A polypyrimidine tract-binding protein-dependent pathway of mRNA stability initiates with CpG activation of primary B cells.
The mRNA encoding CD154, a critical protein involved in both humoral and cell-mediated immune responses, is regulated at the posttranscriptional level by the binding of complex I, a polypyrimidine tract-binding (PTB) protein-containing complex, which acts to increase message stability at late times of activation. Our current work focuses on analyzing a similar complex in B cells, designated B-cpx I, which is increased in B cells activated by CpG engagement of the TLR9 receptor but not by activation through CD40. Expression profiling of transcripts from primary B cells identified 31 mRNA transcripts with elevated PTB binding upon activation. Two of these transcripts, Rab8A and cyclin D(2), contained binding sites for B-cpx I in their 3' untranslated regions (UTRs). Analysis of turnover of endogenous Rab8A transcript in B cells revealed that like CD154, the mRNA half-life increased following activation and insertion of the Rab8A B-cpx I binding site into a heterologous transcript led to a 3-fold increase in stability. Also, short hairpin RNA down-regulation of PTB resulted in a corresponding decrease in Rab8A mRNA half-life. Overall these data strongly support a novel pathway of mRNA turnover that is expressed both in T cells and B cells and depends on the formation of a PTB-containing stability complex in response to cellular activation.
Porter
Joseph F
JF
Department of Cell Biology and Neuroscience, Rutgers University, Piscataway, NJ 08854.
Vavassori
Stefano
S
Covey
Lori R
LR
D001402:B-Lymphocytes / Q000276:immunology*; D001665:Binding Sites; D002478:Cells, Cultured; D056742:Cyclin D2; D016213:Cyclins / Q000235:genetics* / Q000378:metabolism; D015226:Dinucleoside Phosphates / Q000502:physiology*; D020869:Gene Expression Profiling; D006801:Humans; D008213:Lymphocyte Activation; D038941:Polypyrimidine Tract-Binding Protein / Q000378:metabolism*; D011485:Protein Binding; D020871:RNA Stability; D012333:RNA, Messenger / Q000032:analysis / Q000378:metabolism; D020691:rab GTP-Binding Proteins / Q000235:genetics* / Q000378:metabolism
D056742:Cyclin D2; D016213:Cyclins; D015226:Dinucleoside Phosphates; D038941:Polypyrimidine Tract-Binding Protein; D012333:RNA, Messenger; D020691:rab GTP-Binding Proteins; C080336:CCND2 protein, human; C015772:CpG dinucleotide; C082377:RAB8A protein, human