Related Experiment Videos
Deletion of the p16 and p15 genes in human bladder tumors
I Orlow1, L Lacombe, G J Hannon
1Department of Pathology, Memorial Sloan-Kettering Cancer Center, New York, NY 10021, USA.
Background:
Two genes, p16 (also known as CDKN2, INK4A, or MTS1) and p15 (also described as INK4B or MTS2), are found in tandem at chromosome 9p21. These genes are designated as candidate tumor suppressor genes because they encode proteins that function as negative cell cycle regulators. (The encoded polypeptides inactivate specific cyclin-protein kinase complexes that are required for progression through the cell cycle.) Molecular genetic studies have revealed that deletion of the p16 and p15 genes occurs frequently in cancer cell lines and in certain malignant neoplasms.
Purpose:
We evaluated the frequency of p16 and p15 gene alterations in a well-characterized cohort of human transitional cell bladder cancers, and we explored potential associations between alterations in these genes and tumor stage and/or grade.
Methods:
Tumor tissue and normal tissue from 110 patients with transitional cell carcinoma of the urinary bladder were examined. The status of the p16 and p15 genes in these tissues was determined by Southern blotting and hybridization with gene-specific probes, by coupled polymerase chain reaction and single-strand conformation polymorphism analysis (PCR-SSCP), and by sequencing DNA fragments produced during PCR. Associations between alterations in the genes and tumor stage and/or grade were evaluated using the two-tailed Fisher's exact test.
Results:
Homozygous deletion (both alleles lost) of the p16 and the p15 genes was observed in 11 and nine bladder tumors, respectively. Eight of the 11 tumors exhibiting complete loss of the p16 gene also displayed homozygous deletion of the p15 gene. Exclusive loss of either gene was detected in only three tumors. Hemizygous deletion (one allele lost, also referred to as loss of heterozygosity [LOH] of the p16 and/or p15 genes was observed in eight tumors. Rearrangement of the two genes was indicated in three additional tumors. No point mutations were identified in either gene. The overall frequency of alteration in this cohort of bladder tumors was approximately 18% for each gene (in 20 [18.3%, 95% confidence interval (CI) = 11.1%-25.6%] of 109 informative tumors for the p16 gene and in 18 [18%, 95% CI = 10.5%-25.5%] of 100 informative tumors for the p15 gene). A statistically significant association between p16 gene alteration and bladder tumors of low stage (P < .01) and grade (P < .01) was observed; a significant association between p15 gene alteration and tumors of low stage (P < .01) was also detected.
Conclusions:
Alteration of the p16 and p15 genes, especially coincident homozygous deletion, appears to be a common event in bladder cancer.
Insights
Alterations in the p16 and p15 tumor suppressor genes are common in bladder cancer, particularly homozygous deletions. These gene alterations are significantly associated with lower stage and grade bladder tumors.
Area of Science:
- Oncology
- Molecular Genetics
- Cancer Biology
Background:
- The p16 and p15 genes, located at chromosome 9p21, function as crucial negative cell cycle regulators.
- These genes are considered candidate tumor suppressor genes due to their role in controlling cell proliferation.
- Previous studies indicated frequent deletion of p16 and p15 in various cancer cell lines and neoplasms.
Purpose of the Study:
- To determine the frequency of p16 and p15 gene alterations in human transitional cell bladder cancers.
- To investigate the correlation between these gene alterations and tumor stage and grade.
Main Methods:
- Analysis of tumor and normal tissue from 110 bladder cancer patients.
- Utilized Southern blotting, PCR-SSCP, and DNA sequencing to assess p16 and p15 gene status.
- Employed Fisher's exact test to evaluate associations with tumor stage and grade.
Main Results:
- Homozygous deletion of p16 and p15 was observed in 11% and 9% of tumors, respectively.
- Approximately 18% of informative bladder tumors showed alterations in either the p16 or p15 gene.
- Significant associations were found between p16 alterations and low stage/grade tumors, and p15 alterations and low stage tumors.
Conclusions:
- Alterations in the p16 and p15 genes are frequent events in bladder cancer.
- Coincident homozygous deletion of both genes is a notable finding.
- These genetic alterations correlate with less advanced tumor characteristics.