Ectopic Auto-Stimulation of Growth

Abstract

According to dogma nearly every cell in a mammal has the same genes encoded in its DNA and differentiation involves the selective derepression of a different and small proportion of these genes in the cells of different tissues. The gene for a hormone-like growth factor will be present in all cells but only expressed in a source cell from which the factor will be transported in the circulation to a target cell whose growth it regulates. If, by mutation, translocation, or teratogeny (mis-differentiation) the gene becomes expressed in the target cell, then the target cell will stimulate its own proliferation (auto-stimulation) and escape the normal growth regulation controls. Although the normal factor will be acting on the normal receptor to produce a normal response the cell will behave like a tumour cell. An auto-stimulating cell will also grow in culture independently of added growth factor. It has been possible to demonstrate the production of growth factors by tumour cells in tissue culture and that these factors partially explain the reduced requirement of transformed cells for serum in tissue culture.