Neuronal cell lines expressing PC5, but not PC1 or PC2, process Pro-CCK into glycine-extended CCK 12 and 22

Area of Science:

• Neuroendocrinology
• Molecular Biology
• Biochemistry

Background:

• Pro-opiomelanocortin (POMC) convertases like PC1 and PC2 process pro-hormones into bioactive peptides.
• PC5 is another prohormone convertase with known propeptide processing capabilities.
• The processing of cholecystokinin (CCK) is crucial for its biological activity.

Purpose of the Study:

• To investigate the ability of PC5 to process pro-CCK in specific neuronal and neuroblastoma cell lines.
• To determine if PC5 alone can generate fully bioactive amidated CCK.
• To characterize the intermediate processing products of pro-CCK in PC5-expressing cells.

Main Methods:

• Utilized GT1-7 (mouse hypothalamic) and SK-N-MC/SK-N-SH (human neuroblastoma) cell lines.
• Confirmed PC5 expression and absence of PC1/PC2 using RT-PCR and Western blot.
• Analyzed cell media for pro-CCK expression and cleavage products via radioimmunoassay and chromatography after stable CCK overexpression.

Main Results:

• PC5 mRNA and protein were detected in the cell lines, while PC1 and PC2 were absent.
• Pro-CCK was expressed and processed, but no amidated CCK was detected.
• Glycine-extended CCK forms, including CCK 12 Gly and CCK 22 Gly, were identified in the cell media.

Conclusions:

• PC5-expressing cell lines can process pro-CCK into intermediate glycine-extended forms.
• The absence of amidated CCK suggests a lack of essential amidating enzymes in these cells.
• These findings indicate that PC5 contributes to pro-CCK processing, yielding products resembling intestinal, rather than brain, forms.