Genome Regulation: Cancer and Gene Expression

Cancer and Cell Cycle Control

• Cancer results from genetic changes that affect cell cycle control
• Gene regulation systems involved in embryonic development are the same ones that go wrong during cancer

Types of Genes Associated with Cancer

• Cancer can be caused by mutations in genes that regulate cell growth and division
• Tumor viruses can cause cancer in animals, including humans

Oncogenes and Proto-Oncogenes

• Oncogenes are cancer-causing genes
• Proto-oncogenes are normal cellular genes responsible for normal cell growth and division
• Conversion of a proto-oncogene to an oncogene can lead to abnormal stimulation of the cell cycle
• Proto-oncogenes can be converted to oncogenes by:
  • Movement of DNA within the genome
  • Amplification of a proto-oncogene
  • Point mutations in the proto-oncogene or its control elements

Tumor-Suppressor Genes

• Tumor-suppressor genes help prevent uncontrolled cell growth
• Mutations that decrease protein products of tumor-suppressor genes may contribute to cancer onset
• Tumor-suppressor proteins:
  • Repair damaged DNA
  • Control cell adhesion
  • Inhibit the cell cycle in the cell-signaling pathway

Interference with Normal Cell-Signaling Pathways

• Mutations in the ras proto-oncogene and p53 tumor-suppressor gene are common in human cancers
• Mutations in the ras gene can lead to production of a hyperactive Ras protein and increased cell division
• Suppression of the cell cycle can be important in the case of damage to a cell's DNA; p53 prevents a cell from passing on mutations