The Cell Cycle and Cancer

How do we define cancer? Cancer is: 1. a disease of the cell cycle. 2. a group of disorders that cause some of the body’s cells divide uncontrollably and tumors form.

Tumors in Liver Tumor in Colon

What can cancer cells do? Cancer cells: 1. divide more frequently 2. are not inhibited by contact with other cells and can form tumors 3. can invade other tissues, a process called metastasis

Non-cancerous cells form sheets. Cancer cells grow into tumors. Cancer cells can invade other tissues.

The Stages of the Cell Cycle 1. Click on picture for cell cycle animation – will go to 2. Use alt-tab keys to go between website and power point presentation. 3. Click on blank space to proceed to next slide.)

There are several factors that regulate the cell cycle and assure a cell divides correctly. 1.Before a cell divides, the DNA is checked to make sure it has replicated correctly. gene mutation – occur when DNA does not copy itself correctly DNA replication animation:click on DNA picture

2. Chemical Signals tell a cell when to start and stop dividing. (Target cells animation: click on go sign)

How does the cell cycle control cancer? The cell cycle uses: Checkpoints Length of Telomeres Chemical Signals from within and outside the cell

Cell Cycle Checkpoints G1 S G2 cytoplasm doubles chromosomes replicate assembly of components for division cytokinesis P M A T Mitosis DNA Damage Checkpoints Checkpoint ApoptosisCheckpointSpindleAssemblyCheckpoint

Length of Telomeres Telomeres are structures at the ends of chromosomes that shorten with each cell division. After 50 divisions, the shortened length of telomeres causes mitosis to stop. telomeres

Failure to Stop at Cell Cycle Checkpoints… What happens?What does this mean? Mutation occurs in a gene that usually slows the cell cycle Rate of cell division is accelerated. Failure to pause for DNA repair Faulty DNA leads to unregulated cell growth. Loss of control over telomere length Cancer cells have telomerase, an enzyme that elongates telomeres. Cells continue to divide after 50 mitoses.

Chemical Signals that Control the Cell Cycle 1.Cyclin and Kinase - proteins that initiate mitosis -requires buildup of cyclin to pair with kinase 2.Hormones - chemical signals from specialized glands that stimulate mitosis 3.Growth Factors -chemical factors produced locally that stimulate mitosis

Applying Your Knowledge

Neighboring cells communicate with dividing cells to regulate their growth also. (Normal contact inhibition animation: click on petri dish)

DNA mutations disrupt the cell cycle. Mutations may be caused by: 1. radiation 2. smoking 3. pollutants 4. chemicals 5. viruses

While normal cells will stop dividing if there is a mutation in the DNA, cancer cells will continue to divide with mutation.

Due to DNA mutations, cancer cells ignore the chemical signals that start and stop the cell cycle. 2 animations of cancer cells dividing: click on picture

Due to DNA mutations, cancer cells cannot communicate with neighboring cells. Cells continue to grow and form tumors. (cancer cells dividing: click on picture.) Skin cancer

Genetic Mutations That Can Cause Cancer Oncogenes Formed when proto-oncogenes that promote cell division are improperly activated. May lead to: 1. increased expression of the gene in a new location 2. production of fusion proteins with new functions

Ras Proto-Oncogene In response to growth factor binding at receptor, the Ras gene product combines with GTP to promote cell division In cancer cells, the RAS gene product is locked into its GTP-binding shape and does not require a signal at the receptor in order to stimulate cell division

Genetic Mutations That Can Cause Cancer Tumor Suppressor Genes Genes that inhibit cell division are inactivated. –Retinoblastoma, a variety of cancers, and inherited breast cancer is controlled by tumor suppressor genes.

Genetic Mutations That Can Cause Cancer DNA Repair Genes Genes that promote DNA repair are inactivated. –BRCA1 is a tumor suppressor involved in DNA repair. Faulty copies of BRCA1 cause inherited breast cancer.

Applying Your Knowledge

SUMMARY Normal Cell Division 1.DNA is replicated properly. 2. Chemical signals start and stop the cell cycle. 3. Cells communicate with each other so they don’t become overcrowded. Cancer Cells 1.Mutations occur in the DNA when it is replicated. 2. Chemical signals that start and stop the cell cycle are ignored. 3. Cells do not communicate with each other and tumors form.

Treating Cancers Cancer treatments include drugs that can stop cancer cells from dividing.

Good News! There are ways you can reduce your risk of cancer!

Reduce Your Skin Exposure to the Sun Protect your skin with hats, long sleeves and sunscreen Avoid tanning beds Limit time outside Do a self examination of your skin monthly Become familiar with any moles, freckles or other abnormalities on your skin Check for changes once a month. Show any suspicious or changing areas to your health care provider.

Avoid Smoking or Chewing Tobacco Cigarette smoking is the leading cause of preventable death in the US Second hand smoke affects everyone

Be Active…Often Exercise for 30 minutes or more at least 4 days a week.

Fruits and Vegetables Decrease Cancer Risks Cancer rates could decline by up to 20% if everyone consumed 5 fruits and vegetables a day!* Cancer fighting substances: Antioxidants Dietary fiber Carotenoids Flavenoids *American Institute for Cancer Research, 1998.

How Far Have We Come ? Five year survival rate: % % Advances in cancer research continue

American Cancer Society 186,550 The number of lives that could be saved each year if we ate a healthy diet and exercised regularly 186,550 The number of lives that could be saved each year with no tobacco