Functional silencing of guanylyl cyclase/natriuretic peptide receptor-A by microRNA interference: analysis of receptor endocytosis.

Guanylyl cyclase/natriuretic peptide receptor-A (GC-A/NPRA) is the principal receptor for the regulatory action of atrial and brain natriuretic peptides (ANP and BNP) and an important effector molecule in controlling of extracellular fluid volume and blood pressure homeostasis. We have utilized RNA interference to silence the expression of GC-A/NPRA gene (Npr1), providing a novel system to study the internalization and trafficking of NPRA in intact cells. MicroRNA (miRNA)-mediated small interfering RNA (siRNA) elicited functional gene-knockdown of NPRA in stably transfected human embryonic kidney 293 (HEK-293) cells expressing a high density of recombinant NPRA. We artificially expressed three RNA polymerase II-driven miRNAs that specifically targeted the Npr1 gene, but shared no significant sequence homology with any other known mouse genes. Reverse transcription-PCR (RT-PCR) and Northern blot analyses identified two highly efficient Npr1 miRNA sequences to knockdown the expression of NPRA. The Npr1 miRNA in chains or clusters decreased NPRA expression more than 90% as compared with control cells. ANP-dependent stimulation of intracellular accumulation of cGMP and guanylyl cyclase activity of NPRA were significantly reduced in Npr1 miRNA-expressing cells by 90-95% as compared with control cells. Treatment with Npr1 miRNA caused a drastic reduction in the receptor density subsequently a deceased internalization of radiolabeled (125)I-ANP-NPRA ligand-receptor complexes. Only 12%-15% of receptor population was localized in the intracellular compartments of microRNA silenced cells as compared to 70%-80% in control cells.