Protein Kinase C-ζ Activation Markedly Enhances β-Cell Proliferation

An Essential Role in Growth Factor–Mediated β-Cell Mitogenesis

  1. Rupangi C. Vasavada1,
  2. Lin Wang1,
  3. Yuichi Fujinaka1,
  4. Karen K. Takane1,
  5. Taylor C. Rosa1,
  6. Jose M.D. Mellado-Gil1,
  7. Peter A. Friedman2 and
  8. Adolfo Garcia-Ocaña1
  1. 1Department of Medicine, Division of Endocrinology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania
  2. 2Department of Pharmacology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania
  1. Address correspondence and reprint requests to Adolfo Garcia-Ocaña, PhD, Division of Endocrinology, University of Pittsburgh, 200 Lothrop St., BST-E1156, Pittsburgh, PA 15261. E-mail: ocana{at}dom.pitt.edu

Abstract

OBJECTIVE— Diabetes results from a deficiency of functional β-cells. Previous studies have identified hepatocyte growth factor (HGF) and parathyroid hormone–related protein (PTHrP) as two potent β-cell mitogens. The objective of this study is to determine 1) whether HGF and PTHrP have additive/synergistic effects on β-cell growth and proliferation; 2) the signaling pathways through which these growth factors mediate β-cell mitogenesis; and 3) whether activation of this/these signaling pathway(s) enhances human β-cell replication.

RESEARCH DESIGN AND METHODS— We generated and phenotypically analyzed doubly transgenic mice overexpressing PTHrP and HGF in the β-cell. INS-1 and primary mouse and human islet cells were used to identify mitogenic signaling pathways activated by HGF and/or PTHrP.

RESULTS— Combined overexpression of HGF and PTHrP in the β-cell of doubly transgenic mice did not result in additive/synergistic effects on β-cell growth and proliferation, suggesting potential cross-talk between signaling pathways activated by both growth factors. Examination of these signaling pathways in INS-1 cells revealed atypical protein kinase C (PKC) as a novel intracellular target activated by both HGF and PTHrP in β-cells. Knockdown of PKCζ, but not PKCι/λ, expression using specific small-interfering RNAs blocked growth factor–induced INS-1 cell proliferation. Furthermore, adenovirus-mediated delivery of kinase-dead PKCζ completely inhibited β-cell proliferation in primary islet cells overexpressing PTHrP and/or HGF. Finally, adenovirus-mediated delivery of constitutively active PKCζ in mouse and human primary islet cells significantly enhanced β-cell proliferation.

CONCLUSIONS— PKCζ is essential for PTHrP- and HGF-induced β-cell proliferation. PKCζ activation could be useful in therapeutic strategies for expanding β-cell mass in vitro and in vivo.

Footnotes

  • Published ahead of print at http://diabetes.diabetesjournals.org on 8 August 2007. DOI: 10.2337/db07-0461.

    Additional information for this article can be found in an online appendix at http://dx.doi.org/10.2337/db07-0461.

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

    • Received April 3, 2007.
    • Accepted August 4, 2007.
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  1. Diabetes vol. 56 no. 11 2732-2743
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