VIROLOGY - CHAPTER SIX

ONCOGENIC VIRUSES
There are two classes of tumor viruses:

DNA tumor viruses
RNA tumor viruses, the latter also being referred to as RETROVIRUSES.
We shall see that these two classes have very different ways of reproducing themselves but they often have one aspect of their life cycle in common: the ability to integrate their own genome into that of the host cell. Such integration is not, however, a pre-requisite for tumor formation.

If a virus takes up residence in a cell and alters the properties of that cell, the cell is said to be transformed.

TRANSFORMATION BY A VIRUS MAY BE DEFINED AS: CHANGES IN THE BIOLOGIC FUNCTIONS OF A CELL THAT RESULT FROM REGULATION OF THE CELL BY VIRAL GENES AND THAT CONFER ON THE INFECTED CELL CERTAIN PROPERTIES CHARACTERISTIC OF NEOPLASIA. THESE CHANGES OFTEN (BUT NOT ALWAYS) RESULT FROM INTEGRATION OF THE VIRAL GENOME INTO THE HOST CELL GENOME

Transformation often includes loss of growth control, ability to invade extracellular matrix and dedifferentiation. In carcinomas, many epithelial cells undergo an epithelial-mesenchymal transformation. Transformed cells often exhibit chromosomal aberrations.

The region of the viral genome (DNA in DNA tumor-viruses or RNA in RNA-tumor viruses) that can cause a tumor is called an oncogene. This foreign gene can be carried into a cell and cause it to take on new properties such as immortalization and anchorage-independent growth.



http://pathmicro.med.sc.edu/lecture/RETRO.HTM
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