Mouse pulmonary cytochrome P-450 naphthalene hydroxylase: cDNA cloning, sequence, and expression in Saccharomyces cerevisiae.

We have isolated a cDNA clone, Nah-2, encoding the cytochrome P-450Nah (naphthalene hydroxylase) from a mouse lung lambda ZAP cDNA library using anti-cytochrome P-450Nah IgG as a probe. This same antibody selectively blocked [Nagata, K., Martin, B.M., Gillette, J.R., & Sasame, H.A. (1990) Drug Metab. Dispos. 18, 557-564] the cytochrome P-450 in mouse lung microsomes that catalyzed the conversion of naphthalene to (1R,2S)-naphthalene 1,2-oxide, which has been postulated as a causative agent in the naphthalene-induced tissue-specific necrosis of Clara cells in mouse lung. The toxic effect is seen in mouse and not in rat. The cDNA encodes a polypeptide of 491 amino acids with a molecular mass of 50 kDa. Northern blot analysis with an Nah-2-specific probe revealed that the mRNA is expressed in a species- and tissue-specific manner, present only in mouse lung and liver and not in that of rat. The mRNA encoding Nah-2 is constitutively expressed and is not induced by either phenobarbital, pyrazole, pregnenolone 16 alpha-carbonitrile, or 3-methylcholanthrene. Comparative amino acid sequence analyses with other documented members of the P-450 gene superfamily revealed that this encoded protein is in the IIF subfamily. To analyze its substrate specificity, the cDNA was inserted into the vector, pAAH5, and expressed in the Saccharomyces cerevisiae strain, AH22. The presence of cytochrome P-450Nah in the microsomes isolated from transformed cells and analyzed by Western blot was confirmed by immunocomplexing product with anti-cytochrome P450Nah IgG. Furthermore, activity toward naphthalene in the microsomes from the transformed cells established that this clone encodes a naphthalene hydroxylase.(ABSTRACT TRUNCATED AT 250 WORDS)     

Inhibited insulin secretion by recombinant human interleukin-1 beta in adrenalectomized rats: involvement of prostaglandin

An involvement of prostaglandin synthesis in reduced insulin secretion by interleukin-1 was investigated in adrenalectomized (ADX) rats. The recombinant human interleukin-1 beta (IL-1) significantly reduced insulin secretion in ADX rats 2 and 4 hr after the injection, although IL-1 stimulated insulin secretion in intact rats. In ADX rat, IL-1 showed dose-dependent inhibition of pancreatic insulin secretion. In addition, insulin response to intravenous glucose loading was also attenuated in ADX rats with pretreatment by IL-1. At 4 hours after injection, ibuprofen (IBP; 0.5-50.0 mg/kg, ip), selective cyclooxygenase blocker, attenuated insulin inhibition by IL-1 in a dose-dependent manner. These data suggest that IL-1 may suppress in vivo insulin release at least in part through the mediation of prostaglandin synthesis in the absence of adrenal glands.     

Arachidonic acid stimulates phosphoinositide metabolism and catecholamine release from bovine adrenal chromaffin cells

Arachidonic acid (AA) evoked a dose-dependent increase in the accumulation of inositol phosphates in cultured bovine adrenal chromaffin cells, and this effect was specific for AA. AA also induced a rise in [Ca2+]i, but this rise was markedly reduced by removal of extracellular Ca2+. AA-induced accumulation of inositol phosphates was absolutely dependent on extracellular Ca2+, and nicardipine and nifedine partially reduced it but verapamil had no effect. Moreover, AA dose-dependently stimulated catecholamine release from chromaffin cells in the presence of ouabain, and this effect was specific for AA. AA-induced catecholamine release in the presence of ouabain was also inhibited by nicardipine and nifedipine but not by verapamil. Furthermore, the phospholipase C inhibitor neomycin inhibited the release. These results taken together suggest that AA stimulates catecholamine release in the presence of ouabain by stimulation of phosphoinositide metabolism in a Ca2(+)-dependent manner.     

Characterization of a cDNA for the unexpressed form of cytochrome P-450g from the (-g) rat and differentiation of its mRNA from that of the (+g) phenotype using specific oligoprobes

Our laboratory recently isolated a cDNA for cytochrome P-450g (IIC13), a male-specific, highly polymorphic P-450 isozyme, from livers of the high phenotype (+g) of Sprague-Dawley rats [McClellan-Green et al. (1989) Biochemistry 28, 5832-5839]. Hybridization studies using a specific oligonucleotide probe for P-450 (+g) indicated that equivalent amounts of P-450g mRNA were present in livers of both the high and low phenotypes (+g and -g) of male Sprague-Dawley, Fischer (inbred -g), or ACI (inbred +g) rats. In the present study, we isolated one full-length and one nearly full-length cDNA clone coding for the unexpressed form of cytochrome P-450g from a cDNA library constructed from mRNA from a (-g) male Sprague-Dawley rat. The longest cDNA had an open reading frame of 1473 nucleotides which coded for a 490 amino acid polypeptide of Mr 55,839. Although the 5'-noncoding leader sequence and the 3'-noncoding region were unchanged, the coding sequence of the (-g) phenotype differed from that of the cDNA isolated from the (+g) phenotype by nine bases changes. These base changes would result in seven amino acid differences between the protein sequences for the two phenotypes. Two specific oligonucleotide probes for (+) P-450g and (-) P-450g containing three base differences between the (+g) and (-g) sequences hybridized differentially to mRNA from the (+g) and (-g) phenotypes.(ABSTRACT TRUNCATED AT 250 WORDS)     

Involvement of protein kinase C in prostaglandin E2-induced catecholamine release from cultured bovine adrenal chromaffin cells

We recently reported that prostaglandin (PG) E2 stimulated phosphoinositide metabolism in cultured bovine adrenal chromaffin cells and that PGE2 and ouabain induced a gradual secretion of catecholamines from the cells (Yokohama, H., Tanaka, T., Ito, S., Negishi, M., Hayashi, H., and Hayaishi, O. (1988) J. Biol. Chem. 263, 1119-1122). Here we examined the involvement of two signal pathways, Ca2+ mobilization and protein kinase C activation resulting from phosphoinositide metabolism, in the PGE2-induced catecholamine release. Either the Ca2+ ionophore ionomycin or 12-O-tetradecanoylphorbol 13-acetate (TPA) could enhance the release in the presence of ouabain, and ionomycin-induced release was additive to PGE2-induced release, but TPA-induced release was not additive. PGE2 dose-dependently stimulated the formation of diacylglycerol and caused the translocation of 4% of the total protein kinase C activity to become membrane-bound within 5 min. These effects were specific for PGE2 and PGE1 among PGs tested (PGE2 = PGE1 greater than PGF2 alpha greater than PGD2). Furthermore, the phosphoinositide-specific phospholipase C inhibitor neomycin inhibited PGE2-induced accumulation of inositol phosphates, diacylglycerol formation, translocation of protein kinase C, and also stimulation of catecholamine release. Both PGE2- and TPA-induced release were inhibited by the depletion of protein kinase C caused by prolonged exposure to TPA, but ionomycin-induced release was not inhibited. We recently found that the amiloride-sensitive Na+, H+-antiport participates in PGE2-evoked catecholamine release (Tanaka, T., Yokohama, H., Negishi, M., Hayashi, H., Ito, S., and Hayaishi, O. (1990) J. Neurochem. 54, 86-95). In agreement with our recent report, PGE2 and TPA induced a sustained increase in intracellular pH that was abolished by the protein kinase C inhibitor staurosporine but not by the calmodulin inhibitor W-7. Ionomycin also induced a marked increase in intracellular pH, but this increase was abolished by W-7 but not by staurosporine. These results demonstrate that PGE2-induced activation of the Na+, H(+)-antiport and catecholamine release in the presence of ouabain are mediated by activation of protein kinase C, rather than by Ca2+ mobilization, resulting from phosphoinositide metabolism.     

The binding of ATP to the catalytic and the regulatory site of Ca2+,Mg2+-dependent ATPase of the sarcoplasmic reticulum

Two kinds of ATP binding sites were found on the ATPase molecule in deoxycholic acid-treated sarcoplasmic reticulum. One was the catalytic site (1 mol/mol active site) and its affinity was high. Upon addition of Ca²⁺, all the ATP bound to the catalytic site disappeared at 75 mM KCl, while a significant amount of ATP remained bound to the site at 0–2 mM KCl. The latter binding was found to be due to the formation of a slowly exchanging enzyme-ATP complex, which is in equilibrium with phosphoenzyme + ADP. The other binding site was the regulatory one (1 mol/mol active site) and its affinity was low, changing only insignificantly upon addition of Ca²⁺. The ATP binding to the regulatory site shifted the equilibrium between the slowly exchanging complex and EP toward EP.     

An anchorage-dependent locus in the cell cycle for the growth of 3T3 cells

Mouse fibroblasts, 3T3 cells, require a solid surface for continuous growth, but when 3T3 cells, during their exponential phase in Petri dishes, were transferred to a suspension culture, the number of cells roughly doubled by 30 h. During the suspension culture the number of pairing cells (c₂) increased, but that of the single cells decreased. When cells synchronized at mitosis or at the G1-S boundary were transferred to the suspension culture, the number of pairing cells peaked at 30 min and at 10 h, respectively. DNA synthesis began immediately after the cells, which were cultured for 16 h in the suspension, had settled onto the surface of the Petri dishes. When cells in a confluent culture were arrested at an early G1 period and were suspended, the number of pairing cells did not increase. These results indicate that the most important locus for anchorage growth seems to be at a late G1 period of the cell cycle.     

Histochemical studies on catecholaminergic cells in the carp retina

Histochemical studies on catecholaminergic cells were conducted with the carp (Cyprinus carpio) retina. Catecholamine (CA)-containing cell bodies appear sparsely distributed among amacrine cells in the innermost cellular row of the inner nuclear layer (INL) and occasionally in the outer half part of the inner plexiform layer (IPL); only exceptionally are they found among ganglion cells. The fluorescent cells interspersed with the amacrine cells and in the IPL send their fiber processes toward both the outer plexiform layer (OPL) and the IPL; the fine fibers form dense networks in the INL and IPL. Pretreatment of the fish with intramuscular injection of reserpine (20 hr prior to enucleation) completely depleted CA from the retina. The fluorescence of catecholaminergic cells was enhanced, and the number of fluorescent cells visible was increased, by intravitreous injection ofl-DOPA, DA, and NA (3 hr prior to enucleation). A combination of pretreatment with intramuscular reserpine and intravitreous NA was particularly effective. These results indicate that catecholamines may play an important role in the modulation of the membrane potential of horizontal cells.