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BCL-6 Regulates Insulin Signaling Pathway in Adipocytes

By Yili Chen et al.

For insight into transcriptional mechanisms mediating physiologicalresponses to Growth Hormone (GH), data mining was performedon a profile of GH-regulated genes induced or inhibited at differenttimes in highly responsive 3T3-F442A adipocytes. Gene Set EnrichmentAnalysis (GSEA) indicated that GH-regulated genes are enrichedin pathways including phosphoinositide (PI) and insulin signaling,and suggested that SOCS2 and PI3 Kinase regulatory subunit p85{alpha}(Pik3r1) are important targets. Model-based Chinese RestaurantClustering (CRC) identified a group of genes highly regulatedby GH at times consistent with its key physiological actions.This cluster included IGF-1, PI3K p85{alpha}, SOCS2 and CIS. It alsocontains the most strongly repressed gene in the profile, B-celllymphoma 6 (Bcl6), a transcriptional repressor. Quantitativereal-time PCR verified the strong decrease in Bcl6 mRNA followingGH treatment, and induction of the other genes in the cluster.Transcriptional network analysis of the genes implicated SignalTransducer and Activator of Transcription (Stat) 5 as hub regulatingthe most responsive genes, Igf1, Socs2, Cish and Bcl6. Transcriptionalactivation analysis demonstrated that Bcl6 inhibits SOCS2-luciferaseand blunts its stimulation by GH. Occupancy of endogenous Bcl6on SOCS2 DNA decreased after GH treatment, while occupancy ofStat5 increased concomitantly. Thus, GH-mediated inhibitionof Bcl6 expression may reverse the repression of SOCS2 and facilitateSOCS2 activation by GH. Together these analyses identify Bcl6as a participant in GH-regulated gene expression, and suggestan interplay between the repressor Bcl6 and the activator Stat5in regulating genes which contribute to GH responses.


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