Relationship between glucocorticoid-mediated early decrease of protein synthesis and the steady state decreases of glucocorticoid receptor and TGF-β activator protein

Abstract

The present studies were undertaken to better elucidate the mechanism(s) by which glucocorticoids inhibit the process of tissue repair. The aim was to determine the importance of the effect of glucocorticoids on decreasing the nuclear TGF-β activator protein. The relationship amongst inhibition of noncollagen protein synthesis and the steady state levels of glucocorticoid receptor and the TGF-β activator protein was examined. Both collagen and noncollagen synthesis were determined in skin fibroblast cell culture and in dermis. Fetal rat skin fibroblasts were treated for 24 h with dexamethsone. Noncollagen protein synthesis was decreased to approximately one-half that of collagen synthesis. Similar results were obtained in dermis in vivo. At 48 h, dexamethasone treatment resulted in practically no nuclear glucocorticoid receptor being noted and a 40–45% steady state decrease of the TGF-β activator protein. We have recently reported that the TGF-β activator protein exists as a protein complex with SP1 and NFKB (p 49). The present data indicate that although the marked decrease of the nuclear glucocorticoid receptor DNA binding following dexamethasone treatment is not comparable to the early 24 h decrease of noncollagen protein synthesis, the decrease of the TGF-β activator protein complex binding to DNA is. The present studies indicate the importance of the effect of dexamethasone on the steady state level of the TGF-β activator protein complex in the glucocorticoid-mediated process inhibition of tissue repair and the relationship of this decrease to the earlier inhibition of protein synthesis.