p53 is one of the most important
genes in current research into a
cure for cancer. It is a 53 kilo
dalton protein product (hence the name) encoded on the short arm of
chromosome 17. It is one of the primary
proteins responsible for
apoptosis (
programmed cell death), and responses in dealing with
DNA damage. Ordinarily, when a cell is damaged, by radiation or chemicals, p53 becomes active, and prevents cell division. If the cell is too damaged for
DNA repair pathways to mend, it causes the cell to undergo
apoptosis. It is the single most common gene
mutation present in
cancer. When a cell loses p53, through mutation generally, it rapidly accumulates other mutations, which can either kill the cell, or eventually make it cancerous. Most of the cancer tumors that respond well to
radiation and
chemotherapy do not have the p53 mutation. Therefore, when they are damaged by radiation, p53 stops their replication and causes them to apoptose, killing the tumor. This does not happen in tumors lacking p53, so it makes p53 a very appealing target for
gene therapy to insert into cancer cells, making them vulnerable to radiation treatment again.
There is also a genetic disease involving p53 mutation. Because
humans have 2 copies of this gene, sometimes a person will
inherit a defective copy from one
parent, and a normal copy from the other parent. This means that a mutation in the single normal gene results in total loss of p53 in that cell. These individuals have a very high rate of cancer, generally with a very poor
prognosis for recovery.