This indicates that the ERE73 (1 + 2)-ARF (−13) and ERE73 (3 + 4)-ARF (−13) constructs are activated by deregulated E2F activity, but not by physiological E2F activity induced by serum stimulation, suggesting that these artificial promoters are minimally active in normally growing cells but exhibit high activity in cancer cells. Here, CDKN2A is linked to cancer.