Oncogene

An oncogene is a gene that causes a cell to develop into a tumor cell.

Protooncogene

A protooncogene is a gene that is involved in signal transduction and execution of mitogenic signals, usually through its protein product. Upon activation, it (or its product) becomes a tumor inducing agent, an oncogene.

Activation

The protooncogene can become an oncogene by a relatively small modification of its original function. There are two basic activation types:

• A mutation within a protooncogene can cause a change in the protein structure, caused by
  • an increase in protein (enzyme)activity
  • a loss of regulation
  • the creation of a hybrid protein, through a [chromosomal aberration]? during [cell division]?. A distinct aberration in a dividing stem cell in the [bone marrow]? leads to adult leukemia
• An increase in protein concentration, caused by
  • an increase of protein expression (through misregulation)
  • an increase of protein stability, prolonging its existence and thus its activity in the cell
  • a [gene duplication]?, resulting in a doubled amount of protein in the cell

Oncogene

Growth factors

[Growth factor]]s are usually secreted? by few special cells to induce cell proliferation in other cells. If a cell that usually does not produce growth factors suddenly starts to do so (because it developed an oncogene), it will thereby induce its own uncontrolled proliferation ([autocrine loop]?), as well as the proliferation of neighbouring cells.

Protein kinases

There are six known classes of tyrosine kinases that can go onkogene:

1. Receptor tyrosine kinases that become constitutive (permanently) active.
2. Cytoplasmic tyrosine kinases, often products of viral oncogenes.
3. Regulatory GTPases, for example, the [Ras kinase]?.
4. Cytoplasmic Serine?/Threonine? kinases and their regulatory subunits, for example, the [Raf kinase]?, and cycline?s (through overexpression).
5. [Adaptor protein]?s in signal transduction.
6. [Transcription factor]?s.