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Frequent mutation of the E2F-4 cell cycle gene in primary human gastrointestinal tumors
R F Souza1, J Yin, K N Smolinski
1Department of Medicine, University of Maryland School of Medicine and Baltimore Veterans Affairs Medical Center, 21201-1595, USA.
Abstract:
The E2F group of transcription factors transactivates genes that promote progression through the G1-S transition of the cell cycle. Members of the retinoblastoma (Rb) family of proteins bind to E2Fs and inhibit 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 develop cancers, consistent with a tumor-suppressive role for this gene. The exact function of E2Fs has thus been unclear; moreover, direct involvement of this gene in primary human tumorigenesis has not been shown. We, therefore, investigated mutation within the E2F-4 coding region in 16 primary gastric adenocarcinomas, 12 ulcerative colitis-associated neoplasms, 46 sporadic colorectal carcinomas, 9 endometrial cancers, and 3 prostatic carcinomas. We limited our investigation to the serine 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- sporadic colorectal carcinomas. PCR with incorporation of [32P]dCTP was performed using primers flanking the serine trinucleotide (AGC) repeat. Twenty-two of 59 gastrointestinal tumors (37%) contained E2F-4 mutations; these comprised 5 of 16 gastric tumors (31%), 4 of 12 ulcerative colitis-associated neoplasms (33%, including 1 dysplastic lesion), and 13 of 31 sporadic colorectal cancers (42%). No mutation was present in any of the endometrial, prostate, or RER- colorectal tumors. Of note, homozygous mutations occurred in three cases, and two of seven informative patients showed loss of one E2F-4 allele in their tumors. Furthermore, the RER+ sporadic colorectal tumors were evaluated at trinucleotide repeats within the genes for N-cadherin and B-catenin; no tumors demonstrated mutation of these genes. These data suggest that E2F-4 is a target of defective DNA repair in these tumors.
Insights
E2F-4 mutations were found in 37% of gastrointestinal tumors, particularly in gastric and colorectal cancers. These findings suggest E2F-4 is a target of DNA repair defects in tumorigenesis.
Area of Science:
- Molecular Biology
- Oncology
- Genetics
Background:
- E2F transcription factors regulate cell cycle progression.
- Retinoblastoma (Rb) proteins inhibit E2F activity.
- The precise role of E2F family members in human tumorigenesis remains unclear.
Purpose of the Study:
- To investigate mutations in the E2F-4 gene in various human cancers.
- To determine if E2F-4 is a target of defective DNA repair in replication error-positive (RER+) tumors.
Main Methods:
- Analyzed E2F-4 coding regions, specifically the serine repeat, in gastric, colorectal, endometrial, and prostate tumors.
- Utilized PCR with [32P]dCTP incorporation to detect mutations.
- Compared mutation rates in RER+ tumors versus RER- controls.
Main Results:
- E2F-4 mutations were identified in 37% (22/59) of gastrointestinal tumors analyzed.
- Mutations were prevalent in gastric (31%), ulcerative colitis-associated neoplasms (33%), and sporadic colorectal cancers (42%).
- No E2F-4 mutations were found in endometrial, prostate, or RER- colorectal tumors.
Conclusions:
- E2F-4 is frequently mutated in RER+ gastrointestinal tumors.
- These mutations suggest E2F-4 is a target of defective DNA repair mechanisms.
- E2F-4 alterations may play a role in the development of these cancers.