FUNCTIONAL-CHARACTERIZATION IN-VIVO OF MUTANT P53 MOLECULES DERIVED FROM SQUAMOUS-CELL CARCINOMAS OF THE HEAD AND NECK

Loss of wild-type p53, either through deletion or mutation, has been d emonstrated in most squamous cell carcinomas of the head and neck (HNS CC). Whether these mutant molecules contribute to tumor progression pu rely through loss of wild-type functions or by growth-promoting mechan isms, however, remains unclear. To begin to address these issues, we i solated a series of p53 cDNAs from HNSCC cell lines that contain misse nse or nonsense point mutations, insertions, or deletions. The ability of each of these molecules to transform NIH/3T3 cells to a malignant phenotype was assessed by stable transfection and expression under the control of a strong heterologous promoter. NIH/3T3 cells transfected with pLTR6p53, which harbors an H179L missense mutation, formed large tumors rapidly (in less than 4 wk) when transplanted to athymic mice, as did cells expressing pLTR13p53, which had undergone a V173F missens e mutation and an in-frame deletion of 48 bp between codons 208 and 22 3. Cells transfected with pLTR17p53, predicted from the nucleotide seq uence to encode a severely truncated p53 corresponding to the N-termin al 56 amino acids, also formed tumors. Cells transfected with pLTR15p5 3, which was predicted to encode a less severely truncated molecule, f ormed much smaller tumors and at lower frequencies. NIH/3T3 cells tran sfected with pLTR12p53 (exon 7 splice donor mutant), pLTRwtp53 (wild-t ype p53), or vector alone failed to form tumors for up to 2 mo after t ransplantation. pLTR6p53-transfected cells exhibited a highly malignan t phenotype with invasion of regional lymph nodes, mediastinal and lun g metastases, invasion of the abdominal wall, and dissemination throug hout the peritoneal cavity. Histological asssessment of the tumors rev ealed intensely vascularized fibrosarcomas with numerous cellular atyp ia, including frequent and aberrant mitoses. Tumor explants were recul tured, and northern blot analysis of cellular RNA confirmed that the e xpression of exogenous p53 was maintained in each case. These data ind icate that different p53 mutants contribute to tumorigenesis by specif ic mechanisms. Furthermore, the results obtained by using the pLTR17p5 3 transfectants imply that some truncated molecules may overcome the e ffects of wild-type p53 to contribute to malignancy. (C) 1997 Wiley-Li ss, Inc.