Got a burning science question? Send it to Ask@DiscoverMagazine.com and we’ll try to answer it here or in a future issue of the magazine.
If you haven’t noticed, us Discover Magazine bloggers have weaseled our way into the print version through a new monthly feature called Ask Discover. You ask, we answer. Last month Neuroskeptic took on dreaming, but this month, it’s all about intercellular chatter:
Damn, Paul! That’s a big question. Here is my magazine response:
Cells communicate through their own language of chemical signals. Different compounds, such as hormones and neurotransmitters, act like words and phrases, telling a cell about the environment around it or communicating messages. When the pancreas detects a person has just eaten, for example, it releases the hormone insulin to tell other cells in the body to remove glucose from the blood. Just as a person needs ears as much as a mouth to have a conversation, cells use receptor proteins either on the outer cell wall or inside the cell itself to “hear” different signals. Once the signal chemical binds to a receptor, that protein turns on a signaling cascade in the cell that ultimately leads to the cell’s response. Every cell has receptors that can detect a lot of different signals, so they are constantly bombarded with biological conversation. Imagine being in a room and having everyone talking at you at once! So how does a plant use cellular communication to grow toward sunlight? The growing tips of plants produce auxin — a hormone that tells cells to grow and divide — which is then sent to the rest of the plant. The shady parts of a plant receive more auxin, which causes those cells to elongate while the sunny-side cells don’t. When one side lengthens while the other side stays the same, the plant will bend.
I wanted to note, though, that this is the super-short, incredibly oversimplified response. Cellular communication is inexplicably complicated. For example, these are the pathways associated with a single receptor, the B cell antigen receptor:
The tangled web of B cell interactions, from Cell Signaling Technology
Not only do individual receptors do many things, different responses are linked to a wide diversity of receptors and messages. Take the protein Akt, a serine/threonine kinase (which means it adds phosphate groups to serine or threonine amino acids on other proteins). Akt is implicated in signaling cascades throughout the body, and is one of the most important players in cancer signaling:
Akt and its many signaling receptors and targets, from Cell Signaling Technology
Entire careers are dedicated to discovering how different signals or intercellular pathways work. By studying cellular communication, scientists hope to uncover key messages or receivers that can be used to alter how cells act. For example, a breakdown in communication is part of what allows cancer cells to grow unchecked. The belief is that if we can untangle the twisted web of chemical interactions within and between cells, we can find ways to steer living tissues to do what we want, whether it be growing organs in culture dishes, giving plants and animals resistance to pests, or fighting off incurable diseases.
When you think about it, basically all of our pharmaceuticals are chemical messages or designed to stop them. Some drugs either mimic or are identical to natural chemical messengers, so when we pop a pill, we’re influencing the conversation going on in our body. Others look enough like them to get stuck where the real ones would bind, blocking messages from being received.
Sometimes, we send signals to our cells when we don’t intend to. There are a number of chemicals we use industrially, for example, the mimic the hormone estrogen, and thus when they enter our bodies, they start telling cells to do things we don’t want them to do. These xenoestrogens have become a huge regulatory problem, and not only because of us, but also because of the effects they have on plants and animals that they come in contact with.
Whether we ever have a controlled conversation with our bodies or not, the more we understand the ways that cells communicate, the more we appreciate just how complex and intricate the mini-machines are. These tiny computers process millions of signals every day. They communicate across unfathomable distances to coordinate disparate body parts. And though we know a lot about how they work, the microscopic world is still a very foreign place to us metazoans, and we’re only just beginning to understand what goes on at a cellular level.
Here is a pretty fancy video looking at cell communcation from a big-picture perspective: