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: Bruno Ramos-Molina, Iris Lindberg
• Journal: Molecular endocrinology (Baltimore, Md.) (Mol Endocrinol) Vol. 29 Issue 5 Pg. 756-64 (May 2015) ISSN: 1944-9917 [Electronic] United States
• PMID: 25811241 (Publication Type: Journal Article, Research Support, N.I.H., Extramural)

Chemical References

• Endoplasmic Reticulum Chaperone BiP
• Extracellular Matrix Proteins
• Heat-Shock Proteins
• Neuroendocrine Secretory Protein 7B2
• SCG5 protein, human
• Casein Kinase I
• FAM20C protein, human
• Proprotein Convertase 2

Topics

• Alternative Splicing
• Amino Acid Sequence
• Casein Kinase I (metabolism)
• Endoplasmic Reticulum (metabolism)
• Endoplasmic Reticulum Chaperone BiP
• Enzyme Activation
• Extracellular Matrix Proteins (metabolism)
• HEK293 Cells
• Heat-Shock Proteins (metabolism)
• Humans
• Molecular Sequence Data
• Neuroendocrine Secretory Protein 7B2 (genetics, metabolism)
• Phosphorylation
• Proprotein Convertase 2 (metabolism)
• Protein Processing, Post-Translational