Ratnoff and his coworkers recognised that factor XII (XII) stimulates cell growth
and activates mitogen-activated protein kinase. We determined the receptor(s) for
this function and the consequence of this signalling pathway. Investigations show
that the urokinase plasminogen activator receptor serves as the XII binding site on
cultured umbilical vein endothelial cells. When XII binds, it stimulates ERK1/2 and
Akt S473 phosphorylation. These events are distinct because when cell mTORC2 is absent,
XII phosphorylates ERK1/2 but not Akt S473. Zymogen XII is an equal stimulator of
signalling as XIIa or inhibitor-treated XIIa. Peptides from uPAR domain 2 block XII
binding and ERK1/2 and Akt phosphorylation. Furthermore, antibodies to the integrins
β1 and α5 block XII signalling. Likewise, inhibitors to the EGFR block XII-induced
phosphorylation events. XII stimulates cell growth and proliferation. XII induces
angiogenesis ex vivo in normal aortic sprouts and in vivo in matrigel plugs in normal mice, but not in aorta from uPAR knockout mice or matrigel
plugs placed into uPAR-deleted mice. Skin biopsies constitutively or in a wound nine
days after injury show reduced CD31 antigen expression in specimens from XII knockout
mice compared to wild-type mice. These studies indicate that XII stimulates angiogenesis,
a physiologic function independent of contact activation.
Keywords
Angiogenesis and inhibitors, contact phase, urokinase / receptor, factor XII, integrins