¹Department of Biology, York University, 4700 Keele Street, Toronto, Ontario, Canada, M3J 1P3

²Institute for Molecular Biology and Biotechnology, McMaster University, Hamilton, Ontario, Canada, L8S 4K1

Correspondence to: P-A Bédard, Department of Biology, York University, 4700 Keele Street, Toronto, Ontario, Canada, M3J 1P3

^aM Gagliardi and S Maynard contributed equally to this work

The CEF-4/9E3 chemokine gene is expressed constitutively in chicken embryo fibroblasts (CEF) transformed by the Rous sarcoma virus (RSV). This aberrant induction is controlled at the transcriptional and post-transcriptional levels. Transcriptional activation depends on multiple elements of the CEF-4 promoter composing a Src-responsive-Unit or SRU. The SRU includes a TPA responsive element, a PRDII/B domain and a CAAT box. In this report, we identify C/EBP as a component of the trans-acting factor interacting with the CAAT box of the CEF-4 promoter. In addition, we show that C/EBP binds to a second element located in proximity of the TRE. A mutation of this distal CAAT box impaired the activation of the CEF-4 promoter by pp60^v-src indicating that this element is also part of the SRU. Using the RCASBP retroviral vector, we expressed a dominant negative mutant of C/EBP (designated 184-C/EBP) in RSV-transformed CEF. 184-C/EBP decreased the accumulation of the CEF-4 mRNA and activation of the CEF-4 promoter by pp60^v-src. The induction of the Cox-2 gene (CEF-147) was also reduced by 184-C/EBP. The effect of the dominant negative mutant was observed within 1 h of the activation of a thermolabile pp60^v-src suggesting that C/EBP is an early target of v-src transformation. The dominant negative mutant did not inhibit the transformation of CEF by RSV and in fact accentuated the transformed cell phenotype. Therefore, the activation of C/EBP is important for the expression of v-src regulated genes but is not required for the in vitro transformation of CEF by pp60^v-src. Oncogene (2001) 20, 2301-2313.

CEF-4/9E3 chemokine; C/EBP; pp60^v-src