Kringle domains and plasmin denaturation

Inhibition of human MDA-MB-231 breast cancer cell invasion by matrix metalloproteinase 3 involves degradation of plasminogen

Matrix metalloproteinase (MMP)-3 inhibited human MDA-MB-231 breast cancer cell invasion through reconstituted basement membrane in vitro. Inhibition of invasion was dependent upon plasminogen and MMP-3 activation, was impaired by the peptide MMP-3 inhibitor Ac-Arg-Cys-Gly-Val-Pro-Asp-NH2 and was associated with: rapid MMP-3-mediated plasminogen degradation to microplasminogen and angiostatin-like fragments; the removal of single-chain urokinase plasminogen activator from MDA-MB-231 cell membranes; impaired membrane plasminogen association; reduced rate of tissue plasminogen activator (t-PA) and membrane-mediated plasminogen activation; and reduced laminin-degrading capacity. Purified human plasminogen lysine binding site-1 (kringles 1-3) exhibited a similar capacity to inhibit MDA-MB-231 invasion, impair t-PA and cell membrane-mediated plasminogen activation and impair laminin degradation by plasmin. Our data provide evidence that MMP-3 can inhibit breast tumour cell invasion in vitro by a mechanism involving plasminogen degradation to fragments that limit plasminogen activation and the degradation of laminin. This supports the hypothesis that MMP-3, under certain conditions, may protect against tumour invasion, which would help to explain why MMP-3 expression, associated with benign and early stage breast tumours, is frequently lost in advanced stage, aggressive, breast disease.

Preparation and evaluation of polyurethane surfaces containing immobilized plasminogen

Plasminogen has been immobilized onto a segmented polyurethane containing amino groups, using glutaraldehyde as coupling agent. It was also aspecifically adsorbed, for sake of comparison, onto polyurethane films containing different functional groups and, in particular, epsilon-amino caproic acid and lysine residues. The differently immobilized plasminogen has been converted to plasmin by activation with urokinase, and the percentage of active plasmin for the various polymer films was determined using a tripeptide (S-2251) as a synthetic substrate. The biological behaviour of the differently treated polymer films has been evaluated in vitro by measurements of partial thromboplastin time (PTT) and platelet adhesion.

Function of streptokinase fragments in plasminogen activation

Several peptide fragments of streptokinase (SK) were prepared by incubating SK with immobilized human plasmin (hPlm) and purified by h.p.l.c. with a reverse-phase phenyl column. The N-terminal sequences, amino acid compositions and molecular masses of these peptide fragments were determined. The SK peptide fragment of 36 kDa consisting of Ser60-Lys387 (SK-p), was the only peptide fragment that could be tightly bound to immobilized hPlm. Another three large SK peptide fragments, SK-m, SK-n and SK-o, with molecular masses of 7 kDa, 18 kDa and 30 kDa, and consisting of Ile1-Lys59, Glu148-Lys333, Ser60-Lys333 respectively, were also obtained from the supernatant of the reaction mixture. The purified SK-p had high affinity with hPlm and could activate human plasminogen (hPlg) with a kPlg one-sixth that of the native SK. SK-o had low affinity with hPlm and could also activate hPlg, although the catalytic constant was less than 1% of the native SK. SK-n, as well as SK-m, which is the N-terminal 59 amino acid peptide of the native SK, had no activator activity. However, SK-m could enhance the activator activity of both SK-o and SK-p and increase their second-order rate constants by two- and six-fold respectively. It was concluded from these studies that (1) SK-o, the Ser60-Lys333 peptide of SK, was essential for minimal SK activator activity, (2) the C-terminal peptide of SK-p, Ala334-Lys387, was essential for high affinity with hPlm, and (3) the N-terminal 59-amino-acid peptide was important in maintaining the proper conformation of SK to have its full activator activity.

The binding of plasminogen fragments to cultured human umbilical vein endothelial cells

Glu-plasminogen, kringle 1-5, kringle 1-3, and miniplasminogen exhibited strong binding to human umbilical vein endothelial cells (HUVEC). On the other hand, no significant binding was obtained with microplasminogen and kringle 4. Kringle 1-5 and miniplasminogen, which both contained kringle 5, specifically inhibited the binding of plasminogen to HUVEC while kringle 1-3 did not. The results implied plasminogen molecule contained at least two binding sites, with which it interacted HUVEC. The stronger binding site was located in kringle 5 and the weaker one was in kringle 1-3. Kringle 4 and the active site domain exhibited no significant binding to HUVEC. The interaction of plasminogen with HUVEC is mainly through binding site on kringle 5.