Pro-inflammatory secretory phospholipase A2 type IIA binds to integrins alphavbeta3 and alpha4beta1 and induces proliferation of monocytic cells in an integrin-dependent manner.
Secretory phospholipase A2 group IIA (sPLA2-IIA) plays an important role in the pathogenesis of inflammatory diseases. Catalytic activity of this enzyme that generates arachidonic acid is a major target for development of anti-inflammatory agents. Independent of its catalytic activity, sPLA2-IIA induces pro-inflammatory signals in a receptor-mediated mechanism (e.g. through the M-type receptor). However, the M-type receptor is species-specific: sPLA2-IIA binds to the M-type receptor in rodents and rabbits, but not in human. Thus sPLA2-IIA receptors in human have not been established. Here we demonstrated that sPLA2-IIA bound to integrin alphavbeta3 at a high affinity (K(D)=2 x 10(-7) M). We identified amino acid residues in sPLA2-IIA (Arg-74 and Arg-100) that are critical for integrin binding using docking simulation and mutagenesis. The integrin-binding site did not include the catalytic center or the M-type receptor-binding site. sPLA2-IIA also bound to alpha4beta1. We showed that sPLA2-IIA competed with VCAM-1 for binding to alpha4beta1, and bound to a site close to those for VCAM-1 and CS-1 in the alpha4 subunit. Wild type and the catalytically inactive H47Q mutant of sPLA2-IIA induced cell proliferation and ERK1/2 activation in monocytic cells, but the integrin binding-defective R74E/R100E mutant did not. This indicates that integrin binding is required, but catalytic activity is not required, for sPLA2-IIA-induced proliferative signaling. These results suggest that integrins alphavbeta3 and alpha4beta1 may serve as receptors for sPLA2-IIA and mediate pro-inflammatory action of sPLA2-IIA, and that integrin-sPLA2-IIA interaction is a novel therapeutic target.
Saegusa
Jun
J
Department of Dermatology, University of California Davis School of Medicine, Sacramento, California 95817, USA.
Akakura
Nobuaki
N
Wu
Chun-Yi
CY
Hoogland
Case
C
Ma
Zi
Z
Lam
Kit S
KS
Liu
Fu-Tong
FT
Takada
Yoko K
YK
Takada
Yoshikazu
Y
D000818:Animals; D016466:CHO Cells; D049109:Cell Proliferation; D006224:Cricetinae; D003412:Cricetulus; D054501:Group II Phospholipases A2 / Q000737:chemistry / Q000378:metabolism*; D006801:Humans; D039041:Integrin alpha4beta1 / Q000737:chemistry*; D039302:Integrin alphaVbeta3 / Q000737:chemistry*; D020014:K562 Cells; D008954:Models, Biological; D009000:Monocytes / Q000378:metabolism*; D011485:Protein Binding; D015398:Signal Transduction; D020298:U937 Cells
D039041:Integrin alpha4beta1; D039302:Integrin alphaVbeta3; D054501:Group II Phospholipases A2; C516287:PLA2G2A protein, human