Computational and Functional Analysis of Growth Hormone (GH)-Regulated Genes Identifies the Transcriptional Repressor B-Cell Lymphoma 6 (Bc16) as a Participant in GH-Regulated Transcription

For insight into transcriptional mechanisms mediating physiological responses to GH, data mining was performed on a profile of GH-regulated genes induced or inhibited at different times in highly responsive 3T3-F442A adipocytes. Gene set enrichment analysis indicated that GH-regulated genes are enriched in pathways including phosphoinositide and insulin signaling and suggested that suppressor of cytokine signaling 2 (SOCS2) and phosphoinositide 3Ј kinase regulatory subunit p85␣ (Pik3r1) are important targets. Model-based Chinese restaurant clustering identified a group of genes highly regulated by GH at times consistent with its key physiological actions. This cluster included IGF-I, phosphoinositide 3Ј kinase p85␣, SOCS2, and cytokine-inducible SH2-containing protein. It also contains the most strongly repressed gene in the profile, B cell lymphoma 6 (Bcl6), a transcriptional repressor. Quantitative real-time PCR verified the strong decrease in Bcl6 mRNA after GH treatment and induction of the other genes in the cluster. Transcriptional network analysis of the genes implicated signal transducer and activator of transcription (Stat) 5 as hub regulating the most responsive genes, Igf1, Socs2, Cish, and Bcl6. Transcriptional activation analysis demonstrated that Bcl6 inhibits SOCS2-luciferase and blunts its stimulation by GH. Occupancy of endogenous Bcl6 on SOCS2 DNA decreased after GH treatment, whereas occupancy of Stat5 increased concomitantly. Thus, GH-mediated inhibition of Bcl6 expression may reverse the repression of SOCS2 and facilitate SOCS2 activation by GH. Together these analyses identify Bcl6 as a participant in GH-regulated gene expression and suggest an interplay between the repressor Bcl6 and the activator Stat5 in regulating genes, which contribute to GH responses. (Endocrinology 150: 3645-3654, 2009) S equencing of the human genome has provided new tools for addressing long-standing questions regarding transcription regulatory events. Whereas GH has long been recognized as a key regulator of growth and metabolism, new questions continually arise as to how it modulates cellular function. We have made considerable progress in understanding how GH signals through the GH receptor and its associated tyrosine kinase Janus kinase-2 (1, 2) and have achieved some knowledge of how GH regulates gene transcription, through analysis of well-studied GH target genes such as those encoding IGF1, C-fos, Spi2.1, Cyp2, and Cyp3 family members (3-10). However, to understand the diverse and complex events that are modulated by GH, it is informative to gain a global perspective of how GH regulates target genes and how they relate to physiological responses to GH. GH is a major promoter of postnatal longitudinal growth. In addition, GH antagonizes insulin action as part of the coordinated mechanisms by which multiple hormones maintain metabolic homeostasis. In conditions of chronic GH excess, devel