Intramolecular interactions between the AF3 domain and the C-terminus of the human progesterone receptor are mediated through two LXXLL motifs

Abstract

The human progesterone receptor (PR) exists in two major forms, PRA and PRB, which differentially regulate gene transcription in a cell-and promoter-specific manner. The molecular mechanisms underlying this differential transcriptional activity have been attributed to the presence of a unique AF3 domain within PRB that may result in the two isoforms adopting different protein conformations. We demonstrate here that in myometrial cells, PRB exhibits strong progesterone-dependent transcriptional activity that is dependent on the presence of two LXXLL motifs within the AF3 domain. In vitro and in vivo protein interaction assays indicate that these motifs mediate the direct interaction between the AF3 domain and C-PR in a progesterone-dependent manner. Mutation of either of the LXXLL motifs or deletion of the last 30 amino acids within the C-terminus disrupts this interaction and progesterone-dependent transcriptional activity of PRB. Members of the p160 family of co-activators (such as GRIP-1) also interact with C-PR through their LXXLL motifs. However, GRIP-1 does not compete with AF3 but rather acts to synergize these two transactivation domains. Our data suggest that a failure to form an appropriate AF3-C-terminus interaction results in an inability of co-activators to induce maximal PR-dependent transactivation. The absence of an AF3 domain within PRA may account for its inability to activate progesterone-responsive genes, as well as its actions as a dominant trans-repressor.

Progesterone Receptors (PR)-B and -A Regulate Transcription by Different Mechanisms: AF-3 Exerts Regulatory Control over Coactivator Binding to PR-B

“…An FxxLF sequence in androgen receptor (AR) N termini is required for direct N-/C-terminal interactions. The two LxxLL motifs in BUS, akin to nuclear receptor (NR) boxes, subserve a similar function (21). Neither of these motifs competes for binding of p160 coregulators, however, which also contain NR boxes needed to bind receptors (21).…”

“…The two LxxLL motifs in BUS, akin to nuclear receptor (NR) boxes, subserve a similar function (21). Neither of these motifs competes for binding of p160 coregulators, however, which also contain NR boxes needed to bind receptors (21). Indirect N-/C-terminal interactions are also facilitated by bridging factors like steroid receptor coactivator (SRC)-1, SRC-2, JDP-2, and cAMP response element binding protein (CREB)-binding protein (CBP)/p300 for PR (22)(23)(24)(25), Ada2, TBP, and CBP for GR (26,27), and SRC-1, SRC-2, CBP, and the RAP74 subunit of transcription factor IIF for AR (28,29).…”

Anti-estrogenic mechanism of unliganded progesterone receptor isoform B in breast cancer cells

“…The second possible mode of action is that BUS segment synergize with endogenous PR-B to squelch co-activators that are required for ERa activity. It is known that LXXLL motifs in BUS mediate intra-molecular interaction between AF-3 and C-terminus of PR-B that was essential for co-factor binding [32,35,36]. Isolated BUS was also able to interact with LBD of PR-B to elicit cooperative interaction and transactivation, and mutations in 55 LXXLL and 115 LXXLL abolished this interaction [35].…”

Primate-specific Melanoma Antigen-A11 Regulates Isoform-specific Human Progesterone Receptor-B Transactivation

“…MAGE-11 increases human PR-B and AR transcriptional activity through an interaction with NH 2 -terminal ␣-helical motifs involved in ligand-dependent NH 2 -and COOH-terminal interactions (24,35,36). MAGE-11 regulates the single full-length form of human AR through an interaction with the AR NH 2 -terminal FXXLF motif region and has isoform-specific coregulator activity with PR-B through an interaction with the NH 2 -terminal 110 LLXXVLXXLL 119 motif unique to PR-B.…”

“…It is noteworthy that progesterone action in human endometrium is closely linked to cyclic AMP (34), a second messenger signaling molecule that acutely stimulates the expression of MAGE-11 (31). Additionally, the PR-B NH 2 -terminal region absent in PR-A interacts with the PR ligand-binding domain in a hormone-dependent NH 2 -and COOH-terminal interaction similar to AR (24,35,36). The primate-specific expression of MAGE-11, the up-regulation of MAGE-11 in the secretory human endometrium, the close evolutionary relationship between AR and PR, and the importance of AR and PR-B NH 2 -terminal domains in transactivation all suggest that MAGE-11 could be an important coregulator of human PR-B.…”