PERSPECTIVE
Complex Regulation of iNOS in Lung

Bruce R. Pitt and Claudette M. St. Croix

Department of Environmental and Occupational Health, Graduate School of Public Health, University of Pittsburgh, Pittsburgh, Pennsylvania

In a remarkably short period after the identification of nitric oxide (NO) as a novel signaling molecule in mammalian physiology, the critical role of L-arginine biosynthetic pathway in lung function became apparent (1). Numerous cell types within rodent and human lung (2) expressed one or more of the three known nitric oxide synthases (NOS) that catalyzed the five-electron oxidation of the N-terminal guanidino group of L-arginine to NO. The second of these oxidoreductases to be cloned (NOS2) is more commonly referred to as iNOS as a reflection of its unique features, including its (1) activation being independent of transient increases in intracellular calcium; and (2) inducibility at a transcriptional level in response to inflammatory or immunologic stimuli (3). The fundamental role of iNOS-derived NO in host defense contributed to the extraordinary large number of investigations into its regulation at transcriptional and post-transcriptional levels (4). Concurrent with these advances in iNOS regulation was an increasing awareness of the role of hypoxia in gene expression; and, thus, it is not surprising that these two areas of study have intersected. In this issue, Zulueta and colleagues (5) report that although hypoxia per se does not affect iNOS expression in cultured rat pulmonary microvascular endothelial cells, it does modulate IL-1 and TNF- induction of iNOS at pretranscriptional through post-transcriptional levels. The study underscores the complexity of iNOS regulation and provides important observations that can be used to assess cell-, stimulus-, and species-specific differences in such regulation.

	iNOS in Lung

Kobzik and coworkers (2) originally systematically localized iNOS in fixed tissue of rat and human lung. Immunoreactive iNOS was most apparent in rat alveolar macrophage after LPS and occasionally in human macrophage and endothelium in areas of chronic inflammation. Interestingly, both species showed immunoreactive iNOS in airway epithelium in normal tissue, suggesting the possibility of a constitutively active iNOS. Constitutively expressed iNOS in upper and lower airway epithelium was subsequently confirmed by Asano and coworkers (6) and Guo and colleagues (7). These latter investigators noted that this unusual expression was lost when human airway epithelium was cultured (8); and progress has been made in identifying a soluble, heat labile, acid insensitive autocrine-derived mediator that accounts for such expression (9). The role of iNOS-derived NO and secondary reactive nitrogen intermediates in normal lung is unclear, but may be an important component of host defense (3), as well as a source of NO for S-nitrosylation of hemoglobin during its transpulmonary passage (10).

The contribution of intrapulmonary iNOS-derived NO in experimental acute and chronic lung injury has been revealed by pharmacologic and genetic studies. Our laboratory has shown that exposure to mixtures of cytokines and endotoxin of cultured rat type II cells (11) and pulmonary artery (12) or intra-acinar (13) vascular smooth muscle leads to induction of iNOS. It is apparent that virtually every lung cell is capable of such induction, although some (5, 14), but not all (15), cultures of rat pulmonary microvascular endothelium have this capacity. Nonetheless, iNOS null mutant mice are resistant to carrageen-induced pleurisy (16) and ovalbumin-induced airway inflammation (17), and pharmacologic inhibition of iNOS reduces lung injury and permeability changes secondary to smoke inhalation (18), cecal ligation and puncture (19), and hemorrhagic shock (20), suggesting a contributory role of iNOS-derived NO to acute lung injury. We recently reported that cytokine-stimulated cultured rat pulmonary artery vascular smooth muscle cells produce an NO-dependent toxicity to co-cultured rat pulmonary microvascular endothelial cells (15), suggesting an inflammatory effector role for vascular smooth muscle cells. Alternatively, iNOS-derived NO appears to be anti-inflammatory in hyperoxic lung injury (21) and reduces mycoplasma-induced lung injury (22) in intact mice and reduces the sensitivity of cultured sheep pulmonary artery endothelial cells to endotoxin-induced apoptosis (23). It is apparent that the source of iNOS-derived NO and the amount and rate at which it is formed selectively affects various proinflammatory stimuli.

NO is an important mediator in maintaining low vascular resistance in lung and this is readily demonstrable in the transition circulation and in acute and chronic hypoxia. Although the pulmonary circulation of eNOS-deficient mice is hypersensitive to hypoxia (24), there also appears to be a contribution of iNOS-derived NO (28). Chronic hypoxia was previously noted to increase iNOS in lung (29), including increased mRNA levels of iNOS in pulmonary endothelium and smooth muscle of rat (30). In this latter study, the authors demonstrated that hypoxia increased iNOS expression in isolated cultured rat lung endothelial cells and that hypoxia-inducible factor-1 (HIF-1) was essential for such regulation.

	Hypoxic Regulation of iNOS

In addition to the above studies in lung, many (but not all) studies demonstrate a hypoxia-induced increase in iNOS gene expression. Nonetheless, differences between species, cell types, conditions of hypoxia, presence of other inducers, and fundamental differences between in vivo and in vitro experiments underlie a considerable degree of controversy, ambiguity, and diverse results. The first evidence that iNOS was a hypoxic-inducible gene was provided by Melillo and colleagues (31), who showed that hypoxia in combination with IFN- increased iNOS expression in an HIF-1-like dependent fashion in the murine macrophage-like cell (ANA-1). Using transient transfections, promoter-reporter constructs, and targeted mutations, these authors showed the functional importance of a hypoxia responsive enhancer (HRE) in the 5' flanking region of murine iNOS. Chronic hypoxia led to an induction of iNOS in hearts (34, 35) and central nervous system (36), but not the diaphragm (37) of intact rats. It is unclear why hypoxia enhanced IL-1-mediated iNOS induction in cultured rat cardiomyocytes in the study by Jung (38) or in a hypoxic reperfusion model in cell culture by Chen and coworkers (39), but not in the study by Kacimi and colleagues (40). In this latter study (40), hypoxia actually decreased IL-1- mediated iNOS changes. Similar discrepancies exist in hepatocytes (41, 42). Alternatively, hypoxia has been shown to increase iNOS expression in tumor cells (43) and not to affect endotoxin- or IFN--induced increases in iNOS mRNA in mesangial (44) or aortic smooth muscle cells (45). It is clear (46) since the original studies of Melillo and coworkers (31) that reoxygenation is required for iNOS- derived NO production to proceed.

Considerably less is known regarding hypoxic regulation of iNOS in humans. Inducible NOS was elevated in cardiac biopsies in cyanotic children with congenital heart disease (47). Although the underlying mechanism remains to be determined, it is interesting that exhaled NO is elevated in Tibetans and Bolivian Aymara living at high altitude (48). Alternatively, hypoxia decreases exhaled NO in individuals known to be susceptible to high altitude pulmonary edema but not resistant individuals (49). These latter studies suggest that hypoxic-induced changes in intrapulmonary NO production may be a homeostatic response to maintain a low pulmonary vascular resistance during such a stimulus. Support for this hypothesis and iNOS as a mediator of the vascular response to oxygen in the lung was provided in a kinetic study of the effect of altered inspired oxygen tension on NO production in normal human volunteers (50).

	Complex Regulation of iNOS

Most of our current understanding of regulation of iNOS has been derived from analysis of 5'-flanking region of murine (and to a considerably lesser extent, human) iNOS promoter. In mouse, two NF-B binding sites have been identified and the more downstream site accounts for LPS induction of iNOS. An upstream site contains enhancer regions with binding sites for -activated site element and an IRF-1 response element that account for IFN- induction (51). Although these and other sites are contained in a relatively proximal region (< 1000 bp) from start site of initiation of transcription, the mechanistic basis of synergistic effects of cytokines remains unclear. One theory to underscore such synergism between transcription factors and gene regulation suggests that physical interactions between proteins enhances DNA binding affinity and complex stability, resulting in a highly stable multiprotein complex (52). A recent study has shown that IRF-1 and NF-B interact during activation of murine iNOS (53), suggesting that synergism may be secondary to formation of an enhanceosome or structural alterations in DNA conformation leading to bending or looping and enhanced transcription. A similar physical interaction between IRF-1 and HIF-1 in hypoxic murine macrophages (54) may explain why hypoxia, alone, barely affects iNOS expression, whereas when combined with IFN- it greatly enhances expression of iNOS promoter-reporter construct or iNOS mRNA. This is similar to results obtained by Zuleta and colleagues (5) in this issue, where hypoxia and IL-1+TNF- increase activity of rat iNOS promoter in cultured rat pulmonary endothelial cells. Cytokine regulation of human iNOS includes a considerably larger region (3-16 kb) of 5'-flanking sequence compared with mouse (52, 55). Thus, it remains to be determined if hypoxia affects human iNOS in a manner similar to that for rodent iNOS (iNOS-HRE and interaction with IRF-1, NF-B, or other factors).

In the study by Zulueta and colleagues (5), although hypoxia itself did not affect iNOS mRNA levels, hypoxia significantly prolonged the half life of cytokine-induced iNOS mRNA. As the authors indicate, hypoxia has been shown to increase the stability of VEGF mRNA through activation of ELAV-like RNA binding protein, HuR (58). Others (59) have shown that this same protein can bind to the 3'-UTR of human iNOS and contribute to cytokine-induced increase in steady state iNOS mRNA in DLD-1 cells. Accordingly, post-transcriptional regulation of iNOS by hypoxia, especially in the presence of activating cytokines, may contribute to the large steady state increase in iNOS mRNA.

In summary, iNOS-derived NO has diverse functions in lung physiology, including critical roles in host defense and contributory roles in pulmonary vasoregulation. Accordingly, coordinate regulation of iNOS expression by cytokines and hypoxia at transcriptional and post-transcriptional levels in pulmonary endothelium is a fundamental aspect of lung function. In light of the well-known differences in regulation of iNOS between rodents and humans, it will be important to repeat these studies (5) in human pulmonary endothelial cells. Recent studies regarding hypoxia and cytokine regulation of iNOS in its 5' (via multiprotein complexes [54]) and 3' UTR (via RNA binding proteins like HuR [58]) are important leads for future mechanistic studies.

	Footnotes

Address correspondence to: Bruce R. Pitt, Ph.D., Department of Environmental and Occupational Health, Graduate School of Public Health, University of Pittsburgh, Pittsburgh, PA 15260. E-mail: brucep{at}pitt.edu

(Received in original form December 3, 2001).

	References

1. Gaston, B., J. M. Drzen, J. Loscalzo, and J. S. Stamler. 1994. The biology of nitrogen oxides in the airways. Am. J. Respir. Crit. Care Med. 149: 538-551 [Abstract].

2. Kobzik, L., D. S. Bredt, C. J. Lowenstein, J. Drazen, B. Gaston, D. Sugarbaker, and J. S. Stamler. 1993. Nitric oxide synthase in human and rat lung: immunocytochemical and histochemical localization. Am. J. Respir. Cell. Mol. Biol. 9: 371-377 .

3. Nathan, C.. 1997. Inducible nitric oxide synthase: what difference does it make? J. Clin. Invest. 100: 2417-2423 [Medline].

4. Kroncke, K. D., K. Fehsel, C. Suschek, and V. Kolb-Bachofen. 2001. Inducible nitric oxide synthase-derived nitric oxide in gene regulation, cell death and cell survival. Int. Immunopharmacol. 8: 1407-1420 .

5. Zulueta, J. J., R. Sawhney, U. Kayyali, M. Fogel, C. Donaldson, H. Huang, J. J. Lanzillo, and P. H. Hassoun. 2002. Modulation of inducible nitric oxide synthase by hypoxia in pulmonary artery endothelial cells. Am. J. Respir. Cell Mol. Biol. 26: 22-30 [Abstract/Free Full Text].

6. Asano, K., C. B. Chee, B. Gaston, C. M. Lilly, C. Gerard, J. M. Drazen, and J. S. Stamler. 1994. Proc. Natl. Acad. Sci. USA 91: 10089-10093 [Abstract/Free Full Text].

7. Guo, F. H., H. R. DeRaeve, T. W. Rice, D. J. Stuehr, F. B. Thunnissen, and S. C. Erzurum. 1995. Continuous nitric oxide synthesis by inducible nitric oxide synthase in normal human airway epithelium in vivo. Proc. Natl. Acad. Sci. USA 92: 7809-7813 [Abstract/Free Full Text].

8. Guo, F. H., K. Uetani, S. J. Haque, B. R. Williams, R. A. Dweik, F. B. Thunnissen, W. Calhoun, and S. C. Erzurum. 1997. Interferon gamma and interleukin 4 stimulate prolonged expression of inducible nitric oxide synthase in human airway epithelium through synthesis of soluble mediators. J. Clin. Invest. 100: 829-838 [Medline].

9. Uetani, K., M. J. Thomassesen, and S. C. Erzurum. 2001. Nitric oxide synthase 2 through an autocrine loop via respiratory epithelial cell-derived mediator. Am. J. Physiol. Lung Cell Mol. Physiol. 280: L1179-L1188 [Abstract/Free Full Text].

10. Stamler, J. S., L. Jia, J. P. Eu, T. J. McMahon, I. T. Demchenko, J. Bonaventura, K. Gernert, and C. A. Piantadosi. 1997. Blood flow regulation by S-nitrosohemoglobin in the physiological oxygen gradient. Science 276: 2034-2037 [Abstract/Free Full Text].

11. Gutierrez, H. H., B. R. Pitt, M. A. Schwartz, S. C. Watkins, C. Lowenstein, I. Caniggia, P. Chumley, and B. A. Freeman. Pulmonary alveolar epithelial inducible nitric oxide synthase gene expression: regulation by inflammatory mediators. Am. J. Physiol. Lung Cell Mol. Physiol. 12:L501-L508.

12. Nakayama, D. K., D. A. Geller, C. J. Lowenstein, P. Davies, B. R. Pitt, R. L. Simmons, and T. R. Billiar. Cytokines and lipopolysaccharide regulate induction of nitric oxide synthesis in cultured rat pulmonary artery smooth muscle. Am. J. Respir. Cell Mol. Biol. 7:741-746.

13. Johnson, B. A., C. J. Lowenstein, M. A. Brookens, D. K. Nakayama, B. R. Pitt, and P. Davies. 1994. Culture of pulmonary microvascular smooth muscle cells from intraacinar arteries of the rat: characterization and inducible production of nitric oxide. Am. J. Respir. Cell Mol. Biol. 10: 604-612 [Abstract].

14. Geiger, M., A. Stone, S. N. Mason, K. T. Oldham, and K. S. Guice. 1997. Differential nitric oxide production by microvascular and macrovascular endothelial cells. Am. J. Physiol. Lung Cell Mol. Physiol. 273: L275-L281 [Abstract/Free Full Text].

15. Johnson, B. A., B. R. Pitt, and P. Davies. 2000. Pulmonary arterial microvascular smooth muscle cells modulate cytokine and LPS induced cytotoxicity in cocultured endothelial cells. Am. J. Physiol. Lung Cell Mol. Physiol. L460-L468.

16. Cuzzocrea, S., E. Mazzon, G. Calabro, L. Dugo, A. DeSarro, F. A. va DeLoo, and A. P Caputi. 2000. Inducible nitric oxide synthase knockout mice exhibit resistance to pleurisy and lung injury caused by carrageenan. Am. J. Respir. Crit. Care Med. 162:1859-1866.

17. Xiong, Y., G. Karupiah, S. P. Hogan, P. S. Foster, and A. J. Ramsey. 1999. Inhibition of allergic airway inflammation in mice lacking nitric oxide synthase 2.  J. Immunol. 162: 445-452 [Abstract/Free Full Text].

18. Soejima, K., R. Maguire, N. Snyder, T. Uchida, C. Szabo, A. Salzman, L. D. Traber, and D. L. Traber. 2000. The effect of inducible nitrix oxide synthase (iNOS) inhibition on smoke inhalation injury in sheep. Shock 13: 261-266 [Medline].

19. Okamoto, I., M. Abe, K. Shibata, N. Shimuza, N. Sakata, T. Katsuragi, and K. Tanaka. 2000. Evluating the role of inducible nitric oxide synthase using a novel and selective inducible nitric oxide synthase inhibitor in septic lung produced by cecal ligation and puncture. Am. J. Respir. Crit. Care Med. 162: 716-722 [Abstract/Free Full Text].

20. Pittet, J. F., L. N. Lu, D. G. Morris, K. Modelska, W. J. Welch, H. V. Carey, J. Roux, and M. A. Matthay. 2001. Reactive nitrogen species inhibit alveolar epithelial fluid transport after hemorrhagic shock in rats. J. Immunol. 166: 6301-6310 [Abstract/Free Full Text].

21. Kobayashi, H., R. Hataishi, H. Mitsufuji, M. Tanaka, M. Jacobson, T. Tomita, W. M. Zapol, and R. C. Jones. 2001. Antiinflammatory properties of inducible nitric oxide synthase in acute hyperoxic lung injury. Am. J. Respir. Cell Mol. Biol. 24: 390-397 [Abstract/Free Full Text].

22. Hickman-Davis, J., J. Gibbs-Erwin, J. R. Lindsey, and S. Matalon. 1999. Surfactant protein A mediates myocplasmacidal activity of alveolar macrophages by production of peroxynitrite. Proc. Natl. Acad. Sci. USA 96: 4953-4958 [Abstract/Free Full Text].

23. Ceneviva, G. D., E. Tzeng, D. G. Hoyt, E. Yee, A. Gallagher, J. F. Engelhardt, Y. M. Kim, T. R. Billiar, S. C. Watkins, and B. R. Pitt. 1998. Nitric oxide inhibits lipopolysaccharide-induced apoptosis in pulmonary artery endothelial cells. Am. J. Physiol. Lung Cell Mol. Physiol. 275: L717-L728 [Abstract/Free Full Text].

24. Steudel, W., F. Ichinose, P. L. Huang, W. E. Hurford, R. C. Jones, J. A. Bevan, M. C. Fishman, and W. M. Zapol. 1997. Pulmonary vasoconstriction and hypertension in mice with targeted disruption of endothelial nitric oxide synthase (NOS 3) gene. Circ. Res. 81: 31-41 .

25. Steudal, W., M. Scherrer-Crosbie, K. D. Bloch, J. Weimann, P. L. Huang, R. C. Jones, M. H. Picard, and W. M. Zapol. 1998. Sustained pulmonary hypertension and right ventricular hypertrophy after chronic hypoxia in mice with congenital deficiency of nitric oxide synthase 3.  J. Clin. Invest. 101: 2468-2477 [Medline].

26. Fagan, K. A., R. C. Tyler, K. Sato, B. W. Fouty, K. G. Morris, P. L. Huang, I. V. McMurtry, and D. M. Rodman. 1999. Relative contributions of endothelial, inducible and neuronal NOS to tone in the murine pulmonary circulation. Am. J. Physiol. Lung Cell Mol. Physiol. 277: L472-L478 [Abstract/Free Full Text].

27. Fagan, K. A., B. W. Fouty, R. C. Tyler, K. G. Morris, L. K. Hepler, K. Sato, T. D. LeCras, S. H. Abman, H. D. Weinberger, P. L. Huang, I. F. McMurtry, and D. M. Rodman. 1999. The pulmonary circulation of homozygous or heterozygous eNOS null mice is hyperresponsive to mild hypoxia. J. Clin. Invest. 103: 291-299 [Medline].

28. Fagan, K. A., B. Morrissey, B. W. Fouty, K. Sato, J. Wright, Harral, K. G. Morris Jr., M. Hoedt-Miller, S. Vidmar, I. F. McMurtry, and D. M. Rodman. 2001. Upregulation of nitric oxide synthase in mice with severe hypoxia-induced pulmonary hypertension. Respir. Res. 2: 306-313 . [Medline]

29. LeCras, T. D., C. Xue, A. Rengasamy, and R. A. Johns. Chronic hypoxia upregulates endothelial and inducible NO synthase gene and protein expression in rat lung. Am. J. Physiol. Lung Cell Mol. Physiol. 270:L164-L170.

30. Palmer, L. A., G. L. Semenza, M. H. Stoler, and R. A. Johns. 1998. Hypoxia induces type II NOS gene expression in pulmonary artery endothelial cells via HIF-1. Am. J. Physiol. Lung Cell Mol. Physiol. 274: L212-L219 [Abstract/Free Full Text].

31. Melillo, G., T. Musso, A. Sica, L. S. Taylor, G. W. Cox, and L. Varesio. 1995. A hypoxia-responsive element mediates a novel pathway of activation of the inducible nitric oxide synthase promoter. J. Exp. Med. 182: 1683-1693 [Abstract/Free Full Text].

32. Melillo, G., L. S. Taylor, A. Brooks, G. W. Cox, and L. Varesio. 1996. Regulation of inducible nitric oxide synthase expression in IFN-gamma treated murine macrophages cultured under hypoxic conditions. J. Immunol. 157: 2638-2644 [Abstract].

33. Melillo, G., L. S. Taylor, A. Brooks, T. Musso, G. W. Cox, and L. Varesio. 1997. Functional requirement of the hypoxia-responsive element in the activation of the inducible nitric oxide synthase promoter by the iron chelator desferroxamine. J. Biol. Chem. 272: 12236-12343 [Abstract/Free Full Text].

34. Rouet-Benzineb, P., S. Eddahibi, B. Raffestin, M. Laplace, S. Depond, S. Adnot, and B. Crozatier. 1999. Induction of cardiac nitric oxide synthase 2 in rats exposed to chronic hypoxia. J. Mol. Cell. Cardiol. 31: 1697-1708 [Medline].

35. Jung, F., L. A. Palmer, N. Zhou, and R. A. Johns. 2000. Hypoxic regulation of inducible nitric oxide synthase via hypoxia inducible factor-1 in cardiac myocytes. Circ. Res. 86: 319-325 [Abstract/Free Full Text].

36. You, Y., and C. Kaur. 2000. Expression of induced nitric oxide synthase in amoeboid microglia in postnatal rats following an exposure to hypoxia. Neurosci. Lett. 279: 101-104 [Medline].

37. Javeshghani, D., D. Sakkal, M. Mori, and S. N. A. Hussain. 2000. Regulation of diaphragmatic nitric oxide synthase expression during hypobaric hypoxia. Am. J. Physiol. Lung Cell Mol. Physiol. 279: L520-L527 [Abstract/Free Full Text].

38. Jung, F., L. A. Palmer, N. Zhou, and R. A. Johns. 2000. Hypoxic regulation of inducible nitric oxide synthase via hypoxia inducible factor-1 in cardiac myocytes. Circ. Res. 86: 319-325 .

39. Chen, H., D. Li, T. Saldeen, and J. L. Mehta. 2001. TGF-1 modulates NOS expression and phosphorylation of Akt/PKB pathway in rat myocytes exposed to hypoxia-reoxygenation. Am. J. Physiol. Heart Circ. Physiol. 281: H1035-H1039 [Abstract/Free Full Text].

40. Kacimi, R., C. S. Long, and J. S. Karliner. 1997. Chronic hypoxia modulates the interleukin-1 beta stimulated inducible nitric oxide synthase pathway in cardiac myocytes. Circulation 96: 1937-1944 [Abstract/Free Full Text].

41. Inoue, T., A. H. Kwon, M. Oda, M. Kaibori, Y. Kamiyama, M. Nishizawa, S. Ito, and T. Okumura. 2000. Hepatology 32: 1037-1044 [Medline].

42. Vargiu, C., S. Belliardo, C. Cravanzola, M. A. Grillo, and S. Colombatto. 2000. Oxygen regulation of rat hepatocyte iNOS gene expression. J. Hepatol. 32: 567-573 [Medline].

43. Berge, D. L., M. D. Ridder, V. N. Verovski, M. Y. Janssens, C. Monsaert, and G. A. Storme. 2001. Chronic hypoxia modulates tumour cell radioresponse through cytokine inducible nitric oxide synthase. Br. J. Cancer 84: 1122-1129 [Medline].

44. Archer, S. L., K. A. Freude, and P. J. Schultz. 1995. Effect of graded hypoxia on the induction and function of inducible nitric oxide synthase in rat mesangial cells. Circ. Res. 77: 21-28 [Abstract/Free Full Text].

45. Hong, Y., S. Suzuki, S. Yatoh, M. Mizutani, T. Nakajima, S. Bannai, H. Sota, M. Soma, Y. Okuda, and N. Yamada. 2000. Effect of hypoxia on nitric oxide production and its synthase gene expression in rat smooth muscle cells. Biochem. Biophys. Res. Commun. 268: 329-332 [Medline].

46. McCormick, C. C., W. P. Li, and M. Calero. 2000. Oxygen tension limits nitric oxide synthesis by activated macrophages. Biochem. J. 350: 709-716 .

47. Ferriero, C. R., A. C. Chagas, M. H. Carvahallo, A. P. Dantas, M. B. Jatene, L. C. Bento, DeSouza, P. Lemos, and da luz. 2001. Influence of hypoxia on nitric oxide synthase activity and gene expression in children with congenital heart disease: a novel pathophyisological adaptive mechanism Circul. 103: 2272-2278 . [Abstract/Free Full Text]

48. Beall, C. M., D. Laskowski, K. P. Strohl, R. Soria, M. Villena, E. Vargas, A. M. Alarcon, C. Gonzales, and S. C. Erzurum. 2001. Pulmonary nitric oxide in mountain dwellers. Nature 414: 411-412 [Medline].

49. Busch, T., P. Bartsch, D. Pappert, E. Grunig, W. Hildebrandt, H. Elser, K. J. Falke, and E. R. Swenson. 2001. Hypoxia decreases exhaled nitric oxide in mountaineers susceptible to high altitude pulmonary edema. Am. J. Respir. Crit. Care Med. 163: 368-373 [Abstract/Free Full Text].

50. Dweik, R. A., D. Laskowski, H. M. Abu-Soud, F. Kaneko, R. Hutte, D. J. Stuehr, and S. C. Erzurum. 1998. Nitric oxide synthesis in the lung: regulation by oxygen through a kinetic mechanism. J. Clin. Invest. 101: 660-666 [Medline].

51. Lowenstein, C. J., E. W. Alley, P. Raval, A. M. Snowman, S. H. Snyder, S. W. Russell, and W. J. Murphy. 1993. Macrophage nitric oxide synthase gene: two upstream regions mediate induction by interferon gamma and lipopolysaccharide. Proc. Natl. Acad. Sci. USA 90: 9730-9734 [Abstract/Free Full Text].

52. Taylor, B. S., M. E. deVera, R. W. Ganster, Q. Wang, R. A. Shapiro, S. M. Morris Jr., T. R. Billiar, and D. A. Geller. 1998. Multiple NF-kB enhancer elements regulate cytokine induction of the human inducible nitric oxide synthase gene. J. Biol. Chem. 273: 15148-15156 [Abstract/Free Full Text].

53. Saura, M., C. Zaragoza, C. Bao, A. McMillan, and C. J. Lowenstein. 1999. Interaction of interferon regulatory factor-1 and nuclear factor kB during activation of inducible nitric oxide synthase transcription. J. Mol. Biol. 289: 459-471 [Medline].

54. Tendler, D. S., C. Bao, T. Wang, E. L. Huang, E. A. Ratovitski, D. A. Pardoll, and C. J. Lowenstein. 2001. Intersection of interferon and hypoxia signal transduction pathways in nitric oxide induced tumor apoptosis. Canc. Res. 61: 3682-3688 [Abstract/Free Full Text].

55. DeVera, M. E., R. A. Shapiro, A. K. Nussler, J. S. Mudgett, R. L. Simmons, S. M. Morris Jr., T. R. Billiar, and D. A. Geller. 1996. Transcriptional regulation of human inducible nitric oxide synthase (NOS2) gene by cytokines: initial analysis of the human NOS2 promoter. Proc. Natl. Acad. Sci. USA 93: 1054-1059 [Abstract/Free Full Text].

56. Ganster, R. W., B. S. Taylor, L. Shao, and D. A. Geller. 2001. Complex regulation of human inducible nitric oxide synthase gene transcription by Stat 1 and NF-kB. Proc. Natl. Acad. Sci. USA 98: 8638-8643 [Abstract/Free Full Text].

57. Mellott, J. K., H. S. Nick, M. F. Waters, T. R. Billiar, D. A. Geller, and S. E. Chesrown. 2001. Cytokine-induced changes in chromatin structure and in vivo footprints in the inducible NOS promoter. Am. J. Physiol. Lung Cell Mol. Physiol. 280: L390-L399 [Abstract/Free Full Text].

58. Levy, N. S., S. Chung, H. Furneaux, and A. P. Levy. 1998. Hypoxic stabilization of vascular endothelial growth factor mRNA by the RNA binding protein HuR. J. Biol. Chem. 273: 6417-6423 [Abstract/Free Full Text].

59. Rodriguez-Pascual, F., M. Hausding, I. Thrig-Biedert, H. Furneaux, A. P. Levy, U. Forstermann, and H. Kleinert. 2000. Complex contribution of the 3'-untranslated region to the expressional regulation of the human inducible nitric oxide synthase gene. J. Biol. Chem. 275: 26040-26049 [Abstract/Free Full Text].