THE CLONING AND EXPRESSION OF A NEW GUANYLYL CYCLASE ORPHAN RECEPTOR

A novel membrane form of guanylyl cyclase (GC-G) has been identified t hrough the isolation of a full-length cDNA clone; it is predicted to c ontain an extracellular ligand binding domain, a single transmembrane segment, and intracellular protein kinase-like and cyclase catalytic d omains, That GC-G represents a guanylyl cyclase was confirmed by both transient expression in COS-7 cells and stable expression in H293 cell s, Endogenous cyclic GRIP concentrations of transfected or stable cell s, however, were much higher than control cells, suggesting an inabili ty of the cells to effectively regulate GC-G cyclase activity, Of six Cys residues found within the extracellular domain of guanylyl cyclase -il (GC-A) the receptor for atrial natriuretic peptide, five are conse rved within GC G. Ligands for the other cyclase receptors, nevertheles s, failed to stimulate GC-G expressed in transient or stable cells, su ggesting that the unknown ligands possess a structure different from t he natriuretic peptides or heat-stable enterotoxins. I-125-ANP also fa iled to bind to H293 cells overexpressing GC-G, Based on Northern hybr idization, mRNA for GC-G was predominantly expressed in lung, intestin e, and skeletal muscle, Using the candidate gene approach to potential ly define function, the gene for GC-G was mapped to the distal region of mouse chromosome 19 (syntenic with human chromosome 10q), but no hu man genetic defect has been ascribed to the GC-G locus, The finding of a new membrane form of guanylyl cyclase in peripheral tissues suggest s the existence of another family or subfamily of ligands that signal through elevations of cGMP.