Induction of t-PA Synthesis with intravenous bolus injection of vitamin A palmitate in vitamin a deficient rats

Identification of a multihormone responsive enhancer far upstream from the human tissue-type plasminogen activator gene

A 2.4-kilobase (kb) DNA fragment, located 7.1 kb upstream from the human tissue-type plasminogen activator (t-PA) gene (t-PA2.4), acts as an enhancer which is activated by glucocorticoids, progesterone, androgens, and mineralocorticoids. Transient expression of t-PA-chloramphenicol acetyltransferase reporter constructs in HT1080 human fibrosarcoma cells identified a glucocorticoid responsive unit with four functional binding sites for the glucocorticoid receptor, located between bp -7,501 and -7,974. The region from bp -7,145 to -9,578 (t-PA2.4) was found to confer a cooperative induction by dexamethasone and all-trans-retinoic acid (RA) to its homologous and a heterologous promoter, irrespective of its orientation. The minimal enhancer, defined by progressive deletion analysis, comprised the region from -7.1 to -8.0 kb (t-PA0.9) and encompassed the glucocorticoid responsive unit and the previously identified RA-responsive element located at -7.3 kb (Bulens, F., Ibañez-Tallon, I., Van Acker, P., De Vriese, A., Nelles, L., Belayew, A., and Collen, D. (1995) J. Biol. Chem. 270, 7167-7175). The amplitude of the synergistic response to dexamethasone and RA increased by reducing the distance between the enhancer and the proximal t-PA promoter. The synergistic interaction was also observed between the aldosterone and the RA receptors. It is postulated that the t-PA0.9 enhancer might play a role in the hormonal regulation of the expression of human t-PA in vivo.

Generation of monoclonal antibodies against autologous proteins in gene-inactivated mice

Induction of an immune response is strongly dependent on the phylogenetic distance between antigen and recipient. In general, antibodies will not be raised against self-antigens nor against highly conserved domains. In the present study we describe the production and characterization of murine monoclonal "auto-antibodies" against murine tissue-type plasminogen activator (t-PA) raised in "knock-out" mice, homozygously deficient of the functional gene. 203 stable hybridomas were obtained producing murine monoclonal antibodies against murine t-PA. Analysis of the species reactivity revealed that 182 cross-reacted with one or more (t-)PAs originating from other species including rat t-PA, human t-PA, and vampire bat-PA. 121 reacted with epitopes conserved among murine, rat, and human t-PA. In addition, 31 of the monoclonal antibodies were directed against domains present in all four species. Epitope mapping indicated a high frequency of specificity toward diverse epitopes that are highly conserved across species. Comparative analysis of their influence on the enzymatic activity of t-PA and their species cross-reactivity clearly demonstrated that the domains required for the biological activity of plasminogen activators are more conserved (p < 0.02) than non-functional domains. The availability of such unique antibodies against a wide variety of conserved epitopes may facilitate studies on the structural homologies between (t-)PAs isolated from various species. The present approach should also apply to various other classes of proteins, allowing the generation of monoclonal antibodies, against conserved epitopes, which could not be raised in wild-type animals because of their "self-antigen" nature.

Retinoic acid induction of human tissue-type plasminogen activator gene expression via a direct repeat element (DR5) located at -7 kilobases

All-trans-retinoic acid (RA) and retinoids induce synthesis of tissue-type plasminogen activator (t-PA) in endothelial and neuroblastoma cells in vitro and in rats in vivo. In HT1080 fibrosarcoma cells, induction of t-PA-related antigen secretion and t-PA mRNA steady state levels by RA were found to depend on de novo protein and mRNA synthesis. Fragments derived from the 5'-flanking region of the t-PA gene (+197 to -9578 base pairs (bp)) were linked to the chloramphenicol acetyltransferase gene. Transfection studies demonstrated that the region spanning bp -7145 to -9578 mediated induction by RA. A functional retinoic acid response element (RARE), consisting of a direct repeat of the GGGTCA motif spaced by 5 nucleotides (t-PA/DR5), was localized at -7.3 kilobases. The t-PA/DR5 element interacted with the heterodimer composed of retinoic acid receptor alpha and retinoid X receptor alpha in vitro, whereas its mutation abolished induction by RA in transient expression. In human EA.hy926 hybrid endothelial and in SK-N-SH neuroblastoma cells, the activity of t-PA/DR5 was found to be independent of the intervening sequence (-632 to -7144 bp) and of its distance from the transcription initiation site. Staurosporine, an inhibitor of protein kinase activity, inhibited induction by RA, suggesting that it required protein phosphorylation.