Tissue distribution and processing of proSAAS by proprotein convertases

Area of Science:

• Neuroendocrinology
• Protein biochemistry

Background:

• Neuropeptide and peptide hormone biosynthesis relies on regulated secretory proteins like prohormone convertases (PC1, PC2).
• ProSAAS, homologous to the PC2-binding protein 7B2, interacts with PC1, suggesting a role in regulated secretion.
• Understanding proSAAS processing is crucial for elucidating its physiological functions and the generation of bioactive peptides.

Purpose of the Study:

• To determine the tissue localization of proSAAS-derived peptides.
• To investigate the in vitro and in vivo cleavage of proSAAS by prohormone convertases.
• To assess the role of PC2 in proSAAS processing within the brain.

Main Methods:

• Radioimmunoassay (RIA) was developed to quantify a C-terminal proSAAS-derived peptide for tissue localization.
• Recombinant proSAAS was incubated with recombinant mouse proPC2 or furin for in vitro cleavage studies.
• High-pressure gel permeation chromatography and RIA were used to analyze cleavage products.
• ProSAAS processing was examined in the brains of wild-type and PC2 null mice.

Main Results:

• ProSAAS-derived peptide immunoreactivity was predominantly found in the brain (hypothalamus, pituitary) and gut.
• In vitro experiments showed that both PC2 and furin rapidly process the C-terminal peptide of proSAAS.
• In vivo studies in mice revealed that proSAAS is efficiently processed, with PC2 partially responsible for the cleavage of the C-terminal peptide.

Conclusions:

• ProSAAS and its derived peptides are localized in key neuroendocrine and peripheral tissues.
• PC2 and furin are capable of processing proSAAS in vitro, exposing an inhibitory hexapeptide.
• PC2 plays a partial role in the in vivo processing of proSAAS in the mouse brain, impacting bioactive peptide generation.