The C-peptide Signaling

For years an assumption was made that C-peptide, abyproduct of insulin biosynthesis, possessed no appreciablephysiologic role. As other contributions in this volumeamply testify, the time has come to re-evaluate that notion.C-peptide either directly through interaction with its specificcell-surface receptor or indirectly through an interactionwith a related membrane entity, exerts a unique effecton several intracellular processes.We review here results ofstudies attempting to elucidate such molecular effects ofC-peptide in different cell systems and tissues. Lacking apurified C-peptide receptor, we also demonstrate C-peptideeffects on distinct elements of the insulin signal transductionpathways.