Interleukin-4 induces human hepatocyte apoptosis through a Fas-independent pathway.
IL-4 is overexpressed in liver grafts during severe recurrent hepatitis C and rejection. Hepatocyte apoptosis is involved in both these phenomena. We therefore examined the proapoptotic effect of IL-4 on HepG2 cells and human hepatocytes in vitro, together with the underlying mechanisms. We first measured IL-4 receptor expression, STAT6 activation by IL-4, and STAT6 inhibition by an anti-IL-4 antibody or by STAT6 siRNA transfection. We then focused on the pathways involved in IL-4-mediated apoptosis and the role of STAT6 activation in apoptosis initiation. The IL-4 receptor was expressed on both cell types, and STAT6 was activated by IL-4. Both anti-IL-4 and STAT-6 siRNA inhibited this activation. IL-4 induced apoptosis of both HepG2 cells (P=0.008 vs. untreated control) and human hepatocytes (P<0.001 vs. untreated control). IL-4 reduced the mitochondrial membrane potential, activated Bid and Bax, and augmented caspase 3, 8, and 9 activity. STAT6 blockade inhibited IL-4-induced apoptosis. Expression of Fas and Fas ligand was unaffected when HepG2 cells and hepatocytes were cultured with IL-4, and Fas/FasL pathway blockade failed to inhibit IL-4-induced apoptosis. These results show that IL-4 induces apoptosis of human hepatocytes through IL-4 receptor binding, STAT6 activation, decreased mitochondrial membrane potential, and increased caspase activation, independently of the Fas pathway. IL-4 might thus contribute to the progression of severe liver graft damage.
Aoudjehane
Lynda
L
Laboratoire de Biologie Cellulaire, UPRES 1833, Université Paris 5, France.
Podevin
Philippe
P
Scatton
Olivier
O
Jaffray
Patrick
P
Dusanter-Fourt
Isabelle
I
Feldmann
Gérard
G
Massault
Pierre-Philippe
PP
Grira
Lilia
L
Bringuier
Annie
A
Dousset
Bertrand
B
Chouzenoux
Sandrine
S
Soubrane
Olivier
O
Calmus
Yvon
Y
Conti
Filomena
F
D017209:Apoptosis / Q000187:drug effects*; D001483:Base Sequence; D020169:Caspases / Q000378:metabolism; D045744:Cell Line, Tumor; D017931:DNA Primers; D024202:Electrophoretic Mobility Shift Assay; D005434:Flow Cytometry; D022781:Hepatocytes / Q000166:cytology / Q000187:drug effects*; D006801:Humans; D007150:Immunohistochemistry; D020287:In Situ Nick-End Labeling; D015847:Interleukin-4 / Q000235:genetics / Q000494:pharmacology*; D012333:RNA, Messenger / Q000235:genetics; D019948:Receptors, Interleukin-4 / Q000235:genetics; D020133:Reverse Transcriptase Polymerase Chain Reaction; D050800:STAT6 Transcription Factor / Q000037:antagonists & inhibitors; D019014:fas Receptor / Q000378:metabolism*
D017931:DNA Primers; D012333:RNA, Messenger; D019948:Receptors, Interleukin-4; D050800:STAT6 Transcription Factor; D019014:fas Receptor; D015847:Interleukin-4; D020169:Caspases