Question

What distinguishes proto-oncogenes from oncogenes?

Answer 1

Proto-oncogenes are normal genes which helps cells to grow. But whenever a mutation occurs in these genes, it gives rise to an Oncogene or in other words, oncogenes are mutated versions of the proto-oncogenes. Mechanisms responsible for converting proto-oncogenes to oncogenes include:

1. Chromosomal translocations of proto-oncogene, leading to their over-expression e.g. Myc gene in Burkitt’s lymphoma

2. Gene amplification, leading to extra-chromosomal proto-oncogene copies. e.g., Gene amplification mutation in Her2 gene in breast cancer

3. Point mutations (deletion/insertion), leading to increased transcription, therefore more active gene product(s) e.g. point mutation in Ras gene in pancreatic cancer

The difference between proto-oncogenes and oncogenes are listed in tabular form below:

Proto-oncogenes	Oncogenes
Normal genes which help cells grow	Mutated version of proto-oncogene
Encode proteins which · Stimulate cell division · Inhibits cell differentiation · Promote cell death, when damaged or old	Encode proteins which · Stimulate uncontrolled cell division · Decreases the cell differentiation · Inhibits cell death Or, increased production of proteins encoded by proto-oncogenes
Gives rise to cancer only when activated	Gives rise to cancer definitely
Examples: Ras, Cyclin D, HER2, Myc	Examples: Some growth factors (c-Sis); Raf kinase, cyclin-dependent kinase; myc gene (Transcription factor)