[Show abstract][Hide abstract] ABSTRACT: The glucocorticoid receptor (GR) regulates adaptive transcriptional programs that alter metabolism in response to stress. Network properties that allow GR to tune gene expression to match specific physiologic demands are poorly understood. We analyzed the transcriptional consequences of GR activation in murine lungs deficient for KLF15, a transcriptional regulator of amino acid metabolism that is induced by glucocorticoids and fasting. Approximately 7% of glucocorticoid-regulated genes had altered expression in Klf15(-/-) mice. KLF15 formed coherent and incoherent feed forward circuits with GR that correlated with the expression dynamics of the glucocorticoid response. Coherent feed forward gene regulation by GR and KLF15 was characterized by combinatorial activation of linked GR/KLF15 regulatory elements by both factors and increased GR occupancy, while expression of KLF15 reduced GR occupancy at the incoherent target, MT2A. Serum deprivation, which increased KLF15 expression in a GR-independent manner in vitro, enhanced glucocorticoid-mediated induction of feed forward targets of GR and KLF15, such as the amino acid metabolizing enzymes PRODH and AASS. Our results establish feed forward architecture as an organizational principle for the GR network and provide a novel mechanism through which GR integrates signals and regulates expression dynamics.
[Show abstract][Hide abstract] ABSTRACT: Glucocorticoids (GCs), which activate GC receptor (GR) signaling and thus modulate gene expression, are widely used to treat asthma. GCs exert their therapeutic effects in part through modulating airway smooth muscle (ASM) structure and function. However, the effects of genes that are regulated by GCs on airway function are not fully understood. We therefore used transcription profiling to study the effects of a potent GC, dexamethasone, on human ASM (HASM) gene expression at 4 and 24 hours. After 24 hours of dexamethasone treatment, nearly 7,500 genes had statistically distinguishable changes in expression; quantitative PCR validation of a 40-gene subset of putative GR-regulated genes in 6 HASM cell lines suggested that the early transcriptional targets of GR signaling are similar in independent HASM lines. Gene ontology analysis implicated GR targets in controlling multiple aspects of ASM function. One GR-regulated gene, the transcription factor, Kruppel-like factor 15 (Klf15), was already known to modulate vascular smooth and cardiac muscle function, but had no known role in the lung. We therefore analyzed the pulmonary phenotype of Klf15(-/-) mice after ovalbumin sensitization and challenge. We found diminished airway responses to acetylcholine in ovalbumin-challenged Klf15(-/-) mice without a significant change in the induction of asthmatic inflammation. In cultured cells, overexpression of Klf15 reduced proliferation of HASM cells, whereas apoptosis in Klf15(-/-) murine ASM cells was increased. Together, these results further characterize the GR-regulated gene network in ASM and establish a novel role for the GR target, Klf15, in modulating airway function.
American Journal of Respiratory Cell and Molecular Biology 09/2011; 45(3):642-9. DOI:10.1165/rcmb.2010-0369OC · 3.99 Impact Factor