The novel estrogen-responsive B-box protein (EBBP) gene is tamoxifen-regulated in cells expressing an estrogen receptor DNA-binding domain mutant.
We have identified a 2.6-kb mRNA whose steady state levels are increased 2- to 4-fold by treatment of human mammary epithelial cells (HMEC) stably expressing an estrogen receptor (ER) transgene with either estrogen (E) or the antiestrogen, 4-hydroxy-tamoxifen (HT). The cDNA corresponding to this mRNA encodes a 564-amino acid protein, named estrogen-responsive B box protein (EBBP), that is a new member of a subfamily within the B box zinc finger protein family, which includes transcription factors (e.g. TIF1), tumor suppressor proteins (e.g. PML), and proteins implicated in development (e.g. ret finger protein, XNF7). The EBBP mRNA is detectable by Northern blot analysis in most tissues, with the exception of liver and peripheral blood lymphocytes, and the gene has been mapped to human chromosome 17p11.2. In contrast to most B box family members, EBBP has a predominantly cytoplasmic localization. Studies of the estrogenic regulation of EBBP expression demonstrated that the E-dependent increase in EBBP mRNA levels in the ER-transfected HMEC is an early, ER-mediated, and cycloheximide-insensitive process. In HMEC stably transfected with an ER mutant containing a deletion in the second zinc finger of the DNA-binding domain, E and HT had different effects on EBBP gene expression; EBBP regulation by E was dramatically reduced while the effects of HT were augmented. These data indicate that HT can modulate EBBP mRNA expression through a mutated ER, which has little activity when bound by E, and suggest that different molecular mechanisms control the E and HT responsiveness of the EBBP gene.
Liu
H L
HL
Department of Cancer, Berlex Biosciences, Richmond, California 94804, USA.
Golder-Novoselsky
E
E
Seto
M H
MH
Webster
L
L
McClary
J
J
Zajchowski
D A
DA
D000595:Amino Acid Sequence; D001483:Base Sequence; D001665:Binding Sites / Q000235:genetics; D006528:Carcinoma, Hepatocellular / Q000473:pathology; D002874:Chromosome Mapping; D002886:Chromosomes, Human, Pair 17 / Q000235:genetics; D004247:DNA / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000096:biosynthesis / Q000235:genetics*; D004958:Estradiol / Q000494:pharmacology; D004965:Estrogen Antagonists / Q000494:pharmacology*; D005786:Gene Expression Regulation / Q000187:drug effects*; D005796:Genes; D006801:Humans; D008113:Liver Neoplasms / Q000473:pathology; D008969:Molecular Sequence Data; D016366:Open Reading Frames; D016133:Polymerase Chain Reaction; D011960:Receptors, Estrogen / Q000235:genetics* / Q000378:metabolism; D011993:Recombinant Fusion Proteins / Q000096:biosynthesis; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D013347:Subcellular Fractions / Q000737:chemistry; D013629:Tamoxifen / Q000494:pharmacology*; D014157:Transcription Factors / Q000096:biosynthesis / Q000235:genetics*; D000070584:Tripartite Motif Proteins; D014407:Tumor Cells, Cultured; D044767:Ubiquitin-Protein Ligases; D016335:Zinc Fingers / Q000235:genetics*
D004268:DNA-Binding Proteins; D004965:Estrogen Antagonists; D011960:Receptors, Estrogen; D011993:Recombinant Fusion Proteins; D014157:Transcription Factors; D000070584:Tripartite Motif Proteins; D013629:Tamoxifen; D004958:Estradiol; D004247:DNA; C117731:TRIM16 protein, human; D044767:Ubiquitin-Protein Ligases