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The proto-oncogene encode proteins required for a variety of cellular functions, but especially important role belongs to them in regulation of cell growth. OK this process is controlled by extracellular by growth factors and their inhibitors, circulating in the blood. Better than others studied the growth factors of the epidermis (FGA) and platelet growth (TRF). The latter is produced only blood platelet and enters the blood serum. It binds with the receptor cells of the connective tissue (for example, bone cells and stimulates them in the processes of the creation of the cytoskeleton and membranes. Without TRF no growth of cells outside the body, so the serum is added to cultured cells. Synthesis TRF encodes protooncogen sis, functioning only in platelets. Under the influence of oncogene synthesis TRF begins in skin, muscle, bone and other tissues; they begin to multiply rapidly. TRF often found in sarcoma of the bone, cartilage, muscles. FRE inherent in the cells of malignant epithelial tumors.
A variety of growth factors selectively act on sensitive to them cells. Stem cells-predecessor have increased potency of growth, they share quickly. Their descendants after maturation and differentiation share slowing to a complete stop growth. In adult organism the processes of growth and differentiation are in harmonious balance: the proliferation of stem cells provides tissue by new cells to replace dead, and the growth of cells more differentiated restrained. For this there are the cells of a variety of receptors to stimulating and brake signals. In cancer of the equilibrium in the body is too many immature propagation of cells.
Essentially important is the question about the reverse development of tumor cells in normal. Can a cell which has already acquired under the influence of oncogenes malignant properties, becoming a normal and produce healthy offspring? Numerous observations indicate the possibility of such a process.
The phenomenon of return of tumor cells to normal condition called RIVERIA. It is associated with the loss of cell tumors some support malignancy genes. It is believed that reverse the spontaneous development of tumors - fact rare, but we don't know what exactly the number of tumors is exposed rivers, when conditions for tumor growth missing. It is not only in immunological extermination of the parental cancer cells. The tumor may be lacking angiogenic or other factors, ensuring its functioning in multi-cellular level. G. I. deichman rightly points out that the history of individual tumors and metastases is represented by the story of the arising and falling separate cell clones, first transformed, and then tumor. Even accounting for the tumor site, they may die original or separation from a parent basis.
As mentioned, during maturation of normal stem cells are descendants of various degrees of maturity, at the same time receiving from its predecessors two different signals: one stimulates cell turnover (growth factor), the other - its maturation (factor of differentiation). As it turned out recently, each of these factors is presented with several proteins encoded by specific genes. Factors of differentiation link the DNA of cells and growth - with cytoplasmic structures. Of hematopoietic stem cells can form the erythrocyte, platelet, eosinophil, neutrophil, monocyte. For each of these ways of cell development requires a well-defined growth factor. Further, the cells are descendants of demand for its specialization in the course of development (for example, prommonolit-monocyte-macrophage) relevant factors of differentiation.