Phosphorylation of chicken oviduct progesterone receptor by cAMP-dependent protein kinase

The androgen receptor acetylation site regulates cAMP and AKT but not ERK-induced activity

The androgen receptor (AR) regulates ligand-dependent gene transcription upon binding specific DNA sequences. The AR conveys both trans-activation and trans-repression functions, which together contribute to prostate cellular growth, differentiation, and apoptosis. Like histone H3, the AR is post-translationally modified by both acetylation and phosphorylation. The histone acetyltransferase p300 transactivates the AR and directly acetylates the AR in vitro at a conserved motif. Point mutations of the AR acetylation motif that abrogate acetylation reduce trans-activation by p300 without affecting the trans-repression function of the AR. The current studies assessed the functional relationship between acetylation and phosphorylation of the AR. Herein trans-activation of the AR acetylation site mutants were enhanced by the p42/p44 MAPK pathway but were defective in regulation by protein kinase A (PKA) signaling. PKA inhibition augmented ARwt activity but not AR acetylation mutant gene reporter activity and association at an androgen response element in chromatin immunoprecipitation assays. Mutations of the lysine residues at the AR acetylation site reduced trichostatin A (TSA) responsiveness and ligand-induced phosphorylation of the AR. The AR acetylation site mutant formed ligand-induced phosphorylation-dependent isoforms with distinguishable characteristics from wild type AR as determined with two-dimensional electrophoresis. Conversely, point mutation of a subset of AR phosphorylation sites reduced trichostatin A responsiveness and trans-activation by histone acetyltransferases. Together these studies suggest that acetylation and phosphorylation of the AR are linked events and that the conserved AR lysine motif contributes to a select subset of pathways governing AR activity.

Characterization of ligand binding, DNA binding and phosphorylation of progesterone receptor by two novel progesterone receptor antagonist ligands

In order to gain a better understanding of the distinctive mechanisms of the various types of antiprogestins, we have characterized in vitro ligand binding, specific DNA binding and phosphorylation of progesterone receptor (PR) from T47D cells after treatment of cells with progestins (progesterone, R5020) and antiprogestins (RU486, ZK98299, Org 31806 and Org 31710). Treatment of the cells with R5020 or PR antagonists, with the exception of ZK98299, resulted in a quantitative upshift of PR-A and PR-B indicative of ligand/DNA-induced phosphorylation of PR. Treatment of cells with RU486, Org 31710 or Org 31806, but not R5020 or ZK98299 resulted in detectable PR-progesterone response element complexes (PR-PREc) as assessed by gel mobility shift assay. Although treatment of cells with ZK98299, a type I PR antagonist, did not induce phosphorylation, the antiprogestins, Org 31806 and Org 31710, in a manner identical to RU486, did. Our data suggest that Org 31806 and Org 31710 affect properties of PR from T47D cells that are similar to RU486.

Role of phosphorylation on DNA binding and transcriptional functions of human progesterone receptors

To study the function of human progesterone receptor (hPR) phosphorylation, we have tested four sets of serine to alanine substitution mutants: 10 serine clusters, located in regions common to both hPR isoforms (the M-series mutants) were mutated in A-receptors and B-receptors; 6 serine clusters located in the B-upstream segment (BUS; the B-series mutants) were mutated individually and collectively and cloned into B-receptors and into BUS-DBD-NLS, a constitutive transactivator, in which the AF3 function of BUS is fused to the DNA binding domain (DBD) and nuclear localization signal (NLS) of hPR. Transcription by most of the M-series mutants resembles that of wild-type A- or B-receptors. Mutation of 3 sites, Ser190 at the N terminus of A-receptors, a cluster of serines just upstream of the DBD, or Ser676 in the hinge region, inhibits transcription by 20-50% depending on cell or promoter context. These sites lie outside the AF1 activation function. M-series mutants are substrates for a hormone-dependent phosphorylation step, and they all bind well to DNA. Progressive mutation of the B-series clusters leads to the gradual dephosphorylation of BUS, but only the 6-site mutant, involving 10 serine residues, is completely dephosphorylated. These data suggest that in BUS alternate serines are phosphorylated or dephosphorylated at any time. However, even when BUS is completely dephosphorylated, both BUS-DBD-NLS and full-length B-receptors remain strong transactivators. Mutant B-receptors also do not acquire the dominant negative properties of A-receptors, and they retain the ability to activate transcription in synergy with 8-Br-cAMP and antiprogestins. We conclude that phosphorylation has subtle effects on the complex transcriptional repertoire that distinguishes the two hPR isoforms and does not influence transactivation mediated by AF1 or AF3, but subserves other functions.

Steroid hormone receptor phosphorylation: is there a physiological role?

All members of the steroid hormone receptor family are phosphoproteins. Additional phosphorylation occurs in the presence of hormone. This hormone-induced phosphorylation, which is 2- to 7-fold more than the basal phosphorylation, is a rapid process. All steroid receptors are phosphorylated at more than one single site. Most phosphorylation sites are located in the N-terminal domain, and phosphorylation occurs mainly on serine residues. Phosphorylation on threonine residues occurs in only a few cases. Phosphorylation on tyrosine residues has been found only for the estrogen receptor. Six different protein kinases are possibly involved in steroid receptor phosphorylation (estrogen receptor kinase; protein kinase A; protein kinase C; casein kinase II; DNA-dependent kinase; Ser-Pro kinases). Steroid receptor phosphorylation has been directly implicated in: activation of hormone binding, nuclear import of steroid receptors, modulation of binding to hormone response elements, and consequently in transcription activation.

Phosphorylation of immunopurified rat liver glucocorticoid receptor by the catalytic subunit of cAMP-dependent protein kinase

We have examined phosphorylation of the rat liver glucocorticoid receptor (GR) and GR-associated protein kinase (PK) activity in the immunopurified receptor preparations. Affinity labeling of hepatic cytosol with [3H]dexamethasone 21-mesylate showed a covalent association of the steroid with a 94 kDa protein. GR was immunopurified with antireceptor monoclonal antibody BuGR2 (Gametchu & Harrison, Endocrinology 114: 274-279, 1984) to near homogeneity. A 23 degrees C incubation of the immunoprecipitated protein A-Sepharose adsorbed GR with [gamma-32P]ATP,Mg2+ and the catalytic subunit of cAMP-dependent PK (cAMP-PK) from bovine heart, led to an incorporation of radioactivity in the 94 kDa protein. Phosphorylation of GR was not evident in the absence of the added kinase. Of the radioinert nucleotides (ATP, GTP, UTP or CTP) tested, only ATP successfully competed with [gamma-32P]ATP demonstrating a nucleotide specific requirement for the phosphorylation of GR. Other divalent cations, such as Mn2+ or Ca2+, could not be substituted for Mg2+ during the phosphorylation reaction. Phosphorylation of GR was sensitive to the presence of the protein kinase inhibitor, H-8, an isoquinoline sulfonamide derivative. In addition, the incorporation of radioactivity into GR was both time- and temperature-dependent. The phosphorylation of GR by cAMP-PK was independent of the presence of hsp-90 and transformation state of the receptor. The results of this study demonstrate that GR is an effective substrate for action of cAMP-PK and that the immunopurified protein A-Sepharose adsorbed GR lacks intrinsic kinase activity but can be conveniently used for the characterization of the phosphorylation reaction in the presence of an exogenous kinase.