title: Transcriptional activation by estrogen receptor (ERalpha) and steroid receptor coactivator (SRC1) involves distinct mechanisms in yeast and mammalian cells.
abstract: Steroid receptors activate transcription in yeast cells via interactions with endogenous coactivators and/or basal factors. We examined the effects of mutations in the ligand binding domain on the transcriptional activity of ERalpha in yeast. Our results show that mutations in Helix 3 (K366A) and Helix 12 (M547A, L548A) disrupt transcriptional activity of ERalpha in yeast, as previously observed in mammalian cells. However, replacement of a conserved tyrosine residue in Helix 12 with alanine or aspartate (Y541A and Y541D), which renders ERalpha constitutively active in mammalian cells, had only a weak stimulatory effect on ligand-independent reporter activation by ERalpha in yeast. Two-hybrid interaction experiments revealed that a Y541A mutant expressed in yeast was capable of ligand-independent binding to a mammalian coactivator, suggesting that there is a subtle difference in how this mutant interacts with mammalian and yeast cofactors. We also show that the ligand-dependent activities of ERalpha and progesterone receptor (PR) in yeast cells were strongly enhanced by the human p160 protein steroid receptor coactivator (SRC1), but not by CREB-Binding Protein (CBP) or the p300/CBP associated factor (P/CAF). Although the SRC1 activation domains AD1 and AD2 are functional in yeast, deletion of these sequences only partially impaired SRC1 coactivator function in this organism; this is in contrast to similar experiments in mammalian cells. Thus SRC1 sequences involved in recruitment of CBP/p300 and Co-Activator-Associated Arginine Methyltransferase (CARM-1) in mammalian cells are not essential for its function in yeast, suggesting that SRC1 operates via distinct mechanisms in yeast and mammalian cells.
authors.affiliation: Department of Biochemistry, University of Leicester, University Road, Leicester LE1 7RH, UK.
authors.forename: H M
authors.initials: HM
authors.lastname: Sheppard
authors.forename: S
authors.initials: S
authors.lastname: Matsuda
authors.forename: J C
authors.initials: JC
authors.lastname: Harries
authors.forename: K B
authors.initials: KB
authors.lastname: Kindle
authors.forename: D M
authors.initials: DM
authors.lastname: Heery
mesh_terms: D051548:Histone Acetyltransferases; D056920:Nuclear Receptor Coactivator 1; D017354:Point Mutation; D011960:Receptors, Estrogen / Q000235:genetics / Q000378:metabolism*; D012441:Saccharomyces cerevisiae / Q000235:genetics*; D014157:Transcription Factors / Q000502:physiology*; D015533:Transcriptional Activation / Q000502:physiology*
chemical_list: D011960:Receptors, Estrogen; D014157:Transcription Factors; D051548:Histone Acetyltransferases; C538859:NCOA1 protein, human; D056920:Nuclear Receptor Coactivator 1