National Cancer Institute
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Sara Walker

Sara Walker


Arizona State University

Sara Walker works in the School of Life Science and the Beyond Center at Arizona State University. She is also a NASA Astrobiology fellow. She spoke about the deep evolutionary history of life on earth and it’s routes to cancer.


Sara Walker: I was talking about the connection between cancer and astrobiology and how understanding the history of the evolution of life on earth might inform our understanding of cancer. What I’m particularly interested in is the history of oxygen on earth and how that plays a role in some of the major evolutionary transitions. Like the origin of the eukaryotic cell and the origin of multicellularity and what the connections are to cancer; which has some very interesting attributes that are related to oxygen deprivation and things like that, that can potentially map it to states of ancient life.

Pauline Davies: In fact, you were talking about archaea weren’t you? That’s one of the three main forms of life going back billions of years.

Sara Walker: Yes, that’s correct. So Archaea is one of the main domains of life. They are extremely interesting because they are very ancient and they also happen to be closely related to eukaryotes; which are organisms like us basically. They have really interesting features in that they share a lot of the information processing, like transcription and translation, with eukaryotes, but they differ in a lot of ways also.

Pauline Davies: I think you mentioned that they live in low oxygen conditions, and they somehow got together with prokaryotes that were used to oxygen and the two of them combined to do great things for life on earth.

Sara Walker: Yes. That is correct. So archaea live in low oxygen conditions and a eukaryotic cell arose with a merger of an archaea with a bacterium, so people are more used to bacteria. This particular bacteria was the ancestor of modern mitochondria. When the merger happened, it probably was in low oxygen conditions. But this particular bacterium could metabolize in the presence of oxygen or not. So it led to the evolution of mitochondria and modern eukaryotes, which are very dependent on oxygen, even though our ancestor did not like oxygen so much.

Pauline Davies: How would you tie that closely to cancer and possible treatments for cancer? That’s what people always want to know about.

Sara Walker: I think one of the most interesting things to think about is, “What the environment for these early organisms were and how we might use those for targets of therapy”. So a lot of people talk about hypoxic conditions with cancer and that being sort of indicative of cancer, and maybe you might be able to use oxygen as a treatment for cancer because it does not like it as much as do normal healthy human cells. But I think if we can actually start to map cancer in an evolutionary context we can also look at other environmental conditions that were present on early earth and try to understand how they influence what cells in our bodies are doing. And look at analogs in these environments and try to understand them a little bit better. There could be potentially a lot of insights for therapy that way.

Pauline Davies: I noticed at your talk that people were very interested. What you said was mostly new to them wasn’t it? Because most of them are not Astrobiologists, they’re engineers, or physicists, or cancer biologists; so this is all very new. How did you think it would go down?

Sara Walker: (Laugh) I honestly wasn’t very sure. I always like thinking outside of the normal community box, but this was stepping into a community that I am not used to talking to so I wasn’t really sure. But it has been kind of interesting because I think a lot of people saw some connections and that’s what I was hoping for. Just to present something really different and see where people pick up things that sound like something they are interested in and might foster some new questions. There has been some positive response in that which has been really exciting.

Pauline Davies: And you got some money from the PS-OC to conduct a pilot project. Tell me what you’re doing.

Sara Walker: The pilot project is about the connection between cancer and the origin of multicellularity. There is this idea that some of the traits of cancer are actually attributable to the early multi-cellular life forms. What we’re trying to do, is actually couple that with the story of oxygen and the story of metabolism and cancer and try and understand how that might have driven the dynamics and origin of multicellularity. How did single cells that act selfishly, become cooperative aggregates? Cancer falls into that because cancer cells are a version to the selfish unicellular state in some sense. So if we can understand the transition in the forward direction, potentially we can understand why it reverts back in the opposite direction.

Pauline Davies: I think you’re calling them cheater cells?

Sara Walker: Yes, cheater cells. Cancer’s cheats. The cheat’s aspect is really that they are selfish. So they are taking advantage of the cooperative aspects of the quality as a whole by following their own agenda. Which is something that cancer seems to do very well.

Pauline Davies: Interesting research. Good luck with it.

Sara Walker: Thank You very much!