Publisher Summary This chapter discusses the role of plasminogen activators in various biological processes. In specific, it describes two types of plasminogen activators—namely, the urokinase-type plasminogen activator (u-PA) and the tissue-type plasminogen activator (t-PA), which are essentially different gene products. The amino acid sequences of these activators and nucleotide sequences of the corresponding cDNAs have largely been determined, and the cDNAs have been cloned using recombinant techniques. A variety of enzymatic as well as immunological assay and detection methods have also been developed that allows a precise quantification of the activators, a distinction between u-PA and t-PA, determination of whether an activator is present in its active or zymogen form, analysis of the kinetics of different steps of the cascade reaction, and immunocytochemical identification of u-PA and t-PA in tissue sections. Much of the studies on plasminogen activators and cancer has been guided by the hypothesis that proteolysis of the components of extracellular matrix, initiated by the release of plasminogen activator from the cancer cells, plays a decisive role for the degradation of normal tissue, and thereby for invasive growth and metastases.

Plasminogen activators, tissue degradation, and cancer.

The pharmacology and clinical uses of tamoxifen

Synthesis of DNA by DNA polymerase-beta is distributive on single-stranded DNA templates, but short DNA gaps with a 5' PO4 in the gap are filled processively to completion. In vitro studies have suggested a role of beta-polymerase in different types of DNA repair. However, the significance of these studies to the in vivo role of beta-polymerase has remained unclear. Because genetic studies are essential for determining the physiological role of a gene, we established embryonic fibroblast cell lines homozygous for a deletion mutation in the gene encoding DNA polymerase-beta. Extracts from these cell lines were found to be defective in uracil-initiated base-excision repair. The beta-polymerase-deleted cells are normal in viability and growth characteristics, although they exhibit increased sensitivity to monofunctional DNA-alkylating agents, but not to other DNA-damaging agents. Both the deficiency in base-excision repair and hypersensitivity to DNA-alkylating agents are rescued following stable transfection with a wild-type beta-polymerase minitransgene. These studies demonstrate that beta-polymerase functions specifically in base-excision repair in vivo.

Requirement of mammalian DNA polymerase-beta in base-excision repair.

Antibodies to plasminogen activator inhibit human tumor metastasis

The human leukemic myeloblast HL-60 and monoblast U937 cell lines have made important contributions to the disciplines of cancer, hematology, and immunology. As sources of leukemic cells, they have been used for the study of neoplasia and therapeutics. As sources of hemic cells, they have been used for biochemical and biological analysis of regulation and differentiation in myelopoiesis. When stimulated with immunomodulatory factors, the cell lines develop properties of host-defense effector cells. They are also a source of cytokines that affect other cell types.

Human leukemic models of myelomonocytic development: a review of the HL-60 and U937 cell lines.

Induction of plasminogen activator by estrogen in a human breast cancer cell line (MCF-7)

Preparing nuclei from cells in monolayer cultures suitable for counting and for following synchronized cells through the cell cycle

The factors involved in estradiol-17β induced growth stimulation of MCF-7 human breast cancer cells have been examined. Wild type MCF-7 cells (and clone E3) were shown to undergo slow growth in phenol-red-free medium containing specific calf sera. The E3 clone was used to document a mean 6-day growth stimulation of 3.35-fold (doubling time=33±3 h) in cultures supplemented with 10−11
 M estradiol-17β. The serum batch utilized in the culture medium is most important in acquiring significant growth stimulation of MCF-7 cells by estradiol-17β. Regardless of the absence of phenol-red, only selected sera (2 out of 14 tested) supported minimal growth of MCF-7 cells in the absence of added estradiol 17β (doubling time=55±11 h). When a calf-serum-supplemented culture failed to display a complete growth response to estradiol-17β, it was due to the rapid growth of the cells in the control (minus estradiol-17β) flasks. Sera that promoted shorter doubling times for MCF-7 cells cultured in the absence of estradiol-17β were rendered less supportive of growth if treated with dextran-coated charcoal or when cultures were supplemented with the estrogen antagonist ICI 164,384 (10−7
 M). Pooled extracts of these sera were shown to contain stimulatory levels of estradiol-17β. Dextrancoated charcoal treatment of sera removed or deactivated factors (other than estradiol-17β) which were not only required for the growth of MCF-7 cells, but were necessary for estrogen-stimulated growth. Varying the serum-containing medium, buffer, and nutrient mix or the addition of insulin has no effect on the growth response of these cells to estradiol-17β. These investigations document the culture conditions required to produce a maximal and consistent proliferative effect of E2 on MCF-7 cells without exposing the serum constituent to damaging chemical or absorbent agents.

W. Barkley Butler

Papers

Induction of plasminogen activator by estrogen in a human breast cancer cell line (MCF-7)

Preparing nuclei from cells in monolayer cultures suitable for counting and for following synchronized cells through the cell cycle

Optimization of estrogen growth response in mcf-7 cells

Estrogen-bridged purines: a new series of anti-tumor agents which alter cell membrane properties.