Processing of rat preprocortistatin in mouse AtT-20 cells

Area of Science:

• Neuroendocrinology
• Molecular Biology
• Peptide Processing

Background:

• Preprocortistatin (PPCST) is a novel somatostatin (SST)-related gene exclusively expressed in the brain.
• PPCST shares structural similarities with SST-14, featuring cleavage sites for potential cortistatin (CST)-14 and CST-29 peptides.
• The biological functions and natural processing products of PPCST remain largely uncharacterized.

Purpose of the Study:

• To investigate the posttranslational processing and secretion of PPCST in a cellular model.
• To characterize the naturally occurring mature cleavage products of PPCST.
• To determine the relative release of CST-14 and CST-29 from PPCST.

Main Methods:

• Cloning and stable expression of rat PPCST cDNA in AtT-20 pituitary cells.
• High-Performance Liquid Chromatography (HPLC) for separation and identification of peptide products.
• Radioimmunoassay (RIA) using an SST-14 antibody to quantify cortistatin-like immunoreactivity (CST-LI).

Main Results:

• Transfected cells produced and released both CST-14 and CST-29 from PPCST.
• HPLC analysis revealed PPCST is processed into CST-14, CST-29, and unprocessed PPCST.
• CST-14 constituted the majority (63-70%) of the released CST peptides, compared to CST-29 (30-37%).

Conclusions:

• PPCST undergoes efficient posttranslational processing to yield both CST-14 and CST-29.
• Despite similar synthesis levels, CST-14 is preferentially secreted via the regulated secretory pathway.
• These findings highlight distinct processing and release mechanisms for PPCST-derived peptides, suggesting independent biological functions.