Combination E2F-1 and p53 Gene Transfer Does Not Enhance Growth Inhibition in Human Squamous Cell Carcinoma of the Head and Neck1

Ample data exist contending that wild-type p53 and E2F-1 cooperate to mediate apoptosis, that E2F-1-mediated apoptosis is p53 dependent in some situations, and that E2F-1 can induce accumulation of p53 in manunalian cells. These data support the investigation of the biological consequences of combined wild-typep53 and E2F-1 overexpression in human squamous cell carcinoma of the head and neck (SCCHN) for the purpose of developing apoptosisinducing molecular intervention strategies for the management of this devastating disease. The recombinant adenoviriis (Ad) vectors Ad-p53 and Ad-E2F-1 were used for wild-type p53 and E2F-1 gene transfers, respectively, into SCCHN cell lines TU138 and TU167. SCCHN cells transduced with either p53, E2F-1, or both underwent in vitro growth analysis, which revealed that simultaneous p5.3 and E2F-1 gene transfer did not result in enhanced growth inhibition. To explain our growth assay findings on the basis of potential negative molecular interactions between E2F-1 and pS3, Western and Northern blotting analyses were performed to investigate the differential expression of the downstream p53-transactlvated genes, p2l’ ’ and BAX, under various p5.3 and E2F-1 gene transfer conditions. Whereas Western immunoblotting demonstrated that E2F-1 antagonized p53 induction of p21’ ’ and BAX, Northern blotting revealed that this Interference was pretranslationally regulated and p53 dependent. Coimmunoprecipitation assay confirmed that the wild-type p53 and E2F-1 gene products formed protein-protein complexes in our cell lines. Received 3/25/98; revised 5/29/98; accepted 6/9/98. The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked advertisement in accordance with 18 U.S.C. Section 1734 solely to indicate this fact. 1 Supported by an American Cancer Society Clinical Oncology Fellowship Grant (to D. K. F.), National Institute of Dental Research Grant l-P50-DE1 1906 (93-9; to 0. L. C.), National Institute of Health First Investigator Award R29 AD-DEl 1689-O1A1 (to G. L. C.), and Training of the Academic Surgical Oncologist Grant T32 CA60374-03 (to G. L. C.). 2 To whom requests for reprints should be addressed, at Department of Head and Neck Surgery, The University of Texas M. D. Anderson Cancer Center, 1515 Holcombe Boulevard, Box 69, Houston, TX 77030. Phone: (713) 792-6920; Fax: (713) 794-4662. Our in vitro data demonstrated that in SCCHN, E2F-1 interferes with induction of p53-transactivated genes, probably through the formation of protein-protein complexes. Simultaneous p53 and E2F-1 gene transfer is not therapeutically advantageous in this in vitro model of SCCHN.