Immunocytochemical demonstration of tissue-type plasminogen activator in endocrine cells of the rat pituitary gland.

Abstract

We immunocytochemically stained rat pituitary glands using antibodies against plasminogen activators of the tissue type (t-PA) and the urokinase type (u-PA). A large population of endocrine cells in the anterior lobe of the gland displayed intense cytoplasmic immunoreactivity with anti-t-PA. In some areas of the intermediate lobe we found a weak staining, and we observed weakly staining granular structures in the posterior lobe. Controls included absorption of the antibodies with highly purified t-PA. In addition, SDS PAGE followed by immunoblotting of pituitary gland extracts revealed only one band with an electrophoretic mobility similar to that of t-PA when stained with anti-t-PA IgG. No u-PA immunoreactivity was detected in the rat pituitary gland. Sequential staining experiments using antibodies against growth hormone and t-PA demonstrated that the t-PA-immunoreactive cells constitute a large subpopulation of the growth hormone-containing cells. These findings represent the first direct evidence for the presence of t-PA in cell types other than endothelial cells in the intact normal organism. In this article we discuss the implications of the results for a possible role of t-PA in the posttranslational processing of prohormones.Plasminogen activators are serine proteases, able to convert the proenzyme plasminogen into the active protease plasmin. It is well documented that there are at least two types of mammalian plasminogen activators. The two types that can be distinguished by differences in molecular weight (Mr) and immunological reactivity (for reviews see references 1-4) are products of different genes (5-8). Both the urokinase-type plasminogen activator (u-PA), ~ Mr ~ 50,000, and the tissuetype plasminogen activator (t-PA), Mr ~ 70,000, are secreted from cells in culture as partly or completely inactive proenzymes (9-12), and it is generally believed that they exert their biological functions by activation of extracellular plasminogen.Production and release ofplasminogen activators have been implicated in thrombolysis (for reviews see references 2 and 3) and a variety of biological processes involving tissue degradation (for reviews see references 4 and 13), for example Abbreviations used in this paper. TBS, 0.05 M Tris-HC1, pH 7.4, containing 0.15 M NaCl; t-PA, tissue-type plasminogen activator; u-PA, urokinase-type plasminogen activator.

Distribution of urokinase-type plasminogen activator immunoreactivity in the mouse.

“…The plasminogen activator found histochemically in these cells (47,48), at least in human tissue, is of the 70-kdalton Mr type (17,31). These findings support the hypothesis that the type of plasminogen activator playing a natural role in thrombolysis is of the 70-kdalton Mr type (tissue-type) and not of the 50-kdalton Mr (urokinase-type), although the latter type of plasminogen activator has been widely used as a thrombolytic agent (58).…”

“…CRONDAHL-HANSEN,# § P. KRISTENSEN,t and K. DANO* § *Unit of Histochemistry and *Laboratory of Tumor Biology, Institute of Pathology University of Copenhagen, Frederik V's Vej 11; and §Finsen Laboratory, Finsen Institute, 2 100 Copenhagen 0, Denmark is the most studied (2). Recent findings indicate that the Mr -70 Walton type of plasminogen activator (often designated tissue-type plasminogen activator) is a key enzyme in this process (29)(30)(31) . Much attention has also been directed toward a possible role of plasmin in tissue degradation under normal and pathological conditions, e.g., involution ofthe mammary gland, inflammation, arthritis, and invasive growth of trophoblasts and cancer cells (3,5,(32)(33)(34)(35)(36)(37)(38)(39)(40)(41)(59)(60)(61)(62).…”

Induction of morphological differentiation of human neuroblastoma cells is accompanied by induction of tissue‐type plasminogen activator

“…This differs from regulation of PA by specific inhibitors (PAI-1, PAI-2, and PAI-3), in which the complexes are not internalised via the u-PA receptor. The possibilty therefore exists that for certain neuroectodermal cells, as has been suggested for endocrine cells (Kristensen et al, 1985, t-PA may have an intracellular proteolytic function.…”

“…PA production has been associated with invasive tumor cells (Dan0 et al, 1985) and with certain types of normal cells engaged in cell migration and penetration through extracellular matrices. The latter include activated macrophages (Unkeless et al, 1974), stimulated ovarian granulosa cells before rupture of the follicular wall (Beers et al, 1975), trophoblastic cells invading the uterine wall (Strickland et al, 1976), and angiogenic endothelial cells (Gross et al, 1983).…”

“…In all of these processes involving tissue destruction, of the two types of plasminogen activators, u-PA has been implicated. Detection of t-PA in endocrine cells of the rat pituitary gland (Kristensen et al, 1985) and adrenal medulla ) has led to the proposal that intracellular proteolytic processing of hormone precursor molecules may be another function, besides fibrinolysis, in which t-PA has a role. There is some evidence from studies of ovulation that also t-PA may perform an extracellular function in weakening the follicle structure during ovulation (Huarte et al, 1985).…”