Constitutive and inducible levels of egr-1 and c-myc early growth response gene expression in self-renewing B-1 lymphocytes.
B-1 lymphocytes constitute a mature B cell population that differs from conventional B cells in signaling requirements for cell cycle progression, being unusually responsive to PKC agonism but refractory to antigen receptor stimulation. Further, B-1 cells are self-renewing and derive from surface immunoglobulin-positive precursors. A previous report on clonally derived B-1 cells suggested that increased levels of expression of c-myc might underlie these unusual growth characteristics. This issue has now been reexamined using primary B-1 cells. The possible role of egr-1, in addition to c-myc, in specifying the responsiveness of B-1 cells was evaluated by determining levels of gene expression at baseline and after mitogenic treatment. Expression of the two genes was similar in B-1 and B-2 cells prior to stimulation. Subsequently, B-1 cells responded with higher levels of gene expression than B-2 cells regardless of ultimate cell cycle progression, with the exception of stimulation by anti-Ig. Overall, there was no apparent direct correlation between stimulated levels of expression of egr-1 or c-myc and mitogen-induced S phase entry, nor were B-1 cells characterized by constitutively elevated levels of either proto-oncogene that might explain their capacity for self-renewal.
Wang
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Department of Medicine, Boston University Medical Center, Massachusetts 02118, USA.
Morris
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Rothstein
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D000818:Animals; D001402:B-Lymphocytes / Q000145:classification / Q000502:physiology*; D001483:Base Sequence; D004268:DNA-Binding Proteins / Q000235:genetics*; D051766:Early Growth Response Protein 1; D015870:Gene Expression; D016259:Genes, myc; D017874:Immediate-Early Proteins; D008213:Lymphocyte Activation; D008297:Male; D051379:Mice; D008807:Mice, Inbred BALB C; D008969:Molecular Sequence Data; D015345:Oligonucleotide Probes / Q000737:chemistry; D012333:RNA, Messenger / Q000235:genetics; D013997:Time Factors; D014157:Transcription Factors / Q000235:genetics*
D004268:DNA-Binding Proteins; D051766:Early Growth Response Protein 1; C486109:Egr1 protein, mouse; D017874:Immediate-Early Proteins; D015345:Oligonucleotide Probes; D012333:RNA, Messenger; D014157:Transcription Factors