Regulation of chemotactic networks by 'atypical' receptors

Directed cell migration is a fundamental component of numerous biological systems and is critical to the pathology of many diseases. Although the importance of secreted chemoattractant factors in providing navigational cues to migrating cells bearing specific chemoattractant receptors is now well-established, how the function of these factors is regulated is not so well understood and may be of key importance to the design of new therapeutics for numerous human diseases. While regulation of migration clearly takes place on a number of different levels, it is becoming clear that so-called 'atypical' receptors play a role in scavenging, or altering the localisation of, chemoattractant molecules such as chemokines and complement components. These receptors do this through binding and/or internalising their chemoattractant ligands without activating signal transduction cascades leading to cell migration. The atypical chemokine receptor family currently comprises the receptors D6, DARC and CCX-CKR. In this review, we discuss the evidence from in vitro and in vivo studies that these receptors play a role in regulating cell migration, and speculate that other orphan receptors may also belong to this family. Furthermore, with the advent of gene therapy on the horizon, the therapeutic potential of these receptors in human disease is also considered.