Chapter 17, Problem 1CS

Each year in the United States, there are over 230,000 new cases of prostate cancer and almost 28,000 deaths. A 3.8-Mb region on chromosome 8 (8q24), called a gene desert, has very few genes but contains enhancer sequences that potentially confer significant risks for prostate cancer. One particular enhancer allele, which is kncwn to be associated with an elevated risk for prostate cancer, physically interacts with the promoter region of the nearby MYC gene and facilitates its upregulation. Overexpression of MYC, which encodes a cell-cycle regulatory protein, is observed in multiple types of cancer (see Chapter 24). The risk allele has a frequency of 49 percent in men of European descent and 81 percent in men of African ancestry. Most of the differential MYC activity associated with the risk allele occurs during prenatal development, raising the possibility that testing for this allele early in life can be used to identify those in the African-American population who are at very high risk for prostate cancer. However, researchers cannot rule out the possibility that this enhancer causes overexpression of other genes, which may also be involved in prostate cancer.

How do enhancers control the expression of genes located some distance away from the enhancer?