Physiological polyamines are ubiquitous polycations with pleiotropic biochemical activities, including regulation of gene expression, cell proliferation and modulation of cell signalling. Reports that the polyamines with cytoprotective activities were induced by diverse stresses raised the hypothesis that physiological polyamines may play a role in inducing stress response. In a wide range of organisms, physiological polyamines were not only induced by diverse stresses, such as reactive oxygen species (ROS), heat, ultraviolet (UV) and psychiatric stress but were able to confer beneficial effects for survival. Recent biochemical and genetic evidences show that polyamines can function as an ROS scavenger, acid tolerance factor and chemical chaperone, and positive regulators for expression of stress response genes which may explain their protective functions against diverse stresses. Taken together, these data suggest that physiological polyamines can function as primordial stress molecules in bacteria, plants and mammals, and may play an essential role in regulation of pathogen-host interactions.
Annexin I (also called lipocortin 1) is a 37-kDa member of the annexin family of proteins. It has been proposed to be involved in the regulation of cell growth and differentiation, apoptosis, and inflammation. Previously, we have reported that annexin I displays a chaperone-like function (Kim, G.Y., Lee, H.B., Lee, S.O., Rhee, H.J. & Na, D.S. (1997) Biochem. Mol. Biol. Int. 43, 521-528). To determine the possibility that annexin I is a stress protein, we examined whether expression of annexin I and annexin I mRNA increases in response to stresses in A549 and HeLa cells. Treatments of cells with heat, hydrogen peroxide or sodium arsenite resulted in (a) an increase in annexin I and annexin I mRNA and (b) translocation of annexin I from the cytoplasm to the nucleus and perinuclear region. The annexin I gene promoter region, cloned upstream of a reporter gene, was inducible in response to heat, hydrogen peroxide, and sodium arsenite. These results indicate that annexin I serves as a stress protein and annexins may constitute a new class of stress proteins.
Mammalian secretory phospholipases A 2 (sPLA 2 ) have been implicated in cellular eicosanoid biosynthesis but the mechanism of their cellular action remains unknown. To elucidate the spatiotemporal dynamics of sPLA 2 mobilization and determine the site of its lipolytic action, we performed time-lapse confocal microscopic imaging of fluorescently labeled sPLA 2 acting on human embryonic kidney (HEK) 293 cells the membranes of which are labeled with a fluorogenic phospholipid, N-((6-(2,4-dinitrophenyl)amino)hexanoyl)-1-hexadecanoyl-2-(4,4-difluoro-5,7-dimethyl-4-bora-3a,4a-diaza-s-indacene-3-pentanoyl)-sn-glycero-3-phosphoethanolamine. The Western blotting analysis of HEK293 cells treated with exogenous sPLA 2 s showed that not only the affinity for heparan sulfate proteoglycan but also other factors, such as sPLA 2 hydrolysis products or cytokines, are necessary for the internalization of sPLA 2 into HEK293 cells. Live cell imaging showed that the hydrolysis of fluorogenic phospholipids incorporated into HEK293 cell membranes was synchronized with the spatiotemporal dynamics of sPLA 2 internalization, detectable initially at the plasma membrane and then at the perinuclear region. Also, immunocytostaining showed that human group V sPLA 2 induced the translocation of 5-lipoxygenase to the nuclear envelope at which they were co-localized. Together, these studies provide the first experimental evidence that the internalized sPLA 2 acts on the nuclear envelope to provide arachidonate for other enzymes involved in the eicosanoid biosynthesis.
Chlorophyllide a reductase of Rhodobacter sphaeroides, which were reconstituted with the purified subunits of BchX, BchY, and BchZ, reduced ring B of chlorophyllide a using NADH under anaerobic conditions. Interestingly, suppressor mutations rescuing the inability of R. sphaeroides Fe-SOD mutant to grow in succinate-based minimal medium were predominantly mapped to BchZ subunit of chlorophyllide a reductase. The enzyme is labile in the presence of O 2 . However, it generates superoxide at low O 2 . The enzymes reconstituted with BchX, BchY, and the mutein subunit of BchZ from suppressor mutants showed less activity not only for chlorophyllide a reduction but also for superoxide generation compared with the enzyme reconstituted with the wild-type subunits. BchX, which contains FMN, and BchY are iron-sulfur proteins, whereas BchZ is a hemoprotein containing b-type heme. Neither chlorophyllide a reduction nor superoxide generation was observed with the enzyme reconstituted with the wild-type subunits of BchX and BchY, and the apo-subunit of BchZ that had been refolded without heme, in which FMN of BchX was fully reduced. Thus, superoxide is generated not from FMN of BchX but from heme of BchZ. Consistently, the heme of BchZ muteins was half-reduced in its redox state compared with that of wild-type BchZ.Rhodobacter sphaeroides, a facultative photosynthetic bacterium, contains two SODs 3 ; CuZn-SOD is detected only under the conditions where photosynthetic complexes are formed (1), whereas Fe-SOD is constitutively expressed, although its activity of the aerobically grown cell nearly doubled as compared with that of the anaerobically grown cell. The role of CuZn-SOD in protecting the photoheterotrophic cells from periplasmic superoxide upon exposure to O 2 was proposed (1). A cambialistic SOD using manganese or iron is the only SOD found in Rhodobacter capsulatus and is essential for cell viability (2, 3). Oxidative stress defense in R. sphaeroides and R. capsulatus is also mediated by catalases as well as by glutathione-glutaredoxin and thioredoxin systems that act as thiol-disulfide redox buffer to reduce the protein thiols that were oxidized (4, 5). Mutations in glutathione-glutaredoxin and thioredoxin systems lowered the formation of the photosynthetic complex (4, 5).The formation of photosynthetic complexes of R. sphaeroides is redox-dependent. Lowering oxygen tension induces the formation of intracytoplasmic membrane housing the photosynthetic complexes of R. sphaeroides. Light captured by B800 -850 and B875 LH complexes is transferred to reaction center complex, where the redox reactions are initiated to convert light energy into ATP and reducing power. The oxygenregulated expression of apoproteins of LH and reaction center complexes, which are encoded by puc, puf, and puh operons, was elucidated (for reviews see Refs. 6 and 7).The expression of several enzymes for Bchl a synthesis is also subject to anaerobic induction (8 -10). Protoporphyrin IX, which is synthesized from 5-aminolevulinic acid, is a common in...
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