 Inserm U700, Paris, France; and
3 Université Paris 7-Denis Diderot, Faculté de Médecine, Site Xavier Bichat, Paris, France
The IgA Fc receptor (Fc RI) has dual proinflammatory and anti-inflammatory functions that are transmitted through the immunoreceptor tyrosine-based activation motifs (ITAMs) of the associated FcR subunit. Whereas the involvement of Fc RI in inflammation is well documented, little is known of its anti-inflammatory mechanisms. Here we show that monomeric targeting of Fc RI by anti-Fc RI Fab or serum IgA triggers apoptosis in human monocytes, monocytic cell lines, and Fc RI+ transfectants. However, the physiologic ligand IgA induced apoptosis only when cells were cultured in low serum conditions, indicating differences with induction of anti-inflammatory signaling. Apoptosis signaling required the FcR ITAM, as cells transfected with Fc RI or with a chimeric Fc RI-FcR responded to death-activating signals, whereas cells expressing a mutated Fc RIR209L unable to associate with FcR , or an ITAM-mutated chimeric Fc RI-FcR , did not respond. Fc RI-mediated apoptosis signals were blocked by treatment with the pan-caspase inhibitor zVAD-fmk, involved proteolysis of procaspase-3, and correlated negatively with SHP-1 concentration. Anti-Fc RI Fab treatment of nude mice injected subcutaneously with Fc RI+ mast-cell transfectants prevented tumor development and halted the growth of established tumors. These findings demonstrate that, on monomeric targeting, Fc RI functions as an FcR ITAM-dependent apoptotic module that may be fundamental for controlling inflammation and tumor growth.

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