Studies on the mechanism of Ca2+ stimulation of plasminogen activator synthesis/release by Swiss 3T3 cells.
Stimulation of postconfluent Swiss 3T3 cells in serum-free medium with 4.3 mM Ca2+ results in marked increases in both released and cell-associated plasminogen activator (PA). Increased release of PA commenced approximately 10 to 12 hours post-stimulation and continued to increase steadily until 48 hours at which time the stimulates cells (4.3 mM Ca2+) released approximately 14 times more PA than control cells (1.8 mM Ca2+). Sr2+, like Ca2+, also stimulates PA synthesis/release either in the presence or in the absence of 1.8 mM Ca2+ whereas an excess of Mg2+ inhibits Ca2+ stimulation. Supranormal [Pi] in the medium stimulates PA synthesis/release in the presence of 1.8 mM mM Ca2+. Further, optimal stimulation by 4.3 mM Ca2+ requires a normal level of Pi (1.0 mM). Elevation of medium [Ca2+] or [Pi] results in an enhanced uptake of Ca2+. The facts that cycloheximide treatment completely abolishes the Ca2+ stimulatory effect and that an increase in cell associated PA precedes release indicate that PA release is coupled to synthesis of new PA. Ca2+ stimulation of PA synthesis/release also requires continuous energy production and RNA as well as protein synthesis. A hypothesis is proposed to explain the relationship between stimulation of PA production and its enhanced release from cells stimulated by elevated [Ca2+] or [Pi] in the media. The possibility that PA release may be an example of the phenomenon of membrane shedding as opposed to secretion is discussed.
D000818:Animals; D002118:Calcium / Q000494:pharmacology*; D002413:Cations, Divalent; D002460:Cell Line; D004247:DNA / Q000096:biosynthesis; D007700:Kinetics; D051379:Mice; D010085:Oxidative Phosphorylation; D010710:Phosphates / Q000494:pharmacology; D010960:Plasminogen Activators / Q000378:metabolism*; D014176:Protein Biosynthesis; D012313:RNA / Q000096:biosynthesis; D013324:Strontium / Q000494:pharmacology
D002413:Cations, Divalent; D010710:Phosphates; D012313:RNA; D004247:DNA; D010960:Plasminogen Activators; D002118:Calcium; D013324:Strontium