Role of Protein Phosphatase 2A in Osteoblast Differentiation and Function

The reversible phosphorylation of proteins plays hugely important roles in a variety of cellular processes, such as differentiation, proliferation, and apoptosis. These processes are strictly controlled by protein kinases (phosphorylation) and phosphatases (de-phosphorylation). Here we provide a brief history of the study of protein phosphorylation, including a summary of different types of protein kinases and phosphatases. One of the most physiologically important serine/threonine phosphatases is PP2A. This review provides a description of the phenotypes of various PP2A transgenic mice and further focuses on the known functions of PP2A in bone formation, including its role in osteoblast differentiation and function. A reduction in PP2A promotes bone formation and osteoblast differentiation through the regulation of bone-related transcription factors such as Osterix. Interestingly, downregulation of PP2A also stimulates adipocyte differentiation from undifferentiated mesenchymal cells under the appropriate adipogenic differentiation conditions. In osteoblasts, PP2A is also involved in the ability to control osteoclastogenesis as well as in the proliferation and metastasis of osteosarcoma cells. Thus, PP2A is considered to be a comprehensive factor in controlling the differentiation and function of cells derived from mesenchymal cells such as osteoblasts and adipocytes

PKR is necessary for osteoclastogenesis.

Double-stranded RNA-dependent protein kinase (PKR) is involved in cell cycle progression, cell proliferation, cell differentiation, tumorgenesis, and apoptosis. We previously reported that PKR is required for differentiation and calcification in osteoblasts. TNF-α plays a key role in osteoclast differentiation. However, it is unknown about the roles of PKR in the TNF-α-induced osteoclast differentiation. The expression of PKR in osteoclast precursor RAW264.7 cells increased during TNF-α-induced osteoclastogenesis. The TNF-α-induced osteoclast differentiation in bone marrow-derived macrophages and RAW264.7 cells was markedly suppressed by the pre-treatment of PKR inhibitor, 2-aminopurine (2AP), as well as gene silencing of PKR. The expression of gene markers in the differentiated osteoclasts including TRAP, Calcitonin receptor, cathepsin K and ATP6V0d2 was also suppressed by the 2AP treatment. Bone resorption activity of TNF-α-induced osteoclasts was also supressed by 2AP treatment. Inhibition of PKR supressed the TNF-α-induced activation of NF-κB and MAPK in RAW264.7 cells. 2AP inhibited both the nuclear translocation of NF-κB and its transcriptional activity in RAW264.7 cells. 2AP inhibited the TNF-α-induced expression of NFATc1 and c-fos, master transcription factors in osteoclastogenesis. TNF-α-induced nuclear translocation of NFATc1 in mature osteoclasts was clearly inhibited by the 2AP treatment. The PKR inhibitor C16 decreased the TNF-α-induced osteoclast formation and bone resorption in mouse calvaria. The present study indicates that PKR is necessary for the TNF-α-induced osteoclast differentiation in vitro and in vivo

Risk Factors of Glecaprevir/Pibrentasvir-Induced Liver Injury and Efficacy of Ursodeoxycholic Acid

Although glecaprevir/pibrentasvir (GP) therapy is recommended as a first-line treatment for hepatitis C virus (HCV) infection, serious drug-induced liver injury occasionally develops. The present study aimed to elucidate real-world risk factors for GP-induced liver injury and to evaluate the efficacy of add-on ursodeoxycholic acid (UDCA) for liver injury. We analyzed 236 HCV patients who received GP therapy. GP-induced liver injury was defined as any elevation to grade ≥ 1 in total bilirubin (TB), aspartate aminotransferase (AST), alanine aminotransferase (ALT), alkaline phosphatase (ALP), or γ-glutamyl transferase (γ-GT) during treatment without other cause. The frequency of GP-induced liver injury was 61.9% (146/236). Serious elevation to grade ≥ 3 in TB, AST, ALT, ALP, and γ-GT was identified in 3.8% (9/236), 0%, 0%, 0%, and 0.4% (1/209), respectively. Therapy discontinuation and dose reduction were seen in one patient each. Multivariate analysis revealed age and TB as independent risk factors for GP-induced liver injury. In patients with grade ≥ 2 hyperbilirubinemia, TB after onset significantly decreased in the add-on UDCA group but not in the no UDCA group. Careful attention to GP-induced liver injury is warranted for elderly patients with cirrhosis. Add-on UDCA could suppress the aggravation of GP-induced liver injury

Role of Protein Phosphatase 2A in Osteoblast Differentiation and Function

The reversible phosphorylation of proteins plays hugely important roles in a variety of cellular processes, such as differentiation, proliferation, and apoptosis. These processes are strictly controlled by protein kinases (phosphorylation) and phosphatases (de-phosphorylation). Here we provide a brief history of the study of protein phosphorylation, including a summary of different types of protein kinases and phosphatases. One of the most physiologically important serine/threonine phosphatases is PP2A. This review provides a description of the phenotypes of various PP2A transgenic mice and further focuses on the known functions of PP2A in bone formation, including its role in osteoblast differentiation and function. A reduction in PP2A promotes bone formation and osteoblast differentiation through the regulation of bone-related transcription factors such as Osterix. Interestingly, downregulation of PP2A also stimulates adipocyte differentiation from undifferentiated mesenchymal cells under the appropriate adipogenic differentiation conditions. In osteoblasts, PP2A is also involved in the ability to control osteoclastogenesis as well as in the proliferation and metastasis of osteosarcoma cells. Thus, PP2A is considered to be a comprehensive factor in controlling the differentiation and function of cells derived from mesenchymal cells such as osteoblasts and adipocytes

β-Eudesmol, an Oxygenized Sesquiterpene, Reduces the Increase in Saliva 3-Methoxy-4-Hydroxyphenylglycol After the “Trier Social Stress Test” in Healthy Humans: A Randomized, Double-Blind, Placebo-Controlled Cross-Over Study

Hops, the immature inflorescences of the female hop plant (Humulus lupulus L.) are one of the main components of beer and provides flavor and bitterness. β-Eudesmol, an oxygenated sesquiterpene, is reported to accumulate in a particular hop cultivar. Recently, we revealed that β-Eudesmol ingestion affected autonomic nerve activity in an animal model. The effect on humans has not been elucidated, therefore, we investigated the effects of β-Eudesmol on reducing objective and subjective markers related to sympathetic nerve activity after the application of mental stress in healthy participants. Fifty participants (male and female aged 20 to 50 years) were randomly assigned to two groups. Five minutes before taking the Trier Social Stress Test (TSST) as a mental stressor, participants in each group ingested a beverage containing β-Eudesmol, the active beverage, or a placebo beverage that did not contain β-Eudesmol. Saliva 3-methoxy-4-hydroxyphenylglycol (MHPG), a major product of noradrenaline breakdown and a representative marker of sympathetic nerve activity, was significantly lower just after the TSST in the active group compared with the placebo group. Saliva cortisol, a marker of the endocrine stress response system, was not significantly different between the two groups. No adverse events related to test beverage ingestion were observed. This is the first experimental evidence of β-Eudesmol effect for mental stress in human

Effectiveness of Combined Treatment using X-rays and a Phosphoinositide 3-kinase Inhibitor, ZSTK474, on Proliferation of HeLa cells in vitro and in vivo

ZSTK474 is a novel orally applicable PI3K-specific inhibitor and strongly inhibits cancer cell proliferation. To explore further the antitumor effect of ZSTK474 for future clinical usage, combined effects with radiation were studied. The proliferation of HeLa cells was inhibited by the treatment with X-rays alone or ZSTK474 alone. The combination treatment with X-rays and ZSTK474 applied after 24 h post-irradiation for 8 days remarkably enhanced the cell growth inhibition. The combined effect was also observed for the clonogenic survival with continuous ZSTK474 treatment. Western blotting showed enhanced phosphorylation of Akt and GSK-3beta by X-irradiation, whereas the phosphorylation was inhibited by the ZSTK474 treatment alone. The treatment with ZSTK474 after X-irradiation also inhibited the phosphorylation. Combination of ZSTK474 and X-rays also remarkably inhibited xenograft tumor growth. The combined treatment with X-rays and ZSTK474 had a great therapeutic potential than the radiation or the drug therapy alone both in vitro and in vivo