From Drugs.com:
"Mechanism of Action: Glucocorticoids are naturally occurring hormones that prevent or suppress inflammation and immune responses when administered at pharmacological doses. In general, glucocorticoids inhibit the activity of a variety of cell types (e.g., mast cells, eosinophils, neutrophils, macrophages, and lymphocytes) and mediators involved in allergic and nonallergic/irritant-mediated inflammation (e.g., histamine, eicosanoids, leukotrienes, and cytokines). At the molecular level, unbound glucocorticoids readily cross cell membranes and bind with high affinity to specific cytoplasmic receptors. Subsequent to binding, transcription and, ultimately, protein synthesis are affected. The result can include inhibition of leukocyte infiltration at the site of inflammation, interference in the function of mediators of inflammatory response, and suppression of humoral immune responses. The anti-inflammatory actions of corticosteroids are thought to involve phospholipase A2 inhibitory proteins, collectively called lipocortins. Lipocortins, in turn, control the biosynthesis of potent mediators of inflammation such as prostaglandins and leukotrienes by inhibiting the release of the precursor molecule arachidonic acid. Some of the net effects include reduction in edema or scar tissue as well as a general suppression in immune response. The numerous adverse effects related to corticosteroid use usually depend on the dose administered and the duration of therapy."
Now, i dont believe that the affect of protein synthesis would be ALOT. Nothing anywhere near the amount to strongly hinder gains.