Yu Y et al. (2000) Mol Cell Biol "Architectural transcription factors and the SAGA complex function in parallel pathways to activate transcription."

Yu Y, Eriksson P, Stillman DJ

[Mol Cell Biol, 2000]

Recent work has shown that transcription of the yeast HO gene involves the sequential recruitment of a series of transcription factors. We have performed a functional analysis of HO regulation by determining the ability of mutations in SIN1, SIN3, RPD3, and SIN4 negative regulators to permit HO expression in the absence of certain activators. Mutations in the SIN1 (=SPT2) gene do not affect HO regulation, in contrast to results of other studies using an HO:lacZ reporter, and our data show that the regulatory properties of an HO:lacZ reporter differ from that of the native HO gene. Mutations in SIN3 and RPD3, which encode components of a histone deacetylase complex, show the same pattern of genetic suppression, and this suppression pattern differs from that seen in a sin4 mutant. The Sin4 protein is present in two transcriptional regulatory complexes, the RNA polymerase II holoenzyme/mediator and the SAGA histone acetylase complex. Our genetic analysis allows us to conclude that Swi/Snf chromatin remodeling complex has multiple roles in HO activation, and the data suggest that the ability of the SBF transcription factor to bind to the HO promoter may be affected by the acetylation state of the HO promoter. We also demonstrate that the Nhp6 architectural transcription factor, encoded by the redundant NHP6A and NHP6B genes, is required for HO expression. Suppression analysis with sin3, rpd3, and sin4 mutations suggests that Nhp6 and Gcn5 have similar functions. A gcn5 nhp6a nhp6b triple mutant is extremely sick, suggesting that the SAGA complex and the Nhp6 architectural transcription factors function in parallel pathways to activate transcription. We find that disruption of SIN4 allows this strain to grow at a reasonable rate, indicating a critical role for Sin4 in detecting structural changes in chromatin mediated by Gcn5 and Nhp6. These studies underscore the critical role of chromatin structure in regulating HO gene expression.

Fu X et al. (2015) Biochem Biophys Res Commun "An oxidative fluctuation hypothesis of aging generated by imaging HO levels in live Caenorhabditis elegans with altered lifespans."

Dickinson BC, Chang Z, Chang CJ, Tang Y, Fu X

[Biochem Biophys Res Commun, 2015]

Reactive oxygen species (ROS) are important factors mediating aging according to the free radical theory of aging. Few studies have systematically measured ROS levels in relationship to aging, partly due to the lack of tools for detection of specific ROS in live animals. By using the HO-specific fluorescence probe Peroxy Orange 1, we assayed the HO levels of live Caenorhabditis elegans with 41 aging-related genes being individually knocked down by RNAi. Knockdown of 14 genes extends the lifespan but increases HO level or shortens the lifespan but decreases HO level, contradicting the free radical theory of aging. Strikingly, a significant inverse correlation between lifespan and the normalized standard deviation of HO levels was observed (p < 0.0001). Such inverse correlation was also observed in worms cultured under heat shock conditions. An oxidative fluctuation hypothesis of aging is thus proposed and suggests that the ability of animals to homeostatically maintain the ROS levels within a narrow range is more important for lifespan extension than just minimizing the ROS levels though the latter still being crucial.

Loboda A et al. (2016) Cell Mol Life Sci "Role of Nrf2/HO-1 system in development, oxidative stress response and diseases: an evolutionarily conserved mechanism."

Damulewicz M, Dulak J, Jozkowicz A, Loboda A, Pyza E

[Cell Mol Life Sci, 2016]

The multifunctional regulator nuclear factor erythroid 2-related factor (Nrf2) is considered not only as a cytoprotective factor regulating the expression of genes coding for anti-oxidant, anti-inflammatory and detoxifying proteins, but it is also a powerful modulator of species longevity. The vertebrate Nrf2 belongs to Cap 'n' Collar (Cnc) bZIP family of transcription factors and shares a high homology with SKN-1 from Caenorhabditis elegans or CncC found in Drosophila melanogaster. The major characteristics of Nrf2 are to some extent mimicked by Nrf2-dependent genes and their proteins including heme oxygenase-1 (HO-1), which besides removing toxic heme, produces biliverdin, iron ions and carbon monoxide. HO-1 and their products exert beneficial effects through the protection against oxidative injury, regulation of apoptosis, modulation of inflammation as well as contribution to angiogenesis. On the other hand, the disturbances in the proper HO-1 level are associated with the pathogenesis of some age-dependent disorders, including neurodegeneration, cancer or macular degeneration. This review summarizes our knowledge about Nrf2 and HO-1 across different phyla suggesting their conservative role as stress-protective and anti-aging factors.

Gotenstein, J.R. et al. (2017) International Worm Meeting "Genetic suppression of basement membrane defects in C. elegans."

Ho, T.W., Gotenstein, J.R., Koo, C.C., Chisholm, A.D.

[International Worm Meeting, 2017]

Basement membranes are evolutionarily ancient conserved structures that support tissue growth, development, and function. We have previously reported that two basement membrane proteins, Peroxidasin/PXN-2 and F-spondin/SPON-1, are essential for epidermal elongation in C. elegans (Gotenstein, et al. Development. 2010; Woo, et al Development. 2008). We performed large-scale forward genetic screens for suppression of embryonic lethality in pxn-2 or spon-1 mutant backgrounds. F-spondins are conserved ECM proteins whose mechanisms remain unclear. Peroxidasins are extracellular peroxidases thought to catalyze sulfilimine cross-linking of collagen IV in the basement membrane (Bhave, et al. Nat Chem Biol. 2012); genetic interactions between collagen IV and pxn-2 mutants support this role for pxn-2 in C. elegans. Complete loss of function of PXN-2 causes nonconditional lethality and arrest in late embryogenesis. We report that such pxn-2 null mutant phenotypes can be suppressed to viability by gain of function mutations in a variety of extracellular matrix or cell-matrix receptor proteins. We identified over 30 suppressors, 12 of which result in missense alterations in the transmembrane protein myotactin/LET-805. The LET-805 extracellular domain contains 36 Fibronectin type III repeats; our suppressor mutations cluster in two pairs of repeats, suggesting these repeats may play a critical role in LET-805 function. let-805 null mutants are nonconditional embryonic lethal, whereas our suppressors are viable and display no obvious phenotypes other than suppression. Localization of a LET-805::GFP knockin is essentially normal in the suppressor alleles, suggesting they have a subtle effect on LET-805 expression. let-805 suppressor alleles partially suppress lethality in loss of function but not null mutations in other basement membrane components, but do not suppress loss of function in intracellular epidermal cytoskeletal components. pxn-2 mutants have defects in locomotion that are not suppressed by let-805, and we will report our analysis of this possible neural role for PXN-2. . In summary, our results reveal novel compensatory mechanisms in basement membrane receptor complexes that allow key structural or enzymatic components to be bypassed.

Way JC et al. (1994) Bioessays "Cell polarity and the mechanism of asymmetric cell division."

Hung M-S, Run JQ, Way JC, Wang LL

[Bioessays, 1994]

During development, one mechanism for generating different cell types is asymmetric cell division, by which a cell divides and contributes different factors to each of its daughter cells. Asymmetric cell division occurs throughout the eukaryotic kingdom, from yeast to humans. Many asymmetric cell divisions occur in a defined orientation. This implies a cellular mechanism for sensing direction, which must ultimately lead to differences in gene expression between two daughter cells. In this review, we describe two classes of molecules: regulatory factors that are differentially expressed upon asymmetric cell division, and components of a signal transduction pathway that may define cell polarity. The lin-11 and mec-3 genes of C. elegans, the Isl-1 gene of mammals and the HO gene of yeast, encode regulatory factors that determine cell type of one daughter after asymmetric cell division. The CDC24 and CDC42 genes of yeast affect both bud positioning and orientation of mating projections, and thus may define a general cellular polarity. We speculate that molecules such as Cdc24 and Cdc42 may regulate expression of genes such as lin-11, mec-3, Isl-1 and HO upon asymmetric cell division.

Park J et al. (2020) Free Radic Res "CO ameliorates cellular senescence and aging by modulating the miR-34a/Sirt1 pathway."

Joe Y, Park JW, Chung HT, Chen Y, Surh YJ, Song HC, Zheng M, Kim UH, Park J, Kim J

[Free Radic Res, 2020]

Oxidative stress is recognised as a key factor that can lead to cellular senescence and aging. Carbon monoxide (CO) is produced by haemoxygenase-1 (HO-1), which exerts cytoprotective effects in aging-related diseases, whereas the effect of CO on cellular senescence and aging has not been elucidated. In the current study, we clearly demonstrated that CO delays the process of cellular senescence and aging through regulation of miR-34a and Sirt1 expression. CO reduced H₂O₂-induced premature senescence in human diploid fibroblast WI-38 cells measured with SA--Gal-staining. Furthermore, CO significantly decreased the expression of senescence-associated secretory phenotype (SASP), including TNF- IL-6, and PAI-1 and increased the transcriptional levels of antioxidant genes, such as HO-1 and NQO1. Moreover, CO apparently enhanced the expression of Sirt1 through down-regulation of miR-34a. Next, to determine whether Sirt1 mediates the inhibitory effect of CO on cellular senescence, we pre-treated WI-38 cells with the Sirt1 inhibitor Ex527 and a miR-34a mimic followed by the administration of H₂O₂ and evaluated the expression of SASP and antioxidant genes as well as ROS production. According to our results, Sirt1 is crucial for the antiaging and antioxidant effects of CO. Finally, CO prolonged the lifespan of Caenorhabditis <i>elegans</i> and delayed high-fat diet-induced liver aging. Taken together, these findings demonstrate that CO reduces cellular senescence and liver aging through the regulation of miR-34a and Sirt1.

Okano H et al. (2000) Japanese Worm Meeting "The SWI/SNF complex is required for asymmetric cell division in C. elegans"

Kouike H, Sawa H, Okano H

[Japanese Worm Meeting, 2000]

In C. elegans, the polarities of many cells undergoing asymmetric divisions are regulated by LIN-44/Wnt and LIN-17/Frizzled. To identify more genes required for asymmetric division, we are screening for mutants affecting the asymmetric division of the T cell in the tail that is regulated by lin-17 and lin-44. We have so far identified 17 new mutants corresponding to 13 different genes. Lineage analyses have shown that the T cell division can be symmetric in mutants of at least 7 of the genes (psa-1 through psa-7). Using temperature-sensitiveness of the psa-1 and psa-4 mutant, we found that these genes are required during the mitosis of the T cell. We have cloned psa-1 and psa-4 to found that they encode homologs of SWI3 and SWI2 of yeast, respectively. These proteins are known to be components of the complex called SWI/SNF. The complex can remodel chromatin structure by destabilizing histone-DNA interaction. These results suggest that the chromatin structure is altered by the SWI/SNF complex in one of the daughter cells during the T cell division. In budding yeast, the SWI/SNF complex is required for the asymmetric expression of HO endonuclease in the mother but not in the daughter cell. HO catalyzes switching of the mating types in the mother cell. Therefore, our findings demonstrate that at least some aspects of the mechanisms of asymmetric cell division are conserved between yeast and a multicellular organism.

Williams, Kyle C. et al. (2011) International Worm Meeting "Essential Functions of IFA-2 Domains in C. elegans Fibrous Organelles."

Plenefisch, John, Williams, Kyle C.

[International Worm Meeting, 2011]

The C. elegans fibrous organelle (FO) complex consists of apical and basal hemidesmosomes linked by cytoplasmic intermediate filaments (IFs). FOs are found most prominently in the epidermis where they overlie body wall muscle and serve to transmit force from the muscle to the cuticle. IFA-2, one of four epidermally expressed IFs whose loss results in epidermal fragility and failure of muscle-cuticle force transmission, localizes to FOs. Unlike IFB-1 and IFA-3 that are required embryonically, IFA-2, although expressed in the embryo, is not essential for FO function until postembryonic stages. This distinctive phenotype allows us to specifically explore the functions of IFA-2 domains, and map their interactions with other FO associated proteins. All IFs contain three domains: a central rod domain and globular head and tail domains. The rod is essential for assembly of IFs into mature filaments while less is known about the functions of the head and tail domains. Roles of the head and tail domains of IFA-2 were examined by expressing GFP-tagged IFA-2 variants in transgenic animals and examining their phenotype and localization in wild-type and null backgrounds. Mutant variants included IFA-2 deleted for the head domain (DH), deleted for the tail domain (DT), deleted for both (RO), and variants that contained only the head domain (HO) or tail domain (TO). The expression and function of DH is virtually indistinguishable from full-length IFA-2. DT results in a lowered incorporation of IFA-2 into FOs and is unable to rescue a null allele of ifa-2, suggesting the tail domain is essential to IFA-2 function. Though both HO and TO are expressed well in the hypodermis at all stages, incorporation into FOs is variable between individual animals. High levels of early-stage HO incorporation into FOs correlate with a dominant-negative muscle detachment phenotype, while low-level incorporation results in healthy animals. This suggests the head domain interacts with FO components essential to tissue integrity. To determine the protein components of the FOs that interact with the head and tail domains, yeast two-hybrid and co-localization experiments are in progress. This work should help to elucidate the role of IFA-2 in FO function and reveal the underlying defects leading to tissue fragility.

Yan F et al. (2017) J Agric Food Chem "Effects of C-glycosides from Apios americana leaves against oxidative stress during hyperglycemia through regulating MAPKs and Nrf2."

Yu L, Yan F, Yang Y, Zheng X

[J Agric Food Chem, 2017]

Main components of Apios americana leaves extract (ALE) were flavonoid C-glycosides including vitexin (46.7%), schaftoside (18.9%) and orientin (4.32%). In vitro, ALE restored glucose consumption, glucose uptake and glycogen content in glucose-induced hepatic cells. Exposure of HepG2 cells to high glucose resulted in ROS and O2- accumulation, while ALE alleviated these increases by 47 +/- 0.68% and 68 +/- 0.74% respectively. Glucose increased JNK and decreased ERK1/2 and p38 phosphorylation, while ALE reduced p-JNK and p-p38 but not p-ERK1/2, accompanied by Nrf2, HO-1 and NQO1 down-regulation. In vivo, lifespan of Caenorhabditis elegans was more violently shortened by paraquat under hyperglycemia while ALE protected this damage in N2 worms (2.6 times extension) but not in daf-16 mutants. Furthermore, p38/PMK-1 and Nrf2/SKN-1 expressions in worms were suppressed by glucose, which were reversed by ALE treatment. These results suggest that ALE prevents glucose-induced damage via regulating specific MAPKs and Nrf2 pathways.

Chritton JJ et al. (2011) J Biol Chem "A role for the poly(A)-binding protein Pab1p in PUF protein-mediated repression."

Chritton JJ, Wickens M

[J Biol Chem, 2011]

PUF proteins regulate translation and mRNA stability throughout eukaryotes. Using a cell-free translation assay, we examined the mechanisms of translational repression of PUF proteins in the budding yeast Saccharomyces cerevisiae. We demonstrate that the poly(A)-binding protein Pab1p is required for PUF-mediated translational repression for two distantly related PUF proteins: S. cerevisiae Puf5p and Caenorhabditis elegans FBF-2. Pab1p interacts with oligo(A) tracts in the HO 3'-UTR, a target of Puf5p, to dramatically enhance the efficiency of Puf5p repression. Both the Pab1p ability to activate translation and interact with eukaryotic initiation factor 4G (eIF4G) were required to observe maximal repression by Puf5p. Repression was also more efficient when Pab1p was bound in close proximity to Puf5p. Puf5p may disrupt translation initiation by interfering with the interaction between Pab1p and eIF4G. Finally, we demonstrate two separable mechanisms of translational repression employed by Puf5p: a Pab1p-dependent mechanism and a Pab1p-independent mechanism.