Masumi Abe

Frequent Glycine‐to‐Aspartic Acid Mutations at Codon 12 of c‐Ki‐ras Gene in Human Pancreatic Cancer in Japanese

Point mutations at codons 12 and 13 of c‐Ki‐ras gene were analyzed in human pancreatic cancer. DNAs obtained from sample tissues were amplified by means of polymerase chain reaction and were analyzed by dot blot hybridization assays with oligonucleotide probes appropriate for detecting mutations at these codons. Out of 38 evaluated cases, point mutations at codon 12 were found in 35 cases; these mutations resulted in changes of the coded amino acid to aspartic acid in 24 cases, to valine in 9 cases, to arginine in 2 cases and to cysteine in one case. In one case, a glycine‐to‐aspartic acid mutation was found at codon 13. In two cases, two distinct mutations were simultaneously present. The frequency pattern of mutations at codon 12 was somewhat different from those given in two previous reports on the similar analysis of pancreatic cancers in European countries. This may indicate the presence of possible genetic or non‐genetic factors in determining preferential mutational patterns at these particular codons.

Point mutations of c-ras genes in human bladder cancer and kidney cancer

ABSTRACT Point mutations of c‐ras genes at codons 12, 13 and 61 were analyzed in 26 cases of bladder cancer and 16 cases of kidney cancer. DNA prepared from either frozen tissues or 10% formalin‐fixed, paraffin‐embedded tissues were amplified by means of polymerase chain reaction methods, and mutations were analyzed by dot blot hybridization assays with oligonucleotide probes. In three cases of bladder cancer c‐ras mutations were found, at codons 13 and 61 of c‐Ha‐ras and at codon 61 of c‐Ki‐ras, while no mutation was found in kidney cancer. No mutation was found in normal bladder epithelial tissues from the same patients. Our findings, taken together, may indicate relative scarcity of c‐ras mutations in these types of human cancer. The results of dot blot hybridization assays and DNA sequencing showed a G‐to‐C transition of the first nucleotide at codon 13 of c‐Ha‐ras. This is the first time that such a point mutation has been detected in human cancer tissues.

Increased Expression of ras Genes in Non‐Hodgkin's Lymphomas Is not Associated with Oncogenic Activation of Those Genes by Point Mutation

Twenty‐three cases of non‐Hodgkins lymphoma (NHL) were analyzed for expression of ras genes by in situ hybridization utilizing biotinylated DNA probes. Increased expression of Ki‐ras, Ha‐ras and N‐ras genes was observed in 12 cases, 6 cases and 1 case of NHL, respectively. Genomic DNA extracted from these 23 cases of NHL was region‐specifically amplified by means of polymerase chain reaction to examine the presence of point mutations at the 12th, 13th and 61st codons of Ki‐, Ha‐ and N‐ras genes. Dot hybridization assays with appropriate oligonucleotide probes showed no evidence of point mutation in any case of NHL examined. These results indicate that increased expression of ras genes in NHL is not associated with ras gene activation by point mutation.