Molecular biology and respiratory disease. 5. Molecular biology of receptors: implications for lung disease.

Abstract

Receptors have a critical role in regulating lung function in health and disease.' Several such receptors have recently been sequenced, cloned, and genetically expressed. This opens up new vistas for investigating receptor regulation in pulmonary cells, for identifying receptor subtypes, and for understanding how disease may affect these regulatory processes. In the future it may also lead to new and more specific therapeutic approaches.This article attempts to discuss some of the areas in which molecular approaches have been used to study receptor structure and regulation. At present, these novel techniques have hardly been applied to pulmonary tissues and lung disease, but it is clear that these are extraordinarily powerful tools that may now address previously unanswerable questions. difficult to obtain a sufficient quantity of the receptor for the initial sequencing necessary to prepare a probe. More recently, the polymerase chain reaction has been used to amplify the number of mRNA copies in a cell in order to make a series of probes that can then be used to screen a DNA library.3The receptor DNA can also be inserted into an immortal cell line, resulting in its expression and thus providing a source of the receptor, so that the gene product can be characterised pharmacologically. The DNA may be microinjected directly into the large Xenopus (toad) oocyte, or transfected into a cultured mammalian cell that does not normally express the receptor by using a plasmid expression vector (ring of self replicating DNA into which the receptor DNA sequence of interest has been inserted), which after suitable manipulation inserts the DNA into the cultured cell genome. Cultured Chinese hamster ovary (CHO) and B-82 (a mouse L cell line) cells have been found to be very useful for studying neurotransmitter receptors because they lack these receptors but possess other elements such as G proteins and adenylyl cyclase, so that aspects of receptor coupling can be investigated. The cultured cells express the single receptor coded by the inserted DNA and this can be studied directly by radioligand binding and by measuring cellular responses, such as cyclic AMP concentrations or phosphoinositide hydrolysis. With the aid of a series of suitable agonists and antagonists the pure cloned receptor can then be characterised pharmacologically. Factors that influence the pure receptor can then be studied in detail without variations in metabolism and the interfering effects of related receptors.

Lack of Coupling of Muscarinic Receptors to Phosphoinositide Metabolism and Adenylyl Cyclase in Human Lymphocytes and Polymorphonuclear Leukocytes: Studies in Healthy Subjects and Allergic Asthmatic Patients

“…This approach has also been successfully applied to the investi gation of |)-adrcnoccptor changes in relation to allergic asthma [42]. Nevertheless, it should be noted that both the transcriptional and post-transcriptional regulation of re ceptor expression and function may vary between differ ent tissues [43][44][45].…”