Regulation and therapeutic targeting of peptide-activated receptor guanylyl cyclases

Abstract

Cyclic GMP is a ubiquitous second messenger that regulates a wide array of physiologic processes such as blood pressure, long bone growth, intestinal fluid secretion, phototransduction and lipolysis. Soluble and single-membrane-spanning enzymes called guanylyl cyclases (GC) synthesize cGMP. In humans, the latter group consists of GC-A, GC-B, GC-C, GC-E and GC-F, which are also known as NPR-A, NPR-B, StaR, Ret1-GC and Ret2-GC, respectively. Membrane GCs are activated by peptide ligands such as atrial natriuretic peptide (ANP), B-type natriuretic peptide (BNP), C-type natriuretic peptide (CNP), guanylin, uroguanylin, heat stable enterotoxin and GC-activating proteins. Nesiritide and carperitide are clinically approved peptide-based drugs that activate GC-A. CD-NP is an experimental heart failure drug that primarily activates GC-B but also activates GC-A at high concentrations and is resistant to degradation. Inactivating mutations in GC-B cause acromesomelic dysplasia type Maroteaux dwarfism and chromosomal mutations that increase CNP concentrations are associated with Marfanoid-like skeletal overgrowth. Pump-based CNP infusions increase skeletal growth in a mouse model of the most common type of human dwarfism, which supports CNP/GC-B-based therapies for short stature diseases. Linaclotide is a peptide activator of GC-C that stimulates intestinal motility and is in late-stage clinical trials for the treatment of chronic constipation. This review discusses the discovery of cGMP, guanylyl cyclases, the general characteristics and therapeutic applications of GC-A, GC-B and GC-C, and emphasizes the regulation of transmembrane guanylyl cyclases by phosphorylation and ATP.

Fig. 1

Schematic of human transmembrane guanylyl cyclases and their ligands. The structure and function of each cyclase is discussed in the text. Similarity of extracellular domain color represents primary amino acid sequence identity. The blue “P” indicates known phosphorylation sites. Abbreviations are: ANP, atrial natriuretic peptide; BNP, B-type natriuretic peptide; CNP, C-type natriuretic peptide; GC-A, guanylyl cyclase-A; GCAPs, guanylyl cyclase activating proteins; GC-B, guanylyl cyclase-B; GC-C, guanylyl cyclase-C; GC-E, guanylyl cyclase-E; GC-F, guanylyl cyclase-F; Gn, guanylin; ST, heat-stable enterotoxin; Uro, uroguanylin.

Fig. 2

Structure of natural and designer natriuretic peptides and peptides that activate GC-C. All sequences are human unless otherwise noted. Grey boxes indicate identical amino acids. Lighter grey boxes indicate structurally conserved amino acids. Red residues indicate substitutions that reduce degradation of ST. Dark black lines represent disulfide bonds. The triple disulfides over ST apply to ST and Linaclotide. The double disulfide bonds below uroguanylin apply to guanylin and uroguanylin. Abbreviations are: ANP, atrial natriuretic peptide; BNP, B-type natriuretic peptide; CNP, C-type natriuretic peptide; DNP, Dendroaspis natriuretic peptide; ST, heat stable enterotoxin from E. coli.

Fig. 3

Phosphorylation sites in mammalian transmembrane guanylyl cyclases. Red S or T indicates phosphorylation sites that were chemically verified. Black background indicates identical residues in four or more cyclases. Grey background indicates similar amino acids in four or more cyclases. The alignment was initially made with Clustal W2 and then adjusted by hand to maximize alignment of charged residues.