Nm23/PuF does not directly stimulate transcription through the CT element in vivo

Decreased levels of the nm23 gene product have been correlated with increased tumor metastatic potential in a variety of malignancies. At least a subset of the regulatory properties of Nm23 has been proposed to be due to transactivation of the human c-myc oncogene through binding to a homopyrimidine tract 140 base pairs upstream of the transcription start site (termed the CT element or the PuF site). Conventional transcription factors possess DNA binding and transactivation domains; Nm23 fusion proteins were used to address two questions. First, if provided with a well characterized DNA binding domain, does Nm23 possess a transactivation domain capable of stimulating transcription of an appropriate reporter? Second, if provided with a potent transactivation domain, is the DNA binding of Nm23 of sufficient specificity and affinity to direct the fusion protein to a CT-dependent reporter? Since reporter gene expression was not stimulated in either case, we conclude that Nm23 does not directly stimulate transcription through binding to the CT element and that its antimetastatic and other reported functions are likely due to other biochemical activities.