EGFR – one protein’s story  pg. 3

The courier proteins know that a pair of us has received a message because we perform a chemical reaction, called phosphorylation, on ourselves. We take a kind of sticker—a phosphate group—from a molecule called ATP and stick it onto some of our amino acid beads. These phosphate stickers are signals for the courier proteins to interact with us so we can tell them the  message. They then share the information with still other proteins, and eventually the message can make it all the way to the central office, the nucleus, where the DNA is stored.

The messages that make their way to the nucleus affect which plans are copied for the  assembly of new proteins. This is how messages from outside the cell alter the types of proteins being manufactured inside the cell.

Signals from my receptor family will send the cell into a growth mode; the cell will duplicate its DNA and split itself into two cells. With continued growth signals, these two cells can split again, making four, and so on. It doesn’t take long to have a bunch of new cells. This
is good if you’re trying to make a new organ, or replace damaged tissue. It’s bad if the cells are dividing for no healthy reason, like tumor cells do.

I’m sorry to say that my family members and I participate in processes that can turn normal cells into tumor cells. It happens when things go awry—the plans get changed—and the assembly lines churn out way too many of us. Or we’re made a little differently so that we’re
able to send signals all the time, not just in response to EGF.

In situations like these, there are new drugs that aim to keep us in check. Some of these medicines work by jamming up the place where EGF sticks to us. Some, like a new one called Iressa, bind our hands, in a sense, making us unable to put the phosphate “stickers” on ourselves or on other proteins. These drugs may help, but tumor cells are a tricky lot; they’re good at figuring out ways to get around such roadblocks.

As for me, I’m nearing the end of my shift. I’ve put in a good day’s work here at the factory wall, and I’m spent. The cell will replace me with a brand new EGF receptor. And I will board a shuttle bound for the lysosome—our cellular recycling center. There, I will be dismantled so that my amino acid beads can be reused to manufacture some other protein. I’m hoping they don’t end up being used to make one of those central office types!

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