Heme oxygenase-1 (HO-1), the rate-limiting enzyme in heme degradation, is an integral membrane protein of the smooth endoplasmic reticulum. However, we detected an HO-1 immunoreactive signal in the nucleus of cultured cells after exposure to hypoxia and heme or heme/hemopexin. Under these conditions, a faster migrating HO-1 immunoreactive band was enriched in nuclear extracts, suggesting that HO-1 was cleaved to allow nuclear entry. This was confirmed by the absence of immunoreactive signal with an antibody against the C terminus and the lack of a C-terminal sequence by gas chromatographymass spectrometry. Incubation with leptomycin B prior to hypoxia abolished nuclear HO-1 and the faster migrating band on Western analysis, suggesting that this process was facilitated by CRM1. Furthermore, preincubation with a cysteine protease inhibitor prevented nuclear entry of green fluorescent proteinlabeled HO-1, demonstrating that protease-mediated C-terminal cleavage was also necessary for nuclear transport of HO-1. Nuclear localization was also associated with reduction of HO activity. HO-1 protein, whether it was enzymatically active or not, mediated activation of oxidant-responsive transcription factors, including activator protein-1. Nevertheless, nuclear HO-1 protected cells against hydrogen peroxide-mediated injury equally as well as cytoplasmic HO-1. We speculate that nuclear localization of HO-1 protein may serve to up-regulate genes that promote cytoprotection against oxidative stress.Heme oxygenase (HO) 3 catalyzes the degradation of heme and the formation of biliverdin and carbon monoxide. It is highly inducible in response to various stimuli, including oxidative stress, heavy metals, UV radiation, and inflammation (1-4). Cytoprotective roles for HO have been demonstrated in many models; however, the mechanisms by which this occurs are still under intensive study. Many have speculated that either heme catabolites, such as biliverdin, or its derivative, bilirubin, and carbon monoxide or the degradation of the pro-oxidant heme results in cytoprotection against oxidative stress (5-7). Nevertheless, all of the by-products of the HO reaction, despite being potentially cytoprotective, are also cytotoxic. Bilirubin is a potent neurotoxin (8), as is carbon monoxide (9). Furthermore, the HO reaction releases iron, which could interact with cellular oxidants to generate the hydroxyl radical (10). Transfection with an inactive HO-1 mutant protein results in cytoprotection against chemically induced oxidative stress (11). Because this effect of the mutant HO-1 could not be attributable to changes in heme catabolites, it alludes to a role for the HO-1 protein itself. Furthermore, the inactive form of HO-1 increased catalase and glutathione content (11). This suggests that the HO-1 protein itself may play a role in cellular signaling. If this were true, HO-1 would need to migrate to the nucleus or produce nuclear changes that affect transcription. There are several examples of cytoplasmic enzymes serving in nuclear functi...

Hyperoxic exposure can disrupt alveolarization by inhibiting cell growth; however, it is not fully understood how this is mediated. The transcription factor CCAAT/enhancer binding protein-␣ (C/EBP␣) is highly expressed in the lung and plays a role in cell proliferation and differentiation in many tissues. After 72 h of hyperoxia, C/EBP␣ expression was significantly enhanced in the lungs of newborn mice. The increased C/EBP␣ protein was predominantly located in alveolar type II cells. Silencing of C/EBP␣ with a transpulmonary injection of C/EBP␣ small interfering RNA (siRNA) prior to hyperoxic exposure reduced expression of markers of type I cell and differentiation typically observed after hyperoxia but did not rescue the altered lung morphology at 72 h. Nevertheless, when C/EBP␣ hyperoxia-exposed siRNA-injected mice were allowed to recover for 2 wk in room air, lung epithelial cell proliferation was increased and lung morphology was restored compared with hyperoxia-exposed control siRNAinjected mice. These data suggest that C/EBP␣ is an important regulator of postnatal alveolar epithelial cell proliferation and differentiation during injury and repair.CCAAT/enhancer binding protein-␣; developing lung injury; small interfering RNA; recovery POSTNATAL LUNG DEVELOPMENT involves a series of coordinated events, including active cell proliferation and differentiation, to promote proper alveolar formation. Parenchymal lung cells, fibroblasts, endothelial cells, and epithelial type II cells have distinct growth patterns and specific proliferation rates, beginning in the neonatal period (9). Imbalance of growth factors, inflammatory insults, and oxidative stress (reviewed in Ref. 16) could alter these processes, resulting in impaired lung development. Hyperoxic exposure is well known for disrupting alveolarization in the developing lung, because it inhibits the growth of epithelial, fibroblast, and endothelial cells forming the alveoli (5,19). Several studies have demonstrated that hyperoxia results in alveolar growth arrest, induction of cell cycle inhibitory proteins (13), altered surfactant protein (SP) production (reviewed in Ref. 4), and disrupted extracellular matrix signaling (1). The effect of hyperoxia on the proliferation of specific lung cell types is not well defined.The transcription factor CCAAT/enhancer binding protein (C/EBP) family consists of six isoforms. C/EBP␣ is highly expressed in the lung (6) and plays a role in cell proliferation and differentiation in various tissues (17,18), as do C/EBP␤ and C/EBP␦. Given that the newborn lung proliferates and differentiates rapidly, we hypothesized that C/EBP␣ regulates neonatal lung cell proliferation in hyperoxia and during recovery.Here, we demonstrate that C/EBP␣ expression was enhanced in lungs of newborn mice after 72 h of hyperoxia. The increased C/EBP␣ protein was predominantly localized to alveolar type II cells, where altered proliferation was observed. Silencing of C/EBP␣ with a single injection of C/EBP␣ small interfering RNA (siRNA) prior to expo...

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Erinacines E (I), F (II), and G (III), Stimulators of Nerve Growth Factor (NGF)-Synthesis, from the Mycelia of Hericium erinaceum. --(KAWAGISHI, H.; SHIMADA, A.; HOSOKAWA, S.; MORI, H.; SAKAMOTO, H.; ISHIGURO, Y.; SAKEMI, S.; BORDNER, J.; KOJIMA, N.; FURUKAWA, S.; Tetrahedron Lett. 37 (1996) 41, 7399-7402; Dep. Appl. Biol.