title: Cultured human fibroblasts secrete insulin-like growth factor IA prohormone.
abstract: Nucleotide sequencing of the two known cDNAs encoding human insulin-like growth factor I (IGF-I) predicts the existence of two different prohormone forms of IGF-I. The E peptide regions extend the carboxy-terminus of IGF-I by either an additional 35 (IGF-IA) or 77 (IGF-IB) amino acids. With a specific and sensitive RIA employing an antiserum directed against a synthetic peptide that is unique to the E peptide region of IGF-IA prohormone (EIA), we have identified EIA-immunoreactive material in the conditioned medium of fetal and postnatal human fibroblasts in culture. Incubation of postnatal human fibroblasts with GH increased specific immunoreactive EIA secretion 2- to 3-fold. There was no immunologically detectable 7.5K IGF-I or IGF-II peptide in acid-chromatographed human fibroblast-conditioned medium under either basal or GH-stimulated conditions. Acid chromatography of human fibroblast-conditioned medium on Sephadex G-75 revealed a single elution peak of EIA immunoreactivity corresponding to a mol wt of 9-17 K. With neutral chromatography, EIA immunoreactivity eluted at 25-38K mol wt. These data suggest that the E peptide region of IGF-IA is translated and released as part of the prohormone form in cultured human fibroblasts, and that the levels of this prohormone are regulated by GH.
authors.affiliation: Department of Pediatrics, Stanford University, California 94305.
authors.forename: C A
authors.initials: CA
authors.lastname: Conover
authors.forename: B K
authors.initials: BK
authors.lastname: Baker
authors.forename: R L
authors.initials: RL
authors.lastname: Hintz
mesh_terms: D000595:Amino Acid Sequence; D001483:Base Sequence; D002478:Cells, Cultured; D002850:Chromatography, Gel; D003470:Culture Media / Q000032:analysis; D004247:DNA / Q000032:analysis; D005347:Fibroblasts / Q000187:drug effects / Q000378:metabolism; D013006:Growth Hormone / Q000494:pharmacology; D006801:Humans; D007334:Insulin-Like Growth Factor I / Q000096:biosynthesis* / Q000235:genetics / Q000276:immunology; D010446:Peptide Fragments / Q000276:immunology; D011384:Proinsulin / Q000096:biosynthesis* / Q000235:genetics; D014176:Protein Biosynthesis / Q000187:drug effects; D011863:Radioimmunoassay; D013002:Somatomedins / Q000096:biosynthesis*
chemical_list: D003470:Culture Media; D010446:Peptide Fragments; D013002:Somatomedins; C053766:insulin-like growth factor 1A prohormone (91-103); D007334:Insulin-Like Growth Factor I; D013006:Growth Hormone; D004247:DNA; D011384:Proinsulin