title: Upregulation of p21 activates the intrinsic apoptotic pathway in β-cells.
abstract: Diabetes manifests from a loss in functional β-cell mass, which is regulated by a dynamic balance of various cellular processes, including β-cell growth, proliferation, and death as well as secretory function. The cell cycle machinery comprised of cyclins, kinases, and inhibitors regulates proliferation. However, their involvement during β-cell stress during the development of diabetes is not well understood. Interestingly, in a screen of multiple cell cycle inhibitors, p21 was dramatically upregulated in INS-1-derived 832/13 cells and rodent islets by two pharmacological inducers of β-cell stress, dexamethasone and thapsigargin. We hypothesized that β-cell stress upregulates p21 to activate the apoptotic pathway and suppress cell survival signaling. To this end, p21 was adenovirally overexpressed in pancreatic rat islets and 832/13 cells. As expected, p21 overexpression resulted in decreased [(3)H]thymidine incorporation. Flow cytometry analysis in p21-transduced 832/13 cells verified lower replication, as indicated by a decreased cell population in the S phase and a block in G2/M transition. The sub-G0 cell population was higher with p21 overexpression and was attributable to apoptosis, as demonstrated by increased annexin-positive stained cells and cleaved caspase-3 protein. p21-mediated caspase-3 cleavage was inhibited by either overexpression of the antiapoptotic mitochondrial protein Bcl-2 or siRNA-mediated suppression of the proapoptotic proteins Bax and Bak. Therefore, an intact intrinsic apoptotic pathway is central for p21-mediated cell death. In summary, our findings indicate that β-cell apoptosis can be triggered by p21 during stress and is thus a potential target to inhibit for protection of functional β-cell mass.
authors.affiliation: Department of Pediatrics and Herman B. Wells Center for Pediatric Research and.
authors.forename: Angelina M
authors.initials: AM
authors.lastname: Hernandez
authors.forename: E Scott
authors.initials: ES
authors.lastname: Colvin
authors.forename: Yi-Chun
authors.initials: YC
authors.lastname: Chen
authors.forename: Steven L
authors.initials: SL
authors.lastname: Geiss
authors.forename: Lindsay E
authors.initials: LE
authors.lastname: Eller
authors.forename: Patrick T
authors.initials: PT
authors.lastname: Fueger
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000502:physiology*; D002453:Cell Cycle / Q000502:physiology; D045744:Cell Line, Tumor; D049109:Cell Proliferation; D003907:Dexamethasone / Q000494:pharmacology; D003924:Diabetes Mellitus, Type 2 / Q000378:metabolism* / Q000473:pathology / Q000503:physiopathology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D015870:Gene Expression / Q000187:drug effects / Q000502:physiology; D005938:Glucocorticoids / Q000494:pharmacology; D050417:Insulin-Secreting Cells / Q000166:cytology* / Q000502:physiology*; D007340:Insulinoma; D008928:Mitochondria / Q000502:physiology; D015689:Oncogene Protein p21(ras) / Q000235:genetics / Q000378:metabolism*; D010190:Pancreatic Neoplasms; D051381:Rats; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology; D019284:Thapsigargin / Q000494:pharmacology; D015854:Up-Regulation / Q000502:physiology
chemical_list: D004791:Enzyme Inhibitors; D005938:Glucocorticoids; D019284:Thapsigargin; D003907:Dexamethasone; D015689:Oncogene Protein p21(ras)
keywords: cyclin-dependent kinase inhibitor-1a; dexamethasone; islet; stress; thapsigargin