Swart J M, Bergeron D M, Chiles T C
Department of Biology, Boston College, Chestnut Hill, MA 02467, USA.
J Immunol. 2000 Mar 1;164(5):2311-9. doi: 10.4049/jimmunol.164.5.2311.
The cAMP response element (CRE) binding protein (CREB) is emerging as a key regulatory factor of gene transcription in B lymphocytes; however, the postreceptor pathways that regulate CREB activity and CRE-dependent gene transcription remain largely undefined. We investigated B cell Ag receptor (BCR)-mediated phosphorylation and activation of CREB in the surface IgM+ CH31 B cell lymphoma, which undergoes Ag-dependent cell death. The activity of p38 mitogen-activated protein kinase (MAPK) was increased in response to BCR ligation. Phosphorylation of CREB on serine 133, a modification that positively regulates its trans-activation, was concomitantly increased. Inhibition of p38 MAPK by pretreating CH31 B cells with the highly specific bicyclic imidazole inhibitor, SB203580, reduced BCR-induced CREB phosphorylation. BCR cross-linking also led to increased MAPK-activated protein kinase-2 activity, an enzyme that lies immediately downstream from p38 MAPK; MAPK-activated protein kinase-2 immune complexes phosphorylated a peptide substrate containing the CREB serine 133 phosphoacceptor motif. Given the role of CREB in regulating junB gene expression in mature B lymphocytes, we examined whether p38 MAPK activity was necessary for CRE-dependent junB transcription in CH31 B cells. BCR ligation led to increased junB mRNA levels, which were significantly reduced in CH31 B cells pretreated with SB203580. Activation of a CRE-dependent junB promoter/chloramphenicol acetyltransferase (CAT) reporter gene by the BCR was also blocked by SB203580. Similarly, inhibition of p38 MAPK in surface IgM+ WEHI-231 B cell lymphomas resulted in reduced BCR-induced junB mRNA expression and junB promoter activation. The results implicate a p38 MAPK pathway in BCR-mediated CREB phosphorylation and junB transcriptional activation in B cell lymphomas.
环磷酸腺苷反应元件（CRE）结合蛋白（CREB）正逐渐成为B淋巴细胞基因转录的关键调节因子；然而，调节CREB活性和CRE依赖性基因转录的受体后途径仍基本不明。我们研究了在表面IgM+ CH31 B细胞淋巴瘤中B细胞抗原受体（BCR）介导的CREB磷酸化和激活情况，该淋巴瘤会发生抗原依赖性细胞死亡。p38丝裂原活化蛋白激酶（MAPK）的活性在BCR连接后增加。CREB丝氨酸133位点的磷酸化（一种正向调节其反式激活的修饰）也随之增加。用高度特异性的双环咪唑抑制剂SB203580预处理CH31 B细胞来抑制p38 MAPK，可降低BCR诱导的CREB磷酸化。BCR交联还导致MAPK激活的蛋白激酶2活性增加，该酶位于p38 MAPK的直接下游；MAPK激活的蛋白激酶2免疫复合物使含有CREB丝氨酸133磷酸化位点基序的肽底物磷酸化。鉴于CREB在调节成熟B淋巴细胞中junB基因表达方面的作用，我们研究了p38 MAPK活性对于CH31 B细胞中CRE依赖性junB转录是否必要。BCR连接导致junB mRNA水平升高，在用SB203580预处理的CH31 B细胞中，该水平显著降低。BCR对CRE依赖性junB启动子/氯霉素乙酰转移酶（CAT）报告基因的激活也被SB203580阻断。同样，在表面IgM+ WEHI-231 B细胞淋巴瘤中抑制p38 MAPK会导致BCR诱导的junB mRNA表达和junB启动子激活降低。这些结果表明p38 MAPK途径参与了B细胞淋巴瘤中BCR介导的CREB磷酸化和junB转录激活。
