Regulation of BOB.1/OBF.1 stability by SIAH.
The BOB.1/OBF.1 coactivator is critically involved in mediating octamer-dependent transcriptional activity in B lymphocytes. Mice lacking this coactivator show various defects in B-cell development, most notably they completely lack germinal centers. Consistent with this phenotype, BOB.1/OBF.1 levels are massively upregulated in germinal center B cells as compared with resting B cells. We have addressed the mechanism of upregulation and found that only a minor part of this regulation can be attributed to increased levels of BOB.1/OBF.1-specific mRNA. Apparently, BOB.1/OBF.1 is also regulated at the protein level. In support of this suggestion we have been able to identify two related BOB.1/OBF.1 interacting proteins, SIAH1 and SIAH2, in a yeast two-hybrid screen. SIAH1 and SIAH2 are known regulators of protein stability. Cotransfection experiments revealed that coexpression of SIAH results in a destabilization of BOB.1/OBF.1 protein without affecting mRNA levels. Further more, proteasome inhibitors block the degradation of BOB.1/OBF.1 protein. Finally, B-cell receptor cross-linking also resulted in the degradation of BOB.1/OBF.1 and consequently reduced transcriptional activation of BOB.1/OBF.1-dependent reporters.
Boehm
J
J
Institut für Medizinische Strahlenkunde und Zellforschung (MSZ), Universität Würzburg, Versbacher Strasse 5, 97078 Würzburg, Germany.
He
Y
Y
Greiner
A
A
Staudt
L
L
Wirth
T
T
D016475:3T3 Cells; D000818:Animals; D001402:B-Lymphocytes / Q000378:metabolism; D001665:Binding Sites; D002352:Carrier Proteins / Q000378:metabolism; D003546:Cysteine Endopeptidases / Q000378:metabolism; D005786:Gene Expression Regulation; D006801:Humans; D007075:Immunoglobulin M / Q000378:metabolism; D008565:Membrane Proteins / Q000378:metabolism; D051379:Mice; D009097:Multienzyme Complexes / Q000378:metabolism; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism*; D050813:Octamer Transcription Factor-2; D046988:Proteasome Endopeptidase Complex; D015534:Trans-Activators / Q000235:genetics / Q000378:metabolism*; D014158:Transcription, Genetic; D044767:Ubiquitin-Protein Ligases; D000098563:Seven in Absentia Proteins
D002352:Carrier Proteins; D007075:Immunoglobulin M; D008565:Membrane Proteins; D009097:Multienzyme Complexes; D009687:Nuclear Proteins; D050813:Octamer Transcription Factor-2; C091546:POU2AF1 protein, human; C490424:Pou2af1 protein, mouse; D015534:Trans-Activators; D044767:Ubiquitin-Protein Ligases; D000098563:Seven in Absentia Proteins; D003546:Cysteine Endopeptidases; D046988:Proteasome Endopeptidase Complex