3 Growth Factors and Their Receptors

Abstract

I. INTRODUCTION
During development, in regenerative and in reparative processes, growth is highly regulated to coincide with the overall needs of the organism for survival and reproduction. As with homeostatic metabolic adaptations to the environment, complex communication systems must function to integrate organ and cellular responses to the overall needs of the organism. In higher organisms, the nervous and endocrine systems serve this communicator function. Cells receive information via hormones and neurotransmitters that bind to allosteric proteins. These proteins (receptors) have both specific recognition and specialized activity functions. Interaction with these receptor molecules initiates biochemical processes that result in altered biological responses of the cell. The initial interaction of the signaling molecule with its receptor is a bimolecular reaction dependent on the concentration of each reactant as well as on intrinsic affinities dictated by their structures.

[Ligand]+[Receptorinactive]⇌k-1k1[Ligand·Receptoractive]

Extensive control systems determine the concentration of each of the reactants so that appropriate adaptive responses are initiated, modulated, and terminated.

Growth factors and their receptors were recognized initially by their effects on cell proliferation. Like other hormones, they regulate diverse cellular processes in addition to growth and, although the emphasis here is on cell proliferation, signaling information for specialized cell functions may prove equally important. During both development and regeneration, growth must be appropriately initiated and appropriately terminated. Regulation of the synthesis and metabolism of both growth factors and their cognate receptors provides one central mechanism for accomplishing this balance. Failure to do so would result in unrestrained proliferative responses inappropriate to...