A Critical Role for Transcription Factor C/EBP- in Regulating the Expression of Death-Associated Protein Kinase-1

Department of Microbiology & Immunology, Greenebaum Cancer Center, University of Maryland School of Medicine, Baltimore, MD 21201

^* To whom correspondence should be addressed. Email: dkalvako{at}umaryland.edu.

	Abstract

Transcription factor C/EBP- regulates a number of physiologic responses. During an investigation of the growth-suppressive effects of IFNs, we noticed that cebpb ^-/- cells fail to undergo apoptosis upon IFN- treatment compared to the wild-type controls. To examine the basis for this response, we have performed a gene expression profiling of the isogenic wild-type and cebpb ^-/- bone marrow macrophages and identified a number of IFN- regulated genes that are dependent on C/EBP- for their expression. These genes are distinct from those regulated by the JAK-STAT pathways. Genes identified in this screen appear to participate in various cellular pathways. Thus, we identify a new pathway through which the IFNs exert their effects on cellular genes through C/EBP-. One of these genes is the death-associated protein kinase 1 (dapk1). DAPK1 is critical for regulating cell cycle, apoptosis and metastasis. Using site-directed mutagenesis, RNAi and ChIP assays, we show that C/EBP- binds to the promoter of dapk1 and is required for the regulation of dapk1. Both mouse and human dapk1 exhibited similar dependence on C/EBP- for their expression. The expression of the other members of DAPK family occurred independently of C/EBP-. Members of the C/EBP family of transcription factors, other than C/EBP- did not significantly affect dapk1 expression. We identified two elements in this promoter that respond to C/EBP-. One of these is a consensus CBS that constitutively binds to C/EBP-. The other element exhibits homology to the cAMP-response element/activating transcription factor binding sites. C/EBP- binds to this site in an IFN--dependent manner. Inhibition of ERK1/2 or mutation of an ERK1/2 site in the C/EBP- protein suppressed the IFN--induced response of this promoter. Together our data show a critical role for C/EBP- in a novel IFN-induced cell growth-suppressive pathway via DAPK1.