Identification and pharmacological characterization of SRBP-2: a novel SR31747A-binding protein.
SR31747A is a sigma ligand with potent antiproliferative activity against tumor cells and for which three binding proteins have been identified to date: (a) SRBP-1 (also called sigma 1); (b) HIS; and (c) sigma 2. In this study, we characterized an additional SR31747A binding site, i.e., SRBP-2 (SR31747A-binding protein 2). Using an in silico screening approach, we identified this novel sequence, which exhibits 41% homology with HSI. The 1142-bp cDNA was found to encode a 206 amino acid protein not related to SRBP-1. Northern blot analysis of SRBP-2 mRNA expression revealed a single 1.1-kb transcript that was widely expressed in organs; the liver was particularly enriched, and the brain showed the lowest abundance. A murine homologue that exhibited a similar expression pattern was also characterized. Subcellular localization analysis using specific polyclonal antibodies revealed that SRBP-2 had the same nuclear membrane and endoplasmic reticulum localization as other members of the SR31747A-binding protein family. Considering SRBP-2-binding properties, pharmacological analysis clearly highlighted that SRBP-2 was distinct from sigma 2. Scatchard plot analysis revealed K(d) values of 10 and 3 nM for SR31747A and Tamoxifen, respectively. In contrast with HSI, the protein also did not exhibit detectable isomerase activity. When analyzing SRBP-2 expression in human breast cancer biopsies, we obtained evidence that SRBP-2 expression, together with SRBP-1 and HSI, may be of interest as a prognostic marker. These findings demonstrated that SRBP-2 represents an additional molecular target for SR31747A, which could help to understand the immunosuppressive and antiproliferative effects of the molecule.
Vidal
Hubert
H
Immunology-Oncology Department, Sanofi approximately Synthelabo, F-34184 Montpellier cedex 04 , France.
Mondesert
Guillaume
G
Galiègue
Sylvaine
S
Carrière
Dominique
D
Dupuy
Pascal-Henri
PH
Carayon
Pierre
P
Combes
Thérèse
T
Bribes
Estelle
E
Simony-Lafontaine
Joëlle
J
Kramar
Andrew
A
Loison
Gérard
G
Casellas
Pierre
P
D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D001943:Breast Neoplasms / Q000188:drug therapy / Q000401:mortality / Q000473:pathology; D002352:Carrier Proteins / Q000032:analysis* / Q000235:genetics / Q000494:pharmacology; D005260:Female; D006801:Humans; D017403:In Situ Hybridization; D017404:In Situ Hybridization, Fluorescence; D051379:Mice; D008969:Molecular Sequence Data; D011379:Prognosis; D012333:RNA, Messenger / Q000032:analysis; D011817:Rabbits; D011957:Receptors, Opioid; D017480:Receptors, sigma; D013251:Steroid Isomerases / Q000378:metabolism; D014407:Tumor Cells, Cultured; D000097605:Sigma-1 Receptor
D002352:Carrier Proteins; D012333:RNA, Messenger; D011957:Receptors, Opioid; D017480:Receptors, sigma; D013251:Steroid Isomerases; D000097605:Sigma-1 Receptor