The Activated Notch1 Receptor Cooperates with α-Enolase and MBP-1 in Modulating c-myc Activity

Abstract

The Notch signal pathway plays multifaceted roles to promote or suppress tumorigenesis. The Notch1 receptor intracellular domain (N1IC), the activated form of the Notch1 receptor, activates the c-myc proto-oncogene. The complex of N1IC and transcription factor YY1 binds to the human c-myc promoter to enhance c-myc expression in a CBF1-independent manner. Here we demonstrated that N1IC interacted with the c-Myc-regulating proteins α-enolase and c-myc promoter binding protein 1 (MBP-1). Both α-enolase and MBP-1 suppressed the N1IC-enhanced activity of the c-myc promoter in a CBF1-independent manner. The YY1 response element in front of the P2 c-myc promoter was essential and sufficient for the modulation of c-myc by N1IC and α-enolase or MBP-1. Furthermore, N1IC, YY1, and α-enolase or MBP-1 but not CBF1 bound to the c-myc promoter through associating with the YY1 response element. Hemin-induced erythroid differentiation was suppressed by N1IC in K562 cells. This suppression was relieved by the expression of α-enolase and MBP-1. In addition, both α-enolase and MBP-1 suppressed the N1IC-enhanced colony-forming ability through c-myc. These results indicate that the activated Notch1 receptor and α-enolase or MBP-1 cooperate in controlling c-myc expression through binding the YY1 response element of the c-myc promoter to regulate tumorigenesis.

ACKNOWLEDGMENTS

We thank L. M. Boxer for the kind gift of reporter plasmid pLB1530 containing the c-myc promoter and E. Manet for providing the expression construct pSG5Flag-RBP-VP16. RNAi reagents were obtained from the National RNAi Core Facility located at the Institute of Molecular Biology/Genomic Research Center, Academia Sinica.

The National RNAi Core Facility is supported by National Research Program for Genomic Medicine NSC grants (NSC 94-3112-B-001-003 and NSC 94-3112-B-001-018-Y). This work was supported by the National Science Council (grants NSC 96-3112-B-010-019 and NSC 95-2320-B-010-067-MY2) and in part by a grant from the Ministry of Education, Aim for the Top University Plan.