Hi. In this video, I'm going to be talking about tumor viruses. There are many types of tumor viruses, which we also call oncogenic viruses. These are viruses that can cause cancer. They don't always do this, but they have the potential. Somehow, these viruses can do this in a couple of different ways. One way is by actually having the genome integrate into the host cells. The viral genome comes in, infects, and integrates somewhere into the host cell genome, which can be harmful. For example, the virus might integrate its entire genome into something like RAS, which we've discussed, the GTPase. If it's in RAS, that's obviously going to disrupt function, and we know RAS is mutated in many different cancers. This could be extremely harmful and could easily lead to cancer. But other viruses don't necessarily have to integrate to cause or lead to cancer. They could just have proteins that interfere with normal cell functions, leading to cancer. For instance, if you have a protein that blocks a tumor suppressor's activity, you're going to lose the function of the tumor suppressor, resulting in the loss of activity, which can lead to cancer. You can have proteins that interfere with cell cycle control. For example, increased cell cycle control, beneficial for viral replication, or decreased apoptosis, beneficial for the virus. You can imagine how the virus has proteins that decrease apoptosis and increase the cell cycle, allowing the virus to replicate without dying. Other viruses have proteins that can take over the cell's replicative machinery, so cell replication or DNA replication, in order to replicate the genome. So, the virus infects the cell so that it can replicate itself. It has to take advantage of the cell's mechanisms to replicate, meaning these proteins are going to take over all of that machinery and say, "No, I'm going to use it for myself and I'm going to overuse it and overexpress it, so that I can generate a lot of myself," allowing the virus to produce a lot of itself. Here are some example viruses; this is not an exhaustive list, but these are some that you probably should be familiar with. Examples include hepatitis B and C, associated with liver cancer; papillomaviruses, with the most familiar being human papillomavirus, which there's a vaccine against. This can cause cervical cancer as well as head, neck, and throat cancer in both men and women, so it's not just a female cancer. You also have the herpesvirus, which can cause an interesting cancer called Kaposi sarcoma. This is most often associated with retroviruses, not because the retrovirus actually causes Kaposi sarcoma, but because the retrovirus leads to AIDS, a syndrome that significantly decreases your immune system's ability to fight off infections, and then you can get these herpesvirus infections that lead to this cancer. We often say HIV is associated with Kaposi sarcoma, but it's because it lowers your immune system, causing these other viral infections. I mentioned there were some proteins that could interfere with cell functions. I want to introduce a couple. In human papillomavirus, you have a protein called E6 and a protein called E7. When human papillomavirus infects a cell, these proteins are expressed and then interfere with the cell's functions. For instance, the E6 protein can bind the transcription factor P53, a tumor suppressor, leading to its destruction. Destroying a tumor suppressor obviously can promote cancer. Then you have the E7 protein, which can bind to the Retinoblastoma Tumor Suppressor. When it binds to it, it does not destroy it, but it does inhibit its function. Again, inhibiting this tumor suppressor, losing that activity, results in a high probability that a cancer cell or tumor cell will form. So that's an overview of tumor viruses or oncogenic viruses. With that, let's now move on.
20. Cancer
Tumor Viruses
20. Cancer
Tumor Viruses - Online Tutor, Practice Problems & Exam Prep
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concept
Tumor Viruses
Video duration:
4mPlay a video:
Video transcript
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Problem
ProblemMany viruses can cause cancer.
A
True
B
False
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Problem
ProblemWhich of the following viruses can cause head, neck, and throat cancer?
A
Hepatitis B
B
Human Papillomavirus
C
Herpesvirus
D
Retroviruses