A new mechanism for prolactin processing into 16K PRL by secreted cathepsin D.
Cathepsins are lysosomal enzymes that were shown to release the antiangiogenic fragments 16K prolactin (PRL), endostatin, and angiostatin by processing precursors at acidic pH in vitro. However, the physiological relevance of these findings is questionable because the neutral pH of physiological fluids is not compatible with the acidic conditions required for the proteolytic activity of these enzymes. Here we show that cathepsin D secreted from various tissues is able to process PRL into 16K PRL outside the cell. To specifically target extracellular proteolysis, we used tissues from PRL receptor-deficient mice, which are unable to internalize PRL. As assessed by the use of specific inhibitors of proton extruders, we show that the proteolytic activity of cathepsin D requires local acid secretion driven by Na(+)/H(+) exchangers and H(+)/ATPase. Although it is usually assumed that cathepsin-mediated generation of antiangiogenic peptides occurs in the moderately acidic pericellular milieu found in malignant tumors, we propose a new mechanism explaining the extracellular activity of this acidic protease under physiological pH. Our data support the concept that secreted lysosomal enzymes could be involved in the maintenance of angiogenesis dormancy via the generation of active antiangiogenic peptides in nonpathological contexts.
Piwnica
David
D
Institut National de la Santé et de la Recherche Médicale, (INSERM), Unité (U) 808, F-75730 Paris Cedex 15, France.
Fernandez
Isabelle
I
Binart
Nadine
N
Touraine
Philippe
P
Kelly
Paul A
PA
Goffin
Vincent
V
D000818:Animals; D002402:Cathepsin D / Q000378:metabolism*; D002478:Cells, Cultured; D017077:Culture Media, Conditioned; D006863:Hydrogen-Ion Concentration; D008247:Lysosomes / Q000201:enzymology*; D051379:Mice; D018345:Mice, Knockout; D008954:Models, Biological; D009154:Mutation; D011388:Prolactin / Q000378:metabolism*; D006180:Proton-Translocating ATPases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D011981:Receptors, Prolactin / Q000235:genetics / Q000378:metabolism*; D017923:Sodium-Hydrogen Exchangers / Q000037:antagonists & inhibitors / Q000378:metabolism*; D014018:Tissue Distribution
D017077:Culture Media, Conditioned; D011981:Receptors, Prolactin; D017923:Sodium-Hydrogen Exchangers; D011388:Prolactin; D002402:Cathepsin D; D006180:Proton-Translocating ATPases