In search of Glucocorticoid Receptor target genes involved in apoptois

HOIJMAN, E; KORDON, E; KALKO, S; PECCI, A.

Bariloche, Argentina

Simposio; 1. ICGEB Symposium, "Gene Expression and RNA processing"; 2007

1. ICGEB

The effect of activating the Glucocorticoid Receptor (GR), a ligand-dependent transcription factor, appears to be cell-type specific. While it triggers apoptosis of immune cells, prevents apoptosis of ephitelial cells induced by different stimuli. The target genes of GR involved in apoptosis modulation are still unknown. Particularly, in vivo administration of Glucocorticoids (GCs) prevents apoptosis of ephitelial cells of post lactating involuting mammary gland. The aim of this work was to identify GR-regulated genes during this process by performing a genome-wide screen using oligonucleotide microarrays. Mammary involution was induced in BALB/c mice by removing the pups. To study the glucocorticoid effect, subcutaneous injections of Dexamethasone 0.5mg/100g body weight or vehicle, were applied at 0, 24 and 48 hours after weanning. After additional 24 hours, RNA from the mammary gland was prepared and hibridized to the Affymetrix oligonucleotide GeneChip Mouse Genome 430 2.0. From 34000 analized genes, 492 were differentially expressed between the two experimental groups, being 137 induced (fold changes from 1.49 to 32.8) and 355 repressed (fold changes from 0.68 to 0.12) by the GC treatment. Searching overrepresented gene ontology terms with the EASE software, the most interesting category on the molecular function system, was “Tumor suppressor”, comprised 5 genes all down-regulated by GCs. These genes could be potential candidates as mediators of the GCs antiapoptotic action observed in the mammary gland. Eleven of differentially expressed genes were validated by Real-Time PCR. Some of those genes were modulated during the mammary gland development, correlating their greatest expression with the higher GC levels, suggesting an expression control by endogenous GCs. Interestingly, the cell cycle inhibitor p21 was repressed by GCs in mammary ephitelial cells and induced in thymocytes. Considering the ability of p21 to control cell cycle and apoptosis, this gene emerge as a candidate  to mediate cell type specific effect of GR.