The leucine zippers of c-fos and c-jun for progesterone receptor dimerization: A-dominance in the A/B heterodimer

Mohamed, Mohamed K.; Tung, Lin; Takimoto, Glenn S.; Horwitz, Kathryn B.

doi:10.1016/0960-0760(94)90036-1

Cited by 41 publications

(16 citation statements)

References 35 publications

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“…Therefore, to force heterodimerization of hPR, the leucine zippers of c-Fos or c-Jun were fused to the C-terminus of hPR, or hPR, (56). These chimeric hPR retain agonist and antagonist binding capacity, and agonist or antagonist-occupied hPR,-Jun and hPR,-Fos, when each is expressed alone, have the same transcriptional phenotype as the wild-type receptors.…”

Section: A -Receptors Are Transdominant Repressors Of B-receptors Witmentioning

confidence: 99%

Novel Mechanisms of Antiprogestin Action

Horwitz

Tung²,

Takimoto³

1996

Acta Oncologica

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Section: A -Receptors Are Transdominant Repressors Of B-receptors Witmentioning

confidence: 99%

Novel Mechanisms of Antiprogestin Action

Horwitz

Tung²,

Takimoto³

1996

Acta Oncologica

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“…In vitro, PR-B are transcriptional activators of some promoters in a variety of cell types in which PR-A have low activity. PR-A, on the other hand, are dominant repressors of PR-B, estrogen receptors (ERs), and other steroid receptors in a promoter-and cell-type-specific manner (5)(6)(7)(8).…”

Section: Introductionmentioning

confidence: 99%

Breast Cancer Patients with Progesterone Receptor PR-A-Rich Tumors Have Poorer Disease-Free Survival Rates

Hopp

Weiss

Hilsenbeck

et al. 2004

Clinical Cancer Research

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182

149

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Results: Expression of the two isoforms correlated with each other, as well as with ER. Additional analyses revealed that patients with PR-positive tumors but high PR-A:PR-B ratios, which were often caused by high PR-A levels, were 2.76 times more likely to relapse than patients with lower ratios, indicating resistance to tamoxifen.Conclusions: This study suggests that knowledge of the PR-A:PR-B ratio may identify a subgroup of ER-positive/ PR-positive patients with node-positive breast cancer that benefit poorly from endocrine therapy.

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“…In general, B-receptors are stronger transactivators than A-receptors (5,(7)(8)(9), and only B-receptors can activate transcription in the presence of antiprogestins (9 -11). On the other hand, A-receptors can dominantly inhibit B-receptors (9,12,13) as well as other members of the steroid receptor family (14).…”

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confidence: 99%

An N-terminal Inhibitory Function, IF, Suppresses Transcription by the A-isoform but Not the B-isoform of Human Progesterone Receptors

Hovland¹,

Powell

Takimoto

et al. 1998

Journal of Biological Chemistry

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132

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The B-isoform of human progesterone receptors (PR) contains three activation functions (AF3, AF1, and AF2), two of which (AF1 and AF2) are shared with the Aisoform. AF3 is in the B-upstream segment (BUS), the far N-terminal 164 amino acids of B-receptors; AF1 is in the 392-amino acid N-terminal region common to both receptors; and AF2 is in the C-terminal hormone binding domain. B-receptors are usually stronger transactivators than A-receptors due to transcriptional synergism between AF3 and one of the two downstream AFs. We now show that the N terminus of PR common to both isoforms contains an inhibitory function (IF) located in a 292-amino acid segment lying upstream of AF1. IF represses the activity of A-receptors but is not inhibitory in the context of B-receptors due to constraints imparted by BUS. As a result, IF inhibits AF1 or AF2 but not AF3, regardless of the position of IF relative to BUS. IF is functionally independent and strongly represses transcription when it is fused upstream of estrogen receptors. These data demonstrate the existence of a novel, transferable inhibitory function, mapping to the PR N terminus, which begins to assign specific roles to this large undefined region.Transcriptional control in response to extracellular signals involves the binding of regulatory proteins to specific enhancer elements of target genes. These proteins contain activation functions (AFs) 1 through which contact is made with the basal transcription machinery either directly or indirectly by means of intermediary coregulatory proteins (1). Progesterone receptors (PR) are members of the nuclear receptor family of ligandinducible transcription factors. These are structurally complex proteins containing multiple functional domains, including a highly conserved central DNA-binding domain (DBD), a moderately well conserved C-terminal hormone-binding domain (HBD), and a poorly conserved, N-terminal region whose function is largely unknown (1).There are two naturally occurring isoforms of PR. The 933-amino acid B-receptors contain an N-terminal 164-amino acid upstream segment (BUS) that is missing in the truncated 769-amino acid A-receptors (2-5). The two PR isoforms have AF1 and AF2 in common (5,6). AF1 maps to a 91-amino acid "proline-rich" segment located just upstream of the DBD and AF2 is located in the HBD (6). BUS, restricted to B-receptors, contains AF3 (5). In general, B-receptors are stronger transactivators than A-receptors (5, 7-9), and only B-receptors can activate transcription in the presence of antiprogestins (9 -11). On the other hand, A-receptors can dominantly inhibit B-receptors (9, 12, 13) as well as other members of the steroid receptor family (14).In addition to AFs, some transcription factors also contain inhibitory domains (IDs) that modulate the activity of the AFs. Such IDs have been identified by deletion mutagenesis that generate proteins with enhanced transcriptional activities. Examples include members of the AP1 family c-Jun (15), c-Fos, and the related protein, FosB (16); ATF-2, a ...

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The leucine zippers of c-fos and c-jun for progesterone receptor dimerization: A-dominance in the A/B heterodimer

Cited by 41 publications

References 35 publications

Novel Mechanisms of Antiprogestin Action

Novel Mechanisms of Antiprogestin Action

Breast Cancer Patients with Progesterone Receptor PR-A-Rich Tumors Have Poorer Disease-Free Survival Rates

An N-terminal Inhibitory Function, IF, Suppresses Transcription by the A-isoform but Not the B-isoform of Human Progesterone Receptors

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