Making Mutants, the Safe Way
Posted by Jenna Capyk on November 28, 2011
The practice of medicine has come a long way from the days of the four humours. Instead of being filled with a delicate balance blood, snot, and various forms of “bile,” we now understand that our bodies are made of millions of cells, each with a specific job to do. We are now able to pinpoint the exact type of cell not doing its job in many diseases, and to figure out just what job it’s not doing. This knowledge can help us change or replace parts in our cells in order to treat some diseases. In the future, making our own engineered human mutants may help us accomplish medical feats not possible with traditional drugs.
Each cell in our body is specialized to perform a specific function. Our nerve cells conduct electricity to pass messages around the body, our red blood cells carry oxygen, and cells on the inside of our stomachs secrete acids to help with digestion. In order to carry out these jobs, our different types of cells produce specific enzymes and other proteins. Without these specialized components, the cells don’t function like they should. For some diseases there may be only a single protein that is not being produced, and this deficiency results in a whole host of symptoms. For example, type I diabetes is an entire disease caused by the body being unable to make a single protein: insulin. All proteins are made by decoding DNA sequences, and researchers are looking at treating diseases like diabetes by adding back the specific DNA needed to make the proteins that are missing or damaged. By inserting these specific DNA sequences into the genetic material already in our cells, we hope to engineer helpful cellular mutants that can produce missing proteins and reverse disease.
Sticking helpful genes into human cells can be a great way to fill the gap of a missing protein, but there are many dangers inherent in introducing new DNA. If a new piece of DNA is inserted into one of your chromosomes, it can land in any number of places, including in the middle of another gene. This can potentially result in mutation of a different protein, in which case you might cure the first disease but could actually cause another. A more common and potentially more dangerous scenario is if the new piece of DNA disrupts an oncogene (see DNA Repair just doesn’t give me the same Buzz). In this case adding the extra DNA can cause cancer, and this only needs to happen in a single cell to result in life-threatening disease.
While humans have only been sticking extra bits of DNA into cells for a few years, viruses have been accomplishing this task for millennia. For many viruses, part of their life cycle involves taking part of their DNA and inserting it into a chromosome of the cell they’re invading. In order to do this efficiently, viruses use a specific DNA-insertion tool: an enzyme called an integrase. This enzyme recognizes specific sequences on the DNA to be inserted and on the host cell DNA and stitches in the inserted piece at specific sites on the host chromosome.
Nature doesn’t always do what we want it to (sometimes disease happens), but it also produces some pretty useful tools that we can borrow. In the case of gene-based therapies, the danger is not knowing where an introduced piece of DNA will insert into our own DNA, and whether or not that might cause even more problems. By borrowing the ability of viral integrases to insert DNA pieces into specific places in the genome, we drastically cut down this risk. Scientists are now working on giving patients the specific DNA segments needed to replace proteins missing in certain diseases and including viral integrase enzymes to make sure that DNA is inserted in safe spots in our genome.
To most people messing with their DNA, the prospect of cancer, and viral enzymes are all pretty scary concepts. By understanding how each component works, however, we are able to use these concepts to treat diseases in innovative ways. Knowing more about almost anything can help it to be less worrisome and more useful.