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Tissue-type plasminogen activator is a target of the tumor suppressor gene maspin
S Sheng1, B Truong, D Fredrickson
1Division of Cancer Genetics, Dana-Farber Cancer Institute, Harvard Medical School, Boston, MA 02115, USA. ssheng@med.wayne.edu
Abstract:
The maspin protein has tumor suppressor activity in breast and prostate cancers. It inhibits cell motility and invasion in vitro and tumor growth and metastasis in nude mice. Maspin is structurally a member of the serpin (serine protease inhibitors) superfamily but deviates somewhat from classical serpins. We find that single-chain tissue plasminogen activator (sctPA) specifically interacts with the maspin reactive site loop peptide and forms a stable complex with recombinant maspin [rMaspin(i)]. Major effects of rMaspin(i) are observed on plasminogen activation by sctPA. First, rMaspin(i) activates free sctPA. Second, it inhibits sctPA preactivated by poly-D-lysine. Third, rMaspin(i) exerts a biphasic effect on the activity of sctPA preactivated by fibrinogen/gelatin, acting as a competitive inhibitor at low concentrations (< 0.5 microM) and as a stimulator at higher concentrations. Fourth, 38-kDa C-terminal truncated rMaspin(i) further stimulates fibrinogen/gelatin-associated sctPA. rMaspin(i) acts specifically; it does not inhibit urokinase-type plasminogen activator, plasmin, chymotrypsin, trypsin, or elastase. Our kinetic data are quantitatively consistent with a model in which two segregated domains of maspin interact with the catalytic and activating domains of sctPA. These complex interactions between maspin and sctPA in vitro suggest a mechanism by which maspin regulates plasminogen activation by sctPA bound to the epithelial cell surface.
Insights
Maspin, a tumor suppressor protein, interacts with single-chain tissue plasminogen activator (sctPA). This interaction modulates sctPA activity, suggesting a novel mechanism for maspin in regulating cancer cell invasion and metastasis.
Area of Science:
- Biochemistry
- Molecular Biology
- Oncology
Background:
- Maspin exhibits tumor suppressor properties in breast and prostate cancers.
- Maspin inhibits cancer cell motility, invasion, growth, and metastasis.
- Maspin is a structurally unique member of the serpin superfamily.
Purpose of the Study:
- To investigate the interaction between maspin and single-chain tissue plasminogen activator (sctPA).
- To elucidate the functional consequences of this interaction on sctPA activity.
- To propose a mechanism for maspin's role in regulating plasminogen activation.
Main Methods:
- Biochemical assays to study the interaction between recombinant maspin [rMaspin(i)] and sctPA.
- Kinetic analysis of plasminogen activation by sctPA in the presence of rMaspin(i).
- Investigation of truncated rMaspin(i) effects and specificity against other proteases.
Main Results:
- rMaspin(i) forms a stable complex with sctPA.
- rMaspin(i) exhibits differential effects on sctPA activity, including activation and inhibition.
- rMaspin(i) specifically modulates sctPA activity without affecting other proteases like urokinase-type plasminogen activator or plasmin.
Conclusions:
- Maspin and sctPA interact, leading to complex modulation of sctPA's enzymatic activity.
- These findings suggest a novel mechanism where maspin regulates sctPA on cell surfaces, impacting cancer progression.
- Maspin's unique interactions highlight its potential as a therapeutic target in cancer treatment.