Sustaining Proliferative Signalling
External reactions and internal reactions for signal transduction. In: Maxwell, R. BOLO Biology Newsletter: Basics of Cell Communication. October 14, 2013
A ligand, such as a growth factor, binds to a receptor located on the cellular membrane. This connection results in some sort of response, such as cellular proliferation.
T he first Hallmark of Cancer is the cell’s ability to sustain proliferative signaling. In other words, the cell divides and multiplies uncontrollably. Normally, healthy cells have control over factors that affect the growth of a cell. Healthy cells can control how often they divide, how the cells are going to be structured, and what functions the cells will have. A cell’s ability to multiply without a controlled signal is a key characteristic of a cancer cell.
This can happen in several ways. First, the production of growth factors that promote cell division may increase. These growth factors may be generated in neighboring cells and relayed to the cancer cell to increase proliferation. Second, the number of receptors on the surface of the cell may also increase. Receptors are responsible for receiving the signal of the growth factor. The growth factor and receptor work hand-in-hand, just like a basketball and a hoop. If the growth factor is the basketball and the receptor is the hoop, increasing the number of basketballs increases the chance to score. Increasing the number of hoops also increases the chance to score. An increase in the number of receptors may stimulate a cell to proliferate even with a low amount of growth factors. The structure of these receptors may also be altered in order to promote proliferation of the cancer cells.
Another method used by cancer cells is to activate other proteins down the signaling pathway that will also help to promote cell proliferation. Remember that cells work as a network. Oftentimes cancer cells flourish from the help of nearby cells that appear normal or healthy. Attention must also be given to these cells on how they contribute to the growth of cancer cells.
An example of this Hallmark of Cancer can be seen with sex steroid hormone signaling. Estrogen, progesterone, and androgen are hormones that target female and male reproductive organs. Each hormone binds to these tissues through specific receptors. This interaction regulates gene expression. However, if there is problem with these receptors, gene expression may be overstimulated and cell proliferation may be out of control, leading to a cancerous tumor growth on the reproductive organ. A treatment for a type of breast cancer is called Tamoxifen. Tamoxifen targets this first Hallmark of Cancer, sustained proliferation signaling, by trying to slow the growth of cancer cells in the tissue or stop growth signalling all together.