The Role of Annexin II Tetramer in the Activation of Plasminogen

• Published in: The Journal of biological chemistry Vol. 273; no. 8; pp. 4790 - 4799
• Main Authors: Kassam, G, Choi, K S, Ghuman, J, Kang, H M, Fitzpatrick, S L, Zackson, T, Zackson, S, Toba, M, Shinomiya, A, Waisman, D M
• Format: Journal Article
• Language: English
• Published: United States American Society for Biochemistry and Molecular Biology 20-02-1998
• Subjects: Annexin A2 - metabolism; Annexin A2 - physiology; Biopolymers; Cell Line; Cell Membrane - metabolism; Endothelium, Vascular - cytology; Endothelium, Vascular - metabolism; Fibrinolysin - biosynthesis; Humans; Hydrolysis; Kinetics; Plasminogen - metabolism
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.273.8.4790

Annexin II tetramer (AIIt) is a major Ca 2+ -binding protein of endothelial cells which has been shown to exist on both the intracellular and extracellular surfaces of
the plasma membrane. In this report, we demonstrate that AIIt stimulates the activation of plasminogen by facilitating the
tissue plasminogen activator (t-PA)-dependent conversion of plasminogen to plasmin. Fluid-phase AIIt stimulated the rate of
activation of [Glu]plasminogen about 341-fold compared with an approximate 6-fold stimulation by annexin II. AIIt bound to
[Glu]plasminogen(S741C-fluorescein) with a K
d of 1.26 ± 0.04 μ m (mean ± S.D., n = 3) and this interaction resulted in a large conformational change in [Glu]plasminogen. Kinetic analysis established that
AIIt produces a large increase of about 190-fold in the k
cat, app and a small increase in the K
m
,app which resulted in a 90-fold increase in the catalytic efficiency (k cat / K
m ) of t-PA for [Glu]plasminogen. AIIt also stimulated the t-PA-dependent activation of [Lys]plasminogen about 28-fold. Furthermore,
other annexins such as annexin I, V, or VI did not produce comparable activation of t-PA-dependent conversion of [Glu]plasminogen
to plasmin. The stimulation of the activation of [Glu]plasminogen by AIIt was Ca 2+ -independent and inhibited by ε-aminocaproic acid. AIIt bound to human 293 cells potentiated t-PA-dependent plasminogen activation.
AIIt that was bound to phospholipid vesicles or heparin also stimulated the activation of [Glu]plasminogen 5- or 11-fold,
respectively. Furthermore, immunofluorescence labeling of nonpermeabilized HUVEC revealed a punctated distribution of AIIt
subunits on the cell surface. These results therefore identify AIIt as a potent in vitro activator of plasminogen.