ECA39 is regulated by c-Myc in human and by a Jun/Fos homolog, Gcn4, in yeast

Myc oncogenes are transcription factors regulating the level of expression of other genes. Using a subtraction/coexpression strategy, a murine genetic target for Myc regulation was isolated. To further characterize this target gene, named ECA39, we have recently isolated the human, nematode and budding yeast homologs of the mouse gene. The recognition site for Myc binding, located 3' to the start site of transcription in the mouse gene, is conserved in the human homolog. Transfection experiments demonstrated that the Myc binding site of the human gene, mediates activation of a reporter gene in response to over-expression of c-myc. The activation was better executed when the c-Myc binding element was positioned downstream to the promoter, which is the usual position of the c-Myc DNA binding element in its genetic targets. The tissue specific expression of human ECA39 during embryogenesis is similar to that of the mouse homolog. Moreover, ECA39 is expressed in c-myc induced human tumors. It is expressed in Burkitt's lymphoma (where c-myc is translocated and activated) but not in non Burkitt's B-cell lymphoma or in T-cell lymphoma. Thus, it seems that ECA39 is a target for c-myc oncogenesis in humans. In yeast, where c-myc is absent, the ECA39 sequences lack the c-Myc binding element. However, the promoter region of the yeast ECA39 harbors several Gcn4 binding elements. Moreover, ECA39 is markedly down regulated in cells deleted for gcn4, and deletion of Gcn4 binding elements down regulated the transcription from ECA39 promoter. We thus suggest that ECA39 is a target for c-Myc regulation in mammals, while in yeast the regulator is not c-Myc but the c-Jun/c-Fos homolog - Gcn4.