Studies on oncogenes in human oral tumors

Abstract

The role of oncogenes in tumorigenesis has been observed by molecular biology and cell biology. A variety of human cancer cells from carcinomas of the bladder, breast, colon, kidney, liver, lung, ovary, pancreas, and stomach and from hematopoietic tumors and from tumors of mesenchymal origin contains mutant ras genes that are capable of transforming NIH 3 T 3 cells.
In the present study five oral squamous cell cartinoma cell lines were screened for the presence of activated oncogenes by NIH 3 T 3 transfection assay coupled with the in vitro neomycin selection method. Activated c-H-ras-1 was detected in cellular DNAs from two cell lines, ZA and HOC-313, both obtained in our Department from human oral cancer tissues. HOC-313 DNA was found to lose the Msp I recognition sequence within the 11th and 12th codon of the ras protein, suggesting that HOC-313 had activation at the 12th codon, while ZA was sensitive to the enzyme digestion. To know the nature of the activation in ZA, the nucleotide sequences of exon I and exon II of c-H-ras-1 in one of the primary transfectant were determined by dideoxynucleotide chain-termination method. ZA was found to have two point mutations at the 13th and 27th codons within the first coding exon. The former change was associated with amino acid substitution from glycine to arginine but the latter was a silent mutation. The former point mutation was expected to generate a new Bgl I recognition site (GCCNNNNNGGC), which was comfirmed by the restriction analysis of ZA DNA. It is, thus, suggested that the point mutation in codon 13 of ZA c-H-ras-1 was responsible for the activation.
DNAs from 33 human oral tumor tissues and from 9 human oral squamous cell carcinoma cell lines were analyzed for the loss of Msp I recognition site at the 12th codon of c-H-ras-1 using Southern blot hybridization No activation at the 12th codon was observed exceptfor HOC-313.
DNAs from 19 human oral tumor tissues and from 8 human oral squamous cell carcinoma cell lines were also analyzed for the restriction fragment length polymorphism (RFLP) of the L-myc gene. Patients with only the L band (10 kb Eco RI fragment) had poor prognosis compared with those with either the S band (6 kb Eco RI fragment) or the S and L bands.