title: Clic4, a novel protein that sensitizes β-cells to apoptosis.
abstract: OBJECTIVE
  Chloride intracellular channel protein 4 (Clic4) is a ubiquitously expressed protein involved in multiple cellular processes including cell-cycle control, cell differentiation, and apoptosis. Here, we investigated the role of Clic4 in pancreatic β-cell apoptosis.
  
  
  METHODS
  We used βTC-tet cells and islets from β-cell specific Clic4 knockout mice (βClic4KO) and assessed cytokine-induced apoptosis, Bcl2 family protein expression and stability, and identified Clic4-interacting proteins by co-immunoprecipitation and mass spectrometry analysis.
  
  
  RESULTS
  We show that cytokines increased Clic4 expression in βTC-tet cells and in mouse islets and siRNA-mediated silencing of Clic4 expression in βTC-tet cells or its genetic inactivation in islets β-cells, reduced cytokine-induced apoptosis. This was associated with increased expression of Bcl-2 and increased expression and phosphorylation of Bad. Measurement of Bcl-2 and Bad half-lives in βTC-tet cells showed that Clic4 silencing increased the stability of these proteins. In primary islets β-cells, absence of Clic4 expression increased Bcl-2 and Bcl-xL expression as well as expression and phosphorylation of Bad. Mass-spectrometry analysis of proteins co-immunoprecipitated with Clic4 from βTC-tet cells showed no association of Clic4 with Bcl-2 family proteins. However, Clic4 co-purified with proteins from the proteasome suggesting a possible role for Clic4 in regulating protein degradation.
  
  
  CONCLUSIONS
  Collectively, our data show that Clic4 is a cytokine-induced gene that sensitizes β-cells to apoptosis by reducing the steady state levels of Bcl-2, Bad and phosphorylated Bad.
authors.affiliation: Center for Integrative Genomics, University of Lausanne, Genopode Building, CH-1015 Lausanne, Switzerland.
authors.forename: Dhaval
authors.initials: D
authors.lastname: Patel
authors.affiliation: Center for Integrative Genomics, University of Lausanne, Genopode Building, CH-1015 Lausanne, Switzerland.
authors.forename: Damien
authors.initials: D
authors.lastname: Ythier
authors.affiliation: ULB Center for Diabetes Research, Université Libre de Bruxelles (ULB), Brussels, Belgium.
authors.forename: Flora
authors.initials: F
authors.lastname: Brozzi
authors.affiliation: ULB Center for Diabetes Research, Université Libre de Bruxelles (ULB), Brussels, Belgium.
authors.forename: Decio L
authors.initials: DL
authors.lastname: Eizirik
authors.affiliation: Center for Integrative Genomics, University of Lausanne, Genopode Building, CH-1015 Lausanne, Switzerland.
authors.forename: Bernard
authors.initials: B
authors.lastname: Thorens
keywords: Apoptosis; Bcl-2; Clic4; Cytokines; Diabetes; β-cells
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