signal transduction
Meaning of signal transduction: How a message arriving at the cell surface is converted into action inside, growing louder at every step of the relay.
Definition of signal transduction
Signal transduction is the process by which a cell converts a message arriving at its surface into a change in its own behavior. A molecule binds a receptor, the receptor changes shape, and that change starts a chain of reactions inside the cell. Each step activates several molecules at the next, so a few arriving signals produce a large internal response.
What are the steps?
Almost every pathway follows the same shape, whatever the message.
| Step | What happens |
|---|---|
| Reception | A signal molecule binds its receptor |
| Transduction | The receptor activates proteins inside the cell |
| Amplification | Each active protein switches on many others |
| Response | Genes are switched on, or the cell moves, divides or secretes |
| Termination | Enzymes reverse the changes and the pathway resets |
Why does the signal not simply enter the cell?
Most signal molecules are water-soluble and cannot cross the fatty membrane surrounding the cell. The message therefore has to be handed across rather than carried across. The receptor spans the membrane, so binding on the outside changes its shape on the inside, and that inner change is what recruits the first internal protein. Small molecules called second messengers then spread the signal through the cell interior. Steroid hormones are the exception: being fat-soluble, they pass straight through and bind receptors inside the cell.
Why does it matter in disease?
Termination is as important as activation. A pathway that cannot switch off tells the cell to keep dividing when nothing has asked it to. Many cancers carry exactly this fault, in the form of a receptor stuck in the active state or a relay protein that no longer resets. This is why understanding these pathways changed treatment: a drug that blocks the specific faulty step affects the cells depending on it far more than normal cells, and a signal transduction inhibitor works on that principle. It also explains why a tumor can become resistant, since a second change further along the relay restores the signal below the level the drug blocks and lets the cancer continue.
Also known as
Used in a sentence
The tumor carried a mutation causing constitutive signal transduction through the pathway.
Good to know
Faults that prevent a pathway from switching off are a common mechanism in cancer, and resistance to a targeted drug often arises from a further change downstream of the blocked step.
Word origin
Where “signal transduction” comes from
Transduction comes from the Latin transducere, to lead across, from trans, across, and ducere, to lead.