Factor XII Stimulates ERK1/2 and Akt through uPAR, Integrins, and the EGFR to Initiate Angiogenesis.

Abstract

3040 Poster Board II-1016 The physiologic function of factor XII (XII) is not known. New interest in XII has occurred because XII KO mice are protected from thrombosis. Exposed arterial collagen, aggregated protein, RNA, and platelet polysomes are recently recognized entities in developing thrombus that promote XII autoactivation to XIIa increasing thrombus formation, independent of a role in hemostasis. However, these observations do not indicate a constitutive, physiologic function for XII. We sought a physiologic function for zymogen XII. XII has been recognized to stimulate MAP kinase. Cleaved high molecular weight kininogen (HKa) is known to be antiangiogenic. Further, XII and HK mutually block each others binding to endothelial cells. Both XII and HKa bind urokinase plasminogen activator receptor (uPAR) at an overlapping site. We investigated if XII stimulates cells by interacting with uPAR and if this activity influences angiogenesis. XII (3-200 nM) with 0.05 mM Zn ion induces ERK1/2 (MAPK44 and 42) and Akt (Ser473) phosphorylation in endothelial cells. XII-induced phosphorylation of ERK1/2 or Akt is a zymogen activity, not an enzymatic event. ERK1/2 or Akt phosphorylation is blocked upstream by PD98059 or Wortmannin or LY294002, respectively. The uPAR signaling region for XII is on domain 2 adjacent to uPAR's integrin binding site. HKa or peptides from HKa's domain 5 inhibit XII-induced ERK1/2 and Akt phosphorylation. A beta-1-integrin peptide that binds uPAR, antibody 6S6 to beta-1-integrin, or the EGFR inhibitor AG1478 blocks XII-induced phosphorylation of ERK1/2 and Akt. XII induces endothelial cell proliferation and 5-bromo-2'deoxy-uridine incorporation. XII stimulates aortic sprouting in normal but not uPAR deficient mouse aorta and this mechanism is blocked by PD98059, LY294002, AG1478, or HKa. XII also induces angiogenesis in matrigel plugs. Finally, XII knockout mice have reduced constitutive and wound-induced blood vessel number on initial biopsy and 9 days after wound healing, respectively. In sum, XII initiates outside-in signaling mediated by uPAR, beta-1-integrin, and the EGFR leading to HUVEC proliferation, growth, and angiogenesis. XII is a constitutive proangiogenic protein. Disclosures No relevant conflicts of interest to declare.

Genome‐wide protein QTL mapping identifies human plasma kallikrein as a post‐translational regulator of serum uPAR levels

“…KLKB1 has a known proteolytic function, activating a number of proteins including bradykinin and blood clotting factor XII (58). Interestingly, a FXII SNP demonstrated near genome-wide significance with serum scuPAR levels in the current study and FXII has been shown to interact with uPAR to stimulate ERK1/2 and Akt signaling pathways (59). KLKB1 has also been implicated in the stimulation of neutrophil chemotaxis, aggregation, and oxygen consumption (60).…”

Astrocyte elevated gene-1 promotes hepatocarcinogenesis: Novel insights from a mouse model

“…FXII binds to urokinase plasminogen activator receptor or cross-talks with EGFR on HUVEC membranes, leading to activation of MAPK and Akt with subsequent proliferation and differentiation. 21 siRNAmediated knockdown of FXII resulted in a profound inhibition of AEG-1-induced angiogenesis, indicating a central role of FXII in this process. The question is, does AEG-1 also regulate FXII under normal conditions?…”

“…Interestingly, both FXII and TFF3 interacts with EGFR on ECs to augment proliferation and differentiation, hence angiogenesis. 21,24 Thus, there might be a key role of endothelial EGFR in mediating AEG-1 function, a hypothesis that needs to be experimentally validated.…”

The contact activation and kallikrein/kinin systems: pathophysiologic and physiologic activities

“…Factor XII stimulates cell proliferation and angiogenesis through uPAR and HK blocks both. [15]. Like single-chain urokinase, FXII binding to uPAR initiates signaling through b 1 integrin and the epidermal growth factor to phosphorylate ERK1/2 and AktS 473 [15].…”