V

tumor suppressor

signal transduction signal transduction

apoptosis signals

(EHUD

messages bind to specific receptor proteins on the surface of the surrounding cells. The gene expression of these cells is changed as a result of the messages.

A hyperplastic cell or a cancerous cell will stimulate neighboring cells to grow by secreting growth factors. Several types of genes can be mutated in tumor cells: oncogenes, tumor suppressor genes, DNA repair genes, and genes involved in cell mortality.

Oncogenes. These genes are involved in signal transduction, and some are involved in the various phases of the cell cycle. Mutations in cell-cycle regulation or signal transduction can "push" the cell into dividing rapidly and without regard to its surroundings. Over 100 oncogenes have been identified so far. They include genes such as ABL1 (Abelson murine strain leukemia viral homolog) and EGFR (Epidermal Growth Factor Receptor).

Tumor Suppressor Genes. These genes inhibit cell division, working in a manner opposite to that of the oncogenes. Surrounding cells secrete growth-inhibitory signals that help prevent proliferation. These growth-inhibitory signals work in conjunction with tumor suppressor genes. If a tumor suppressor gene is mutated, proliferating cells can ignore these inhibitory messages. This group includes the genes p53, BRCA1, and BRCA2.

DNA Repair Genes. These are the genes that provide the cell with the ability to sense and correct damage to the DNA. Damage to the DNA can be caused by radiation, chemicals, ultraviolet light, or errors in transcription. If these errors are not corrected, they accumulate in the genome and can

Multiple systems interact to control the cell cycle, ensuring that cell division occurs only when it is advantageous for the organism and when undamaged DNA is availale for replication. Cancer may occur when any one of these systems is disrupted.

hyperplastic cell cell that is growing at an increased rate compared to normal cells, but is not yet cancerous

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