Proinflammatory secreted phospholipase A2 type IIA (sPLA-IIA) induces integrin activation through direct binding to a newly identified binding site (site 2) in integrins αvβ3, α4β1, and α5β1.
Integrins are activated by signaling from inside the cell (inside-out signaling) through global conformational changes of integrins. We recently discovered that fractalkine activates integrins in the absence of CX3CR1 through the direct binding of fractalkine to a ligand-binding site in the integrin headpiece (site 2) that is distinct from the classical RGD-binding site (site 1). We propose that fractalkine binding to the newly identified site 2 induces activation of site 1 though conformational changes (in an allosteric mechanism). We reasoned that site 2-mediated activation of integrins is not limited to fractalkine. Human secreted phospholipase A2 type IIA (sPLA2-IIA), a proinflammatory protein, binds to integrins αvβ3 and α4β1 (site 1), and this interaction initiates a signaling pathway that leads to cell proliferation and inflammation. Human sPLA2-IIA does not bind to M-type receptor very well. Here we describe that sPLA2-IIA directly activated purified soluble integrin αvβ3 and transmembrane αvβ3 on the cell surface. This activation did not require catalytic activity or M-type receptor. Docking simulation predicted that sPLA2-IIA binds to site 2 in the closed-headpiece of αvβ3. A peptide from site 2 of integrin β1 specifically bound to sPLA2-IIA and suppressed sPLA2-IIA-induced integrin activation. This suggests that sPLA2-IIA activates αvβ3 through binding to site 2. sPLA2-IIA also activated integrins α4β1 and α5β1 in a site 2-mediated manner. We recently identified small compounds that bind to sPLA2-IIA and suppress integrin-sPLA2-IIA interaction (e.g. compound 21 (Cmpd21)). Cmpd21 effectively suppressed sPLA2-IIA-induced integrin activation. These results define a novel mechanism of proinflammatory action of sPLA2-IIA through integrin activation.
From the Departments of Dermatology and Biochemistry and Molecular Medicine, UC Davis School of Medicine, Sacramento, California 95817, Department of Clinical Immunology and Rheumatology, The Tazuke-Kofukai Medical Research Institute, Kitano Hospital, Osaka 530-8480, Japan.
Masaaki
M
Fujita
From the Departments of Dermatology and.
Kan
K
Zhu
Department of Clinical Immunology and Rheumatology, The Tazuke-Kofukai Medical Research Institute, Kitano Hospital, Osaka 530-8480, Japan.
Chitose K
CK
Fujita
From the Departments of Dermatology and.
Min
M
Zhao
Biochemistry and Molecular Medicine, UC Davis School of Medicine, Sacramento, California 95817.
Kit S
KS
Lam
Department of Chemistry, UC Davis, Davis, California 95616, and.
Mark J
MJ
Kurth
From the Departments of Dermatology and Biochemistry and Molecular Medicine, UC Davis School of Medicine, Sacramento, California 95817.
Yoko K
YK
Takada
From the Departments of Dermatology and Biochemistry and Molecular Medicine, UC Davis School of Medicine, Sacramento, California 95817, ytakada@ucdavis.edu.
Yoshikazu
Y
Takada
D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D016466:CHO Cells; D003412:Cricetulus; D004791:Enzyme Inhibitors / Q000737:chemistry / Q000494:pharmacology; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism; D005786:Gene Expression Regulation; D054501:Group II Phospholipases A2 / Q000037:antagonists & inhibitors / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D006801:Humans; D007249:Inflammation / Q000235:genetics / Q000378:metabolism / Q000473:pathology; D039041:Integrin alpha4beta1 / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D039302:Integrin alphaVbeta3 / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D020014:K562 Cells; D008958:Models, Molecular; D062105:Molecular Docking Simulation; D008969:Molecular Sequence Data; D010455:Peptides / Q000138:chemical synthesis / Q000737:chemistry; D011485:Protein Binding; D019030:Receptors, Vitronectin / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D016415:Sequence Alignment; D015398:Signal Transduction
D004791:Enzyme Inhibitors; D039041:Integrin alpha4beta1; D039302:Integrin alphaVbeta3; D010455:Peptides; D019030:Receptors, Vitronectin; D011994:Recombinant Proteins; C094340:integrin alphavbeta1; D054501:Group II Phospholipases A2
Adhesion; Allosteric Regulation; Docking Simulation; Fractalkine; Inflammation; Integrin; Integrin Activation; Peptides; Secreted Phospholipase A2 Type IIA