Oncogene Health Article

Definition

In a cell with normal control regulation (non-cancerous), genes produce proteins that provide regulated cell division. Cancer is the disease caused by cells that have lost their ability to control their regulation. The abnormal proteins allowing the non-regulated cancerous state are produced by genes known as oncogenes. The normal gene from which the oncogene evolved is called a proto-oncogene.

History

The word oncogene comes from the Greek term oncos, which means tumor. Oncogenes were originally discovered in certain types of animal viruses that were capable of inducing tumors in the animals they infected. These viral oncogenes, called v-onc, were later found in human tumors, although most human cancers do not appear to be caused by viruses. Since their original discovery, hundreds of oncogenes have been found but only a small number of them are known to affect humans. Although different oncogenes have different functions, they are all somehow involved in the process of transformation (change) of normal cells to cancerous cells.

The transformation of normal cells into cancerous cells

The process by which normal cells are transformed into cancerous cells is a complex, multi-step process involving a breakdown in the normal cell cycle. Normally, a somatic cell goes through a growth cycle in which it produces new cells. The two main stages of this cycle are interphase (genetic material in the cell duplicates) and mitosis (the cell divides to produce two other identical cells). The process of cell division is necessary for the growth of tissues and organs of the body and for the replacement of damaged cells. Normal cells have a limited life span and only go through the cell cycle a limited number of times.

Different cell types are produced by the regulation of which genes in a given cell are allowed to be expressed. One way cancer is caused, is by de-regulation of those genes related to control of the cell cycle; the development of oncogenes. If the oncogene is present in a skin cell, the patient will have skin cancer; in a breast cell, breast cancer will result, and so on.

Cells that loose control of their cell cycle and replicate out of control are called cancer cells. Cancer cells undergo many cell divisions often at a quicker rate than normal cells and do not have a limited life span. This allows them to eventually overwhelm the body with a large number of abnormal cells and eventually affect the functioning of the normal cells.

A cell becomes cancerous only after changes occur in a number of genes that are involved in the regulation of its cell cycle. A change in a regulatory gene can cause it to stop producing a normal regulatory protein or can produce an abnormal protein that does not regulate the cell in a normal manner. When changes occur in one regulatory gene this often causes changes in other regulatory genes. Cancers in different types of cells can be caused by changes in different types of regulatory genes.

Proto-oncogenes and tumor-suppressor genes are the two most common genes involved in regulating the cell cycle. Proto-oncogenes and tumor-suppressor genes have different functions in the cell cycle. Tumor-suppressor genes produce proteins that are involved in prevention of uncontrolled cell growth and division. Since two of each type of gene are inherited, two of each type of tumor-suppressor gene are also inherited. Both tumor suppressor genes of a pair need to be changed in order for the protein produced to stop functioning as a tumor suppressor. Mutated tumor-suppressor genes therefore act in an autosomal recessive manner.

Proto-oncogenes produce proteins that are largely involved in stimulating the growth and division of cells in a controlled manner. Each proto-oncogene produces a different protein that has a unique role in regulating the cell cycles of particular types of cells. We inherit two of each type of proto-oncogene. A change in only one proto-oncogene of a pair converts it into an oncogene. The oncogene produces an abnormal protein, which is somehow involved in stimulating uncontrolled cell growth. An oncogene acts in an autosomal dominant manner since only one proto-oncogene of a pair needs to be changed in the formation of an oncogene.