Oncogenes are the mutated forms of normal cellular genes (proto-oncogenes).
The protein products of proto-oncogenes stimulate cell division and/or inhibit cell death.
Proto-oncogenes can be likened to the gas pedal in a car.
Normally, internal and external signals strictly regulate the activity of the proto-oncogenes, but oncogenes are defective and are 'on' even when they do not receive appropriate signals.
Oncogenes also help cells to ignore negative signals that would prevent a healthy cell from dividing.
Oncogenes can cause cells to divide continuously even in the absence of any pro-growth signals.
The following list describes different cellular roles for a few of the many known oncogenes:
HER-2/neu
HER-2/neu encodes for a cell surface receptor that can stimulate cell division
The HER-2/neu gene is amplified in up to 30% of human breast cancers
RAS
The Ras gene products are involved in kinase signaling pathways that ultimately control transcription of genes, regulating cell growth and differentiation.
Overexpression and amplification of RAS can lead to continuous cell proliferation.
MYC
The Myc protein is a transcription factor and controls expression of several genes.
Myc is thought to be involved in avoiding the cell death mechanism.
MYC oncogenes may be activated by gene rearrangement or amplification.
SRC
SRC was the first oncogene ever discovered.
The Src protein is a tyrosine kinase which regulates cell activity.
hTERT
hTERT codes for an enzyme (telomerase) that maintains chromosome ends.
In most normal cells telomerase is only present during fetal development.
Activation of hTERT in adult cells gives them the ability to divide indefinitely.
BCL-2
The Bcl-2 protein works to prevent cell death (apoptosis).
Overexpression of BCL-2 allows continued division of mutated cells.
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