title: Differential endocytosis of tissue plasminogen activator by serpins PAI-1 and PAI-2 on human peripheral blood monocytes.
abstract: Generation of the broad spectrum protease plasmin is facilitated by the tissue (t-PA) and urokinase (u-PA) plasminogen activators, within multiple physiological and disease states. Finely tuned control of this proteolytic cascade is exerted by the plasminogen activator inhibitors type-1 (PAI-1/SERPINE1) and 2 (PAI-2/SERPINB2). Expression of this network of activators and inhibitors by cells of myeloid lineage appears to be highly interchangeable between physiological environments, and whilst the role of PAI-1 and PAI-2 in regulating u-PA-dependent functions is well established, the interaction between t-PA and PAI-2 on these cell types is poorly characterised. To this end, we used freshly isolated peripheral blood monocytes (PBM) as a model of a t-PA-dependent cellular environment. We demonstrate that while both PAI-1 and PAI-2 could inhibit surface-bound t-PA and are internalised predominately via low-density-lipoprotein receptor family members, PAI-1 enhanced the endocytosis of t-PA, whereas PAI-2 did not. Surface plasmon resonance analyses revealed differential binding affinities between the very-low-density-lipoprotein receptor and t-PA and t-PA:PAI-1 complexes in addition to those previously described with low-density-lipoprotein receptor-related protein. Moreover, t-PA:PAI-2 bound to both endocytosis receptors with similar kinetics to t-PA. These differential biochemical interactions between t-PA and the t-PA:PAI complexes may underlie the observed differences in endocytosis mechanisms on the PBMs. This suggests that while PAI-1 and PAI-2 function similarly in the control of cellular plasmin generation by t-PA, they may have disparate effects on the alternative functions of t-PA via modulation of its engagement with endocytosis receptors.
authors.affiliation: School of Biological Sciences, University of Wollongong, Northfields Avenue, Wollongong, New South Wales, Australia.
authors.forename: Jodi A
authors.initials: JA
authors.lastname: Lee
authors.forename: David R
authors.initials: DR
authors.lastname: Croucher
authors.forename: Marie
authors.initials: M
authors.lastname: Ranson
mesh_terms: D004705:Endocytosis; D005434:Flow Cytometry; D006801:Humans; D007700:Kinetics; D009000:Monocytes / Q000378:metabolism*; D017395:Plasminogen Activator Inhibitor 1 / Q000378:metabolism*; D017396:Plasminogen Activator Inhibitor 2 / Q000378:metabolism*; D011485:Protein Binding; D011973:Receptors, LDL / Q000378:metabolism; D011994:Recombinant Proteins / Q000378:metabolism; D020349:Surface Plasmon Resonance; D010959:Tissue Plasminogen Activator / Q000378:metabolism*
chemical_list: D017395:Plasminogen Activator Inhibitor 1; D017396:Plasminogen Activator Inhibitor 2; D011973:Receptors, LDL; D011994:Recombinant Proteins; C051321:SERPINE1 protein, human; C036053:VLDL receptor; D010959:Tissue Plasminogen Activator