New Insights into Tumor Promotion from Molecular Studies of Protein Kinase C
Research on growth factors, growth factor receptors and signal transduction pathways have provided an exciting conceptual framework for understanding multistage carcinogenesis1. Fig. 1 displays in schematic form how certain extracellular growth factors are perceived by cellular receptors, which are often located at the cell surface, and how the occupancy of these receptors leads to a cascade of signal transduction, through the cytoplasm and eventually into the nucleus, thus altering patterns of gene expression. This figure also emphasizes the central role that a series of protein kinase enzymes plays in several pathways of signal transduction. A general theme that has emerged is that the proto-oncogenes represent a subset of genes that normally code for components in these pathways of signal transduction. Alterations in the structure and function of these proto-oncogenes can convert them to “activated” oncogenes, which cause aberrations in signal transduction and thus disrupt normal growth, differentiation and inter-cellular coordination.
KeywordsPhorbol Ester Tumor Promoter Phorbol Ester Tumor Promoter Phorbol Ester Tumor Exponential Doubling Time
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