Processing of proSAAS in neuroendocrine cell lines.
ProSAAS, a recently discovered granin-like protein, potently inhibits prohormone convertase (PC)1, and might also perform additional functions. In the present study, the processing of proSAAS was compared in two neuroendocrine cell lines overexpressing this protein: the AtT-20 mouse pituitary corticotrophic line and the PC12 rat adrenal phaeochromocytoma line. The processing of proSAAS was examined by pulse-chase analysis using [(3)H]leucine, by MS, and by chromatography and radioimmunoassay. Various smaller forms of proSAAS were detected, including peptides designated as little SAAS, PEN and big LEN. Because the PC-12 cells used in the present study do not express either PC1 or PC2, the finding that these cells efficiently cleave proSAAS indicates that these cleavages do not require either enzyme. Two of the peptides identified in AtT-20 media represent novel C-terminally truncated forms of PEN. In both cell lines, the secretion of the small proSAAS-derived peptides is stimulated by secretagogues. However, long-term treatment of wild-type AtT-20 cells with two different secretagogues (8-bromo-cAMP and a phorbol ester) does not affect levels of proSAAS mRNA; this treatment significantly increases PC1 mRNA by approx. 60-80%. The lack of co-regulation of proSAAS and PC1 mRNA implies that enzyme activity can be induced without an accompanying increase in the inhibitor. In addition, the finding that the peptides are secreted via the regulated pathway is consistent with the proposal that they may function as neuropeptides.
Mzhavia
Nino
N
Department of Pharmacology, New York University School of Medicine, New York, NY 10016, U.S.A.
Qian
Yimei
Y
Feng
Yun
Y
Che
Fa-Yun
FY
Devi
Lakshmi A
LA
Fricker
Lloyd D
LD
D000818:Animals; D016282:Aspartic Acid Endopeptidases / Q000037:antagonists & inhibitors / Q000235:genetics; D002460:Cell Line; D002851:Chromatography, High Pressure Liquid; D005786:Gene Expression Regulation; D051379:Mice; D009479:Neuropeptides / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D009490:Neurosecretory Systems / Q000378:metabolism*; D016716:PC12 Cells; D045664:Proprotein Convertase 1; D043484:Proprotein Convertases; D011498:Protein Precursors / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D011499:Protein Processing, Post-Translational; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D051381:Rats; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization; D014162:Transfection
D009479:Neuropeptides; C403532:PCSK1N protein, human; D011498:Protein Precursors; D012333:RNA, Messenger; D011994:Recombinant Proteins; D043484:Proprotein Convertases; C473656:Pcsk1 protein, mouse; D045664:Proprotein Convertase 1; D016282:Aspartic Acid Endopeptidases