Overexpression Of CBP Research Articles

Bringing the Inhibitor Close

The Src family of nonreceptor tyrosine kinases is negatively regulated by tyrosine phosphorylation by the Csk kinase. Src is associated with the intracellular leaflet of the plasma membrane through lipid modifications, but Csk lacks any intrinsic means for associating with the membrane. Kawabuchi et al . identified a transmembrane protein, Csk-binding protein (Cbp), that could be coprecipitated with Csk from brain lysates. Cbp is phosphorylated on tyrosine residues, ubiquitously expressed, and enriched in the detergent-insoluble membrane fraction. Tyrosine 314 was found to be essential for interaction with Csk and for proper recruitment of Csk to the plasma membrane in transfected cells. Overexpression of Cbp inhibited Src kinase activity in cells, and this inhibition was not present in Csk-deficient cells. Their data suggest a functional role for Cbp in regulating Src activity through the recruitment of Csk to the membrane where it phosphorylates and inhibits Src activity. Kawabuchi, M., Satomi, Y., Takao, T., Shimonishi, Y., Nada, S., Nagai, K., Tarakhovsky, A., and Okada, M. (2000) Transmembrane phosphoprotein Cbp regulates the activities of Src-family tyrosine kinases. Nature 404 : 999-1003. [Online Journal]

Role of cyclic AMP response element-binding protein in cyclic AMP inhibition of NF-kappaB-mediated transcription.

The NF-kappaB family of transcription factors regulates the inducible expression of a variety of genes. Recently, we showed that elevation of intracellular cyclic AMP inhibits NF-kappaB-mediated transcription in human monocytes and endothelial cells without preventing nuclear translocation of NF-kappaB complexes. The present study examined the molecular mechanism of this inhibition. We hypothesized that activation of the protein kinase A signaling pathway may inhibit NF-kappaB-mediated transcription by phosphorylating proteins, such as cAMP response element-binding protein (CREB), which compete for limiting amounts of the coactivator CBP. Here, we show that the amino-terminal region (amino acids 1-450) of CBP specifically interacts with the carboxyl-terminal region (amino acids 286-551) of NF-kappaB p65 (RelA) both in vitro and in vivo. Functional studies using human endothelial cells demonstrated that overexpression of CBP rescued cAMP inhibition of NF-kappaB-mediated transcription and transcription mediated by a chimeric protein, GAL4-p65(286-551), which contained the GAL4 DNA binding domain fused to the carboxyl-terminal region of p65 (amino acids 286-551). In contrast, overexpression of CREB inhibited GAL4-p65(286-551)-mediated transcription. These results suggest that activation of the protein kinase A pathway inhibits NF-kappaB transcription by phosphorylating CREB, which competes with p65 for limiting amounts of CBP.

Nuclear integration of JAK/STAT and Ras/AP-1 signaling by CBP and p300.

We report that interferon gamma (IFN-gamma) inhibits transcription of the macrophage scavenger receptor gene by antagonizing the Ras-dependent activities of AP-1 and cooperating ets domain transcription factors, apparently as a result of competition between AP-1/ets factors and activated STAT1 for limiting amounts of CBP and p300. Consistent with this model, STAT1 alpha interacts directly with CBP in cells, and microinjection of anti-CBP and anti-p300 antibodies blocks transcriptional responses to IFN-gamma. Cells lacking STAT1 fail to inhibit AP-1/ets activity, and overexpression of CBP both potentiates IFN-gamma-dependent transcription and relieves AP-1/ets repression. Thus, CBP and p300 integrate both positive and negative effects of IFN-gamma on gene expression by serving as essential coactivators of STAT1 alpha, modulating gene-specific responses to simultaneous activation of two or more signal transduction pathways.