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Nr4a1 and Nr4a3 upregulate cell cycle genes upregulated in the Nkx6.1 β-cell proliferation pathway

ABSTRACT: Loss of functional β-cell mass is a hallmark of Type 1 and Type 2 diabetes, and methods for restoring these cells are needed. Nkx6.1 induces β-cell proliferation, but the pathway by which Nkx6.1 activates β-cell expansion has not been defined. Here we demonstrate that Nkx6.1 induces expression of the Nr4a1 and Nr4a3 orphan nuclear receptors, and that these factors are both necessary and sufficient for Nkx6.1-mediated β-cell proliferation. Overexpression of the Nr4a receptors results in increased expression of key cell cycle inducers E2F1 and cyclin E1. Furthermore, Nr4a receptors induce components of the anaphase-promoting complex, including Ube2c.

ORGANISM(S): Rattus norvegicus

PROVIDER: GSE55078 | GEO | 2014/02/18

SECONDARY ACCESSION(S): PRJNA238471

REPOSITORIES: GEO

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Project description:The homeodomain transcription factor Nkx6.1 plays an important role in pancreatic islet Î²-cell development, but its effects on adult Î²-cell function, survival, and proliferation are not well understood. In the present study, we demonstrated that treatment of primary rat pancreatic islets with a cytomegalovirus promoter-driven recombinant adenovirus containing the Nkx6.1 cDNA (AdCMV-Nkx6.1) causes dramatic increases in [methyl-3H] thymidine and 5-bromo-2'-deoxyuridine (BrdU) incorporation and in the number of cells per islet relative to islets treated with a control adenovirus (AdCMV-Î²GAL), whereas suppression of Nkx6.1 expression reduces thymidine incorporation. Immunocytochemical studies reveal that >80% of BrdU-positive cells in AdCMV-Nkx6.1-treated islets are Î² cells. Microarray, real-time PCR, and immunoblot analyses reveal that overexpression of Nkx6.1 in rat islets causes concerted upregulation of a cadre of cell cycle control genes, including those encoding cyclins A, B, and E, and several regulatory kinases. Cyclin E is upregulated earlier than the other cyclins, and adenovirus-mediated overexpression of cyclin E is shown to be sufficient to activate islet cell proliferation. Moreover, chromatin immunoprecipitation assays demonstrate direct interaction of Nkx6.1 with the cyclin A2 and B1 genes. Overexpression of Nkx6.1 in rat islets caused a clear enhancement of glucose-stimulated insulin secretion (GSIS), whereas overexpression of Nkx6.1 in human islets caused an increase in the level of [3H]thymidine incorporation that was twice the control level, along with complete retention of GSIS. We conclude that Nkx6.1 is among the very rare factors capable of stimulating Î²-cell replication with retention or enhancement of function, properties that may be exploitable for expansion of Î²-cell mass in treatment of both major forms of diabetes. Keywords: Insulin secretion, islet biology, transcription factor, cell cycle regulation, diabetes We utilized a âsample x referenceâ experimental design strategy in which RNA extracted from rat pancreatic islets was hybridized to the microarray slide in the presence of labeled rat reference RNA (RRR, Stratagene, LaJolla, CA). Cultures were treated with adenoviruses expressing either the hamster form of Nkx6.1 or the beta-galactosidase enzyme. 5 biological replicates each representing independent islet isolations were used for microarray analysis. Briefly, five hundred nanograms of total RNA were used for gene expression profiling following reverse transcription and T-7 polymerase-mediated amplification/labeling with Cyanine-5. Labeled subject cRNA was co-hybridized to Operon rat 27K oligonucleotide arrays with equimolar amounts of Cyanine-3 labeled RRR. Slides were hybridized, washed, and scanned on a Gene Pix 5000 microarray scanner.

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Nr4a1 and Nr4a3 upregulate cell cycle genes upregulated in the Nkx6.1 β-cell proliferation pathway

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