ABSTRACT

Growth signals Growth signals are of different kinds, and include extracellular matrix (ECM) components, cell-cell adhesion/interaction molecules, and mostly, diffusible growth factors. There are dozens of growth factor families, such as the epidermal growth factor (EGF), transforming growth factor (TGF)-β, and vascular endothelial growth factor (VEGF). Many growth factors are versatile, stimulating cellular division in numerous different cell types, while others are specific to a particular cell-type. Growth signals are produced, when needed, by one cell type to stimulate the proliferation of another cell type. This process is known as heterotypic signaling. The signal from the producing cell to the receiving cell can be conveyed either systemically (endocrine modulation) or by paracrine signaling, a

form of signaling in which the target cell is close to the signal-releasing cell and the signal is broken down chemically too quickly to be carried to other parts of the body.