Compositions comprising natriuretic peptides and methods of use thereof

Cloning, Production, and Purification of NC2 Streptag

[0287]An Fc-CNP fusion protein was designed as shown in FIGS. 8A and 8B. This protein, termed “NC2 Streptag” or “NC2st,” has a 25-amino acid N-terminal signal sequence that is cleaved during expression. The mature protein has the following domain structure, from N terminus to C terminus: Strep-tag II sequence (to facilitate purification) flanked by short linker sequences; TEV protease cleavage sequence, followed by a short linker; Fc domain of human IgG-1; 16-amino acid glycine-rich linker; and CNP22.

[0288]The coding sequence for NC2st was chemically synthesized (FIG. 8C, SEQ ID NO: 801) and inserted in a small cloning plasmid using standard techniques known in the art. The coding sequence of NC2st was then inserted in a mammalian expression vector and transiently transfected in a proprietary HEK293 cell line (Biotechnology research institute, NRCC, Animal Cell Technology Group, Montreal). NC2st was secreted in the culture medium for

Whole Cell Guanylyl Cyclase Assay

[0291]HEK293S cells in a semi-confluent 75 cm2 flask are transfected with 30 μg of plasmid DNA coding for the appropriate receptor, e.g., human NPR-B or NPR-A, using Lipofectamine-2000CD. Alternatively, a stable polyclonal HEK293 S cell line expressing either human NPR-B or NPR-A was used. 24 hours after transfection, cells are trypsinized and plated into 48-well plates at 1×105 cells / well. Guanylyl cyclase assay is carried out 24 hours post-plating. Cells are first incubated for 30 minutes at 37° C. with serum-free DMEM medium. Then, they are incubated in triplicate with or without increasing concentrations of reference or test proteins in serum-free DMEM supplemented with 1 mM IBMX and 0.5% BSA, at 37° C. for 30 minutes to one hour. CNP serves as a suitable reference for NPR-B, while ANP is a suitable reference for NPR-A. Finally, cells are washed with ice-cold PBS and solubilized in lysis buffer from Catchpoint cGMP kit (Molecular devices). Concent

Membrane Guanylyl Cyclase Assay

[0292]HEK293 cells expressing either NPR-B or NPR-A are used to prepare crude membrane preparations: Cells are resuspended in TH buffer (50 mM Hepes, 50 mM NaCl, pH 7.4, 10% glycerol, Protease inhibitor tablet (Roche cat. number 11697498001, one tablet for 35 mL of buffer), 50 mM sodium fluoride, 10 mM sodium pyrophosphate, 25 mM glycerol 2-phosphate) and homogenized using a polytron homogenizer. After centrifugation for 30 minutes at 38,000 g, cells are homogenized again and this washing procedure is repeated two more times. The crude membrane pellet is then homogenized in FB buffer (50 mM Hepes, 50 mM NaCl, 250 mM sucrose, 1 mM MgCl2, pH 7.4, 10% glycerol, Protease inhibitor cocktail (Roche cat. number 11873580001, one tablet for 25 mL of buffer), 50 mM sodium fluoride, 25 mM glycerol 2-phosphate), aliquoted at 200 μL into 1.5 mL eppendorf tubes and quickly frozen in liquid nitrogen before storing at −80° C. Membranes are then used to generate cGMP dose