Intracellular and peptide interactions of C-peptide

<p>Proinsulin C-peptide is depleted together with insulin in type I diabetic patients. The supplement of insulin to these patients is necessary for their survival, but it is also likely that the loss of C-peptide may contribute to both short- and long-term complications. In this thesis, molecular effects of C-peptide have been investigated. In particular, nuclear effects of C-peptide and C-peptide involved in oligomerization have been studied, as well as method development to facilitate further protein interaction analysis.</p><p>C-peptide is a small peptide hormone with known membrane-binding properties that is thought to stimulate G-protein coupled receptor associated pathways. In this thesis we report that C-peptide not only acts extracellularly, but that it is internalized via specific mechanims and interacts with cytoskeletal proteins. We show that C-peptide is transferred to the nucleus, and specifically to the rRNA-synthesizing organelle nucleolus where it stimulates transcription of rDNA.</p><p>Transcription of rDNA is related to a complex of proteins at the promoter region including histone 4 that gets acetylated upon interaction with C-peptide. We further link this transcriptional activity of C-peptide to proliferation in a model system relevant to the bone growth retardation observed in type I diabetic patients suffering from fractures. To understand more of C-peptide’s effects on the basis of the transcriptional activity observed, a genome analysis of proximal tubular cells isolated from type I diabetic rats was performed. It revealed that C-peptide within 2 hrs exerts tight effects on transcription with ~500 genes affected and the majority of them being repressed. This observation suggests that C-peptide treatment corrects malfunctioning pathways, especially pathways of circulatory and inflammatory diseases.We have also studied oligomerization of C-peptide, and find that C-peptide oligomers are disrupted by insulin in addition to a previous study reporting that C-peptide disrupts insulin hexamers. The C-peptide oligomers are formed via electrostatic interactions, and can further lead to aggregates with a high content of ß-sheets.</p><p>In summary, this thesis provides data on C-peptide being an intracrine hormone with intracellular effects in addition to having extracellular activity via classical endocrinological pathways. We also discuss the implications of the C-peptide oligomers we observe, which provide evidence that C-peptide may act as an insulin chaperone. It is evident that a fine-balanced homestasis of C-peptide is necessary for optimal health in both type I and II diabetic patients.</p><h3>List of scientific papers</h3><p>I. Lindahl E, Nyman U, Melles E, Sigmundsson K, Ståhlberg M, Wahren J, Öbrink B, Shafqat J, Joseph B, Jörnvall H. (2007) Cellular internalization of proinsulin C-peptide. Cell Mol Life Sci. 64(4):479-86. <br><a href="https://doi.org/10.1007/s00018-007-6467-6">https://doi.org/10.1007/s00018-007-6467-6</a><br><br> </p><p>II. Lindahl E, Nyman U, Zaman F, Palmberg C, Cascante A, Shafqat J, Takigawa M, Sävendahl L, Jörnvall H, Joseph B. (2010) Proinsulin C-peptide regulates ribosomal RNA expression. J Biol Chem. 285(5):3462-9. <br><a href="https://doi.org/10.1074/jbc.M109.053587">https://doi.org/10.1074/jbc.M109.053587</a><br><br> </p><p>III. Lindahl E, Nordquist L, Müller P, Agha E, Friederich M, Dahlman-Wright K, Palm F, Jörnvall H. Early transcriptional regulation by C-peptide in freshly isolated rat proximal tubular cells. [Submitted]</p><p>IV. Jägerbrink T, Lindahl E, Shafqat J, Jörnvall H. (2009) Proinsulin C-peptide interaction with protein tyrosine phosphatase 1B demonstrated with a labeling reaction. Biochem Biophys Res Commun. 387(1):31-5. <br><a href="https://doi.org/10.1016/j.bbrc.2009.06.074">https://doi.org/10.1016/j.bbrc.2009.06.074</a><br><br> </p><p>V. Jörnvall H, Lindahl E, Astorga-Wells J, Lind J, Holmlund A, Melles E, Alvelius G, Nerelius C, Mäler L, Johansson J. (2010) Oligomerization and insulin interactions of proinsulin C-peptide: Threefold relationships to properties of insulin. Biochem Biophys Res Commun. 391(3):1561-6. <br><a href="https://doi.org/10.1016/j.bbrc.2009.12.125">https://doi.org/10.1016/j.bbrc.2009.12.125</a><br><br> </p><p>VI. Lind J, Lindahl E, Perálvarez-Marín A, Holmlund A, Jörnvall H, Mäler L. (2010) Structural features of proinsulin C-peptide oligomeric and amyloid states. FEBS J. 277(18):3759-3768. <br><a href="https://doi.org/10.1111/j.1742-4658.2010.07777.x">https://doi.org/10.1111/j.1742-4658.2010.07777.x</a><br><br> </p>