Growth factor regulation

As the various features of growth factor action in the GI tract noted above indicate, collectively these peptides form a network which helps to preserve mucosal integrity. An important characteristic of that network, which has already emerged from this still fragmentary definition of its dimensions, is the redundancy present on several planes. Multiple factors appear to have overlapping functional properties. Conversely, each peptide appears to have multiple biological activities. Though not considered in this section, in several instances a peptide growth factor may have more than one specific cell receptor, and, conversely, there appears to be at least some promiscuity in receptor specificity, as exemplified by the overlapping receptors for the peptides of the insulin family and the common recognition of EGF and TGFα by a single receptor. At the cellular level, each factor may be expressed by several distinct cell types and, conversely, may have multiple cellular targets. Much future work will be needed to determine fully the functional features of this redundant network. It will first depend upon continued intensive characterization of the full spectrum of individual growth modulatory peptides and their mechanisms of action.