ABSTRACT
Numerous membrane receptors for hormones and growth factors have been demonstrated to function as protein kinases (PKs), and phosphorylation of these receptors, proteins themselves, plays a key role in regulating the enzymatic activity. In this chapter, the authors review the evidence that suggests that phosphorylation/dephosphorylation reactions play a key role in regulating glucocorticoid-receptor activity. They focus on more recent data that suggest that the purified, activated/transformed glucocorticoid receptor either is itself a PK or is very closely associated with a distinct PK. The various experimental conditions required for maximal receptor-mediated kinase activity (autophosphorylation, histone phosphorylation, and nuclear matrix phosphorylation), as well as the biochemical reagents that have been utilized to probe the structure of the kinase, are also discussed. However, the activity of histone phosphorylation leads to speculation that glucocorticoid receptor-mediated phosphorylation of nuclear proteins may be a component of gene activation.
