Activation of AP-1 in primary B lymphocytes by surface immunoglobulin requires de novo Jun-B synthesis.
We demonstrate herein that resting primary B lymphocytes do not contain detectable levels of AP-1 (TRE)-binding activity. Upon cross-linking of surface immunoglobulin (sIg) receptors, TRE-binding activity is induced within 2 hr and its appearance requires de novo protein synthesis. Antisera to Jun-B inhibits the vast majority of TRE-binding activity, indicating that Jun-B is a primary component of B cell TRE-binding complexes. In keeping with this, Jun-B protein is not detectable in cytosol or nuclear extracts from resting B lymphocytes, as determined by immunoblotting with Jun-B antisera. However, the nuclear expression of Jun-B is induced within 2 hr following sIg cross-linking and is completely blocked by cycloheximide. 35S-labeling studies suggest that the increase in Jun-B expression results from de novo protein synthesis. Moreover, Jun-B migrates in SDS-polyacrylamide gels as two distinct electrophoretic proteins that correspond to a 41-kDa species and a phosphorylated 47-kDa form. These results suggest that the induction of AP-1-binding activity in primary B lymphocytes following sIg cross-linking does not result from post-translational phosphorylation of a preexisting cellular pool of Jun-B protein, but rather is coupled to the stimulation of de novo Jun-B synthesis. Thus Jun-B synthesis represents an integral event in the production of receptor-mediated AP-1 in B cells. The significance of these results with respect to the role of Jun-B in controlling gene expression during the activation of primary B cells is discussed.
Tanguay
D A
DA
Department of Biology, Boston College, Chestnut Hill, Massachusetts 02167.
Dickinson
J A
JA
McManus
B J
BJ
Huo
L
L
Rothstein
T L
TL
Chiles
T C
TC
D000818:Animals; D001402:B-Lymphocytes / Q000378:metabolism*; D015153:Blotting, Western; D004268:DNA-Binding Proteins / Q000378:metabolism; D004586:Electrophoresis / Q000379:methods; D008297:Male; D051379:Mice; D008807:Mice, Inbred BALB C; D011233:Precipitin Tests; D014176:Protein Biosynthesis; D016755:Proto-Oncogene Proteins c-jun / Q000096:biosynthesis*; D011947:Receptors, Antigen, B-Cell / Q000502:physiology; D012045:Regulatory Sequences, Nucleic Acid; D018808:Transcription Factor AP-1 / Q000378:metabolism*
D004268:DNA-Binding Proteins; D016755:Proto-Oncogene Proteins c-jun; D011947:Receptors, Antigen, B-Cell; D018808:Transcription Factor AP-1