Research Use Only

uPA ELISA

Intended Use
The uPA ELISA is an enzyme-linked immunoassay used to quantitate pro-, high molecular weight (HMW) and low molecular weight (LMW)-uPA (urokinase-type plasminogen activator) found in human serum or plasma. This assay is for research use only and is not to be used for diagnostic purposes.

Background
uPA is a 52-kDa serine proteinase. It participates in the proteolytic process, which takes place in tissue remodeling, cell migration, and angiogenesis, as well as tumor cell invasion and metastasis. uPA is secreted by cells as an inactive single-chain precursor, pro-uPA. Enzymatic cleavage of pro-uPAat lysine 158 produces an active heterodimer, called high molecular weight-uPA (HMW-uPA), consisting of two subunits, A and B. When pro-uPA is secreted, it binds to a receptor (uPAR) on the cell surface through an EGF-like domain on the A chain. Subsequent binding of plasmin to uPA can convert pro-uPA into the proteolytically active heterodimer. In turn, active uPArapidly converts the inactive plasmin precursor, plasminogen, to enzymatically active plasmin, which is directly involved in extracellular matrix degradation as well as in the activation of other procollagenases and latent growth factors [1–4]. Additional cleavage of uPA after lysine 135 releases the 17-kDa amino-terminal fragment (ATF), leaving the carboxy-terminal 33-kDa low molecular weight-uPA (LMW-uPA), which retains full catalytic activity [5].

The enzymatic activity of uPA is regulated by two plasminogen activator inhibitors called PAI-1 and PAI-2. These can bind to the catalytically active B chain of uPA. When active uPA is bound to its receptor, subsequent PAI-1 binding results in internalization and degradation of the complex [6].

Secreted uPA may originate from several cell types, including tumor tissue [7], adjacent stromal cells, or fibroblasts [8]. The significance of uPA expression and subsequent proteinase activity has been the subject of detailed studies in a variety of models. In 1992, Huber, et al. [9], examined plasma levels of uPA and alpha-fetoprotein (AFP) in liver cancer and showed that by combining the information from the two tumor markers, the accuracy of detection of liver cancer was increased. In 1993, Huber, et al., showed similar results in colon cancer using plasma levels of uPA and CA 19-9 [10]. In an earlier study, it was determined that breast cancer patients had elevated plasma uPA levels in comparison to normal controls [11]. More recently, another report showed that elevated uPA levels can serve as a prognostic factor in metastatic breast cancer, and that metastatic breast cancer patients with elevated uPA levels have a shorter time to progression and shorter survival when treated with second line hormonal therapy [12]. Studies have also discovered elevated uPA levels in colon and pancreatic cancer patients; for example, one study reported that serum uPA levels were elevated in 28 of 80 (35%) female pancreatic cancer patients and 53
of 108 (49%) male pancreatic cancer patients compared to controls [13,14].

Although more work is needed, clearly plasma or serum as a sample can be useful for examining the potential clinical utility of uPA in a variety of cancers and at any time during cancer development. Serum or plasma samples can be analyzed for all forms of uPA using the uPA ELISA.

Assay Principle
The uPA ELISA is a sandwich enzyme immunoassay that utilizes two different monoclonal anti- bodies to human uPA as the capture reagents. The capture antibody has been immobilized on the interior surface of microplate wells. To perform the test, an appropriate volume of specimen is incubated in the coated well to allow binding of the antigen by the capture antibody. The immobilized antigen is then reacted with the uPA detector rabbit antiserum. The amount of detector antibody bound to antigen is measured by binding it with a goat-anti-rabbit IgG horseradish peroxidase (HRP) conjugate. Color development by incubation with OPD (o-phenylenediamine) substrate enables quantitation of captured uPA. The colored reaction product is quantitated by spectrophotometry and reflects the amount of uPA analyte in the sample. The uPA ELISA is completely formulated and offers convenient testing options for customers.

Selected References

1. Danø KJ, Andreasen PA, Grondahl-Hansen J, et al. Plasminogen activators, tissue degradation, and cancer. Adv Cancer Res 1985;44:139–266.
2. Ossowski L. Invasion of connective tissue by human carcinoma cell lines: Requirement for urokinase, urokinase receptor, and interstitial collagenase. Cancer Res 1992 Dec 15;52(24):6754–6760.
3. Liotta LA, Steeg PS, Stetler-Stevenson WG. Cancer metastasis and angiogenesis: An imbalance of positive and negative regulation. Cell 1991 Jan 25;64(2):327–336.
4. Pollänen J, Stephens R, and Vaheri A. Directed plasminogen activation at the surface of normal and malignant cells. Adv Cancer Res 1991;57:273–328.
5. Blasi F and Verde P. Urokinase-dependent cell surface proteolysis and cancer. Semin Cancer Biol 1990 Apr;1(2):117–126.
6. Cubellis MV, Wun T-C, and Blasi F. Receptor-mediated internalization and degradation of urokinase is caused by its specific inhibitor PAI-1. The EMBO Journal 1990;9:1079–1085.
7. Markus G, Camiolo SM, Kohga S, et al. Plasminogen activator secretion of human tumors in short-term organ culture; comparison of primary and metastatic colon tumors. Cancer Research 1983;43:5517–5525.
8. Pyke C, Kristensen P, Ralfkiær E, et al. Urokinase-type plasminogen activator is expressed in stromal cells and its receptor in cancer cells at invasive foci in human colon adenocarcinomas. American Journal of Pathology 1991;138:1059–1067.
9. Huber K, Kirchheimer JC, Ermler D, et al. Determination of plasma urokinase-type activator antigen in patients with primary liver cancer: Characterization as tumor-associated antigen and comparison with alpha-fetoprotein. Cancer Research 1992;52:1717–1720.
10. Huber K, Kirchheimer JC, Sedlmayer A, et al. Clinical value of determination of urokinase-type plasminogen activator antigen in plasma for detection of colorectal cancer: Comparison with circulating tumor-associated antigens CA 19-9 and carcinoembryonic antigen. Cancer Research 1993;53:1788–1793.
11. Grøndahl-Hansen J, Agerlin N, Munkholm-Larsen P, et al. Sensitive and specific enzyme-linked immunosorbent assay for urokinase-type plasminogen activator and its application to plasma from patients with breast cancer. J Laboratory Clinical Medicine 1988;111:42–51.
12. Clarke L, Leitzel K, Ali SM, et al. Serum urokinase-type plasminogen activator as a prognostic factor in metastatic breast cancer. ECCO, 2001.
13. Jarosz DE, Morris LD, Tighe WJ. uPA and uPA:PAI-1 complexes in serum and plasma. ISOBM 2002, 23 (Suppl 1) #073.
14. Marx JH, Leitzel K, Ali SM, et al. Serum urokinase-type plasminogen activator (uPA) in patients with pancreatic cancer. AACR 2002 Abstract #1973.