E2F-1- and E2Ftr-mediated apoptosis: the role of DREAM and HRK.
Bottom Line: HRK up-regulation did not require the E2F-1 transactivation domain.Hrk knockdown by Hrk siRNA was associated with significantly reduced wtE2F-1- and E2Ftr-induced apoptosis.The homodimerization of DREAM resulting from wtE2F-1 and E2Ftr overexpression may contribute to the decreased binding activity of DREAM to the 3'-untranslated region of the Hrk gene as shown by electromobility shift assay.
Affiliation: Department of Surgery, University of Louisville School of Medicine, and J. Graham Brown Cancer Center, Louisville, KY, USA.Show MeSH
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Mentions: E2F-1 is the best-characterized member of the E2F family of transcription factors, which comprise nine E2F subunits with the ability to control transcription, cell cycle, apoptosis and senescence [1-4]. The full-length E2F-1 contains a highly conserved DNA binding domain, a hydrophobic heptad repeat domain required for dimerization (dimerization domain), a transactivation domain and other domains required for associations with cyclin A/cdk2 and Rb family members (Fig. 1A) [5-11]. The E2Ftr (1–375) is a C-terminal truncation of E2F-1 that lacks the entire transactivation and pRb-binding domains (Fig. 1A). The full-length E2F-1, but not a truncation mutant (E2Ftr), was able to induce colony formation in NIH-3T3 cells in semi-solid agar . This implies that the transactivation domain of E2F-1 is required for the oncogenic activity of this gene. Studies on the molecular basis of E2F-1-induced apoptosis demonstrated that the transactivation and apoptosis functions of E2F-1 are separable [13-15]. A number of reports indicate that the E2Ftr has stronger pro-apoptotic activity than the full-length protein but without stimulating DNA synthesis [13-15]. Therefore, the clinical development of E2Ftr, which maintains its apoptotic function but no longer possesses oncogenic function, may improve the potential clinical utility of this therapeutic gene. In order to further investigate the death-inducing function of E2Ftr and explore its potential therapeutic activity in vitro and in vivo, we have constructed an E2Ftr adenovirus and tested its in vitro and in vivo anti-tumoural activity [16, 17]. We showed that E2Ftr induced apoptosis in a variety of cancer cell lines with little cytotoxicity to normal cell lines, and that E2Ftr exhibited more than an 80% decrease in tumour size in a mouse melanoma xenograft model [16, 17]. Hence, E2Ftr may be a suitable transgene with significant potential therapeutic activity both in vitro and in vivo.
Affiliation: Department of Surgery, University of Louisville School of Medicine, and J. Graham Brown Cancer Center, Louisville, KY, USA.