Expression of apoptosis-related genes in human head and neck squamous cell carcinomas undergoing p53-mediated programmed cell death

Human head and neck squamous cell carcinoma (HNSCC) lines infected with a replication-defective Ad5CMV-p53 vector bearing a wild-type human p53 gene were used to examine alterations in the production of proteins implicated in regulating apoptosis. Because HNSCC lines express abundant levels of c-myc, and simultaneous expression of c-myc and p53 is known to trigger apoptosis in other cells, cooperation between these two genes was examined. Surprisingly, levels of c-myc mRNA and protein were rapidly and profoundly suppressed after infection with wildtype p53. Suppression of c-myc using antisense oligodeoxynucleotides (in the absence of p53) was sufficient to trigger apoptosis in Tu-138 cells, raising the possibility that the reduction of c- myc may be involved in at least one of the cell death pathways mediated by p53. Expression of a panel of Bcl-2 homology proteins was also examined in HNSCC lines undergoing p53-mediated apoptosis. No changes in Bcl-2, Bak, or Bcl-x(s) were found after p53 expression. Increased levels of the apoptosis- accelerating protein Bax were found in HNSCC lines after infection with Ad5CMV-p53. Induction of the apoptosis-inhibiting protein Bcl-x(L) was observed in Tu-167 cells and may account for the delayed onset of apoptosis in these cells. These studies suggest that multiple pathways may regulate apoptosis after transient overexpression of p53.