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The following points highlight the five main changes of cell surface property of transformed cells.
1. The glycolipids and glycoproteins present on the surface of the normal cells are altered in transformed cells. The general structure of the plasma membrane is not modified. But the cell surface proteins are much more mobile in transformed cells than in normal cells.
As a result, the cytoskeletal elements linking with surface protein are modified by transformation. Such a modified linkage may also be the basis for the altered morphology of transformed cells.
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2. Normal non-dividing cells in monolayer culture become covered with a dense fibrillar network containing fibronectin. Even dividing cells have a diffuse covering of fibronectin. But transformed cells either totally lack fibronectin or have greatly reduced amounts.
3. When a retrovirus transforms a normal cell into a tumour cell, the misbehavior is often brought about by a gene that is carried by the virus. The transforming gene of the Rous sarcoma virus, a retrovirus, is called the v-src gene. It is classified as a oncogene, because, when it is introduced into a normal cell, it can transform it into a tumour cell.
It encodes the src-protein, a tyrosine-specific protein kinase. The hyperactive v-src tyrosine-kinase activity appears to loosen cell adhesions—either by phosphorylating the fibronectin receptor or by causing a protease to be secreted that destroys fibronectin and other matrix molecules.
4. During malignant transformation, due to change of cell surface property followed. by loss of cell adhesions, the loose mass of cells invade blood vessels allowing metastasis to occur.
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5. In culture, normal fibroblastic cells axe motile. When two normal cells moving around in a culture dish come into contact one or both of them will stop and form a gap junction between other. This phenomenon is known as contact inhibition of movement. So they grow as a monolayer on glass surface.
Transformed cells lack contact inhibition of movement due to change of cell surface property and loss of many receptors. So, unlike normal cells, they continue to grow and pile up on top of one another as they proliferate.
