FREQUENT MUTATION OF THE E2F-4 CELL-CYCLE GENE IN PRIMARY HUMAN GASTROINTESTINAL TUMORS

The E2F group of transcription factors transactivates genes that promo te progression through the G(1)-S transition of the cell cycle. Member s of the retinoblastoma (Rb) family of proteins bind to E2Fs and inhib it this function. E2F-4, one example of the E2F group, functions as an oncogene when transfected into nontransformed cells in vitro. On the other hand, mice that are homozygously lacking a normal E2F-1 gene dev elop cancers, consistent,vith a tumor-suppressive role for this gene. The exact function of E2Fs has thus been unclear; moreover, direct inv olvement of this gene in primary human tumorigenesis has not been show n. We, therefore, investigated mutation within the E2F-4 coding region in 16 primary gastric adenocarcinomas, 12 ulcerative colitis-associat ed neoplasms, 46 sporadic colorectal carcinomas, 9 endometrial cancers , and 3 prostatic carcinomas. We limited our investigation to the seri ne repeat within E2F-4, reasoning that this tract might be altered in genetically unstable tumors (replication error-positive, or RER+). All tumors were RER+, with the exception of a control group of 15 RER- sp oradic colorectal carcinomas. PCR with incorporation of [P-32]dCTP was performed using primers flanking the serine trinucleotide (AGC) repea t. Twenty-two of 59 gastrointestinal tumors (37%) contained E2F-4 muta tions; these comprised 5 of 16 gastric tumors (31%), 4 of 12 ulcerativ e colitis-associated neoplasms (33%, including 1 dysplastic lesion), a nd 13 of 31 sporadic colorectal cancers (42%). No mutation was present in any of the endometrial, prostate, or RER- colorectal tumors. Of no te, homozygous mutations occurred in three cases, and two of seven inf ormative patients showed loss of one E2F-4 allele in their tumors. Fur thermore, the RER+ sporadic colorectal tumors were evaluated at trinuc leotide repeats within the genes for N-cadherin and B-catenin; no tumo rs demonstrated mutation of these genes. These data suggest that E2F-4 is a target of defective DNA repair in these tumors.