Endocrine Abstracts

The glucocorticoid receptor is constitutively expressed and fundamental to life. Activity of GR is partially governed by interacting partners whose actions skew the frequency with which GR produces meaningful transcriptional outcomes. Moreover, the tissue-specific actions of GR are themselves defined, with binding patterns being distinct in various tissue types. These features mean full molecular understanding of this steroid hormone receptor remains incomplete. As glucocorticoid activation of GR and the enzyme poly(ADP-ribosyl) polymerase1 (PARP1) have prominent roles in the regulation of inflammation we sought to establish if PARP1 influences the genome binding and transcriptional productivity of GR. Murine muscle C2C12 cells were transfected with silencing RNA targeting PARP1 then treated ± dexamethasone (1uM) for 2 and 24 hours (n = 5). RNAseq was conducted on lysates to understand short and longer-term influence PARP1 holds over GR behaviour. Knockdown of PARP1 had no influence over the ability of dexamethasone to activate archetype target genes including DUSP1, MURF1, ATROGIN1 and GILZ. Silencing PARP1 significantly impacted the expression of 434 genes with Dexamethasone treatment (2hours) (164 up regulated and 270 genes down regulated). Pathway analysis of these genes show that cell-cycle regulation was significantly overrepresented (adjP = 0 .0002). Significant changes were measured in cytoskeletal tubulin genes (TUBA1A adjP = 0 .008, TUBA4A adjP = 0 .003, TUBB2A adjP = 0 .01, TUBB5 adjP = 0 .04 and TUBB4B adjP = 0 .02). ChIPseq of Dexamethasone treated C2C12s revealed shifts in GR and PARP1 binding enrichment, indicating PARP1 moderates its activity in response to glucocorticoids. Analysis of siPARP1 RNA treated for 24 hours Dexamethasone resulted in modest changes in change expression. (23 significant changes 20 upregulated and 3 downregulated). These data suggest PARP1 influences short-term transcriptional behaviours of the glucocorticoid receptor and glucocorticoids themselves impact PARP1-genome interaction events. These findings not only have importance in the understanding of general GR mechanisms but also to the wdespread functional decline observed during chronic glucocorticoid excess.