Cellular internalization of proinsulin C-peptide.

Area of Science:

• Cell Biology
• Endocrinology
• Molecular Biology

Background:

• Proinsulin C-peptide binds cell membranes and has intracellular effects.
• Cellular internalization of C-peptide has not been previously demonstrated.

Purpose of the Study:

• To investigate the internalization of proinsulin C-peptide in target cells.
• To determine the mechanism and intracellular localization of C-peptide.

Main Methods:

• Confocal microscopy using immunostained or rhodamine-labeled C-peptide.
• Cellular uptake studies at varying temperatures (37°C vs. 4°C) and with pertussis toxin.
• Surface plasmon resonance to identify intracellular binding proteins.

Main Results:

• C-peptide is internalized into the cytosol of Swiss 3T3 and HEK-293 cells.
• Nuclear transport of C-peptide was observed.
• Internalization is energy-dependent, pertussis toxin-sensitive, and occurs without rapid degradation.
• Intracellular proteins bind to C-peptide.

Conclusions:

• C-peptide internalization occurs via a specific, regulated mechanism.
• The data support C-peptide acting as an intracrine peptide hormone.
• C-peptide may possess additional intracellular sites of action.