SV40, tumor virus

DNA viruses. Some DNA viruses also cause human cancer, but by different mechanisms. Three DNA tumor virus families, SV40, papillomavirus, and adenovirus, encode proteins that inactivate pRb and p53. By interfering with the Gl/S checkpoint, these oncoproteins increase the probability that mutations in oncogenes and tumor suppressor genes will be incorporated into the genome of infected cells, thereby increasing the probability of transformation. The Epstein-Barr virus encodes a Bcl-2 protein that restricts apoptosis of the infected cell. 

Immortal or Extended Life Span of Human Cells. More than 30 years ago, it was demonstrated for the hrst time that SV40 [17], a DNA tumor virus of the papova... 

The block in ganglioside biosynthesis observed in a variety of SV40- and Py-transformed mouse cells suggests that the alteration is related to some function common to both of these DNA tumor viruses (Mora et al., 1971). Several considerations have to be explored. 

Viral Action at the Level of Translation. It is known that in eukaryotic cells induction and repression of enzyme synthesis can occur at the level of messenger RNA (Tomkins and Martin, 1970). Thus, the SV40, polyoma, and Moloney sarcoma viruses could contain the genetic information for a common repressor molecule which could interfere with the synthesis of aminosugar transferase. Both DNA viruses can code for 5-10 polypeptides (Eckhart, 1969), and the potential coding capacity of the large RNA tumor viruses is extensive. 

DNA viruses that can trigger tumors are found in the classes of the polyomaviruses, the adenoviruses and the papUloma viruses. The polyoma viruses with the SV40 virus as a well studied representative, adenoma virus and human papUloma virus (HPV) are associated with formation of tumors in humans and have genes coding for proteins with the properties of oncoproteins. The oncoproteins of aU three viruses interfere with the pRb function by Ufting its inhibition of transcription factor E2F. It is assumed that the tumor-promoting activity of the proteins is due, in particular, to this property. 

The family Polyomaviridae includes both polyomavirus and simian virus 40 (SV40), whose structures are both known at atomic resolution (Liddington et at, 1991 Stehle et al., 1994, 1996). These viruses had been grouped within the Papovavirus family with other tumor-inducing papillomaviruses that have been studied by electron microscopy, but not at atomic resolution (Baker et al., 1991 Trus et al, 1997). The families have now been recategorized separately (van Regenmortel et al, 2000). They share similar genetic structure, but little sequence similarity between capsid proteins, and show some differences in overall dimensions (Baker et al, 1991). 

The pattern in certain mammalian tumor cells varies from that discussed above. Thus, Tyr-tRNA from HeLa cells, Ehrlich ascites tumor cells, and adenovirus-7 transformed cells was resolved into two peaks corresponding to both epithelial and fibroblast types. This, however, is not an invariant pattern Tyr-tRNA from SV40 virus transformed cells is predominatly of the fibroblastic type, whereas that from human lymphatic leukemia cells is largely of the epithelial type. 

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