title: Phosphorylation and Alternative Splicing of 7B2 Reduce Prohormone Convertase 2 Activation.
abstract: FAM20C is a secretory kinase responsible for the phosphorylation of multiple secreted proteins in mammalian cells; it has been shown to phosphorylate serine residues within a variety of different bone proteins. In this work we demonstrate that FAM20C also phosphorylates threonines, specifically those within the N-terminal domain of the neuroendocrine chaperone 7B2. Analysis of the primary sequence of 7B2 revealed that three threonine residues in its N-terminal domain are located within FAM20C consensus motifs: Thr73, Thr99, and Thr111. The individual substitution of Thr73 and Thr111 residues by neutral alanines caused a marked decrease in the total phosphorylation of 7B2. Furthermore, the phosphomimetic substitution of Thr111 by Glu clearly diminished the ability of 7B2 to activate pro-prohormone convertase 2 (PC2) in 7B2-lacking SK-N-MC neuroblastoma cells, suggesting that the phosphorylation of this residue critically impacts the 7B2-proPC2 interaction. However, the phosphomimetic mutation did not alter 7B2's ability to function as an antiaggregant for human islet amyloid polypeptide. FAM20C-mediated phosphorylation of a common alternatively spliced variant of human 7B2 that lacks Ala100 (thus eliminating the Thr99 phosphorylation consensus site) was similar to the Ala-containing protein, but this variant did not activate proPC2 as efficiently as the Ala-containing protein. Although threonines within 7B2 were phosphorylated efficiently, FAM20C was incapable of performing the well-known regulatory threonine phosphorylation of the molecular chaperone binding immunoglobulin protein. Taken together, these results indicate that FAM20C plays a role in 7B2-mediated proPC2 activation by phosphorylating residue Thr111; and that 7B2 function is regulated by alternative splicing.
authors: Department of Anatomy and Neurobiology, School of Medicine, University of Maryland-Baltimore, Baltimore, Maryland 21201.
authors: Bruno
authors: B
authors: Ramos-Molina
authors: Iris
authors: I
authors: Lindberg
mesh_terms: D017398:Alternative Splicing; D000595:Amino Acid Sequence; D047389:Casein Kinase I / Q000378:metabolism; D004721:Endoplasmic Reticulum / Q000378:metabolism; D000091342:Endoplasmic Reticulum Chaperone BiP; D004789:Enzyme Activation; D016326:Extracellular Matrix Proteins / Q000378:metabolism; D057809:HEK293 Cells; D006360:Heat-Shock Proteins / Q000378:metabolism; D006801:Humans; D008969:Molecular Sequence Data; D051859:Neuroendocrine Secretory Protein 7B2 / Q000235:genetics / Q000378:metabolism*; D010766:Phosphorylation; D045706:Proprotein Convertase 2 / Q000378:metabolism*; D011499:Protein Processing, Post-Translational
chemical_list: D000091342:Endoplasmic Reticulum Chaperone BiP; D016326:Extracellular Matrix Proteins; D006360:Heat-Shock Proteins; D051859:Neuroendocrine Secretory Protein 7B2; C497678:SCG5 protein, human; D047389:Casein Kinase I; C524449:FAM20C protein, human; D045706:Proprotein Convertase 2