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Processing of proSAAS in neuroendocrine cell lines.
Nino Mzhavia1, Yimei Qian, Yun Feng
1Department of Pharmacology, New York University School of Medicine, New York, NY 10016, U.S.A.
The Biochemical Journal
|December 18, 2001
Summary
ProSAAS processing occurs independently of PC1/PC2 enzymes in neuroendocrine cells. Secretagogues stimulate the release of smaller peptides, suggesting potential neuropeptide functions for these ProSAAS derivatives.
Area of Science:
- Neuroendocrinology
- Molecular Biology
- Protein Biochemistry
Background:
- ProSAAS (pro-Granin-associated neuroendocrine protein) is a granin-like protein that inhibits prohormone convertase 1 (PC1).
- Understanding ProSAAS processing is crucial for elucidating its diverse functions beyond enzyme inhibition.
Purpose of the Study:
- To compare the processing of ProSAAS in two distinct neuroendocrine cell lines: AtT-20 and PC12.
- To investigate the role of prohormone convertases (PC1/PC2) in ProSAAS cleavage.
- To examine the regulation of ProSAAS processing and secretion by secretagogues.
Main Methods:
- Pulse-chase analysis using [(3)H]leucine.
- Mass spectrometry (MS).
- Chromatography and radioimmunoassay.
Main Results:
- ProSAAS is processed into smaller peptides (little SAAS, PEN, big LEN) in both AtT-20 and PC12 cells.
- Cleavage of ProSAAS occurs efficiently in PC12 cells, which lack PC1 and PC2, indicating these enzymes are not required for initial processing.
- Secretagogues stimulate the secretion of ProSAAS-derived peptides.
- Treatment with secretagogues increases PC1 mRNA but not ProSAAS mRNA in AtT-20 cells.
Conclusions:
- ProSAAS processing is not dependent on PC1 or PC2 activity.
- The regulated secretion of ProSAAS-derived peptides suggests they may function as neuropeptides.
- ProSAAS and PC1 mRNA levels are not co-regulated, implying independent induction of enzyme activity and inhibitor levels.