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.
There are six known classes of
tyrosine kinases that can go onkogene:
- Receptor tyrosine kinases that become constitutive (permanently) active.
- Cytoplasmic tyrosine kinases, often products of viral oncogenes.
- Regulatory GTPases, for example, the [Ras kinase]?.
- Cytoplasmic Serine?/Threonine? kinases and their regulatory subunits, for example, the [Raf kinase]?, and cycline?s (through overexpression).
- [Adaptor protein]?s in signal transduction.
- [Transcription factor]?s.