Chapter 23, Problem 25
Mutations in tumor-suppressor genes are associated with many types of cancers. In addition, epigenetic changes (such as DNA methylation) of tumor-suppressor genes are also associated with tumorigenesis [Otani et al. (2013). Expert Rev Mol Diagn 13:445–455].
Knowing that tumors release free DNA into certain surrounding body fluids through necrosis and apoptosis Kloten et al. [(2013). Breast Cancer Res. 15(1):R4] outline an experimental protocol for using human blood as a biomarker for cancer and as a method for monitoring the progression of cancer in an individual.
Video transcript
Genetic tests that detect mutations in the BRCA1 and BRCA2 tumor-suppressor genes are widely available. These tests reveal a number of mutations in these genes—mutations that have been linked to familial breast cancer. Assume that a young woman in a suspected breast cancer family takes the BRCA1 and BRCA2 genetic tests and receives negative results. That is, she does not test positive for the mutant alleles of BRCA1 or BRCA2. Can she consider herself free of risk for breast cancer?
Explain the apparent paradox that both hypermethylation and hypomethylation of DNA are often found in the same cancer cell.
As part of a cancer research project, you have discovered a gene that is mutated in many metastatic tumors. After determining the DNA sequence of this gene, you compare the sequence with those of other genes in the human genome sequence database. Your gene appears to code for an amino acid sequence that resembles sequences found in some serine proteases. Conjecture how your new gene might contribute to the development of highly invasive cancers.
Mutations in tumor-suppressor genes are associated with many types of cancers. In addition, epigenetic changes (such as DNA methylation) of tumor-suppressor genes are also associated with tumorigenesis [Otani et al. (2013). Expert Rev Mol Diagn 13:445–455].
How might hypermethylation of the TP53 gene promoter influence tumorigenesis?
A study by Bose and colleagues [(1998). Blood 92:3362–3367] and a previous study by Biernaux and others [(1996). Bone Marrow Transplant 17:(Suppl. 3) S45–S47] showed that BCR-ABL fusion gene transcripts can be detected in 25 to 30 percent of healthy adults who do not develop chronic myelogenous leukemia (CML). Explain how these individuals can carry a fusion gene that is transcriptionally active and yet do not develop CML.
Those who inherit a mutant allele of the RB1 tumor-suppressor gene are at risk for developing a bone cancer called osteosarcoma. You suspect that in these cases, osteosarcoma requires a mutation in the second RB1 allele, and you have cultured some osteosarcoma cells and obtained a cDNA clone of a normal human RB1 gene. A colleague sends you a research paper revealing that a strain of cancer-prone mice develop malignant tumors when injected with osteosarcoma cells, and you obtain these mice. Using these three resources, what experiments would you perform to determine (a) whether osteosarcoma cells carry two RB1 mutations, (b) whether osteosarcoma cells produce any pRB protein, and (c) if the addition of a normal RB1 gene will change the cancer-causing potential of osteosarcoma cells?