title: Characterization of a plasma membrane-resident albumin-binding protein associated with the proliferation of estrogen-target, serum-sensitive cells.
abstract: Estrogens control the proliferation of their target cells through a receptor-mediated pathway. Recently presented evidence suggests that estradiol cancels the proliferative inhibition exerted by human albumin (HA) and recombinant human albumin (rHA) on estrogen-target serum-sensitive cells (indirect-negative hypothesis). We postulate that this mechanism requires the presence of a plasma membrane estrogen receptor (mER) and a plasma membrane albumin-binding protein (mABP). Direct evidence confirming the presence of mERalpha in MCF7 cells has recently been presented. Herein, we now show that Western blot analysis of purified T47D membrane proteins with the C542 ERalpha specific monoclonal antibody also revealed specific, multiple M(r) mERs (67, 110, and 130k M(r)). In addition, Western blot analysis with an ABP antiserum revealed a potential 60k M(r) ABP in both MCF7 and T47D plasma membrane extracts. No such evidence was observed in similar extracts from ER-negative, serum-insensitive MDA-MB231 cells. Ligand blot analysis of similar plasma membrane extracts with bovine serum albumin confirmed the presence of a 60k M(r) ABP in MCF7 and T47D cells; again, no such evidence was observed in comparable extracts from MDA-MB231 cells. Fluorescence and confocal microscopy of MCF7 cells fixed in 2.0% paraformaldehyde/0.1% glutaraldehyde identified specific membrane ABP antigenic sites by immunocytochemistry. Serum-insensitive MDA-MB231 cells fixed and labeled similarly did not exhibit this mABP. These results suggest that the proposed mABP is expressed only in serum-sensitive estrogen-target cells and is not expressed in cells insensitive to the proliferative inhibition of HA and rHA. Also, the present data suggest that the proposed mABP may be the recognition mechanism by which both HA and rHA inhibit MCF7 and T47D cell proliferation.
authors.affiliation: Department of Anatomy and Cellular Biology, Tufts University School of Medicine, 136 Harrison Avenue, Boston, MA 02111, USA.
authors.forename: Charles E
authors.initials: CE
authors.lastname: Powell
authors.forename: Ana M
authors.initials: AM
authors.lastname: Soto
authors.forename: Cheryl L
authors.initials: CL
authors.lastname: Michaelson
authors.forename: Fantahun
authors.initials: F
authors.lastname: Diba
authors.forename: Françoise
authors.initials: F
authors.lastname: Mounier
authors.forename: Pierre J
authors.initials: PJ
authors.lastname: Verroust
authors.forename: Carlos
authors.initials: C
authors.lastname: Sonnenschein
mesh_terms: D015153:Blotting, Western; D002455:Cell Division / Q000187:drug effects / Q000502:physiology*; D045744:Cell Line, Tumor; D004967:Estrogens / Q000494:pharmacology; D006801:Humans; D007150:Immunohistochemistry; D008565:Membrane Proteins / Q000032:analysis* / Q000378:metabolism / Q000502:physiology; D010446:Peptide Fragments / Q000494:pharmacology; D011485:Protein Binding; D025941:Protein Interaction Mapping; D011960:Receptors, Estrogen / Q000032:analysis; D012709:Serum Albumin / Q000378:metabolism / Q000494:pharmacology*
chemical_list: D004967:Estrogens; D008565:Membrane Proteins; D010446:Peptide Fragments; D011960:Receptors, Estrogen; D012709:Serum Albumin