Hyo-Won Oh

The regulatory mechanism of 4-phenylbutyric acid against ER stress-induced autophagy in human gingival fibroblasts

Endoplasmic reticulum (ER) stress is closely connected to autophagy. When cells are exposed to ER stress, cells exhibit enhanced protein degradation and form autophagosomes. In this study, we demonstrate that the chemical chaperone, 4-phenylbutyric acid (4-PBA), regulates ER stressinduced cell death and autophagy in human gingival fibroblasts. We found that 4-PBA protected cells against thapsigargin-induced apoptotic cell death but did not affect the reduced cell proliferation. ER stress induced by thapsigargin was alleviated by 4-PBA through the regulation of several ER stress-inducible, unfolded protein response related proteins including GRP78, GRP94, C/EBP homologous protein, phospho-eIF-2α, eIF-2α, phospho-JNK1 (p46) and phospho-JNK2/3 (p54), JNK1, IRE-1α, PERK, and sXBP-1. Compared with cells treated with thapsigargin alone, cells treated with both 4-PBA and thapsigargin showed lower levels of Beclin-1, LC-3II and autophagic vacuoles, indicating that 4-PBA also inhibited autophagy induced by ER stress. This study suggests that 4-PBA may be a potential therapeutic agent against ER stress-associated pathologic situations.

Effect of Cytosolic Phospholipase A2 on Proinflammatory Cytokine-induced Bone Resorptive Genes Including Receptor Activator of Nuclear Factor Kappa B Ligand in Human Dental Pulp Cells

INTRODUCTION Although cytokines stimulate prostaglandin E(2) (PGE(2)) production and cyclooxygenase-2 (COX-2) gene expression in human dental pulp cells (HDPCs), the involvement of cytosolic phospholipase A(2) (cPLA(2)) has not been assessed. The purpose of this study was to examine the role of cPLA(2) on the regulation of proinflammatory cytokine-stimulated genes associated with osteoclast differentiation or bone resorption. METHODS Tumor necrosis factor-alpha (TNF-alpha) and interleukin-1alpha (IL-1alpha)-induced COX-2 and receptor activator of nuclear factor kappa B ligand (RANKL) mRNA and protein expression in the HDPCs was determined by using reverse transcription-polymerase chain reaction (RT-PCR) and Western blot analysis. PGE(2) release and osteoclast-related gene expression were measured by enzyme-linked immunosorbent assay and RT-PCR. RESULTS Stimulation with TNF-alpha and IL-1alpha synergistically increased levels of COX-2 as well as RANKL mRNA and protein expression. Osteoclast markers (macrophage colony-stimulating factor [M-CSF], matrix metalloproteinase-9 [MMP-9], and tartrate-resistant acid phosphatase [TRAP]) and osteolysis regulating cytokines or osteoclastogenic cytokines (IL-6, IL-11, and Il-17) were up-regulated in HDPCs after IL-1alpha and TNF-alpha treatment. A cPLA(2) inhibitor attenuated both the cytokine-stimulated PGE(2) release as well as changes in osteoclast differentiation-related genes like RANKL. CONCLUSIONS These results suggest that cPLA(2) is involved in inflammatory cytokine-induced osteoclastogenic gene expression and consequent damage or destruction.

4-phenylbutyric Acid Regulates Collagen Synthesis and Secretion Induced by High Concentrations of Glucose in Human Gingival Fibroblasts.

High glucose leads to physio/pathological alterations in diabetes patients. We investigated collagen production in human gingival cells that were cultured in high concentrations of glucose. Collagen synthesis and secretion were increased when the cells were exposed to high concentrations of glucose. We examined endoplasmic reticulum (ER) stress response because glucose metabolism is related to ER functional status. An ER stress response including the expression of glucose regulated protein 78 (GRP78), C/EBP homologous protein (CHOP), inositol requiring enzyme alpha (IRE-1α) and phosphoreukaryotic initiation factor alpha (p-eIF-2α) was activated in the presence of high glucose. Activating transcription factor 4 (ATF-4), a downstream protein of p-eIF-2α as well as a transcription factor for collagen, was also phosphorylated and translocalized into the nucleus. The chemical chaperone 4-PBA inhibited the ER stress response and ATF-4 phosphorylation as well as nuclear translocation. Our results suggest that high concentrations of glucose-induced collagen are linked to ER stress and the associated phosphorylation and nuclear translocation of ATF-4.

N-Nitrosodimethylamine induced lung fibroblast cell death is associated with JNK activation

N-Nitrosodialkylamines are considered a potential health hazard for humans. Among various N-nitrosodialkylamines compound, N-nitrosodimethylamine (NDMA), was applied to lung cells, MLG. In order to examine the effect of NDMA in lung cells, cell death was first examined. NDMA induced cell death in a dose-dependent manner. Mitogen activated protein kinase (MAPK) involvement was tested using SP600125 for JNK, SB203580 for P38 MAPK, or PD98059 for ERK. SP compound induced a significant reduction of cell death, compared with other inhibitors. NDMA induced an increase in expression of ER stress response proteins, including GRP78, IRE-1α, CHOP, GRP94, p-eIF2α, p-JNK, or sXBP-1. Pretreatment with SP compound regulated expression of CHOP, the transcription factor associated with proapoptotic gene induction. This study showed that NDMA-induced cell death was resulted due to JNK activation. ER stress was also induced in the toxic situations. Study of the meaning of ER stress will be necessary in the near future.