ALTERED MESSENGER-RNA AND UNIQUE MUTATIONAL PROFILES OF P53 AND RB INHUMAN ESOPHAGEAL CARCINOMAS

Seventy-nine esophageal carcinoma patients were studied for genetic ab normalities in the p53 and Rb tumor suppressor genes. Single-strand co nformation polymorphism analysis and DNA sequencing were used to detec t p53 point mutations. Northern blotting was used to examine abnormal expression of p53 and Rb, and polymerase chain reaction and Southern b lotting were used to analyze allelic loss. Twenty-rive cases were anal yzed by DNA sequencing to detect mutations in p53. Fourteen samples co ntained mutations within exons 5 through 9 of p53; seven had missense mutations giving rise to single amino acid substitutions. The remainin g seven (50%) contained nonsense mutations leading to premature termin ation, five due to single base pair substitutions, and two that were t he result of frameshift mutations. In other human tumors, p53 mutation s are predominantly missense mutations, but our data as well as those from other groups show that nonsense mutations are common in human eso phageal cancer. All but one of the constitutionally heterozygous sampl es containing mutations also manifested loss of the normal p53 allele; the one exception without allelic loss contained a silent mutation, w hich should not have had any affect on the p53 protein product. In add ition, Northern blotting analysis revealed abnormalities (altered tran script size or mRNA levels) in 5 of 7 cases involving p53 and in 2 of 7 cases analyzed for Rb. Thirty-four cases were informative for alleli c loss studies of both p53 and Rb; of these, 25 (74%) lost heterozygos ity of p53, Rb, or both. When point mutations and mRNA expression abno rmalities were also considered, 33 of 45 (73%) tumors informative for allelic loss assays of both genes as well as for mRNA or point mutatio n studies showed one or more abnormalities in p53 or Rb. Our results s trongly suggest that a unique profile of molecular alterations involvi ng p53 and Rb characterizes human esophageal cancer and that these spe cific genetic lesions are important in the development and/or progress ion of most human esophageal carcinomas.