CD40 Induces Antigen Transporter and Immunoproteasome Gene Expression in Carcinomas via the Coordinated Action of NF-κB and of NF-κB-Mediated De Novo Synthesis of IRF-1

Abstract

Cancer cells may evade immune surveillance as a result of defective antigen processing and presentation. In this study, we demonstrate that CD40 ligation overcomes this defect through the coordinated action of the transcription factors NF-κB and interferon regulatory factor 1 (IRF-1). We show that unlike interferon signaling, which triggers the STAT1-mediated transcriptional activation of IRF-1, the ligation of CD40 in carcinomas induces the rapid upregulation of IRF-1 in a STAT1-independent but NF-κB-dependent manner. The transcriptional activation of IRF-1 is controlled largely by the recruitment of p65 (RelA) NF-κB to the IRF-1 promoter following the engagement of a TAK1/IκB kinase β/IκBα signaling pathway downstream of CD40. NF-κB and de novo-synthesized IRF-1 converge to regulate the expression of genes involved in antigen processing and transport, as evident from the sequential recruitment of NF-κB and IRF-1 to the promoters of the genes encoding transporter for antigen processing 1 (TAP1), TAP2, tapasin, and low-molecular-mass polypeptides LMP2 and LMP10. Moreover, the RNA interference-mediated knockdown of IRF-1 reduced, whereas the inhibition of NF-κB abolished, the effects of CD40 on TAP1 and LMP2 upregulation in carcinoma cells. Collectively, these data reveal a novel “feed-forward” mechanism induced by NF-κB which ensures that acutely synthesized IRF-1 operates in concert with NF-κB to amplify the immunoproteasome and antigen-processing functions of CD40.

ACKNOWLEDGMENTS

We are grateful to Angelica Loskog, University of Uppsala, Sweden, for providing us the VM-CUB-1 cell line and to Zhenguo Wu, Hong Kong University of Science and Technology, for the TAK1 constructs.

This work was supported by an Association for Cancer Research (AICR, United Kingdom) grant and the European Commission FP6 funded program Apotherapy (EC contract number 037344; http://apotherapy.med.uoc.gr) to A.G.E.