Antiphospholipid antibodies from patients with the antiphospholipid syndrome induce monocyte tissue factor expression through the simultaneous activation of NF-kappaB/Rel proteins via the p38 mitogen-activated protein kinase pathway, and of the MEK-1/ERK pathway.
OBJECTIVE
Antiphospholipid syndrome (APS) is characterized by thrombosis and the presence of antiphospholipid antibodies (aPL). In patients with primary APS, expression of tissue factor (TF) on the surface of monocytes is increased, which may contribute to thrombosis in these patients. However, the intracellular mechanisms involved in aPL-mediated up-regulation of TF on monocytic cells are not understood. This study was undertaken to investigate the intracellular signals induced by aPL that mediate TF activation in monocytes from APS patients.


METHODS
We analyzed, both in vivo and in vitro, aPL interactions with proteins that have signaling functions, including mitogen-activated protein kinases (MAP kinases) and NF-kappaB/Rel proteins.


RESULTS
In vivo studies demonstrated significantly higher levels of both TF messenger RNA and TF protein in monocytes from APS patients compared with controls. At the molecular level, increased proteolysis of IkappaBalpha and activation of NF-kappaB were observed. Constitutive activation of both p38 and ERK-1 MAP kinases was also found. Treatment of normal monocytes with aPL activated ERK-1 and p38 MAP kinases, as well as the IkappaB/NF-kappaB pathway, in a dose-dependent manner. NF-kappaB activation and IkappaBalpha degradation induced by aPL were inhibited by the NF-kappaB inhibitor SN50 and the p38 MAP kinase inhibitor SB203580, thus suggesting crosstalk between these pathways. However, the MEK-1/ERK inhibitor PD98059 did not affect aPL-induced NF-kappaB binding activity. TF expression induced by aPL was significantly inhibited by combined treatment with the 3 inhibitors.


CONCLUSIONS
Our results suggest that aPL induces TF expression in monocytes from APS patients by activating, simultaneously and independently, the phosphorylation of MEK-1/ERK proteins, and the p38 MAP kinase-dependent nuclear translocation and activation of NF-kappaB/Rel proteins.
López-Pedrera
Chary
C
Unidad de Investigación, Reina Sofía University Hospital, Avda. Menéndez Pidal s/n, E-14004 Cordoba, Spain. rosario.lopez.exts@juntadealdalucia.es
Buendía
Paula
P
Cuadrado
Maria José
MJ
Siendones
Emilio
E
Aguirre
Maria Angeles
MA
Barbarroja
Nuria
N
Montiel-Duarte
Cristina
C
Torres
Antonio
A
Khamashta
Munther
M
Velasco
Francisco
F
D000328:Adult; D017152:Antibodies, Antiphospholipid / Q000502:physiology*; D016736:Antiphospholipid Syndrome / Q000276:immunology*; D005260:Female; D006801:Humans; D048369:MAP Kinase Kinase 1 / Q000502:physiology*; D048728:MAP Kinase Kinase Kinase 1 / Q000502:physiology*; D008297:Male; D008875:Middle Aged; D009000:Monocytes / Q000276:immunology*; D016328:NF-kappa B / Q000502:physiology*; D010766:Phosphorylation; D021381:Protein Transport; D013925:Thromboplastin / Q000096:biosynthesis*; D048051:p38 Mitogen-Activated Protein Kinases / Q000502:physiology*
D017152:Antibodies, Antiphospholipid; D016328:NF-kappa B; D013925:Thromboplastin; D048051:p38 Mitogen-Activated Protein Kinases; D048728:MAP Kinase Kinase Kinase 1; D048369:MAP Kinase Kinase 1