Difference in molecular size of receptors for alpha-rat atrial natriuretic polypeptide among the kidney, aorta, and adrenal gland as identified by direct UV-photoaffinity labeling

Mouse brain opioid receptor identification by direct ultraviolet photoaffinity labeling

[3H]Morphine, PL-017[prolyl-3,4-3H,D-prolyl,3,4-3H] ([3H]PL-017) and enkephalin-(2-D-penicillamine,5-D-penicillamine)[tyrosyl-2,6-3H] ([3H]DPDPE) were directly cross-linked to mouse brain opiate receptors by an ultraviolet (254 nm) irradiation procedure. [3H]Morphine preferentially and specifically labeled a 58 kDa protein. The labeling of this protein was suppressed by the addition of excess naloxone. Dithiothreitol reduced the irreversible binding of [3H]morphine and [3H]PL-017 to the receptor protein. In the acid hydrolysate of [3H]DPDPE-labeled opiate receptors, dityrosine, was detected. These results suggest that the [3H]tyrosine residue of [3H]DPDPE covalently bound the tyrosine residue of delta-opioid receptors. The direct UV-photoaffinity labeling method using commercially available radioactive opiates described here should be a useful tool for characterization and purification of the opiate receptors.

Aortic smooth muscle contains guanylate-cyclase-coupled 130-kDa atrial natriuretic factor receptor as predominant receptor form. Spontaneous switching to 60-kDa C-receptor upon cell culturing

Photoaffinity labeling of atrial natriuretic factor (ANF) receptor in the plasma membranes from bovine aortic smooth muscle tissue using N alpha 5-(4-azidobenzoyl)-ANF-(5-28)- peptide labeled with 125I yielded a 130-kDa band. However, when smooth muscle cells from the same bovine aorta were placed in culture, the 130-kDa receptor quickly disappeared and a 60-kDa band began to appear at high density. After three passages, essentially no 130-kDa band was found and only the 60-kDa band was strongly labeled. The primary structures of the two receptor forms were compared by radiochemical peptide mapping after endoproteinase Glu-C digestion of photoaffinity-labeled and detergent-solubilized 130-kDa receptor from the aorta or the 60-kDa receptor from the cultured cells. The peptide mapping showed courses of digestion that were significantly different from each other, suggesting difference in their primary structures. The basal guanylate cyclase activity in the aortic membranes was 1.0 pmol cGMP produced.min-1.mg protein-1 at 37 degrees C using Mn(2+)-GTP as substrate. The corresponding activity in the membranes from the cultured cells was 20 fmol cGMP.min-1.mg protein-1. Binding studies gave a density of binding sites (Bmax) of 82 fmol/mg protein for the aortic membranes and 850 fmol/mg protein for the cultured cell membranes. These data suggest that the major form of ANF receptor in the cultured cells, namely the 60-kDa receptor, lacked guanylate cyclase activity. Northern blot analysis of poly(A)-RNA extracted form bovine thoracic aorta or adrenal cortex gave a single 3.6-kb band when 32P-labeled human A-type ANF receptor cDNA was used as a hybridization probe. However, no band was detected when C-receptor cDNA was used as a probe. In addition to the major 130-kDa band, extended SDS/PAGE revealed two additional faint bands with estimated molecular masses of 126 kDa and 135 kDa. Treatment with endoglycosidase H resulted in disappearance of the 126-kDa band and appearance of a 100-kDa band. The 130-kDa and 135-kDa bands were unchanged. Treatment by endoglycosidase F or glycopeptidase F reduced all three bands to a single 100-kDa band. These results suggest that the slight difference in mobility is due to different states of glycosylation.(ABSTRACT TRUNCATED AT 400 WORDS)

Differential antimitogenic effectiveness of atrial natriuretic peptides in primary versus subcultured rat aortic smooth muscle cells: relationship to expression of ANF-C receptors

Previous studies have shown that atrial natriuretic peptides inhibit mitogenesis in subcultured aortic smooth muscle cells by a mechanism that appears to be mediated via the C-type or "clearance" receptor. In the current study, we have compared the antimitogenic effect of these peptides in serum-stimulated primary aortic smooth muscle cell cultures and in subcultured cells. A series of atrial peptides, including rANF99-126, rANF103-126, and rANF103-125, were only poorly antimitogenic in serum-stimulated primary cultures, whereas des[Cys105,Cys121] rANF104-126 which binds selectively to the ANF-C receptors had no antimitogenic activity. In contrast, in subcultured cells (between subcultures 3 and 25), rANF99-126, rANF103-126, rANF103-126, Cys116rANF102-116, and des[Cys105,Cys121] rANF104-126 inhibited serum-induced [3H]thymidine incorporation (IC50 in the range of 10-50 nM), with maximal inhibition of 40-70%. The lack of antimitogenic activity in primary cultures did not appear to be related to the lack of cGMP elevation elicited by atrial peptides or to an inherent insensitivity to the action of antimitogens, because primary cultures were responsive to the cGMP-elevating effect of atrial peptides and the cells were more rather than less sensitive to the antimitogenic effect of the nitric-oxide-generating vasodilator, SNAP, as compared to subcultured cells. Analysis of the affinity and binding capacity of freshly isolated aortic membranes, and primary or secondary cultures for [125I]rANF99-126, revealed that the number of ANF receptors increased by tenfold, following subculture. Moreover, subcultured cells contained receptors with increased binding affinity for peptide analogues selective for the ANF-C-type receptor. Covalent cross-linking studies with (125I)rANF99-126 confirmed that membranes prepared from fresh aortae predominantly expressed the ANF-A/guanylate cyclase receptor, whereas in subcultured cells the predominantly cross-linked protein was the ANF-C-type receptor, with receptors in primary cultures occupying an intermediate position. These results suggest that the binding and antimitogenic activity of atrial peptides in aortic smooth muscle cells depends on the phenotypic state of these cells. Moreover, the increased antimitogenic potency of atrial peptides in secondary cultures may reflect increased expression of the ANF-C-type receptors.

Proteolytic cleavage of atrial natriuretic factor receptor in bovine adrenal membranes by endogenous metalloendopeptidase. Effects on guanylate cyclase activity and ligand-binding specificity

Atrial natriuretic factor (ANF) is a peptide hormone from the heart atrium with potent natriuretic and vasorelaxant activities. The natriuretic activity of ANF is, in part, mediated through the adrenal gland, where binding of ANF to the 130-kDa ANF receptor causes suppression of aldosterone secretion. Incubation of bovine adrenal membranes at pH < 5.6 caused a rapid and spontaneous cleavage of the 130-kDa ANF receptor, yielding a 65-kDa polypeptide that could be detected by photoaffinity labeling by 125I-labeled N alpha 4-azidobenzoyl-ANF(4-28) followed by SDS/PAGE under reducing conditions. Within 20 min of incubation at pH 4.0, essentially all the 130-kDa receptor was converted to a 65-kDa ANF binding protein. This cleavage reaction was completely inhibited by inclusion of 5 mM EDTA. When SDS/PAGE was carried out under non-reducing conditions, the apparent size of the ANF receptor remained unchanged at 130 kDa, indicating that the 65-kDa ANF-binding fragment was still linked to the remaining part(s) of the receptor polypeptide through a disulfide bond(s). The disappearance of the 130-kDa receptor was accompanied by a parallel decrease in guanylate cyclase activity in the membranes. Inclusion of EDTA in the incubation not only prevented cleavage of the 130-kDa receptor, but also protected guanylate cyclase activity, indicating that proteolysis, but not the physical effects of the acidic pH, causes inactivation of guanylate cyclase. The 130-kDa ANF receptor in adrenal membranes was competitively protected from photoaffinity labeling by ANF(1-28) or ANF(4-28), but not by atriopeptin I [ANF(5-25)] or C-ANF [des-(18-22)-ANF(4-23)-NH2]. On the contrary, the 65-kDa ANF-binding fragment generated after incubation at pH 4.0 was protected from labeling by any of the above peptides, indicating broader binding specificity. After incubation in the presence of EDTA, the 130-kDa ANF receptor, which was protected from proteolysis, retained binding specificity identical to that of the 130-kDa receptor in untreated membranes. The results indicate that the broadening of selectivity is caused by cleavage, but not by the physical effect of acidic pH. Spontaneous proteolysis of ANF receptor by an endogenous metalloendopeptidase, occurring with concomitant inactivation of guanylate cyclase activity and broadening of ligand-binding selectivity, may be responsible for the generation of low-molecular-mass receptors found in the adrenal gland and other target organs of ANF. The proteolytic process may play a role in desensitization or down-regulation of the ANF receptor.

Regulation of atrial natriuretic peptide receptors in glomeruli during chronic salt loading

The effects of chronic salt loading on atrial natriuretic peptide (ANP) receptor density and affinity were studied in isolated renal glomeruli of male Sprague-Dawley rats, which received 0.9% saline as drinking fluid (NaCl-rats) and a normal rat chow diet for 35 days (N = 12). Animals on a low sodium intake received the same diet, but deionized water and served as controls (C) (N = 12). After 35 days blood pressure was only slightly increased to 136 +/- 9 in NaCl-rats versus 120 +/- 2 mm Hg in C (NS). Glomerular filtration rate, plasma cGMP and plasma ANP remained unaltered. Determination of total ANP receptor characteristics in these rats indicated a significant down-regulation of ANP receptors in salt loaded rats. Since ANP-stimulated cGMP formation was not affected by salt loading, the roles of clearance (C) and of biologically active (B) receptors were further evaluated at 21 degrees C on freshly isolated and acid washed (pH 5) glomeruli in seven animals after 35 days of salt loading and in seven animals on a low sodium intake. B-receptors were assessed by blocking C-receptors with 4-23 cANP. C-receptor numbers were lower in NaCl-rats (97 +/- 8 vs. 184 +/- 14 fmol/mg protein in C; N = 7; P less than 0.02), while C-receptor affinity was increased (Kd: 12 +/- 3 pM in NaCl-rats vs. 22 +/- 5 pM in C; P less than 0.02).(ABSTRACT TRUNCATED AT 250 WORDS)

Photoaffinity labelling of atrial natriuretic factor (ANF)-R1 receptor by underivatized 125I-ANF. Involvement of lipid peroxidation

In bovine adrenal zona glomerulosa, atrial natriuretic factor (ANF) exerts its physiological effect through high-affinity binding to specific membrane receptors. On studying further the molecular properties of the ANF receptor binding domain, we have observed that incubation of intact or solubilized bovine adrenal zona glomerulosa membranes with 125I-ANF-(99-126) followed by u.v. irradiation results in the irreversible labelling of a 130 kDa protein corresponding to the ANF-RI receptor. This process is time-, protein- and 125I-ANF-dependent. The apparently covalent nature of this complex is documented by its resistance to heat, guanidine hydrochloride, urea and trichloroacetic acid denaturation. Photolabelling with underivatized 125I-ANF is much more efficient with the ANF-R1 than with the ANF-R2 receptor. After photolysis, the covalently linked 125I-ANF is still sensitive to digestion by carboxypeptidase A, suggesting that ANF is linked by its N-terminal end to the receptor upon u.v. irradiation and that its C-terminal end is still freely accessible. Aerobic conditions and lipids are required for the photolabelling, suggesting a role in this process for malondialdehyde, a highly reactive secondary product associated with u.v.-induced lipid peroxidation. This simple method should provide a powerful tool in the accurate characterization of the hormone-binding domain of the ANF receptor.

Degradation and clearance of atrial natriuretic factors (ANF)

Atrial natriuretic factor, the first well defined natriuretic hormone is synthesized in the human heart as 151 aminoacid (AA) preprohormone and stored as 126 AA prohormone in atrial granules. Upon appropriate stimulation, the prohormone is cleaved into a 98 AA N-terminal fragment and a 28 AA C-terminal fragment, the biological active ANF(99-126), both circulating in plasma. Circulating ANF(99-126) is cleared by various organs, such as lung, liver and intestine, kidney and upper and lower limbs. Reported arterial-venous extraction ratios vary greatly, but are not much different between organs, the average extraction ratio being about 35%. Due to marked differences of organ blood flow, the contribution of various organs to total body ANF clearance differs considerably. Major mechanisms for ANF clearance are uptake by clearance receptors and degradation by an endoprotease (EC 3.4.24.11.). Clearance receptors, distinct from the receptors mediating the biological actions of ANF, have been demonstrated in various organs. Characterization of the ANF degrading enzyme activity has been performed in kidney tissue. Whether and how pathophysiological states affect ANF clearance is still poorly understood. Inhibition of clearance by ANF analogues binding to clearance receptors and by inhibitors of degrading peptidase can increase the biological action of circulating ANF. This may prove to be a therapeutic approach in diseases with smooth muscle contraction or volume overload.

Binding characteristics of atrial natriuretic factor and the production of cyclic GMP in kidneys of Dahl salt-sensitive and salt-resistant rats

The binding of atrial natriuretic factor (ANF) was studied in kidney membranes of inbred salt-sensitive (S) and inbred salt-resistant (R) rats on high or low salt diet. Important differences between strains were seen in the rate of dissociation of ANF from its renal receptor(s) and this was dependent on salt (NaCl) intake. On low salt diet ANF dissociation rates were similar between strains. R rats responded to high salt diet with a decrease in the rate of ANF dissociation from its renal receptor, but ANF dissociation in S rats was not altered by dietary salt. Receptor density was similar between strains. Basal cGMP production was slightly higher for renal membranes of S rats, but ANF stimulation of cGMP production was similar between strains and was not influenced by salt intake in either strain. Since strain-related salt-induced changes in ANF-receptor binding kinetics were not reflected in any strain-related salt-induced changes in ANF stimulated cGMP production, it is tentatively concluded that the ANF receptor likely to be different between S and R strains is the ANF receptor not linked to cGMP production.

Purification and subunit composition of atrial natriuretic peptide receptor

A receptor for atrial natriuretic peptide (ANP) was purified 2700-fold, to apparent homogeneity, from cultured bovine aortic smooth muscle cells by affinity chromatography. The native ANP receptor has a molecular weight of 125,000 as determined by both metrizamide gradient centrifugation and nonreducing NaDodSO4/polyacrylamide gel electrophoresis. With 125I-labeled ANP as ligand, the purified receptor bound a maximum of 5.70 nmol of ligand per mg of protein and the dissociation constant was 4.0 X 10(-10)M. Upon treatment with 10 mM dithiothreitol, the purified receptor migrated as a single band at Mr 60,500 in NaDodSO4/polyacrylamide gel electrophoresis. These findings show that the holoreceptor for ANP in vascular tissue is composed of two subunits of identical apparent molecular weight, presumably linked by a disulfide bridge(s).