How do proto-oncogenes stimulates the cell growth?
A proto oncogene is a normal gene that could become an oncogene due to mutations or increased expressions.
Upon acquiring an activating mutation, a proto oncogene becomes a tumor inducing agent i.e. an oncogene.
An example of proto oncogene is Bcr Abl, seen in chronic Myelogenic Leukaemia. This occurs due to translocation of pieces from chromosomes leading to uncontrolled cell proliferation. The unregulated expression of this protein activates other proteins that are involved in the cell cycles do cell division which can cause a cell to grow and divide uncontrollably.