Byung-Chul Oh

Bone Morphogenetic Protein-2 Stimulates Runx2 Acetylation

Runx2/Cbfa1/Pebp2aA is a global regulator of osteogenesis and is crucial for regulating the expression of bone-specific genes. Runx2 is a major target of the bone morphogenetic protein (BMP) pathway. Genetic analysis has revealed that Runx2 is degraded through a Smurf-mediated ubiquitination pathway, and its activity is inhibited by HDAC4. Here, we demonstrate the molecular link between Smurf, HDACs and Runx2, in BMP signaling. BMP-2 signaling stimulates p300-mediated Runx2 acetylation, increasing transactivation activity and inhibiting Smurf1-mediated degradation of Runx2. HDAC4 and HDAC5 dea-cetylate Runx2, allowing the protein to undergo Smurf-mediated degradation. Inhibition of HDAC increases Runx2 acetylation, and potentiates BMP-2-stimulated osteoblast differentiation and increases bone formation. These results demonstrate that the level of Runx2 is controlled by a dynamic equilibrium of acetylation, deacetylation, and ubiquitination. These findings have important medical implications because BMPs and Runx2 are of tremendous interest with regard to the development of therapeutic agents against bone diseases.

Biochemical properties and substrate specificities of alkaline and histidine acid phytases

Abstract Phytases are a special class of phosphatase that catalyze the sequential hydrolysis of phytate to less-phosphorylated myo-inositol derivatives and inorganic phosphate. Phytases are added to animal feedstuff to reduce phosphate pollution in the environment, since monogastric animals such as pigs, poultry, and fish are unable to metabolize phytate. Based on biochemical properties and amino acid sequence alignment, phytases can be categorized into two major classes, the histidine acid phytases and the alkaline phytases. The histidine acid phosphatase class shows broad substrate specificity and hydrolyzes metal-free phytate at the acidic pH range and produces myo-inositol monophosphate as the final product. In contrast, the alkaline phytase class exhibits strict substrate specificity for the calcium–phytate complex and produces myo-inositol trisphosphate as the final product. This review describes recent findings that present novel viewpoints concerning the molecular basis of phytase classification.

Crystal structures of a novel, thermostable phytase in partially and fully calcium-loaded states.

Phytases hydrolyze phytic acid to less phosphorylated myo-inositol derivatives and inorganic phosphate. A thermostable phytase is of great value in applications for improving phosphate and metal ion availability in animal feed, and thereby reducing phosphate pollution to the environment. Here, we report a new folding architecture of a six-bladed propeller for phosphatase activity revealed by the 2.1 Å crystal structures of a novel, thermostable phytase determined in both the partially and fully Ca2+-loaded states. Binding of two calcium ions to high-affinity calcium binding sites results in a dramatic increase in thermostability (by as much as ∼30°C in melting temperature) by joining loop segments remote in the amino acid sequence. Binding of three additional calcium ions to low-affinity calcium binding sites at the top of the molecule turns on the catalytic activity of the enzyme by converting the highly negatively charged cleft into a favorable environment for the binding of phytate.

CD26/DPP4 Levels in Peripheral Blood and T Cells in Patients With Type 2 Diabetes Mellitus

CONTEXT Dipeptidyl peptidase 4 (CD26/DPP4) is expressed on blood T cells and also circulates in a soluble form (sCD26/DPP4). OBJECTIVE We aimed to evaluate blood T cell and circulating CD26/DPP4 and its association with metabolic parameters in patients with type 2 diabetes mellitus (T2DM). DESIGNS We measured CD26/DPP4 expression (percentage of CD26(+) cells using flow cytometry) on CD4(+) and CD8(+) T cells, serum CD26/DPP4 level and activity, and various metabolic parameters in T2DM patients not on DPP4 inhibitor therapy (n = 148). Nondiabetic subjects (n = 50) were included as a control group. RESULTS Compared with the healthy controls, CD26/DPP4 expression on CD4(+) T cells and CD8(+) T cells was higher in T2DM patients. Serum CD26/DPP4 levels and enzymatic activities were also higher in patients with T2DM than in the control group only when metformin and/or thiazolidinedione-treated T2DM patients were excluded; metformin and/or thiazolidinedione-treated T2DM patients had lower values compared with other T2DM patients. Various parameters in T2DM patients were related to CD26/DPP4 expression on the T cells (hemoglobin A1c), serum sCD26/DPP4 (hemoglobin A1c and insulin resistance assessed by updated homeostasis model assessment), and serum CD26/DPP4 activity (insulin resistance assessed by updated homeostasis model assessment, γ-glutamyl transferase, and alanine aminotransferase) by multivariate analyses. After active glucose control for 12 weeks in drug-naive T2DM patients (n = 50), CD26/DPP4 expression on blood T cells was significantly decreased. CONCLUSIONS Our results suggest that the CD26/DPP4 level on blood T cells was associated with glucose control status in patients with T2DM.

Rho-kinase regulates energy balance by targeting hypothalamic leptin receptor signaling

Leptin regulates energy balance. However, knowledge of the critical intracellular transducers of leptin signaling remains incomplete. We found that Rho-kinase 1 (ROCK1) regulates leptin action on body weight homeostasis by activating JAK2, an initial trigger of leptin receptor signaling. Leptin promoted the physical interaction of JAK2 and ROCK1, thereby increasing phosphorylation of JAK2 and downstream activation of Stat3 and FOXO1. Mice lacking ROCK1 in either pro-opiomelanocortin (POMC) or agouti-related protein neurons, mediators of leptin action, displayed obesity and impaired leptin sensitivity. In addition, deletion of ROCK1 in the arcuate nucleus markedly enhanced food intake, resulting in severe obesity. Notably, ROCK1 was a specific mediator of leptin, but not insulin, regulation of POMC neuronal activity. Our data identify ROCK1 as a key regulator of leptin action on energy homeostasis.

Regulation of Glucose Transport by ROCK1 Differs from That of ROCK2 and Is Controlled by Actin Polymerization

A role of Rho-associated coiled-coil-containing protein kinase (ROCK)1 in regulating whole-body glucose homeostasis has been reported. However, cell-autonomous effects of ROCK1 on insulin-dependent glucose transport in adipocytes and muscle cells have not been elucidated. To determine the specific role of ROCK1 in glucose transport directly, ROCK1 expression in 3T3-L1 adipocytes and L6 myoblasts was biologically modulated. Here, we show that small interfering RNA-mediated ROCK1 depletion decreased insulin-induced glucose transport in adipocytes and myoblasts, whereas adenovirus-mediated ROCK1 expression increased this in a dose-dependent manner, indicating that ROCK1 is permissive for glucose transport. Inhibition of ROCK1 also impaired glucose transporter 4 translocation in 3T3-L1 adipocytes. Importantly, the ED₅₀ of insulin for adipocyte glucose transport was reduced when ROCK1 was expressed, leading to hypersensitivity to insulin. These effects are dependent on actin cytoskeleton remodeling, because inhibitors of actin polymerization significantly decreased ROCK1s effect to promote insulin-stimulated glucose transport. Unlike ROCK2, ROCK1 binding to insulin receptor substrate (IRS)-1 was not detected by immunoprecipitation, although cell fractionation demonstrated both ROCK isoforms localize with IRS-1 in low-density microsomes. Moreover, insulins ability to increase IRS-1 tyrosine 612 and serine 632/635 phosphorylation was attenuated by ROCK1 suppression. Replacing IRS-1 serine 632/635 with alanine reduced insulin-stimulated phosphatidylinositol 3-kinase activation and glucose transport in 3T3-L1 adipocytes, indicating that phosphorylation of these serine residues of IRS-1, which are substrates of the ROCK2 isoform in vitro, are crucial for maximal stimulation of glucose transport by insulin. Our studies identify ROCK1 as an important positive regulator of insulin action on glucose transport in adipocytes and muscle cells.

Runt-Related Transcription Factor RUNX3 Is a Target of MDM2-Mediated Ubiquitination

The p14(ARF)-MDM2-p53 pathway constitutes an effective mechanism for protecting cells from oncogenic stimuli such as activated Ras and Myc. Importantly, Ras activation induces p14(ARF) and often occurs earlier than p53 inactivation during cancer development. Here, we show that RUNX3, a tumor suppressor in various tumors including stomach, bladder, colon, and lung, is stabilized by Ras activation through the p14(ARF)-MDM2 signaling pathway. RUNX3 directly binds MDM2 through its Runt-related DNA-binding domain. MDM2 blocks RUNX3 transcriptional activity by interacting with RUNX3 through an acidic domain adjacent to the p53-binding domain of MDM2 and ubiquitinates RUNX3 on key lysine residues to mediate nuclear export and proteasomal degradation. Our data indicate that the lineage-specific tumor suppressor RUNX3 and the ubiquitous p53 protein are both principal responders of the p14(ARF)-MDM2 cell surveillance pathway that prevents pathologic consequences of abnormal oncogene activation.

Cancers with Higher Density of Tumor-Associated Macrophages Were Associated with Poor Survival Rates

Background: Macrophages are a component of a tumor’s microenvironment and have various roles in tumor progression and metastasis. This study evaluated the relationships between tumor-associated macrophage (TAM) density and clinical outcomes in 14 different types of human cancers. Methods: We investigated TAM density in human tissue microarray sections from 14 different types of human cancers (n = 266) and normal thyroid, lung, and breast tissues (n = 22). The five-year survival rates of each cancer were obtained from the 2011 Korea Central Cancer Registry. Results: Among 13 human cancers, excluding thyroid cancer, pancreas, lung, and gallbladder cancers had the highest density of CD163-positive macrophages (7.0±3.5%, 6.9±7.4%, and 6.9 ± 5.5%, respectively). The five-year relative survival rates of these cancers (pancreas, 8.7%; lung, 20.7%; gallbladder, 27.5%) were lower than those of other cancers. The histological subtypes in thyroid cancer exhibited significantly different CD163-positive macrophages densities (papillary, 1.8 ± 1.6% vs anaplastic, 22.9 ± 17.1%; p < .001), but no significant difference between histological subtypes was detected in lung and breast cancers. Moreover, there was no significant difference in CD163-positive macrophages densities among the TNM stages in lung, breast, and thyroid cancers. Conclusions: Cancers with higher TAM densities (pancreas, lung, anaplastic thyroid, and gallbladder) were associated with poor survival rate.

Pim‐1 kinase phosphorylates and stabilizes RUNX3 and alters its subcellular localization

The loci of the Pim and Runx gene families have been identified as targets for viral insertions in CD2‐myc mice. Synergistic cooperation between Pim and RUNX was also found in the CD2‐Runx2 transgenic mouse lymphoma model. RUNX genes have come to prominence recently because of their roles as essential regulators of cell fate in development. Paradoxically, they appear to function either as tumor‐suppressor genes or dominant oncogenes according to the cellular context. However, the molecular mechanism of the ambiguous roles played by this family of transcription factors in cancer has remained largely uninvestigated. Here we demonstrate that Pim‐1 phosphorylates four Ser/Thr residues within the Runt domain and stabilizes RUNX3 protein. In addition, Pim‐1 markedly altered the cellular localization of RUNX3 from the nucleus to the cytoplasm. Our results demonstrate that the subcellular localization of RUNX3 is altered by phosphorylation. We propose that RUNX family members may behave as oncogenes if mislocalized to a cellular micro‐compartment. J. Cell. Biochem. 105: 1048–1058, 2008.

Ginsenoside Rh2 inhibits osteoclastogenesis through down-regulation of NF-κB, NFATc1 and c-Fos

Ginsenoside Rh2 is one of the most active components of red ginseng, controlling cancer and other metabolic diseases including osteoclast differentiation. However, the molecular mechanism underlying the inhibition of osteoclast differentiation by ginsenoside Rh2 remains poorly understood. In the present study, it was found that ginsenoside Rh2 suppressed osteoclast differentiation from bone marrow macrophages (BMMs) treated with receptor activator of nuclear factor κB ligand (RANKL) without any cytotoxicity. Ginsenoside Rh2 significantly reduced RANKL-induced expression of transcription factors, c-Fos and nuclear factor of activated T-cells (NFATc1), as well as osteoclast markers, TRAP and OSCAR. In defining the signaling pathways, ginsenoside Rh2 was shown to moderately inhibit NF-κB activation and ERK phosphorylation in response to RANKL stimulation in BMM cells without any effect on p38 and c-Jun N-terminal kinase (JNK). Finally, ginsenoside Rh2 blocked osteoporosis in vivo as confirmed by restored bone mineral density (BMD) and other markers associated osteoclast differentiation. Hence, it is suggested that ginsenoside Rh2 could suppress RANKL-induced osteoclast differentiation in vitro and in vivo through the regulation of c-Fos and NFATc1 expressions, not excluding the involvement of NF-κB and ERK. Ginsenoside Rh2 is also suggested to be developed as a therapeutic drug for prevention and treatment of osteoporosis.