ligand. When methylprednisolone from the plasma or interstitial fluid diffuses passively across the cell membrane, it binds to the GR inducing a conformational change and GC-GR dimerization. It was previously thought that this conformational change was necessary to dissociate the multiprotein complex to allow the ligand bound receptor to translocate to the nucleus. However, recent studies have indicated that chaperones play a role in nuclear import. The now active methylprednisolone-GR complex can either transduce non-genomic changes in the cytoplasm or translocate to the nucleus and regulate transcriptional activity of target genes by direct, tethering or composite mechanisms. Genomic signaling Genomic mechanisms, regardless of which type, elicit responses with a slow onset and a slow dissipation. This is attributed to the duration of mRNA transcription and translation. Glucocorticoids have the ability to regulate roughly 100 to 1000 genes with specificity to cell-type. Three major mechanisms have described how the MP-GR complex alter gene expression by either binding to DNA or transcription modulators. One mechanism of genomic signaling occurs when the MP-GR complex directly binds to DNA sequences called glucocorticoid response elements (GREs). GREs are located in regulatory regions of target genes and mediate their transactivation or transrepression. For example, the activation of lipocortin 1 (ANAX1) negatively interferes with the production of prostaglandins and leukotrienes, known pro-inflammatory signals. Likewise, negative GREs (nGREs) are responsible for repressing genes involved in immune cell activation. Post transcriptional modifications Post translational modifications (PTMs) also contribute to methylprednisolone signaling and can produce genomic and non-genomic effects. The GR has contains several sites for phosphorylation, sumoylation, ubiquitination, and acetylation that primarily occurs after intracellular methylprednisolone binding to the GR. PTMs modulate many functions including nuclear translocation, strength and duration of receptor signaling and cofactor interaction. A specific example is the deacetylation by histone deacetylase 2 (HDACe) was necessary for transrepression of NF-κB. Non-genomic signaling The mechanisms of non-genomic signaling are distinct from genomic signaling, yet mediate similar pathways and provide therapeutic relevance. These mechanisms are characterized as having a rapid onset (less than 15 minutes), because they do not rely on time-consuming transcription or translation and are not modified by inhibitors of transcription. Methylprednisolone induced non-genomic signaling is classified by three mechanisms: (1) cytoplasmic glucocorticoid receptor (cGR)-mediated non-genomic effects, (2) membrane-bound glucocorticoid receptor (mGR) non-genomic effects, and (3) physiochemical interactions with cellular membranes (non-specific non-genomic effects). Proteins that dissociate from the activated GC-cGR complex, initiate intracellular transcription-independent mechanisms.