THE PEXICRINE PATHWAY - A MODEL FOR THE REGULATION OF GROWTH-FACTOR BIOAVAILABILITY

Many growth factors are localized outside their target cells in what is presumed to be a biologically inactive form. Because they adhere (pexi-) to specific structures in the local environment (matrix, cell surface, proteoglycans ... ), after they arc secreted (crine) by cells and appear to be biologically inert, we describe this phenomenon as crinopexy. This << pexicrine >> pathway has led to the development of a model to describe the regulation of numerous autocrine and paracrine factors and predicts the existence of specific signals responsible for their activation. These include an enzymatic release from the matrix stores, post-translational modification and changes in high and low affinity receptor expression. In this review, we fully describe this pexicrine pathway, define the criteria a molecule must meet to be considered a << crinopexin >>, present how these molecules might be regulated and discuss the physiological significance of the model,