why are some cellular adhesion molecule inducible whilst others are constitutively expressed?
Let me start off with an explanation of the two phenomena you mentioned to make this more accessible to readers of all academic levels: a cellular mechanism that is inducible means that it can be turned on or off while something that is constitutively expressed is constantly on. If everything was constantly on (constitutively expressed), we would never be able to balance homeostasis. An iconic example of this is the glucagon/insulin feedback system. Non-diabetic pancreases only produce insulin when blood sugar is raised in order to facilitate glucose entry into cells. If insulin was constantly being produced and wasn’t able to be shut off, we’d all be in a constant state of hypoglycemia (low blood sugar). On the other hand, some things do constantly need to be expressed, such as GAPDH (which is why we often use this or Actb as a control when we do protein expression assays, e.g. western blotting).
Cellular adhesion molecules (CAMs) essentially glue cells together. An example of a inducible CAM would be the integrin responsible for coagulation. If this mechanism wasn’t inducible, we would all die of blood clots.
I’m having difficulty finding examples of constitutively expressed CAMs, which kind of makes sense. The most consistent thing I’m seeing is a protein called ICAM1, but it seems like its constitutive expression is related to cancer/chronic inflammation. CAMs really aren’t my area of expertise, so if anyone would like to add to this, please feel free.
