title: Serpinin: a novel chromogranin A-derived, secreted peptide up-regulates protease nexin-1 expression and granule biogenesis in endocrine cells.
abstract: Previously we demonstrated that chromogranin A (CgA) promoted secretory granule biogenesis in endocrine cells by stabilizing and preventing granule protein degradation in the Golgi, through up-regulation of expression of the protease inhibitor, protease nexin-1 (PN-1). However, the mechanism by which CgA signals the increase of PN-1 expression is unknown. Here we identified a 2.9-kDa CgA-C-terminus peptide, which we named serpinin, in conditioned media from AtT-20 cells, a corticotroph cell line, which up-regulated PN-1 mRNA expression. Serpinin was secreted from AtT-20 cells upon high potassium stimulation and increased PN-1 mRNA transcription in these cells, in an actinomycin D-inhibitable manner. CgA itself and other CgA-derived peptides, when added to AtT-20 cell media, had no effect on PN-1 expression. Treatment of AtT-20 cells with 10 nm serpinin elevated cAMP levels and PN-1 mRNA expression, and this effect was inhibited by a protein kinase A inhibitor, 6-22 amide. Serpinin and a cAMP analog, 8-bromo-cAMP, promoted the translocation of the transcription factor Sp1 into the nucleus, which is known to drive PN-1 expression. Additionally, an Sp1 inhibitor, mithramycin A inhibited the serpinin-induced PN-1 mRNA up-regulation. Furthermore, a luciferase reporter assay demonstrated serpinin-induced up-regulation of PN-1 promoter activity in an Sp1-dependent manner. When added to CgB-transfected 6T3 cells, a mutant AtT20 cell line, serpinin induced granule biogenesis as evidenced by the presence of CgB puncta accumulation in the processes and tips. Our findings taken together show that serpinin, a novel CgA-derived peptide, is secreted upon stimulation of corticotrophs and plays an important autocrine role in up-regulating PN-1-dependent granule biogenesis via a cAMP-protein kinase A-Sp1 pathway to replenish released granules.
authors: Section on Cellular Neurobiology, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland 20892, USA.
authors: Hisatsugu
authors: H
authors: Koshimizu
authors: Niamh X
authors: NX
authors: Cawley
authors: Taeyoon
authors: T
authors: Kim
authors: Alfred L
authors: AL
authors: Yergey
authors: Y Peng
authors: YP
authors: Loh
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D002460:Cell Line; D053379:Chromogranin A / Q000378:metabolism* / Q000494:pharmacology; D017077:Culture Media, Conditioned / Q000737:chemistry; D055098:Endocrine Cells / Q000378:metabolism*; D051379:Mice; D008969:Molecular Sequence Data; D010446:Peptide Fragments / Q000378:metabolism* / Q000494:pharmacology; D010902:Pituitary Gland / Q000166:cytology / Q000378:metabolism; D014176:Protein Biosynthesis / Q000187:drug effects; D022142:Secretory Vesicles / Q000378:metabolism*; D016415:Sequence Alignment; D058258:Serpin E2 / Q000235:genetics* / Q000378:metabolism; D015843:Serpins; D015398:Signal Transduction / Q000187:drug effects; D014158:Transcription, Genetic / Q000187:drug effects; D015854:Up-Regulation
chemical_list: D053379:Chromogranin A; D017077:Culture Media, Conditioned; D010446:Peptide Fragments; D058258:Serpin E2; C511869:Serpine2 protein, mouse; D015843:Serpins; C561289:serpinin protein, mouse