Cell-surface processing of pro-ADAMTS9 by furin.

Area of Science:

• Biochemistry
• Molecular Biology
• Cell Biology

Background:

• Proprotein convertases (PCs) like furin typically process polypeptide precursors intracellularly, mainly in the trans-Golgi network.
• The specific processing mechanisms for ADAMTS proteases, a family of secreted metalloproteinases, are not fully elucidated.

Purpose of the Study:

• To investigate the intracellular or extracellular processing site of the ADAMTS9 zymogen.
• To determine the specific proprotein convertase(s) responsible for ADAMTS9 maturation.
• To understand the implications of ADAMTS9 processing for secreted protein maturation.

Main Methods:

• Pulse-chase analysis in HEK293F cells.
• Utilizing proprotein convertase inhibitors.
• Employing furin-deficient cell lines and rescue experiments.
• Down-regulation of furin using small interference RNA (siRNA).

Main Results:

• ADAMTS9 propeptide is not excised intracellularly; the intact zymogen is secreted to the cell surface.
• Extracellular processing of ADAMTS9 occurs on the cell surface before its release into the medium.
• Processing is dependent on furin, as evidenced by inhibitor studies, furin-deficient cells, and furin rescue experiments.
• Furin down-regulation reduced ADAMTS9 processing.
• PC5A can also process pro-ADAMTS9, but processed forms are not found intracellularly.

Conclusions:

• ADAMTS9 undergoes cell-surface, furin-dependent extracellular maturation, establishing a precedent for secreted proproteins.
• This study highlights diverse mechanisms for the processing of ADAMTS proteases.
• The findings expand our understanding of post-translational modifications and secreted protein activation.