Functional properties of the N-terminal region of progesterone receptors and their mechanistic relationship to structure.
Progesterone receptors (PR) are present in two isoforms, PR-A and PR-B. The B-upstream segment (BUS) of PR-B is a 164 amino acid N-terminal extension that is missing in PR-A and is responsible for the functional differences reported between the two isoforms. BUS contains an activation function (AF3) which is defined by a core domain between residues 54-154 whose activity is dependent upon a single Trp residue and two LXXLL motifs. We have also identified sites both within and outside of BUS that repress the strong synergism between AF3 and AF1 in the N-terminal region and AF2 in the hormone binding domain. One of these repressor sites is a consensus binding motif for the small ubiquitin-like modifier protein, SUMO-1 (387IKEE). The DNA binding domain (DBD) structure is also important for function. When BUS is linked to the glucocorticoid receptor DBD, AF3 activity is substantially attenuated, suggesting that binding to a DNA response element results in allosteric communication between the DBD and N-terminal functional regions. Lastly, biochemical and biophysical analyses of highly purified PR-B and PR-A N-terminal regions reveal that they are unstructured unless the DBD is present. Thus, the DBD stabilizes N-terminal structure. We propose a model in which the DBD through DNA binding, and BUS through protein-protein interactions, stabilize active receptor conformers within an ensemble distribution of active and inactive conformational states. This would explain why PR-B are stronger transactivators than PR-A.
Takimoto
Glenn S
GS
Department of Medicine, Molecular Biology Program, University of Colorado Health Sciences Center, Denver, CO 80262, USA. glenn.takimoto@uchsc.edu
Tung
Lin
L
Abdel-Hafiz
Hany
H
Abel
Michael G
MG
Sartorius
Carol A
CA
Richer
Jennifer K
JK
Jacobsen
Britta M
BM
Bain
David L
DL
Horwitz
Kathryn B
KB
D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D019556:COS Cells; D002522:Chlorocebus aethiops; D006367:HeLa Cells; D006801:Humans; D008969:Molecular Sequence Data; D016296:Mutagenesis; D010446:Peptide Fragments / Q000737:chemistry; D020033:Protein Isoforms / Q000737:chemistry / Q000502:physiology; D011980:Receptors, Progesterone / Q000737:chemistry* / Q000235:genetics / Q000502:physiology*; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D014158:Transcription, Genetic; D014162:Transfection
D010446:Peptide Fragments; D020033:Protein Isoforms; D011980:Receptors, Progesterone; D011994:Recombinant Proteins; C101118:progesterone receptor A; C097314:progesterone receptor B