Jiyun Yoo

Smad3 Signaling Is Required for Epithelial-Mesenchymal Transition of Lens Epithelium after Injury

Lens epithelial cells undergo epithelial-mesenchymal transition (EMT) after injury as in cataract extraction, leading to fibrosis of the lens capsule. Fibrosis of the anterior capsule can be modeled in the mouse by capsular injury in the lens, which results in EMT of the lens epithelium and subsequent deposition of extracellular matrix without contamination of other cell types from outside the lens. We have previously shown that signaling via Smad3, a key signal-transducing element downstream of transforming growth factor (TGF)-beta and activin receptors, is activated in lens epithelial cells by 12 hours after injury and that this Smad3 activation is blocked by administration of a TGF-beta 2-neutralizing antibody in mice. We now show that EMT of primary lens epithelial cells in vitro depends on TGF-beta expression and that injury-induced EMT in vivo depends, more specifically, on signaling via Smad3. Loss of Smad3 in mice blocks both morphological changes of lens epithelium to a mesenchymal phenotype and expression of the EMT markers snail, alpha-smooth muscle actin, lumican, and type I collagen in response to injury in vivo or to exposure to exogenous TGF-beta in organ culture. The results suggest that blocking the Smad3 pathway might be beneficial in inhibiting capsular fibrosis after injury and/or surgery.

Smad3 is required for dedifferentiation of retinal pigment epithelium following retinal detachment in mice

Retinal pigment epithelial (RPE) cells dedifferentiate and undergo epithelial–mesenchymal transition (EMT) following retinal detachment, playing a central role in formation of fibrous tissue on the detached retina and vitreous retraction (proliferative vitreoretinopathy (PVR)). We have developed a mouse model of subretinal fibrosis with implications for PVR in which retinal detachment is induced without direct damage to the RPE cells. Transforming growth factor-β (TGF-β) has long been implicated both in EMT of RPEs and the development of PVR. Using mice null for Smad3, a key signaling intermediate downstream of TGF-β and activin receptors, we show that Smad3 is essential for EMT of RPE cells induced by retinal detachment. De novo accumulation of fibrous tissue derived from multilayered RPE cells was seen following experimental retinal detachment in eyes of wild type, but not Smad3-null mice. Expression of α-smooth muscle actin, a hallmark of EMT in this cell type, and extracellular matrix components, lumican and collagen VI, were also not observed in eyes of Smad3-null mice. Our data show that induction of PDGF-BB by Smad3-dependent TGF-β signaling is likely an important secondary proliferative component of the disease process. The results suggest that blocking the Smad3 pathway might be beneficial in prevention/treatment of PVR.

RhoGDI2 Expression Is Associated with Tumor Growth and Malignant Progression of Gastric Cancer

Purpose: Rho GDP dissociation inhibitor 2 (RhoGDI2) has been identified as a regulator of Rho family GTPase. However, there is currently no direct evidence suggesting whether RhoGDI2 activates or inhibits Rho family GTPase in vivo (and which type), and the role of RhoGDI2 in tumor remains controversial. Here, we assessed the effects of RhoGDI2 expression on gastric tumor growth and metastasis progression. Experimental Design: Proteomic analysis was done to investigate the tumor-specific protein expression in gastric cancer and RhoGDI2 was selected for further study. Immunohistochemistry was used to detect RhoGDI2 expression in clinical samples of primary gastric tumor tissues which have different pathologic stages. Gain-of-function and loss-of-function approaches were done to examine the malignant phenotypes of the RhoGDI2-expressing or RhoGDI2-depleting cells. Results: RhoGDI2 expression was correlated positively with tumor progression and metastasis potential in human gastric tumor tissues, as well as cell lines. The forced expression of RhoGDI2 caused a significant increase in gastric cancer cell invasion in vitro, and tumor growth, angiogenesis, and metastasis in vivo, whereas RhoGDI2 depletion evidenced opposite effects. Conclusion: Our findings indicate that RhoGDI2 is involved in gastric tumor growth and metastasis, and that RhoGDI2 may be a useful marker for tumor progression of human gastric cancer.

Inhibition of p38MAP kinase suppresses fibrotic reaction of retinal pigment epithelial cells

Proliferative vitreoretinopathy (PVR) is one of the major causes of the failure of retinal detachment surgery. Its pathogenesis includes a fibrotic reaction by the retinal pigment epithelium and other retina-derived non-neural cells, leading to fixation of the detached retina. We examined the role of p38 mitogen-activated protein kinase (MAPK) in transforming growth factor (TGF)-β2-dependent enhancement of the fibrogenic reaction in a human retinal pigment epithelial cell line, ARPE-19, and also evaluated the therapeutic efficacy of inhibiting p38MAPK by adenoviral gene transfer of dominant-negative (DN) p38MAPK in a mouse model of PVR. Exogenous TGF-β2 activates p38MAPK in ARPE-19 cells. It also suppresses cell proliferation, but this was unaffected by addition of the p38MAPK inhibitor, SB202190. SB202190 interfered with TGF-β2-dependent cell migration and production of collagen type I and fibronectin, but had no effect on basal levels of these activities. While SB202190 did not affect phosphorylation of the C-terminus of Smads2/3, it did suppress the transcriptional activity of Smads3/4 as indicated by a reporter gene, CAGA12-Luc. Gene transfer of DN-p38MAPK attenuated the post-retinal detachment fibrotic reaction of the retinal pigment epithelium in vivo in mice, supporting its effectiveness in preventing/treating PVR.

Gadd45b Mediates Fas-induced Apoptosis by Enhancing the Interaction between p38 and Retinoblastoma Tumor Suppressor

Gadd45b has been known as a positive mediator of apoptosis induced by certain cytokines and oncogenes. Here, we identified Gadd45b as an effector of Fas-induced apoptosis and found that p38-mediated Rb hyperphosphorylation is one of the mechanisms of Fas-induced apoptosis in murine hepatocyte AML12 cells. Gadd45b has been shown to activate p38 through its physical interaction with MTK1 and induce apoptosis. However, in this study, we have showed that the function of Gadd45b during Fas-induced apoptosis in AML12 cells is different from that reported in previous studies. Depletion of Gadd45b expression did not inhibit the phosphorylation of p38, but it suppressed p38-mediated Rb phosphorylation and apoptosis in response to Fas stimulation by reducing the interaction between p38 and Rb. Ectopic expression of Gadd45b was sufficient to enhance this interaction. These findings suggest that Gadd45b mediates p38-induced Rb phosphorylation by enhancing the interaction between p38 and Rb during Fas-induced apoptosis in murine hepatocytes.

RhoGDI2 as a therapeutic target in cancer

Importance of the field: Rho GDP dissociation inhibitor 2 (RhoGDI2) has been identified as a regulator of Rho GTPases that play important roles in the development of numerous aspects of the malignant phenotype, including cell cycle progression, resistance to apoptotic stimuli, neovascularization, tumor cell motility, invasiveness, and metastasis. Although RhoGDI2 has been known to be expressed only in hematopoietic tissues, recent studies suggest that this protein is also aberrantly expressed in several human cancers and contributes to aggressive phenotypes, such as invasion and metastasis. Hence, RhoGDI2 appears to be a target of interest for therapeutic manipulation. Areas covered in this review: Here, we summarize the role of RhoGDI2 in human cancers, specifically metastasis-related processes, and discuss its potential as a therapeutic target. What the reader will gain: RhoGDI2 modulates the invasiveness and metastatic ability of cancer cells through regulation of Rac1 activity. Take home message: RhoGDI2 may be a useful marker for tumor progression in human cancers, and interruption of the RhoGDI2-mediated cancer cell invasion and metastasis by an interfacial inhibitor may be a powerful therapeutic approach to cancer.

VEGF-C mediates RhoGDI2-induced gastric cancer cell metastasis and cisplatin resistance

Rho GDP dissociation inhibitor 2 (RhoGDI2) expression is correlated with tumor growth, metastasis and chemoresistance in gastric cancer. However, the mechanisms by which RhoGDI2 promotes tumor cell survival and metastasis remain unclear. In this study, we clearly demonstrate that RhoGDI2 upregulates VEGF‐C expression and RhoGDI2 expression is positively correlated with VEGF‐C expression in human gastric tumor tissues as well as parental gastric cancer cell lines. VEGF‐C depletion suppressed RhoGDI2‐induced gastric cancer metastasis and sensitized RhoGDI2‐overexpressing cells to cisplatin‐induced apoptosis in vitro and in vivo. Secreted VEGF‐C enhanced gastric cancer cell invasion and conferred cisplatin resistance to RhoGDI2‐overexpressing cells. We also show that RhoGDI2 positively regulates Rac1 activity in gastric cancer cells. Inhibition of Rac1 expression suppressed RhoGDI2‐induced VEGF‐C expression, and this inhibition was associated with decreased invasiveness and increased sensitivity to cisplatin in RhoGDI2‐overexpressing cells. Our results indicate that RhoGDI2 might be a potential therapeutic target for simultaneously reducing metastasis risk and enhancing chemotherapy efficacy in gastric cancer.

Proteomics-based strategy to delineate the molecular mechanisms of RhoGDI2-induced metastasis and drug resistance in gastric cancer.

Rho GDP dissociation inhibitor 2 (RhoGDI2) was initially identified as a regulator of the Rho family of GTPases. Our recent works suggest that RhoGDI2 promotes tumor growth and malignant progression, as well as enhances chemoresistance in gastric cancer. Here, we delineate the mechanism by which RhoGDI2 promotes gastric cancer cell invasion and chemoresistance using two-dimensional gel electrophoresis (2-DE) on proteins derived from a RhoGDI2-overexpressing SNU-484 human gastric cancer cell line and control cells. Differentially expressed proteins were identified using matrix-assisted laser desorption ionization-time-of-flight mass spectrometry (MALDI-TOF-MS). In total, 47 differential protein spots were identified; 33 were upregulated, and 14 were downregulated by RhoGDI2 overexpression. Upregulation of SAE1, Cathepsin D, Cofilin1, CIAPIN1, and PAK2 proteins was validated by Western blot analysis. Loss-of-function analysis using small interference RNA (siRNA) directed against candidate genes reveals the need for CIAPIN1 and PAK2 in RhoGDI2-induced cancer cell invasion and Cathepsin D and PAK2 in RhoGDI2-mediated chemoresistance in gastric cancer cells. These data extend our understanding of the genes that act downstream of RhoGDI2 during the progression of gastric cancer and the acquisition of chemoresistance.

Effect of Sparassis crispa Extracts on Immune Cell Activation and Tumor Growth Inhibition

Sparassis crispa is an edible mushroom with medicinal properties that contains more than 40% βglucan. The role of S. crispa in regulating the functional activation of macrophages has yet to be fully elucidated. The objective of this study was to investigate the molecular mechanism underlying the immune-stimulatory function of S. crispa soluble β-glucan and extracts on macrophages. In this study, we showed that S. crispa soluble β-glucan was able to stimulate TNF-α and IL-1β production through NF-kB activation in Raw 264.7 cells. We also showed that S. crispa extracts could not only enhance TNF-α production in Raw 264.7 cells, but also suppress tumor growth in vivo. All of our results suggest that S. crispa could be developed as a promising immunostimulatory principle, applicable to cancer patients.Sparassis crispa is an edible mushroom with medicinal properties that contains more than 40% β-glucan. The role of S. crispa in regulating the functional activation of macrophages has yet to be fully elucidated. The objective of this study was to investigate the molecular mechanism underlying the immune-stimulatory function of S. crispa soluble β-glucan and extracts on macrophages. In this study, we showed that S. crispa soluble β-glucan was able to stimulate TNF-α and IL-1β production through NF-kB activation in Raw 264.7 cells. We also showed that S. crispa extracts could not only enhance TNF-α production in Raw 264.7 cells, but also suppress tumor growth in vivo. All of our results suggest that S. crispa could be developed as a promising immunostimulatory principle, applicable to cancer patients.

Downregulation of SGK1 Expression is Critical for TGF-β-induced Apoptosis in Mouse Hepatocytes Cells

Transforming growth factor (TGF)-β-dependent apoptosis is important in the elimination of damaged or abnormal cells from normal tissues, especially in liver, in vivo. To investigate which gene expressions are critical for TGF-β-induced apoptosis in hepatocytes, gene expression profiling experiments were performed with TGF-β-treated and non-treated mouse hepatocytes AML12 cells. Findings showed that serum and glucocorticoid-inducible protein kinase1 (SGK1) expression is markedly downregulated during TGF-β-induced apoptosis. Findings confirmed that expression of SGK1 protein, as well as mRNA, is also markedly decreased with TGF-β treatment. Infection of adenoviral vector encoding constitutively active SGK1 (CA-SGK1), but not kinase dead SGK1 (KD-SGK1), attenuated TGF-β-induced apoptosis. All of these results suggest that downregulation of SGK1 expression is critical for TGF-β-induced apoptosis in AML12 cells.