Id3 upregulates BrdU incorporation associated with a DNA damage response, not replication, in human pancreatic β-cells

Islets. Nov-Dec 2011;3(6):358-66. doi: 10.4161/isl.3.6.17923. Epub 2011 Nov 1.

Abstract

Elucidating mechanisms of cell cycle control in normally quiescent human pancreatic β-cells has the potential to impact regeneration strategies for diabetes. Previously we demonstrated that Id3, a repressor of basic Helix-Loop-Helix (bHLH) proteins, was sufficient to induce cell cycle entry in pancreatic duct cells, which are closely related to β-cells developmentally. We hypothesized that Id3 might similarly induce cell cycle entry in primary human β-cells. To test this directly, adult human β-cells were transduced with adenovirus expressing Id3. Consistent with a replicative response, β-cells exhibited BrdU incorporation. Further, Id3 potently repressed expression of the cyclin dependent kinase inhibitor p57 (Kip2 ) , a gene which is also silenced in a rare β-cell hyperproliferative disorder in infants. Surprisingly however, BrdU positive β-cells did not express the proliferation markers Ki67 and pHH3. Instead, BrdU uptake reflected a DNA damage response, as manifested by hydroxyurea incorporation, γH2AX expression, and 53BP1 subcellular relocalization. The uncoupling of BrdU uptake from replication raises a cautionary note about interpreting studies relying solely upon BrdU incorporation as evidence of β-cell proliferation. The data also establish that loss of p57 (Kip2) is not sufficient to induce cell cycle entry in adult β-cells. Moreover, the differential responses to Id3 between duct and β-cells reveal that β-cells possess intrinsic resistance to cell cycle entry not common to all quiescent epithelial cells in the adult human pancreas. The data provide a much needed comparative model for investigating the molecular basis for this resistance in order to develop a strategy for improving replication competence in β-cells.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Bromodeoxyuridine / metabolism*
  • Cell Cycle / genetics
  • Cell Cycle / physiology
  • Cell Growth Processes / genetics
  • Cell Growth Processes / physiology
  • Cyclin-Dependent Kinase Inhibitor p57 / antagonists & inhibitors
  • Cyclin-Dependent Kinase Inhibitor p57 / biosynthesis*
  • Cyclin-Dependent Kinase Inhibitor p57 / genetics
  • DNA Damage*
  • Gene Expression Regulation
  • Histones / metabolism
  • Humans
  • Immunohistochemistry
  • Inhibitor of Differentiation Proteins / genetics
  • Inhibitor of Differentiation Proteins / metabolism*
  • Insulin-Secreting Cells / cytology
  • Insulin-Secreting Cells / metabolism*
  • Intracellular Signaling Peptides and Proteins / metabolism
  • Ki-67 Antigen / metabolism
  • Male
  • Mice
  • Mice, Inbred ICR
  • Transfection
  • Tumor Suppressor p53-Binding Protein 1
  • Up-Regulation

Substances

  • Cyclin-Dependent Kinase Inhibitor p57
  • H2AX protein, human
  • Histones
  • Inhibitor of Differentiation Proteins
  • Intracellular Signaling Peptides and Proteins
  • Ki-67 Antigen
  • TP53BP1 protein, human
  • Tumor Suppressor p53-Binding Protein 1
  • Idb3 protein, mouse
  • Bromodeoxyuridine