Identification of ERdj3 and OBF-1/BOB-1/OCA-B as direct targets of XBP-1 during plasma cell differentiation.
Plasma cell differentiation is accompanied by a modified unfolded protein response (UPR), which involves activation of the Ire1 and activating transcription factor 6 branches, but not the PKR-like endoplasmic reticulum kinase branch. Ire1-mediated splicing of XBP-1 (XBP-1(S)) is required for terminal differentiation, although the direct targets of XBP-1(S) in this process have not been identified. We demonstrate that XBP-1(S) binds to the promoter of ERdj3 in plasmacytoma cells and in LPS-stimulated primary splenic B cells, which corresponds to increased expression of ERdj3 transcripts in both cases. When small hairpin RNA was used to decrease XBP-1 expression in plasmacytoma lines, ERdj3 transcripts were concomitantly reduced. The accumulation of Ig gamma H chain protein was also diminished, but unexpectedly this occurred at the transcriptional level as opposed to effects on H chain stability. The decrease in H chain transcripts correlated with a reduction in mRNA encoding the H chain transcription factor, OBF-1/BOB-1/OCA-B. Chromatin immunoprecipitation experiments revealed that XBP-1(S) binds to the OBF-1/BOB-1/OCA-B promoter in the plasmacytoma line and in primary B cells not only during plasma cell differentiation, but also in response to classical UPR activation. Gel shift assays suggest that XBP-1(S) binding occurs through a UPR element conserved in both murine and human OBF-1/BOB-1/OCA-B promoters as opposed to endoplasmic reticulum stress response elements. Our studies are the first to identify direct downstream targets of XBP-1(S) during either plasma cell differentiation or the UPR. In addition, our data further define the XBP-1(S)-binding sequence and provide yet another role for this protein as a master regulator of plasma cell differentiation.
Shen
Ying
Y
Department of Tumor Cell Biology, St. Jude Children's Research Hospital, 332 North Lauderdale Street, Memphis, TN 38105, USA.
Hendershot
Linda M
LM
D000818:Animals; D001483:Base Sequence; D002454:Cell Differentiation / Q000235:genetics; D017124:Conserved Sequence; D004268:DNA-Binding Proteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D018507:Gene Expression Regulation, Developmental; D006801:Humans; D007142:Immunoglobulin gamma-Chains / Q000235:genetics*; D008565:Membrane Proteins / Q000235:genetics*; D051379:Mice; D008969:Molecular Sequence Data; D010950:Plasma Cells / Q000166:cytology / Q000276:immunology*; D011401:Promoter Regions, Genetic; D034741:RNA, Small Interfering / Q000235:genetics / Q000494:pharmacology; D000071701:Regulatory Factor X Transcription Factors; D015534:Trans-Activators / Q000235:genetics*; D014157:Transcription Factors / Q000037:antagonists & inhibitors / Q000235:genetics* / Q000378:metabolism*; D014158:Transcription, Genetic; D000071717:X-Box Binding Protein 1
D004268:DNA-Binding Proteins; C524313:ERdj3 protein, mouse; D007142:Immunoglobulin gamma-Chains; D008565:Membrane Proteins; C490424:Pou2af1 protein, mouse; D034741:RNA, Small Interfering; D000071701:Regulatory Factor X Transcription Factors; D015534:Trans-Activators; D014157:Transcription Factors; D000071717:X-Box Binding Protein 1; C000605543:XBP1 protein, human; C000605544:Xbp1 protein, mouse