Malignant transformation
Under a malignant transformation is defined as the transition from normal, controlled in their growth cells to uncontrolled growing tumor cells. This transformation can be initiated, for example, under the influence of chemical substances, or by so-called transforming ( oncogenic ) viruses such as Rous sarcoma virus, or the SV40. The process of malignant transformation is of great importance for the understanding of carcinogenesis.
Transformation in the cell culture
The concept of malignant transformation is now being used for the conversion of normal cells to cancerous cells in an organism, even though it was originally used for the change of cells in a cell culture in vitro. Transformed cells in a cell culture show all the characteristics of tumor cells, such as uncontrolled growth, changes in cell contacts, growth in so-called soft agar ( cell culture medium with a share of 0.5-1% agar) and tumor formation after injection of the cells into animals.
In a culture of adherent, that is, on the surface of normal cells adhering the further growth of the cells is inhibited by contact with neighboring cells, so that it mostly occurs only to form a single layer ( monolayer ) of cells. A transformation this inhibition and derived from a transformed cell clones continue to divide and stratify in several layers does not occur. This is even with the naked eye to detect the formation of cell condensations, called foci (plural of focus). The malignantly transformed cells change their morphology and lose typical features of the original cell types ( dedifferentiation ).
In the same cell culture after expression of the ras proto-oncogene: Malignant transformation, beginning the formation of a focus
In the same cell culture by expression of the large T-antigen of SV40: Malignant transformation concerning
Transforming factors
The malignant transformation was first described as an effect in cell cultures infected with certain virus species. Since individual proteins of these viruses could also cause a transformation at introduction into cells alone, these proteins have been called a transformation proteins. The genes for these proteins are the viral transformation oncogenes. The best-known transformation protein is the " large T antigen " (T for Transformation ), the SV40 virus, in which the transformation was first discovered. Other proteins are the E1A protein of human adenovirus (type 12, 18) and the E7 protein of the Papillomaviridae.
Swell
- Rolf Knippers: Molecular Genetics, 7th edition 1997
- Alfred Pühler et al. (Ed.): Encyclopedia of Biochemistry and Molecular Biology, Stuttgart 2000