Genes and Mutations that Contribute to the Development of Cancer

Proto-oncogenes code for proteins that contribute to normal stimulation of cell division needed for growth and

repair. The different types of proteins are underlined in the flow chart below.

Growth factors bind to growth factor receptors

→ activate series of signaling enzymes

→ activate protein transcription factors

→ increased transcription of genes that code for proteins

that stimulate cell division

→ increased cell division = cell proliferation

Growth factor

Receptor-

Cell nucleus

Normal Growth-Control Pathway

Signaling enzymes

Transcription

factors

DNA

Cell proliferation

(Figure from http://www.ncbi.nlm.nih.gov/books/NBK20362)

An oncogene is a mutated proto-oncogene which codes for an abnormal protein that stimulates excessive cell

division and thus can contribute to the formation of a tumor.

One type of tumor suppressor gene codes for proteins that inhibit cell division, e.g., by interfering with one of

the proteins that stimulate cell division. If both copies of a tumor suppressor gene are mutated and code for

inactive proteins, this eliminates one of the inhibitory controls on cell division, which can result in excessive

cell division and the formation of a tumor./nThe development of an invasive or malignant cancer typically requires the accumulation of at least five

mutations in the same cell line, including:

mutations of proto-oncogenes to oncogenes

mutations of tumor suppressor genes so they code for inactive proteins

other types of mutations that contribute to the varied abnormal characteristics of cancer cells./n3. Why do all of us need to have proto-oncogenes in the DNA of our cells? What would go wrong if

our cells had mutated proto-oncogenes that coded for inactive proteins? (5 pts)