Is the Cytoskeleton an Intracellular Receptor for Adrenomedullin and PAMP?

Classical transmembrane receptors have been described for both adrenomedullin (AM) and proadrenomedullin N-terminal 20 peptide (PAMP). Through interactions with these membrane receptors, AM and PAMP exert a variety of endocrine, paracrine, and autocrine functions. In addition to these better known activities, recent publications have shown that both peptides can bind directly to the cytoskeleton resulting in important cellular physiological responses. In vitro and in vivo experiments show that the peptides bind to major components of the cytoskeleton: tubulin and kinesin for PAMP and a number of microtubule-associated proteins (MAPs) in the case of AM. Physiological experiments show that PAMP contributes to microtubule fluidity and increases kinesin speed. Lack of AM and PAMP results in hyperpolymerization of the cytoskeleton and a reduced motility of intracellular organelles. These data suggest that the cytoskeleton may have a novel function as an intracellular receptor, acting as the binding site and the signal transducer for specific peptide hormones such as PAMP.