Akt
Meaning of Akt: Named after a mouse tumor virus, this switch sits at the center of how a cell decides to grow, survive or store fuel.
Definition of Akt
Akt is a family of three closely related enzymes that pass signals along inside a cell by attaching phosphate groups to other proteins. Each one is switched on at the inner face of the cell membrane after insulin or a growth factor binds outside. Their targets block cell death, permit growth, and direct how sugar and fat are handled.
How does the switch get thrown?
A signal lands on the outside of the cell: insulin, or a growth factor. The receptor it binds turns on an enzyme called PI3 kinase, which tags the inner face of the cell membrane with a lipid marker. Akt is drawn to that tag, moves to the membrane, and is then switched on by two further kinase enzymes, each adding a phosphate at a different spot. Full activity needs both. A counter-enzyme called PTEN erases the lipid tag and shuts the line down, so a cell that loses PTEN leaves Akt switched on with nothing arriving from outside.
What does it do once active?
It travels through the cell attaching phosphate to dozens of target proteins, and what the tag does depends on which protein receives it. Proteins that would otherwise start a cell's self-destruction are silenced, so the cell survives. A growth controller called mTOR is released, so the cell builds protein and enlarges. In muscle and fat, the same enzyme sends glucose transporters to the cell surface, which is how insulin clears sugar out of the blood. One switch, several unrelated-looking jobs.
Do the three members differ?
| Member | Most active in | Main job |
|---|---|---|
| Akt1 | Most tissues | Survival and cell growth |
| Akt2 | Muscle, fat and liver | Insulin action and sugar uptake |
| Akt3 | Brain | Brain growth and size |
The naming is a historical mess worth untangling. Akt is taken from a mouse tumor virus in which the gene was first spotted, and carries no meaning about what the enzyme does. Protein kinase B is the same molecule under a second name, given for its close resemblance to two enzymes already called protein kinase A and protein kinase C. The pathway is among the most frequently overactive in human cancer, usually because the brake is lost or a switch upstream is stuck rather than because Akt itself is faulty.
Also known as
Used in a sentence
Staining showed strong Akt activation throughout the tumor cells.
Good to know
Akt and protein kinase B name the same enzyme, and the number after the name identifies one of three family members rather than a stage or grade, with Akt2 tied to insulin action and Akt3 to brain growth.