The regulated cell surface zymogen activation of the proprotein convertase PC5A directs the processing of its secretory substrates.
The proprotein convertases are synthesized as zymogens that acquire activity upon autocatalytic removal of their NH(2)-terminal prosegment. Based on the convertase furin, to fold properly and gain activity, the convertases PC5A, PACE4, and PC7 are presumed to undergo two sequential prosegment cleavages in the endoplasmic reticulum and then in the trans-Golgi network. However, biochemical and immunocytochemical experiments revealed that mouse PC5A is complexed to its prosegment at the plasma membrane. This labeling is lost upon treatment with heparin and is increased by overexpressing members of the syndecan family and CD44, suggesting attachment of secreted PC5A-prosegment complex to heparan sulfate proteoglycans. Following stimulation of Y1 cells with adrenocorticotropic hormone or 8-bromo-cyclic AMP, the cell surface labeling of the prosegment of PC5A is greatly diminished, whereas the signal for mature PC5A is increased. Moreover, after stimulation, the protease activity of PC5A is enhanced, as evidenced by the cleavage of the PC5A substrates Lefty, ADAMTS-4, endothelial lipase, and PCSK9. Our data suggest a novel mechanism for PC5A activation and substrate cleavage at the cell surface, through a regulated removal of its prosegment. A similar mechanism may also apply to the convertase PACE4, thereby extending our knowledge of the molecular details of the zymogen activation and functions of these heparan sulfate proteoglycan-bound convertases.
Laboratory of Biochemical Neuroendocrinology, Clinical Research Institute of Montreal, Montréal, Quebec H2W 1R7, Canada.
Gaétan
G
Mayer
Josée
J
Hamelin
Marie-Claude
MC
Asselin
Antonella
A
Pasquato
Edwidge
E
Marcinkiewicz
Meiyi
M
Tang
Siamak
S
Tabibzadeh
Nabil G
NG
Seidah
D051722:ADAM Proteins / Q000235:genetics / Q000378:metabolism; D000071121:ADAMTS4 Protein; D000818:Animals; D016466:CHO Cells; D019556:COS Cells; D002522:Chlorocebus aethiops; D006224:Cricetinae; D003412:Cricetulus; D004721:Endoplasmic Reticulum / Q000201:enzymology* / Q000235:genetics; D004789:Enzyme Activation / Q000502:physiology; D004792:Enzyme Precursors / Q000235:genetics / Q000378:metabolism*; D045683:Furin / Q000235:genetics / Q000378:metabolism; D006056:Golgi Apparatus / Q000201:enzymology* / Q000235:genetics; D006801:Humans; D018960:Hyaluronan Receptors / Q000235:genetics / Q000378:metabolism; D055458:Left-Right Determination Factors; D008049:Lipase / Q000235:genetics / Q000378:metabolism; D051379:Mice; D011348:Procollagen N-Endopeptidase / Q000235:genetics / Q000378:metabolism; D045702:Proprotein Convertase 5 / Q000235:genetics / Q000378:metabolism*; D000071449:Proprotein Convertase 9; D043484:Proprotein Convertases / Q000235:genetics / Q000378:metabolism; D012697:Serine Endopeptidases / Q000235:genetics / Q000378:metabolism; D013381:Subtilisins / Q000235:genetics / Q000378:metabolism; D053667:Syndecans / Q000235:genetics / Q000378:metabolism; D016212:Transforming Growth Factor beta / Q000235:genetics / Q000378:metabolism
C497483:CD44 protein, human; C476399:Cd44 protein, mouse; D004792:Enzyme Precursors; D018960:Hyaluronan Receptors; C526161:LEFTY1 protein, human; D055458:Left-Right Determination Factors; D053667:Syndecans; D016212:Transforming Growth Factor beta; C410382:LIPG protein, human; D008049:Lipase; C498741:Lipg protein, mouse; C080654:PCSK6 protein, human; C099101:PCSK7 protein, human; C472125:PCSK9 protein, human; C513086:Pcsk6 protein, mouse; C490930:Pcsk7 protein, mouse; C472126:Pcsk9 protein, mouse; D045702:Proprotein Convertase 5; D000071449:Proprotein Convertase 9; D043484:Proprotein Convertases; D012697:Serine Endopeptidases; D013381:Subtilisins; D045683:Furin; D051722:ADAM Proteins; D011348:Procollagen N-Endopeptidase; D000071121:ADAMTS4 Protein; C000603918:ADAMTS4 protein, human; C000603919:Adamts4 protein, mouse