Viruses cancer-causing

Although the ability of viruses to cause tumors in animals has been proved for many years, the relationship of viruses to cancer in... 

It is important to highlight that c-Src or cellular Src behaves as described above however there is a second form of Src termed v-Src or viral Src. v-Src was originally discovered as a component of the Rous Sarcoma virus, which causes cancer in chickens. The sequences of c-Src and v-Src are nearly identical. The major difference in the two proteins occurs in the C-terminal tail. While c-Src is regulated through phosphorylation of the C-terminus, v-Src has no C-terminal phosphorylation site and therefore is constitutively active and unregulated. 

Infection with a retroviras is the most common way in which viruses cause cancer (see above). The first work that led to the discovery that a virus could cause cancer was that of Dennis Burkitt which was published in 1958 (Box 21.1). As... 

Certain RNA viruses, particularly retroviruses, have also proven capable of inducing cancer. Retroviruses known to induce cancer in animals include Rous sarcoma virus, Kirsten murine sarcoma virus, avian myelocytomatosis virus, as well as various murine leukaemia viruses. Thus far, the only well-characterized human RNA transforming virus is that of human T cell lymphocytotropic virus-1 (HTLV-1), which can induce adult T cell leukaemia/lymphoma (ATL). Identification of antigens uniquely associated with various tumour types, and identification of additional cancer-causing viruses, remain areas of very active research. 

Du Pont s medical diagnostics and pharmaceutical businesses are underpinned by substantial basic research in molecular biology and biochemistry. For example, Du Pont recently announced an improved, more reliable test for detection of antibodies to the virus that causes acquired immunodeficiency syndrome. In another program the protein interleukin-2 produced in Du Pont s laboratories by recombinant DNA methods is being used in some very promising cancer research. 

One further comment on the multistep nature of carcinogenesis In our discussion here, we focused on some of the early steps in the process that lead to uncontrolled growth but said nothing about those transitions that convert transformed cells into invasive cells. We also concentrated on oncogenes related to cancer-causing viruses because these are most likely to be the first understood in terms of their biochemical function. 

Dulbecco proposed that cancer-causing viruses insert their oncogenes into the host genome. It appears that... 

Figure 24.16. Genome of a normal retrovirus and the Rous sarcoma retrovirus. Rous sarcoma virus (RSV) is an acute transforming retrovirus that contains an assimilated cellular gene called Src, which is responsible for the cancer-causing properties of the virus.

About 20% of all cancers have been traced to tumour viruses, although the number of people infected is probably much larger than the number of people who actually develop cancer. Moreover, cancer-causing viruses may only be one of many contributing factors. DNA tumour viruses are probably more important as cancer-causing agents than RNA retroviruses (Table 17.1). 

A specific mutation in the genetic material has been detected in people exposed to aflatoxin. An important factor in determining susceptibility may be individual variation in the metabolism of aflatoxin. A significant risk factor in liver cancer is infection by the virus that causes hepatitis B, and it appears that a combination of aflatoxin exposure and the viral infection makes individuals especially susceptible. 

---