Impaired NH2-Terminal Processing of Human Proislet Amyloid Polypeptide by the Prohormone Convertase PC2 Leads to Amyloid Formation and Cell Death

  1. Lucy Marzban1,
  2. Christopher J. Rhodes2,
  3. Donald F. Steiner3,
  4. Leena Haataja4,
  5. Philippe A. Halban5 and
  6. C. Bruce Verchere1
  1. 1Department of Pathology and Laboratory Medicine and Child and Family Research Institute, University of British Columbia, Vancouver, British Columbia, Canada
  2. 2Pacific Northwest Research Institute, University of Washington, Seattle, Washington
  3. 3Department of Biochemistry and Molecular Biology, Howard Hughes Medical Institute, University of Chicago, Chicago, Illinois
  4. 4Larry Hillblom Islet Research Center, University of California, Los Angeles, California
  5. 5Department of Genetic Medicine and Development, University Medical Center, Geneva, Switzerland
  1. Address correspondence and reprint requests to Dr. Lucy Marzban, Child and Family Research Institute, Rm. 2071-950 West 28th Ave., Vancouver, BC, Canada V5Z 4H4. E-mail: marzban{at}interchange.ubc.ca

Abstract

Islet amyloid, formed by aggregation of islet amyloid polypeptide (IAPP; amylin), is a pathological characteristic of the pancreas in type 2 diabetes and may contribute to the progressive loss of β-cells in this disease. We tested the hypothesis that impaired processing of the IAPP precursor proIAPP contributes to amyloid formation and cell death. GH3 cells lacking the prohormone convertase 1/3 (PC1/3) and IAPP and with very low levels of prohormone convertase 2 (PC2) were transduced with adenovirus (Ad) expressing human or rat (control) proIAPP linked to green fluorescent protein, with or without Ad-PC2 or Ad-PC1/3. Expression of human proIAPP increased the number of transferase-mediated dUTP nick-end labeling (TUNEL)-positive cells 96 h after transduction (+hIAPP 8.7 ± 0.4% vs. control 3.0 ± 0.4%; P < 0.05). COOH-terminal processing of human proIAPP by PC1/3 increased (hIAPP+PC1/3 10.4 ± 0.7%; P < 0.05), whereas NH2-terminal processing of proIAPP by addition of PC2 markedly decreased (hIAPP+PC2 5.5 ± 0.5%; P < 0.05) the number of apoptotic GH3 cells. Islets from mice lacking PC2 and with β-cell expression of human proIAPP (hIAPP+/+/PC2−/−) developed amyloid associated with β-cell death during 2-week culture. Rescue of PC2 expression by ex vivo transduction with Ad-PC2 restored NH2-terminal processing to mature IAPP and decreased both the extent of amyloid formation and the number of TUNEL-positive cells (−PC2 26.5 ± 4.1% vs. +PC2 16.1 ± 4.3%; P < 0.05). These findings suggest that impaired NH2-terminal processing of proIAPP leads to amyloid formation and cell death and that accumulation of the NH2-terminally extended human proIAPP intermediate may be a critical initiating step in amyloid formation.

Footnotes

  • The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

    • Accepted May 1, 2006.
    • Received December 2, 2005.
| Table of Contents