A proto-oncogene is a normal gene that can become an oncogene due to mutations or increased expression. The resultant protein can be called an oncoprotein. Proto-oncogenes code for proteins that help to regulate cell growth and differentiation. Proto-oncogenes are often involved in signal transduction and execution of mitogenic signals, usually through their protein products. Upon "activation", a proto-oncogene (or its product) becomes a tumor-inducing agent, an oncogene.