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cells are coated with sugar!

Let’s think back to biochemistry for a second, what happens when a protein links to a carbohydrate? Well, we get something called a glycoprotein, a transmembrane protein, or in other words, a sugar.

• These glycoproteins are attached to the integral membrane proteins in our cells, and they sort of stick out of the cell to form a coating
  • So in other words, if are cells are peanuts, and the glycoproteins are chocolate, then we can think of them as peanut covered M&Ms
• Except, it’s not as simple as that— these sugars are pretty complex, and we know that they actually play a huge role in cell to cell signaling, attachment and recognition, and triggering an immune response, which I will get into
• Recently, we’ve learned that these sugars might be trying to communicate with us (well not to us, rather to our bodies) in two different ways
  1. Determining our blood type
  2. Possibility for cancer

our blood type

Based on your blood type, the glycoproteins that make up the outside of your cell, will have different arrangements and combinations of polysaccharides and enzymes

• As you can see here [reference image] these sugars are called antigens— so the type of sugar on the cell surface is going to determine our blood type
  • And this is determined by genes that code for certain enzymes that allow for the addition of these specific sugars, such as galactose, or N-acetylgalactosamine
• Blood transfusions, one of the most well known and life saving medical procedures in the world, so if your body doesn’t like the sugars on the new red blood cells, you’re at high risk for rejection of the blood

potential for cancer

Something as simple as the amount and density of these sugars you have on your cell membrane can tell us if we have cancer

• In particular, some cancer cells tend to have an increased amount of a sugar called sialic acid, which as we’ve heard before, an alpha keto acid
• [insert diagram of normal cell vs cancer cell on this slide]
  • In a normal cell, there is a close gap between the membrane and the ECM, or the extracellular matrix, and the glycoproteins are relatively spaced out
  • Now if we take a look at a cancer cell, this excess in long glycoproteins causes a bigger gap between the membrane and the ECM
    • This physical gap alters the cell’s signaling functionality, as it is physically changing how the surface receptors are arranged, resulting in rampant cell growth and survival which is what we tend to see with cancer cells

Now, why do we care that cancer cells have this extra layer of sugar on their cell membranes? Well, let’s think of how our immune system actually fights cancer.

• Our immune cells, or white blood cells, go around the body and are able to recognize and differentiate among different cells
  • Our immune cells don’t touch our regular cells, or else we’d all have autoimmune diseases
• In particular, when an immune cell finds a cancer cell, it releases antibodies that can bind to antigens and destroy the cancerous cell
  • When we realized this, we thought, why not treat cancer by enhancing or stimulating our immune system
  • And thats exactly what we did, which allowed for very aggressive cancers such as melanoma to be in remission
• So back to sugar, if we have a cancer cell that has this dense layer (or M&M chocolate coating) of sialic acid on it, when those immune cells go and try to recognize if the cell is healthy or not, the sialic acid is essentially going to act as a disguise, or its going to trick/manipulate the immune cell into thinking that the cell in question is okay.
  • There’s a particular protein on the immune cell that “grabs” these glycoproteins, these sialic acid molecules, and if it gets “stuck” in the synapse between immune cell and the cancer cell, then the cancer cell has manipulated the immune cell into thinking everything is fine
  • Because the immune cell is not able to see the cancer cell as something that needs to be destroyed, its able to go on and do its business, trying to destroy other cells that might be harmful

why should we care?