The CD-loop of PAI-2 (SERPINB2) is redundant in the targeting, inhibition and clearance of cell surface uPA activity.
BACKGROUND
Plasminogen activator inhibitor type-2 (PAI-2, SERPINB2) is an irreversible, specific inhibitor of the urokinase plasminogen activator (uPA). Since overexpression of uPA at the surface of cancer cells is linked to malignancy, targeting of uPA by exogenous recombinant PAI-2 has been proposed as the basis of potential cancer therapies. To this end, reproducible yields of high purity protein that maintains this targeting ability is required. Herein we validate the use in vitro of recombinant 6 x His-tagged-PAI-2 lacking the intrahelical loop between C and D alpha-helices (PAI-2 Delta CD-loop) for these purposes.


RESULTS
We show that PAI-2 Delta CD-loop expressed and purified from the pQE9 vector system presents an easier purification target than the previously used pET15b system. Additionally, PAI-2 Delta CD-loop gave both higher yield and purity than wild-type PAI-2 expressed and purified under identical conditions. Importantly, absence of the CD-loop had no impact on the inhibition of both solution phase and cell surface uPA or on the clearance of receptor bound uPA from the cell surface. Furthermore, uPA:PAI-2 Delta CD-loop complexes had similar binding kinetics (KD approximately 5 nM) with the endocytosis receptor Very Low Density Lipoprotein Receptor (VLDLR) to that previously published for uPA:PAI-2 complexes.


CONCLUSIONS
We demonstrate that the CD-loop is redundant for the purposes of cellular uPA inhibition and cell surface clearance (endocytosis) and is thus suitable for the development of anti-uPA targeted cancer therapeutics.
School of Biological Sciences, University of Wollongong, NSW, 2522, Australia. blake@uow.edu.au
Blake J
BJ
Cochran
Lakshitha P
LP
Gunawardhana
Kara L
KL
Vine
Jodi A
JA
Lee
Sergei
S
Lobov
Marie
M
Ranson
D004791:Enzyme Inhibitors; D005822:Genetic Vectors; D006801:Humans; D017396:Plasminogen Activator Inhibitor 2 / Q000302:isolation & purification / Q000378:metabolism*; D011485:Protein Binding; D017433:Protein Structure, Secondary; D011994:Recombinant Proteins / Q000302:isolation & purification / Q000378:metabolism*; D021241:Spectrometry, Mass, Electrospray Ionization; D014568:Urokinase-Type Plasminogen Activator / Q000037:antagonists & inhibitors*
D004791:Enzyme Inhibitors; D017396:Plasminogen Activator Inhibitor 2; D011994:Recombinant Proteins; D014568:Urokinase-Type Plasminogen Activator