Evidence for cross-talk between atrial natriuretic peptide and nitric oxide receptors

Guanylyl cyclases (GCs), a ubiquitous family of enzymes that metabolize GTP to cyclic GMP (cGMP), are traditionally divided into membrane-bound forms (GC-A-G) that are activated by peptides and cytosolic forms that are activated by nitric oxide (NO) and carbon monoxide. However, recent data has shown that NO activated GC's (NOGC) also may be associated with membranes. In the present study, interactions of guanylyl cyclase A (GC-A), a caveolae-associated, membrane-bound, homodimer activated by atrial natriuretic peptide (ANP), with NOGC, a heme-containing heterodimer (alpha/beta) beta1 isoform of the beta subunit of NOGC (NOGCbeta1) was specifically focused. NOGCbeta1 co-localized with GC-A and caveolin on the membrane in human kidney (HK-2) cells. Interaction of GC-A with NOGCbeta1 was found using immunoprecipitations. In a second set of experiments, the possibility that NOGCbeta1 regulates signaling by GC-A in HK-2 cells was explored. ANP-stimulated membrane guanylyl cyclase activity (0.05 +/- 0.006 pmol/mg protein/5 min; P < 0.01) and intra cellular GMP (18.1 +/- 3.4 vs. 1.2 +/- 0.5 pmol/mg protein; P < 0.01) were reduced in cells in which NOGCbeta1 abundance was reduced using specific siRNA to NOGCbeta1. On the other hand, ANP-stimulated cGMP formation was increased in cells transiently transfected with NOGCbeta1 (530.2 +/- 141.4 vs. 26.1 +/- 13.6 pmol/mg protein; P < 0.01). siRNA to NOGCbeta1 attenuated inhibition of basolateral Na/K ATPase activity by ANP (192 +/- 22 vs. 92 +/- 9 nmol phosphate/mg protein/min; P < 0.05). In summary, the results show that NOGCbeta1 and GC-A interact and that NOGCbeta1 regulates ANP signaling in HK-2 cells. The results raise the novel possibility of cross-talk between NOGC and GC-A signaling pathways in membrane caveolae.