Cytogenetic studies in a 70-year-old woman with chronic myelogenous leukemia (CML) demonstrate a t(9;22) chromosomal translocation. Which of the following best explains the role of this translocation in the pathogenesis of leukemia in this patient?: (A) Altered DNA methylation status, (B) Enhanced expression of telomerase gene, (C) Expansion of a trinucleotide repeat, (D) Protooncogene activation
Answer is D. Philadelphia chromosome is the best-known example of an acquired chromosomal translocation in a human cancer It is found in 95% of patients with CML. The c-abl protooncogene on chromosome 9 is translocated to chromosome 22 The c-abl gene and bcr region unite to produce a hybrid oncogene that codes for an aberrant protein with very high levels of tyrosine kinase activity, which generates mitogenic and antiapoptotic signals.