Cell Division and Survival

The most prominent characteristic of cancer, uncontrolled cell division, is caused by dysregulation of the cell cycle clock [Weinberg 1996]. Cell cycle progression is promoted externally by growth factors and internally by a series of protein kinases that induce cell division in accord with the needs of the whole organism. The two principal quality control mechanisms in cell proliferation are cell cycle arrest and apoptosis. Proto-oncogenes physiologically induce cell division or survival by operating in the pathways, through which cells recognize and respond to growth factors or prevent programmed cell death. Conversely, tumor suppressor gene products antagonize proto-oncogenes either by activating cell cycle checkpoints or by inducing apoptosis. The abnormal growth rate of cancerous cells is mediated by the activation of genetic programs that promote cell cycle progression and overcome the otherwise dominant control mechanisms of cell cycle arrest and apoptosis.