To survive in hypoxic environments, organisms must be able to cope with redox imbalance and oxygen deficiency. The SIRT1 deacetylase and the HIF-1alpha transcription factor act as redox and oxygen sensors, respectively. Here, we found that SIRT1 binds to HIF-1alpha and deacetylates it at Lys674, which is acetylated by PCAF. By doing so, SIRT1 inactivated HIF-1alpha by blocking p300 recruitment and consequently repressed HIF-1 target genes. During hypoxia, SIRT1 was downregulated due to decreased NAD(+) levels, which allowed the acetylation and activation of HIF-1alpha. Conversely, when the redox change was attenuated by blocking glycolysis, SIRT1 was upregulated, leading to the deacetylation and inactivation of HIF-1alpha even in hypoxia. In addition, we confirmed the SIRT1-HIF-1alpha interaction in hypoxic mouse tissues and observed in vivo that SIRT1 has negative effects on tumor growth and angiogenesis. Our results suggest that crosstalk between oxygen- and redox-responsive signal transducers occurs through the SIRT1-HIF-1alpha interaction.

Arrest defective 1 (ARD1), an acetyltransferase, is essential for the yeast life cycle. Although its human homologue (hARD1) has been identified, its biological functions in human cells remain unclear. In the present study, we examined the biological function of hARD1. In H1299 and A549 lung cancer cells, hARD1-silencing RNA inhibited cell proliferation and induced G 1 arrest. Cyclin D1 was also found to be downregulated in these growth-arrested cells, and the ectopic expression of cyclin D1 rescued cell growth. hARD1 knockdown repressed the promoter activity of the cyclin D1 gene, which inhibited the transcription of cyclin D1. Moreover, hARD1 knockdown reduced the binding of B-catenin/TCF4 transcription factor to cyclin D1 promoter and repressed its transcriptional activity. Inversely, hARD1 expression increased the transcriptional activity of B-catenin. Both endogenous and ectopically expressed hARD1 was coimmunoprecipitated with B-catenin. hARD1 knockdown did not affect B-catenin expression or degradation but noticeably reduced acetylated B-catenin. The B-catenin binding and acetylation by hARD1 were observed in vitro. Therefore, it is suggested that hARD1 participates in proliferation of lung cancer cells via the activation of

Hypoxia-inducible factor-1 (HIF-1) is composed of HIF-1alpha and HIF-1beta, and is a master regulator of oxygen homeostasis, playing critical roles in physiological and pathological processes. Normally, the formation and transcriptional activity of HIF-1 depend on the amount of HIF-1alpha, and the expression of HIF-1alpha is tightly controlled by the cellular oxygen tension. Recent progress in the study of its regulation mechanism provided clues as to how HIF-1alpha is regulated by oxygen. It appears that HIF-1alpha is not regulated only by the oxygen tension, but also by various other stimuli, such as transition metals, nitric oxide, reactive oxygen species, growth factors, and mechanical stresses. In this review, we summarize the oxygen-dependent and -independent regulation of HIF-1alpha, and the respective physiological and pathological meanings.

Bortezomib (PS-341), a proteasome inhibitor, has been examined clinically for the treatment of multiple myeloma and several solid tumors. Bortezomib directly induces tumor cell death and has also been reported to inhibit tumor adaptation to hypoxia by functionally inhibiting hypoxia-inducible factor-1␣ (HIF-1␣). However, the mechanism underlying HIF-1 inhibition by bortezomib remains obscure. In the present study, we demonstrated that bortezomib attenuated the hypoxic induction of erythropoietin and vascular endothelial growth factor at subnanomolar concentrations in multiple myeloma and liver cancer cell lines, regardless of cytotoxic concentrations of bortezomib. Bortezomib repressed HIF-1␣ activity by inhibiting the recruitment of p300 coactivator. Specifically, bortezomib targeted HIF-1␣ C-terminal transactivation domain (CAD) but not the CAD lacking Asn803, which is a hydroxylation site by the factor inhibiting HIF-1 (FIH). Accordingly, this effect of bortezomib on CAD was augmented by FIH expression and abolished by FIH knock-down. Furthermore, bortezomib stimulated the interaction between CAD and FIH under hypoxic conditions, and FIH inhibition reversed the suppressions of erythropoietin and vascular endothelial growth factor by bortezomib. We propose that the mechanism underlying the inhibitory effects of bortezomib on tumor angiogenesis and hypoxic adaptation involves the repression of HIF-1␣ transcriptional activity by reinforcing the FIH-mediated inhibition of p300 recruitment. IntroductionHypoxia commonly develops in solid tumors because tumor growth outpaces vessel formation and because the blood supply is compromised due to aberrant vasculature formation. 1 Tumor hypoxia contributes to angiogenesis and modulates tumor energy metabolism, which are both essential required for tumor growth. 2 In multiple myeloma (MM), hypoxia is also an important environmental factor because bone marrow is intrinsically hypoxic in nature. 3 Thus, MM cells must survive and grow under such hypoxic conditions, and this requires the expressions of many genes essential for adaptation. Hypoxic adaptation is mainly provided by hypoxia-inducible factor-1 (HIF-1), which orchestrates cellular adaptation to hypoxia by transactivating about 60 genes. 4 HIF-1 is composed of HIF-1␣ and HIF-1␤/aryl hydrocarbon nuclear translocator (ARNT), 5 and of these, HIF-1␣ is the key protein that determines the presence of HIF-1 and transactivates genes. Under normoxic conditions, HIF-1␣ is hydroxylated at its Pro402 and Pro564 residues by HIF-1 prolyl hydroxylases (PHDs), and thus, targeted by von Hippel-Lindau protein (pVHL), ubiquitinated, and finally degraded by 26S proteasomes. [6][7][8][9][10] In addition, the C-terminal transactivation domain (CAD) of HIF-1␣ is hydroxylated at Asn803 by the factor inhibiting HIF-1 (FIH), which represses the transcriptional activity of HIF-1␣ by blocking the recruitment of p300 coactivator. 11,12 However, PHD and FIH activities depend on oxygen tension, and as a result HIF-1␣ is stabilized and activated...

ObjectiveThe purpose of this study was to compare the precision of three-dimensional (3D) images acquired using iTero® (Align Technology Inc., San Jose, CA, USA) and Trios® (3Shape Dental Systems, Copenhagen, Denmark) digital intraoral scanners, and to evaluate the effects of the severity of tooth irregularities and scanning sequence on precision.MethodsDental arch models were fabricated with differing degrees of tooth irregularity and divided into 2 groups based on scanning sequence. To assess their precision, images were superimposed and an optimized superimposition algorithm was employed to measure any 3D deviation. The t-test, paired t-test, and one-way ANOVA were performed (p < 0.05) for statistical analysis.ResultsThe iTero® and Trios® systems showed no statistically significant difference in precision among models with differing degrees of tooth irregularity. However, there were statistically significant differences in the precision of the 2 scanners when the starting points of scanning were different. The iTero® scanner (mean deviation, 29.84 ± 12.08 µm) proved to be less precise than the Trios® scanner (22.17 ± 4.47 µm).ConclusionsThe precision of 3D images differed according to the degree of tooth irregularity, scanning sequence, and scanner type. However, from a clinical standpoint, both scanners were highly accurate regardless of the degree of tooth irregularity.