c-Src couples PI 3 kinase/Akt and MAPK signaling to PDGF-induced DNA synthesis in mesangial cells

Pan-Src kinase inhibitor treatment attenuates diabetic kidney injury via inhibition of Fyn kinase-mediated endoplasmic reticulum stress

Src family kinases (SFKs) have been implicated in the pathogenesis of kidney fibrosis. However, the specific mechanism by which SFKs contribute to the progression of diabetic kidney disease (DKD) remains unclear. Our preliminary transcriptome analysis suggested that SFK expression was increased in diabetic kidneys and that the expression of Fyn (a member of the SFKs), along with genes related to unfolded protein responses from the endoplasmic reticulum (ER) stress signaling pathway, was upregulated in the tubules of human diabetic kidneys. Thus, we examined whether SFK-induced ER stress is associated with DKD progression. Mouse proximal tubular (mProx24) cells were transfected with Fyn or Lyn siRNA and exposed to high glucose and palmitate (HG-Pal). Streptozotocin-induced diabetic rats were treated with KF-1607, a novel pan-Src kinase inhibitor (SKI) with low toxicity. The effect of KF-1607 was compared to that of losartan, a standard treatment for patients with DKD. Among the SFK family members, the Fyn and Lyn kinases were upregulated under diabetic stress. HG-Pal induced p70S6 kinase and JNK/CHOP signaling and promoted tubular injury. Fyn knockdown but not Lyn knockdown inhibited this detrimental signaling pathway. In addition, diabetic rats treated with KF-1607 showed improved kidney function and decreased ER stress, inflammation, and fibrosis compared with those treated with losartan. Collectively, these findings indicate that Fyn kinase is a specific member of the SFKs implicated in ER stress activation leading to proximal tubular injury in the diabetic milieu and that pan-SKI treatment attenuates kidney injury in diabetic rats. These data highlight Fyn kinase as a viable target for the development of therapeutic agents for DKD.

Insights into a signaling pathway that promotes diabetic kidney disease could lead to new therapies that protect against this major cause of kidney failure. Past studies have suggested that the various Src family kinase (SFK) signaling proteins play a part in the cell death and scar tissue formation associated with diabetic kidney disease. Hunjoo Ha of Ewha Womans University, Seoul, South Korea, and colleagues have now focused on one particular SFK, Fyn, as a direct driver of the kidney damage seen in mouse models of diabetes. Genetic interventions that selectively inhibit Fyn suppressed this damage, as did treatment with an oral drug that broadly inactivates SFKs. This experimental drug proved as effective as controlling inflammation and oxidative damage in the kidney as an already clinically approved treatment, confirming the significance of SFK signaling in this condition.

Src Activation Aggravates Podocyte Injury in Diabetic Nephropathy via Suppression of FUNDC1-Mediated Mitophagy

Background and purpose: Mitophagy plays a significant role in the progression of diabetic nephropathy (DN), although the regulatory mechanisms remain unclear. Recently, accumulating evidence demonstrated that impaired mitochondrial function and mitophagy are involved in DN. Here, we are aimed to explore the role of c-Src (Src) and FUNDC1-related mitophagy in the development of DN.

Methods: The db/db mice were used to establish a DN mice model. The mice accepted PP2 (Src inhibitor) treatment to study the role of Src in DN. Kidney function was measured via biochemical testing. Renal histopathology and morphometric analysis were conducted via hematoxylin-eosin (HE), periodic acid-Schiff (PAS), Masson’s staining, and transmission electron microscopy (TEM). We measured degree of apoptosis in kidney by TUNEL assay. Indices of mitophagy (LC3 and p62) were evaluated by Western blotting and immunofluorescence. Complementary in vitro assays were conducted using human podocytes subjected to high glucose in combination with PP2 treatment or FUNDC1 small interfering RNAs (siRNAs). Flow cytometry was used to detect the apoptotic cells. Mitochondrial function was evaluated by JC-1 staining. Double immunofluorescence labeling of LC3 and TOMM20 used to assess the degree of mitophagy.

Results: Increased Src activation was detected in the kidneys of db/db mice, and its expression was positively correlated with mitochondrial damage, podocyte apoptosis, and renal dysfunction. Inhibition of Src activation with PP2 protected against mitochondrial damage and podocyte apoptosis. In vitro experiments in podocytes established that high glucose increased Src activation, promoting FUNDC1 phosphorylation and inhibiting mitophagy. Consistent with the mouse model, inhibiting Src activity protected podocytes against mitochondrial damage. FUNDC1 silencing negated the actions of PP2, indicating that FUNDC1-mediated mitophagy is downstream pathway of Src.

Conclusion: In summary, our data indicated that Src is a culprit factor in diabetic renal damage via suppression of FUNDC1-mediated mitophagy, promoting the development of DN.

KF-1607, a Novel Pan Src Kinase Inhibitor, Attenuates Obstruction-Induced Tubulointerstitial Fibrosis in Mice

Src family kinases (SFKs), an important group of non-receptor tyrosine kinases, are suggested to be excessively activated during various types of tissue fibrosis. The present study investigated the effect of KF-1607, an orally active and a newly synthesized Src kinase inhibitor (SKI) with proposed low toxicity, in preventing the progression of renal interstitial fibrosis. Unilateral ureteral obstruction (UUO) surgery was performed in 6-week-old male C57BL/6 mice to induce renal interstitial fibrosis. Either KF-1607 (30 mg/kg, oral gavage) or PP2 (2 mg/kg, intraperitoneal injection), a common experimental SKI, was administered to mice for seven days, started one day prior to surgery. UUO injury-induced SFK expression, including Src, Fyn, and Lyn kinase. SFK inhibition by KF-1607 prevented the progression of tubular injury in UUO mice, as indicated by decreases in albuminuria, urinary KIM-1 excretion, and kidney NGAL protein expression. Renal tubulointerstitial fibrosis was attenuated in response to KF-1607, as shown by decreases in α-SMA, collagen I and IV protein expression, along with reduced Masson’s trichrome and collagen-I staining in kidneys. KF-1607 also inhibited inflammation in the UUO kidney, as exhibited by reductions in F4/80 positive-staining and protein expression of p-NFκB and ICAM. Importantly, the observed effects of KF-1607 were similar to those of PP2. A new pan Src kinase inhibitor, KF-1607, is a potential pharmaceutical agent to prevent the progression of renal interstitial fibrosis.

Lipid oversupply induces CD36 sarcolemmal translocation via dual modulation of PKCζ and TBC1D1: an early event prior to insulin resistance

Lipid oversupply may induce CD36 sarcolemmal translocation to facilitate fatty acid transport, which in turn causes dyslipidemia and type 2 diabetes. However, the underlying mechanisms of CD36 redistribution are still yet to be unraveled.

Methods: High fat diet fed mice and palmitate/oleic acid-treated L6 cells were used to investigate the initial events of subcellular CD36 recycling prior to insulin resistance. The regulation of CD36 sarcolemmal translocation by lipid oversupply was assessed by insulin tolerance test (ITT), oral glucose tolerance test (OGTT), glucose/fatty acid uptake assay, surface CD36 and GLUT4 detection, and ELISA assays. To elucidate the underlying mechanisms, specific gene knockout, gene overexpression and/or gene inhibition were employed, followed by Western blot, co-immunoprecipitation, immunostaining, and kinase activity assay.

Results: Upon lipid/fatty acid overload, PKCζ activity and TBC1D1 phosphorylation were enhanced along with increased sarcolemmal CD36. The inhibition of PKCζ or TBC1D1 was shown to block fatty acid-induced CD36 translocation and was synergistic in impairing CD36 redistribution. Mechanically, we revealed that AMPK was located upstream of PKCζ to control its activity whereas Rac1 facilitated PKCζ translocation to the dorsal surface of the cell to cause actin remodeling. Furthermore, AMPK phosphorylated TBC1D1 to release retained cytosolic CD36. The activated PKCζ and phosphorylated TBC1D1 resulted in a positive feedback regulation of CD36 sarcolemmal translocation.

Conclusion: Collectively, our study demonstrated exclusively that lipid oversupply induced CD36 sarcolemmal translocation via dual modulation of PKCζ and TBC1D1, which was as an early event prior to insulin resistance. The acquired data may provide potential therapy targets to prevent lipid oversupply-induced insulin resistance.

Compound C Inhibits B16-F1 Tumor Growth in a Syngeneic Mouse Model Via the Blockage of Cell Cycle Progression and Angiogenesis

We recently observed that Compound C (CompC), a reversible inhibitor of AMP-activated protein kinase, reduced the cell viability of B16-F1 melanoma cells. To establish its molecular mechanism(s) of action, the cell cycle was examined by flow cytometry and the expression of cell cycle regulatory proteins and angiogenesis-related proteins were examined by western blot analysis. In addition, its effect on tumor growth was investigated using C57BL/6 syngeneic mice bearing B16-F1 xenografts. We found that CompC induced G2/M cell cycle arrest, which was associated with reduced levels of cell cycle regulatory proteins, such as phosphorylated pRB, cyclin-dependent protein kinases (Cdks), cyclins, and phosphorylated P-Ser¹⁰-histone H3, and increased levels of Cdk inhibitors, such as p21 and p53. We also found that CompC inhibits proliferation, migration, and tube formation of human umbilical vascular endothelial cells via the inhibition of vascular endothelial growth factor receptor-induced signaling pathways. As expected, CompC significantly reduced the tumor size of B16-F1 xenografts in the syngeneic mouse model. Inhibition of tumor growth may be attributed to reduced cell proliferation via cell cycle inhibition and in part to decreased angiogenesis in CompC-treated mice. These findings suggest the potential use of CompC against melanoma development and progression.

Quantitative Proteomics of TRAMP Mice Combined with Bioinformatics Analysis Reveals That PDGF-B Regulatory Network Plays a Key Role in Prostate Cancer Progression

Transgenic adenocarcinoma of the mouse prostate (TRAMP) mice is a widely used transgenic animal model of prostate cancer (PCa). We performed a label-free quantitative proteomics analysis combined with a bioinformatics analysis on the entire prostate protein extraction from TRAMP mice and compared it with WT littermates. From 2379 total identified proteins, we presented a modest mice prostate reference proteome containing 919 proteins. 61 proteins presented a significant expression difference between two groups. The integrative bioinformatics analysis predicted the overexpression of platelet-derived growth factor B (PDGF-B) in tumor tissues and supports the hypothesis of the PDGF-B signaling network as a key upstream regulator in PCa progression. Furthermore, we demonstrated that Crenolanib, a novel PDGF receptor inhibitor, inhibited PCa cell proliferation in a dose-dependent manner. Finally, we revealed the importance of PDGF-B regulatory network in PCa progression, which will assist us in understanding the role and mechanisms of PDGF-B in promoting cancer growth and provide valuable knowledge for future research on anti-PDGF therapy.

Silicon dioxide nanoparticles induce COX-2 expression through activation of STAT3 signaling pathway in HaCaT cells

Silicon dioxide nanoparticles (SiO₂-NPs) are widely used in biomedicines and consumer products, such as sunscreens and cosmetics. However, SiO₂-NPs can cause adverse effects on human health, depending on the size and concentration of nanoparticles. The present study was aimed at investigating the molecular mechanism underlying SiO₂-NPs-induced inflammation in human keratinocyte (HaCaT) cells. Incubation of HaCaT cells with SiO₂-NPs induced the expression of cyclooxygenase-2 (COX-2) mRNA and protein. Treatment of cells with SiO₂-NPs also induced the phosphorylation, DNA binding and the reporter gene activity of signal transducer and activator of transcription 3 (STAT3). Transfection of cells with STAT3 siRNA abrogated SiO₂-NPs-induced COX-2 expression. Moreover, SiO₂-NPs enhanced the phosphorylation of Janus kinase2 (JAK2), Src and Akt. Pharmacological inhibition of either JAK2, Src or Akt abrogated SiO₂-NPs-induced STAT3 transcriptional activity and the expression of COX-2. Treatment with LY294002 also attenuated SiO₂-NPs-induced Src phosphorylation, while, JAK2 phosphorylation was not changed. In addition, SiO₂-NPs generated reactive oxygen species (ROS) and treatment of N-acetyl cysteine (NAC) attenuated the phosphorylation of JAK2, Src, Akt and STAT3, as well as the expression of COX-2 in SiO₂-NPs-treated HaCaT cells. Taken together, our study provides the first report that SiO₂-NPs induce COX-2 expression in HaCaT cells by activating the STAT3 signaling through ROS-mediated phosphorylation of upstream kinases, Akt/Src and JAK2.

Tyrosines-740/751 of PDGFRβ contribute to the activation of Akt/Hif1α/TGFβ nexus to drive high glucose-induced glomerular mesangial cell hypertrophy

Glomerular mesangial cell hypertrophy contributes to the complications of diabetic nephropathy. The mechanism by which high glucose induces mesangial cell hypertrophy is poorly understood. Here we explored the role of the platelet-derived growth factor receptor-β (PDGFRβ) tyrosine kinase in driving the high glucose-induced mesangial cell hypertrophy. We show that high glucose stimulates the association of the PDGFRβ with PI 3 kinase leading to tyrosine phosphorylation of the latter. High glucose-induced Akt kinase activation was also dependent upon PDGFRβ and its tyrosine phosphorylation at 740/751 residues. Inhibition of PDGFRβ activity, its downregulation and expression of its phospho-deficient (Y740/751F) mutant inhibited mesangial cell hypertrophy by high glucose. Interestingly, expression of constitutively active Akt reversed this inhibition, indicating a role of Akt kinase downstream of PDGFRβ phosphorylation in this process. The transcription factor Hif1α is a target of Akt kinase. siRNAs against Hif1α inhibited the high glucose-induced mesangial cell hypertrophy. In contrast, increased expression of Hif1α induced hypertrophy similar to high glucose. We found that inhibition of PDGFRβ and expression of PDGFRβ Y740/751F mutant significantly inhibited the high glucose-induced expression of Hif1α. Importantly, expression of Hif1α countered the inhibition of mesangial cell hypertrophy induced by siPDGFRβ or PDGFRβ Y740/751F mutant. Finally, we show that high glucose-stimulated PDGFRβ tyrosine phosphorylation at 740/751 residues and the tyrosine kinase activity of the receptor regulate the transforming growth factor-β (TGFβ) expression by Hif1α. Thus we define the cell surface PDGFRβ as a major link between high glucose and its effectors Hif1α and TGFβ for induction of diabetic mesangial cell hypertrophy.

Src family kinases in chronic kidney disease

Src family kinases (SFKs) belong to nonreceptor protein tyrosine kinases and have been implicated in the regulation of numerous cellular processes, including cell proliferation, differentiation, migration and invasion, and angiogenesis. The role and mechanisms of SFKs in tumorgenesis have been extensively investigated, and some SFK inhibitors are currently under clinical trials for tumor treatment. Recent studies have also demonstrated the importance of SFKs in regulating the development of various fibrosis-related chronic diseases (e.g., idiopathic pulmonary fibrosis, liver fibrosis, renal fibrosis, and systemic sclerosis). In this article, we summarize the roles of SFKs in various chronic kidney diseases, including glomerulonephritis, diabetic nephropathy, human immunodeficiency virus-associated nephropathy, autosomal dominant form of polycystic kidney disease, and obesity-associated kidney disease, and discuss the mechanisms involved.

PI3K inhibitor LY294002, as opposed to wortmannin, enhances AKT phosphorylation in gemcitabine-resistant pancreatic cancer cells

LY294002 and wortmannin are chemical compounds that act as potent inhibitors of phosphoinositide 3-kinases (PI3Ks). Both of them are generally used to inhibit cell proliferation as cancer treatment by inhibiting the PI3K/protein kinase B (AKT) signaling pathway. In this study, LY294002 (but not wortmannin) showed an abnormal ability to enhance AKT phosphorylation (at Ser472) specifically in gemcitabine (GEM)-resistant pancreatic cancer (PC) cell lines PK59 and KLM1-R. LY294002 was shown to activate AKT and accumulate phospho-AKT at the intracellular membrane in PK59, which was abolished by treatment with AKTi-1/2 or wortmannin. Inhibiting AKT phosphorylation by treatment with AKTi-1/2 or wortmannin further enhanced LY294002-induced cell death in PK59 and KLM1-R cells. In addition, treatment with wortmannin alone failed to inhibit cell proliferation in both PK59 and KLM1-R cells. Thus, our results reveal that LY294002 displays the opposite effect on PI3K-dependent AKT phosphorylation, which maintains cell survival from the cytotoxicity introduced by LY294002 itself in GEM-resistant pancreatic cancer cells. We suggest that targeting the PI3K/AKT signaling pathway with inhibitors may be counterproductive for patients with PC who have acquired GEM-resistance.

CD248/endosialin critically regulates hepatic stellate cell proliferation during chronic liver injury via a PDGF-regulated mechanism

INTRODUCTION

CD248 (endosialin) is a stromal cell marker expressed on fibroblasts and pericytes. During liver injury, myofibroblasts are the main source of fibrotic matrix.

OBJECTIVE

To determine the role of CD248 in the development of liver fibrosis in the rodent and human setting.

DESIGN

CD248 expression was studied by immunostaining and quantitative PCR in both normal and diseased human and murine liver tissue and isolated hepatic stellate cells (HSCs). Hepatic fibrosis was induced in CD248(-/-) and wild-type controls with carbon tetrachloride (CCl4) treatment.

RESULTS

Expression of CD248 was seen in normal liver of humans and mice but was significantly increased in liver injury using both immunostaining and gene expression assays. CD248 was co-expressed with a range of fibroblast/HSC markers including desmin, vimentin and α-smooth muscle actin (α-SMA) in murine and human liver sections. CD248 expression was restricted to isolated primary murine and human HSC. Collagen deposition and α-SMA expression, but not inflammation and neoangiogenesis, was reduced in CD248(-/-) mice compared with wild-type mice after CCl4 treatment. Isolated HSC from wild-type and CD248(-/-) mice expressed platelet-derived growth factor receptor α (PDGFR-α) and PDGFR-β at similar levels. As expected, PDGF-BB stimulation induced proliferation of wild-type HSC, whereas CD248(-/-) HSC did not demonstrate a proliferative response to PDGF-BB. Abrogated PDGF signalling in CD248(-/-) HSC was confirmed by significantly reduced c-fos expression in CD248(-/-) HSC compared with wild-type HSC.

CONCLUSIONS

Our data show that deletion of CD248 reduces susceptibility to liver fibrosis via an effect on PDGF signalling, making it an attractive clinical target for the treatment of liver injury.

Naringin suppresses the metabolism of A375 cells by inhibiting the phosphorylation of c-Src

Elevation of glycolysis, increase in lactic acid production, and enhancement of mitochondrial biogenesis are all the changes of energy metabolism of melanoma cells. Melanoma cells' metabolism and energy production networks play an important role in cancer proliferation, survival, motility, invasiveness, metastasis, and angiogenesis. Since the Warburg theory was put forward in the 1930s, more researchers focus on finding new ways for effectively eliminating cancer cells by targeting their energy metabolism. In this study, we found naringin has the inhibitory effects on the glucose metabolism of A375 cells, a melanoma cell line, in a concentration-dependent manner. We also found that naringin could significantly reduce the phosphorylation of c-Src. In summary, we demonstrated that naringin inhibits the malignant phenotype of A375 cells by suppressing c-Src and its downstream signaling pathway. More importantly, we provide the novel mechanism that, as a natural inhibitor of c-Src, naringin could be an effective candidate for the treatment of melanoma.

Src inhibition blocks renal interstitial fibroblast activation and ameliorates renal fibrosis

Increased Src activity has been associated with the pathogenesis of renal tumors and some glomerular diseases, but its role in renal interstitial fibrosis remains elusive. To evaluate this, cultured renal interstitial fibroblasts (NRK-49F) were treated with PP1, a selective inhibitor of Src. This resulted in decreased expression of α-smooth muscle actin, fibronectin, and collagen I in response to serum, angiotension II, or transforming growth factor-β1 (TGF-β1). Silencing Src with siRNA also inhibited expression of those proteins. Furthermore, inhibition of Src activity blocked renal fibroblast proliferation. In a murine model of renal interstitial fibrosis induced by unilateral ureteral obstruction, the active form of Src (phopsho-Src Tyr416) was upregulated in both renal interstitial fibroblasts and renal tubular cells of the fibrotic kidney. Its inactivation reduced renal fibroblast activation and attenuated extracellular matrix protein deposition. Src inhibition also suppressed activation of TGF-β1 signaling, activation of the epidermal growth factor receptor and STAT3, and reduced the number of renal epithelial cells arrested at the G2/M phase of the cell cycle after ureteral obstruction. Thus, Src is an important mediator of renal interstitial fibroblast activation and renal fibrosis, and suggest that Src is a potential therapeutic target for treatment of chronic renal fibrosis.

Rapamycin Enhances the Anti-Cancer Effect of Dasatinib by Suppressing Src/PI3K/mTOR Pathway in NSCLC Cells

Src and the mammalian target of rapamycin (mTOR) signaling are commonly activated in non-small cell lung cancer (NSCLC) and hence potential targets for chemotherapy. Although the combined use of Src inhibitor Dasatinib with other chemotherapeutic agents has shown superior efficacy for cancer treatment, the mechanisms that lead to enhanced sensitivity of Dasatinib are not completely understood. In this study, we found that Rapamycin dramatically enhanced Dasatinib-induced cell growth inhibition and cell cycle G1 arrest in human lung adenocarcinoma A549 cells without affecting apoptosis. The synergistic effects were consistently correlated with the up-regulation of cyclin-dependent kinases inhibitor proteins, including p16, p19, p21, and p27, as well as the repression of Cdk4 expression and nuclear translocation. Mechanistic investigations demonstrated that FoxO1/FoxO3a and p70S6K/4E-BP1, the molecules at downstream of Src-PI3K-Akt and mTOR signaling, were significantly suppressed by the combined use of Dasatinib and Rapamycin. Restraining Src and mTOR with small interfering RNA in A549 cells further confirmed that the Src/PI3K/mTOR Pathway played a crucial role in enhancing the anticancer effect of Dasatinib. In addition, this finding was also validated by a series of assays using another two NSCLC cell lines, NCI-H1706 and NCI-H460. Conclusively, our results suggested that the combinatory application of Src and mTOR inhibitors might be a promising therapeutic strategy for NSCLC treatment.

Phytochemical regulation of Fyn and AMPK signaling circuitry

During the past decades, phytochemical terpenoids, polyphenols, lignans, flavonoids, and alkaloids have been identified as antioxidative and cytoprotective agents. Adenosine monophosphate-activated protein kinase (AMPK) is a kinase that controls redox-state and oxidative stress in the cell, and serves as a key molecule regulating energy metabolism. Many phytochemicals directly or indirectly alter the AMPK pathway in distinct manners, exerting catabolic metabolism. Some of them are considered promising in the treatment of metabolic diseases such as type II diabetes, obesity, and hyperlipidemia. Another important kinase that regulates energy metabolism is Fyn kinase, a member of the Src family kinases that plays a role in various cellular responses such as insulin signaling, cell growth, oxidative stress and apoptosis. Phytochemical inhibition of Fyn leads to AMPK-mediated protection of the cell in association with increased antioxidative capacity and mitochondrial biogenesis. The kinases may work together to form a signaling circuitry for the homeostasis of energy conservation and expenditure, and may serve as targets of phytochemicals. This review is intended as a compilation of recent advancements in the pharmacological research of phytochemicals targeting Fyn and AMPK circuitry, providing information for the prevention and treatment of metabolic diseases and the accompanying tissue injuries.

Control of vascular smooth muscle function by Src-family kinases and reactive oxygen species in health and disease

Reactive oxygen species (ROS) are now recognised as second messenger molecules that regulate cellular function by reversibly oxidising specific amino acid residues of key target proteins. Amongst these are the Src-family kinases (SrcFKs), a multi-functional group of non-receptor tyrosine kinases highly expressed in vascular smooth muscle (VSM). In this review we examine the evidence supporting a role for ROS-induced SrcFK activity in normal VSM contractile function and in vascular remodelling in cardiovascular disease. VSM contractile responses to G-protein-coupled receptor stimulation, as well as hypoxia in pulmonary artery, are shown to be dependent on both ROS and SrcFK activity. Specific phosphorylation targets are identified amongst those that alter intracellular Ca(2+) concentration, including transient receptor potential channels, voltage-gated Ca(2+) channels and various types of K(+) channels, as well as amongst those that regulate actin cytoskeleton dynamics and myosin phosphatase activity, including focal adhesion kinase, protein tyrosine kinase-2, Janus kinase, other focal adhesion-associated proteins, and Rho guanine nucleotide exchange factors. We also examine a growing weight of evidence in favour of a key role for SrcFKs in multiple pro-proliferative and anti-apoptotic signalling pathways relating to oxidative stress and vascular remodelling, with a particular focus on pulmonary hypertension, including growth-factor receptor transactivation and downstream signalling, hypoxia-inducible factors, positive feedback between SrcFK and STAT3 signalling and positive feedback between SrcFK and NADPH oxidase dependent ROS production. We also discuss evidence for and against the potential therapeutic targeting of SrcFKs in the treatment of pulmonary hypertension.

MK-2206 induces cell cycle arrest and apoptosis in HepG2 cells and sensitizes TRAIL-mediated cell death

It has become evident that AKT inhibitors have great potential in cancer treatment. In this study, we investigate the anticancer activity of MK-2206, a novel AKT inhibitor, on HepG2 hepatocellular carcinoma cell, and to show whether MK-2206 enhances the apoptosis-inducing potential of tumor necrosis factor-related apoptosis-inducing ligand (TRAIL). The cell growth inhibition was evaluated by MTT assay and colony formation assay. Cell cycle distribution was assessed by propidium iodide flow cytometry. Apoptosis was determined by AnnexinV-FITC/PI double staining assay and caspase-9, casapse-7, caspase-3, and PARP cleavage. The results of present study showed that MK-2206-induced G1-phase arrest was associated with a marked decrease in the protein expression of cyclin D1 with concomitant induction of p21 and p27. MK-2206-induced apoptosis was characterized by cleavage of a pro-caspase in a concentration-dependent manner. Moreover, the MAP family kinases p38 kinase and JNK were activated by exposure to MK-2206. SB203580, an p38-specific inhibitor, partially blocked MK-2206-induced death of HepG2 cells and caspase activation. A combination of MK-2206 with TRAIL significantly inhibited growth of TRAIL resistant HepG2 cells. Taken together, our findings provide a new insight to better understand anticancer mechanisms of MK-2206, at least in HepG2 cell. Using of MK-2206 as a potent sensitizer to TRAIL-induced apoptotic cell death offers a promising means of enhancing the efficacy of TRAIL-based HCC treatments.

A positive feedback loop involving Erk5 and Akt turns on mesangial cell proliferation in response to PDGF

Platelet-derived growth factor BB and its receptor (PDGFRβ) play a pivotal role in the development of renal glomerular mesangial cells. Their roles in increased mesangial cell proliferation during mesangioproliferative glomerulonephritis have long been noted, but the operating logic of signaling mechanisms regulating these changes remains poorly understood. We examined the role of a recently identified MAPK, Erk5, in this process. PDGF increased the activating phosphorylation of Erk5 and tyrosine phosphorylation of proteins in a time-dependent manner. A pharmacologic inhibitor of Erk5, XMD8-92, abrogated PDGF-induced DNA synthesis and mesangial cell proliferation. Similarly, expression of dominant negative Erk5 or siRNAs against Erk5 blocked PDGF-stimulated DNA synthesis and proliferation. Inhibition of Erk5 attenuated expression of cyclin D1 mRNA and protein, resulting in suppression of CDK4-mediated phosphorylation of the tumor suppressor protein pRb. Expression of cyclin D1 or CDK4 prevented the dominant negative Erk5- or siErk5-mediated inhibition of DNA synthesis and mesangial cell proliferation induced by PDGF. We have previously shown that phosphatidylinositol 3-kinase (PI3-kinase) contributes to PDGF-induced proliferation of mesangial cells. Inhibition of PI3-kinase blocked PDGF-induced phosphorylation of Erk5. Since PI3-kinase acts through Akt, we determined the role of Erk5 on Akt phosphorylation. XMD8-92, dominant negative Erk5, and siErk5 inhibited phosphorylation of Akt by PDGF. Interestingly, we found inhibition of PDGF-induced Erk5 phosphorylation by a pharmacological inhibitor of Akt kinase and kinase dead Akt in mesangial cells. Thus our data unfold the presence of a positive feedback microcircuit between Erk5 and Akt downstream of PI3-kinase nodal point for PDGF-induced mesangial cell proliferation.

Cordyceps sinensis polysaccharide CPS-2 protects human mesangial cells from PDGF-BB-induced proliferation through the PDGF/ERK and TGF-β1/Smad pathways

CPS-2, a Cordyceps sinensis polysaccharide, has been demonstrated to have significant therapeutic activity against chronic renal failure. However, little is known about the underlying molecular mechanism. In this study, we found that CPS-2 could inhibit PDGF-BB-induced human mesangial cells (HMCs) proliferation in a dose-dependent manner. In addition, CPS-2 notably suppressed the expression of α-SMA, PDGF receptor-beta (PDGFRβ), TGF-β1, and Smad 3 in PDGF-BB-treated HMCs. Furthermore, PDGF-BB-stimulated ERK activation was significantly inhibited by CPS-2, and this inhibitory effect was synergistically potentiated by U0126. CPS-2 could prevent the PDGFRβ promoter activity induced by PDGF-BB, and return expression of PDGFRβ, TGF-β1, and TGFβRI to normal levels while cells were under PDGFRβ and ERK silencing conditions and transfected with DN-ERK. Taken together, these findings demonstrated that CPS-2 reduces PDGF-BB-induced cell proliferation through the PDGF/ERK and TGF-β1/Smad pathways, and it may have bi-directional regulatory effects on the PDGF/ERK cellular signaling pathway.

Src tyrosine kinase mediates platelet-derived growth factor BB-induced and redox-dependent migration in metanephric mesenchymal cells

The adult kidney is derived from the interaction between the metanephric blastema and the ureteric bud. Platelet-derived growth factor (PDGF) receptor β is essential for the development of the mature glomerular tuft, as mice deficient for this receptor lack mesangial cells. This study investigated the role of Src tyrosine kinase in PDGF-mediated reactive oxygen species (ROS) generation and migration of metanephric mesenchymal cells (MMCs). Cultured embryonic MMCs from wild-type and PDGF receptor-deficient embryos were established. Migration was determined via wound-healing assay. Unlike PDGF AA, PDGF BB-induced greater migration in MMCs with respect to control. This was abrogated by neutralizing an antibody to PDGF BB. Phosphatidylinositol 3-kinase (PI3K) inhibitors suppressed PDGF BB-induced migration. Conversely, mitogen-activated protein kinase/extracellular signal-regulated kinase (MEK) inhibitors had no effect. Src inhibitors inhibited PDGF-induced cell migration, PI3K activity, and Akt phosphorylation. Adenoviral dominant negative Src (AD DN Src) abrogated PDGF BB-induced Akt phosphorylation. Hydrogen peroxide stimulated cell migration. PDGF BB-induced wound closure was inhibited by the antioxidants N-acetyl-l-cysteine, tiron, and the flavoprotein inhibitor diphenyleneiodonium. These cells express the NADPH oxidase homolog Nox4. Inhibiting Nox4 with antisense oligonucleotides or small interfering RNA (siRNA) suppressed PDGF-induced wound closure. Inhibition of Src with siRNA reduced PDGF BB-induced ROS generation as assessed by 2',7'-dichlorodihydrofluorescein diacetate fluorescence. Furthermore, PDGF BB-stimulated ROS generation and migration were similarly suppressed by Ad DN Src. In MMCs, PDGF BB-induced migration is mediated by PI3K and Src in a redox-dependent manner involving Nox4. Src may be upstream to PI3K and Nox4.

Role of PKCα activation of Src, PI-3K/AKT, and ERK in EGF-stimulated proliferation of rat and human conjunctival goblet cells

PURPOSE

To determine the order and components of the signaling pathway utilized by epidermal growth factor (EGF) to stimulate conjunctival goblet cell proliferation.

METHODS

Goblet cells from rat bulbar and forniceal conjunctiva and human bulbar conjunctiva were grown in organ culture. Goblet cells (GCs) were serum starved for 24 hours and preincubated with inhibitors for 30 minutes or small interfering RNA (siRNA) for 48 hours prior to addition of EGF. Proliferation was then measured or Western blot analysis was performed using antibodies against phosphorylated protein kinase B (AKT), extracellular signal-regulated kinase 1/2 (ERK1/2), or the non-receptor tyrosine kinase Src. Rat GCs were also incubated with adenoviruses expressing dominant negative protein kinase Cα (DNPKCα) or constitutively activated protein kinase Cα (myrPKCα), and activation of AKT and ERK1/2 was determined by Western blot analysis.

RESULTS

Inhibitors of phosphoinositol-3 kinase (PI-3K)/AKT pathway blocked EGF-stimulated ERK1/2 activation and GC proliferation. Inhibitors of EGF-stimulated ERK1/2 activity did not inhibit AKT activation but blocked proliferation. DNPKCα blocked EGF-stimulated activation of AKT and ERK1/2 while myrPKCα increased activation of these kinases. Inhibitors of PI-3K, ERK1/2, and protein kinase C (PKC) blocked myrPKCα-stimulated GC proliferation. EGF and myrPKCα increased phosphorylation of Src, and inhibition of Src with the chemical inhibitor PP1 or siRNA inhibited EGF-stimulated GC proliferation.

CONCLUSIONS

We found that EGF activates a major pathway to stimulate goblet cell proliferation. This pathway consists of induction of phospholipase C (PLC)γ to activate PKCα. Active PKCα phosphorylates Src to induce PI-3K to phosphorylate AKT that subsequently activates the ERK1/2 cascade to stimulate goblet cell proliferation.

Inactivation of Nuclear Factor-Y Inhibits Vascular Smooth Muscle Cell Proliferation and Neointima Formation

Objective—

Atherosclerosis and restenosis are multifactorial diseases associated with abnormal vascular smooth muscle cell (VSMC) proliferation. Nuclear factor-Y (NF-Y) plays a major role in transcriptional activation of the CYCLIN B1 gene ( CCNB1 ), a key positive regulator of cell proliferation and neointimal thickening. Here, we investigated the role of NF-Y in occlusive vascular disease.

Approach and Results—

We performed molecular and expression studies in cultured cells, animal models, and human tissues. We find upregulation of NF-Y and cyclin B1 expression in proliferative regions of murine atherosclerotic plaques and mechanically induced lesions, which correlates with higher binding of NF-Y to target sequences in the CCNB1 promoter. NF-YA expression in neointimal lesions is detected in VSMCs, macrophages, and endothelial cells. Platelet-derived growth factor-BB, a main inductor of VSMC growth and neointima development, induces the recruitment of NF-Y to the CCNB1 promoter and augments both CCNB1 mRNA expression and cell proliferation through extracellular signal–regulated kinase 1/2 and Akt activation in rat and human VSMCs. Moreover, adenovirus-mediated overexpression of a NF-YA-dominant negative mutant inhibits platelet-derived growth factor-BB–induced CCNB1 expression and VSMC proliferation in vitro and neointimal lesion formation in a mouse model of femoral artery injury. We also detect NF-Y expression and DNA-binding activity in human neointimal lesions.

Conclusions—

Our results identify NF-Y as a key downstream effector of the platelet-derived growth factor-BB–dependent mitogenic pathway that is activated in experimental and human vasculoproliferative diseases. They also identify NF-Y inhibition as a novel and attractive strategy for the local treatment of neointimal formation induced by vessel denudation.

Inhibition of platelet-derived growth factor receptor tyrosine kinase and downstream signaling pathways by Compound C

AMP-activated protein kinase (AMPK) has been implicated in anti-proliferative actions in a range of cell systems. Recently, it was observed that Compound C, an inhibitor of AMPK, also reduced the cell viability in human diploid fibroblasts (HDFs). Compound C-induced growth arrest was associated with a decrease in the cell cycle regulatory proteins, such as proliferating cell nuclear antigen, phosphorylated pRB, cyclin-dependent protein kinases (Cdk 2 and 4), cyclins (D and E), and the Cdk inhibitors (p21, p16, and p27). Therefore, the present study examined the molecular mechanism of the antiproliferative effects of Compound C. Although Compound C inhibited serum-induced phosphorylation of Akt and its substrate, glycogen synthase kinase-3β, it did not affect the Akt activity in vitro. Compound C significantly inhibited the receptor tyrosine phosphorylation and the activity of downstream signaling molecules, such as p85 phosphoinositide 3-kinase, phospholipase C-γ1, and extracellular signal-regulated kinase 1/2, induced by platelet-derived growth factor (PDGF) but not by epidermal growth factor- and insulin-like growth factor. In vitro growth factor receptor tyrosine kinase activity profiling revealed the IC50 for PDGF receptor-β (PDGFRβ) to be 5.07μM, whereas the IC50 for the epidermal growth factor receptor and insulin-like growth factor receptor was ≥100μM. The inhibitory effect of Compound C on PDGFRβ and Akt was also observed in AMPKα1/α2-knockout mouse embryonic fibroblasts, indicating that its inhibitory effect is independent of the AMPK activity. The inhibitory effect of Compound C on cell proliferation and PDGFRβ tyrosine phosphorylation was also demonstrated in various PDGFR-expressing cells, including MRC-5, BEAS-2B, rat aortic vascular smooth muscle cells, and A172 glioblastoma cells. These results indicate that Compound C can be used as a potential antiproliferative agent for PDGF- or PDGFR-associated diseases, such as cancer, atherosclerosis, and fibrosis.

The endosomal adaptor protein APPL1 impairs the turnover of leading edge adhesions to regulate cell migration

Cell migration is a complex process that requires the integration of signaling events that occur in distinct locations within the cell. Adaptor proteins, which can localize to different subcellular compartments, where they bring together key signaling proteins, are emerging as attractive candidates for controlling spatially coordinated processes. However, their function in regulating cell migration is not well understood. In this study, we demonstrate a novel role for the adaptor protein containing a pleckstrin-homology (PH) domain, phosphotyrosine-binding (PTB) domain, and leucine zipper motif 1 (APPL1) in regulating cell migration. APPL1 impairs migration by hindering the turnover of adhesions at the leading edge of cells. The mechanism by which APPL1 regulates migration and adhesion dynamics is by inhibiting the activity of the serine/threonine kinase Akt at the cell edge and within adhesions. In addition, APPL1 significantly decreases the tyrosine phosphorylation of Akt by the nonreceptor tyrosine kinase Src, which is critical for Akt-mediated cell migration. Thus, our results demonstrate an important new function for APPL1 in regulating cell migration and adhesion turnover through a mechanism that depends on Src and Akt. Moreover, our data further underscore the importance of adaptor proteins in modulating the flow of information through signaling pathways.

The non-receptor tyrosine kinase c-Src mediates the PDGF-induced association between Furin and pro-MT1-MMP in HPAC pancreatic cells

Furin is a member of the proprotein convertase family, which is capable of cleaving the precursors of a wide variety of substrates including membrane-type 1 matrix metalloproteinase (MT1-MMP) proenzyme. c-Src is activated by growth factors, and has been linked with a poor prognosis in pancreatic cancer (PCa). Both c-Src and Furin play crucial roles in tumorigenesis, and the mechanism controlling their association is not understood. Modulation of the association between Furin and pro-MT1-MMP by c-Src inhibitor PP2 was evaluated by western blotting, assay of in vitro enzyme, co-immunoprecipitation (co-IP), and confocal immunofluorescence microscopy. Human platelet-derived growth factor BB (PDGF-BB) activated c-Src and induced c-Src-dependent association of Furin with pro-MT1-MMP in HPAC pancreatic cancer cells. Co-IP and confocal immunofluorescence assays revealed that c-Src interacts with Furin in vivo. The SH2 domain appeared to be important for c-Src interaction with Furin. In addition, we showed that Furin protein is tyrosine phosphorylated. Association between Furin and MT1-MMP is regulated by the tyrosine kinase c-Src.

Sustained inhibition of epsilon protein kinase C inhibits vascular restenosis after balloon injury and stenting

BACKGROUND

ε protein kinase C (εPKC) is involved in vascular smooth muscle cell (VSMC) activation, but little is known about its function in vascular pathology. We aimed at assessing the role of εPKC in the development of restenosis.

METHODS AND RESULTS

Rat models of aortic balloon injury with or without subsequent stenting were used. Rats were treated with the selective ψεPKC activator ε receptor for activated protein kinase C (ψεRACK), the selective εPKC inhibitor εV1-2, or saline. Both down-stream cascades of the platelet-derived growth factor receptor via extracellular signal-regulated kinase and Akt, respectively, were evaluated in vivo and in VSMC cultures. Intimal hyperplasia with luminal obliteration developed in saline-treated balloon-injured rat aortas (20.3±8.0%), and ψεRACK significantly promoted neointima development (32.4±4.9%, P=0.033), whereas εV1-2 significantly inhibited luminal narrowing (9.2±4.3%, P=0.039). εPKC inhibition led to significantly reduced VSMC extracellular signal-regulated kinase phosphorylation in vivo, whereas Akt phosphorylation was not markedly affected. Neointimal proliferation in vivo and platelet-derived growth factor-induced VSMC proliferation/migration in vitro were significantly inhibited by εV1-2. The inhibition of the platelet-derived growth factor pathway was mediated by inhibiting down-stream extracellular signal-regulated kinase and Akt phosphorylation. In vitro, εV1-2 showed inhibitory properties on endothelial cell proliferation, but that did not prevent reendothelialization in vivo. εV1-2 showed proapoptotic effects on VSMC in vitro. After stent implantation, luminal restenosis (quantified by optical coherence tomography imaging) was significantly reduced with εV1-2 (8.0±2.0%) compared with saline (20.2±9.8%, P=0.028).

CONCLUSIONS

εPKC seems to be centrally involved in the development of neointimal hyperplasia. We suggest that εPKC inhibition may be mediated via inhibition of extracellular signal-regulated kinase and Akt activation. εPKC modulation may become a new therapeutic target against vascular restenosis.

BAPTA-AM, an intracellular calcium chelator, inhibits RANKL-induced bone marrow macrophages differentiation through MEK/ERK, p38 MAPK and Akt, but not JNK pathways

To examine the roles of intracellular calcium in RANKL-induced bone marrow macrophages (BMMs) differentiation, the effects of intracellular calcium chelator BAPTA-AM on RANKL-induced BMMs differentiation, and the activation of its relating signal proteins (MAPKs, and the PI3K/Akt) were studied. BMMs were cultured with various concentrations of BAPTA-AM in the presence of M-CSF (25 ng/ml) and RANKL (25 ng/ml) for 7 days, osteoclastogenic ability, cytosolic free Ca(2+) concentration, osteoclast survival and the expression of phosphorylated ERK1/2, SAPK/JNK, Akt and p38 MAPK were measured by TRAP staining, spectrofluorometer and Western blotting. BAPTA-AM inhibited osteoclastogenesis and osteoclast survival of BMMs by RANKL induction. In osteoclasts without the pretreatment of BAPTA-AM, the increased response of [Ca(2+)](i) was observed within 15 min and the maximum was about 1.2 times that of control. This response was sustained for 30 min and returned to the control level at 1h after RANKL-inducing, and the increased response of [Ca(2+)](i) was completely abolished and sustained to at least 8h by BAPTA-AM. Although immunoblotting data revealed that RANKL could activate the phosphorylation of ERK1/2, SAPK/JNK, Akt and p38 MAPK, the expression of ERK1/2, Akt and p38 MAPK phosphorylation was inhibited by BAPTA-AM dose-dependently. These results revealed that BAPTA-AM inhibit osteoclastogenic ability of BMMs via suppressing the increase of [Ca(2+)](i) which lead to inhibit RANKL-induced the phosphorylation of ERK, Akt and p38 MAPK, but not JNK. This finding may be useful in the development of an osteoclastic inhibitor that targets intracellular signaling factors.

Fyn is involved in angiotensin II type 2 receptor-induced neurite outgrowth, but not in p42/p44mapk in NG108-15 cells

In NG108-15 cells, activation of p42/p44(mapk) is essential for induction of neurite outgrowth by angiotensin II (Ang II) type 2 receptor (AT(2)). The aim was to verify whether Fyn, a member of the Src family kinases (SFK), is involved in neurite outgrowth induced by AT(2) activation. Preincubation of cells with PP1, a general inhibitor of the SKF, decreased activation of Rap1 and p42/p44(mapk) and abolished TrkA activation by Ang II or by the AT(2) agonist, CGP42112A. NG108-15 cells were transfected with a Fyn-WT and a Fyn-DN expressing vector. Fyn-WT was sufficient to induce neurite outgrowth, although transfection with Fyn-DN abolished neurite elongation. However, the Fyn-DN form failed to affect activation of TrkA, Rap1 or p42/p44(mapk) by Ang II. Thus, although SKF activity is required to achieve AT(2)-induced activation of TrkA, Rap1 and p42/p44(mapk), Fyn is essential for AT(2) receptor-induced neurite outgrowth, but not in AT(2) signaling leading to p42/p44(mapk) activation.

Fyn-dependent regulation of energy expenditure and body weight is mediated by tyrosine phosphorylation of LKB1

Fyn null mice display reduced adiposity associated with increased fatty acid oxidation, energy expenditure, and activation of the AMP-dependent protein kinase (AMPK) in skeletal muscle and adipose tissue. The acute pharmacological inhibition of Fyn kinase activity with SU6656 in wild-type mice reproduces these metabolic effects and induced a specific reduction in fat mass with no change in lean mass. LKB1, the main upstream AMPK kinase (AMPKK) in peripheral tissues, was redistributed from the nucleus into the cytoplasm of cells treated with SU6656 and in cells expressing a kinase-deficient, but not a constitutively kinase-active, Fyn mutant. Moreover, Fyn kinase directly phosphorylated LKB1 on tyrosine 261 and 365 residues, and mutations of these sites resulted in LKB1 export into the cytoplasm and increased AMPK phosphorylation. These data demonstrate a crosstalk between Fyn tyrosine kinase and the AMPK energy-sensing pathway, through Fyn-dependent regulation of the AMPK upstream activator LKB1.

Phosphatidylinositol 3 kinase/Akt signal relay cooperates with smad in bone morphogenetic protein-2-induced colony stimulating factor-1 (CSF-1) expression and osteoclast differentiation

Murine spleen cells produce mature osteoclasts when cocultured with osteoblastic cells. Colony-stimulating factor (CSF)-1 is the growth factor required for differentiating the monocyte-macrophage precursor cells into preosteoclasts. Bone morphogenic protein (BMP) signaling in osteoblasts regulates bone mass in mice, suggesting a role of BMP in osteoclastogenesis along with osteoblast activity. The intracellular signal transduction cross talk regulating the osteoblastic production of CSF-1 as a mechanism of BMP-induced osteoclastogenesis is described in this report. We have recently described the involvement of Smad 1/5 in BMP-2-induced CSF-1 expression and osteoclast formation. In this study, using the pharmacological inhibitors and the adenovirus (Ad) vectors expressing dominant-negative (DN) phosphatidylinositol 3 kinase (PI3K), the PI3K-signaling inhibitor, phosphatase and tensin homolog deleted in chromosome 10 (PTEN) or DN Akt kinase in the in vitro coculture assay, we show an essential role of the lipid kinase cascade in BMP-2-mediated multinucleated osteoclast formation and CSF-1 mRNA expression, transcription, and secretion. Inhibition of PI3K/Akt signaling blocked the binding of Smads 1/5 to the CSF-1 BMP-responsive element present in the CSF-1 promoter, resulting in attenuation of Smad-dependent CSF-1 transcription. Furthermore, PI3K inhibition and DN Akt prevented association of the transcriptional coactivator, CREB (cAMP response element binding protein) binding protein (CBP), with Smads 1/5. Together, these data for the first time demonstrate that PI3K-dependent Akt activation regulates BMP-2-induced CSF-1 expression and provides a mechanism for osteoblastic cell-assisted osteoclast differentiation.

Platelet-derived growth factor mediates survival of leukemic large granular lymphocytes via an autocrine regulatory pathway

Large granular lymphocyte (LGL) leukemia results from chronic expansion of cytotoxic T cells or natural killer (NK) cells. Apoptotic resistance resulting from constitutive activation of survival signaling pathways is a fundamental pathogenic mechanism. Recent network modeling analyses identified platelet-derived growth factor (PDGF) as a key master switch in controlling these survival pathways in T-cell LGL leukemia. Here we show that an autocrine PDGF regulatory loop mediates survival of leukemic LGLs of both T- and NK-cell origin. We found high levels of circulating PDGF-BB in platelet-poor plasma samples from LGL leukemia patients. Production of PDGF-BB by leukemic LGLs was demonstrated by immunocytochemical staining. Leukemic cells expressed much higher levels of PDGFR-beta transcripts than purified normal CD8(+) T cells or NK cells. We observed that phosphatidylinositol-3-kinase (PI3 kinase), Src family kinase (SFK), and downstream protein kinase B (PKB)/AKT pathways were constitutively activated in both T- and NK-LGL leukemia. Pharmacologic blockade of these pathways led to apoptosis of leukemic LGLs. Neutralizing antibody to PDGF-BB inhibited PKB/AKT phosphorylation induced by LGL leukemia sera. These results suggest that targeting of PDGF-BB, a pivotal regulator for the long-term survival of leukemic LGLs, may be an important therapeutic strategy.

Angiotensin II receptor blocker attenuates PDGF-induced mesangial cell migration in a receptor-independent manner

BACKGROUND

Clinical studies have shown that angiotensin II (Ang II) type 1 (AT1) receptor blockers (ARBs) are able to provide renoprotection independent of their blood pressure lowering effects. ARBs also are reported to suppress oxidative stress, inflammation and certain other cellular responses in a receptor-independent manner. We investigated the effects of an ARB, olmesartan, on the cell migration induced by platelet-derived growth factor (PDGF), a major mitogen involved in the pathogenesis of glomerulonephritis in rat mesangial cells (RMCs).

METHODS

Cell migration was determined by a modified Boyden chamber assay. The intracellular signalling pathway was examined by western blotting. AT1 receptor expression was knocked down by small interfering RNAs. The intracellular reactive oxygen species (ROS) was measured by using a fluorescent probe. The O(2)(.-) scavenging activities were studied by the electron paramagnetic resonance-spin trapping method.

RESULTS

PDGF-induced cell migration was inhibited by olmesartan in AT1 receptor knockdown RMCs. Olmesartan attenuated big mitogen-activated protein (MAP) kinase 1 (BMK1) and Src activation by PDGF in AT1 receptor knockdown RMCs. PDGF-induced BMK1 activation was suppressed by the Src family tyrosine kinase inhibitors, indicating that Src exists upstream of BMK1. The NADPH oxidase inhibitors inhibited not only PDGF-induced BMK1 and Src activation but also RMC migration. The elevation in ROS generation induced by PDGF was decreased by olmesartan. Olmesartan displayed neither directly ROS scavenging activity nor the inhibition of ROS-mediated intracellular signalling in RMCs.

CONCLUSIONS

Olmesartan attenuates ROS generation by PDGF, leading to the subsequent inhibition of Src/ BMK1/migration in an AT1 receptor-independent manner in RMCs.

Fyn kinase function in lipid utilization: a new upstream regulator of AMPK activity?

The balance of cellular energy levels in response to changes of nutrient availability, stress stimuli or exercise is a critical step in maintaining tissue and whole body homeostasis. Disruption of this balance is associated with various pathologies, including the metabolic syndrome. Recently, accumulating evidence has demonstrated that the AMP-activated protein kinase (AMPK) plays a central role in sensing changes in energy levels. The regulation of AMPK activity is currently the subject of significant investigation since this enzyme is a potential therapeutic target in both metabolic disorders and tumorigenesis. In this review, we present novel evidence of crosstalk between Fyn, one member of the Src kinase family, and AMPK.

Toggle switches, pulses and oscillations are intrinsic properties of the Src activation/deactivation cycle

Src-family kinases (SFKs) play a pivotal role in growth factor signaling, mitosis, cell motility and invasiveness. In their basal state, SFKs maintain a closed autoinhibited conformation, where the Src homology 2 domain interacts with an inhibitory phosphotyrosine in the C-terminus. Activation involves dephosphorylation of this inhibitory phosphotyrosine, followed by intermolecular autophosphorylation of a specific tyrosine residue in the activation loop. The spatiotemporal dynamics of SFK activation controls cell behavior, yet these dynamics remain largely uninvestigated. In the present study, we show that the basic properties of the Src activation/deactivation cycle can bring about complex signaling dynamics, including oscillations, toggle switches and excitable behavior. These intricate dynamics do not require imposed external feedback loops and occur at constant activities of Src inhibitors and activators, such as C-terminal Src kinase and receptor-type protein tyrosine phosphatases. We demonstrate that C-terminal Src kinase and receptor-type protein tyrosine phosphatase underexpression or their simultaneous overexpression can transform Src response patterns into oscillatory or bistable responses, respectively. Similarly, Src overexpression leads to dysregulation of Src activity, promoting sustained self-perpetuating oscillations. Distinct types of responses can allow SFKs to trigger different cell-fate decisions, where cellular outcomes are determined by the stimulation threshold and history. Our mathematical model helps to understand the puzzling experimental observations and suggests conditions where these different kinetic behaviors of SFKs can be tested experimentally.

Catalytically inactive SHIP2 inhibits proliferation by attenuating PDGF signaling in 3T3-L1 preadipocytes

Inadequate proliferation and/or differentiation of preadipocytes may lead to adipose tissue dysfunction characterized by hypertrophied, insulin-resistant adipocytes. Platelet-derived growth factor (PDGF) may alter adipose tissue function by promoting proliferation of preadipocytes. Two principal signaling pathways that regulate proliferation are PI3K/PI(3,4,5)P3/Akt and Shc/Ras/ERK1/2. SH2 domain-containing inositol 5-phosphatase 2 (SHIP2) dephosphorylates PI(3,4,5)P3, and also binds to Shc. Our goal was to determine how SHIP2 affects these PDGF signaling routes. To assess the role of the 5-phosphatase domain, we expressed wild-type or catalytically inactive dominant-negative SHIP2 (P686A-D690A-R691A; PDR/AAA) in 3T3-L1 preadipocytes. Surprisingly, SHIP2 PDR/AAA inhibited proliferation more potently than wild-type SHIP2. After three days of proliferation, phospho-Akt, phospho-ERK1/2, and PDGF receptor (PDGFR) levels were reduced in PDR/AAA-expressing preadipocytes. SHIP2 PDR/AAA interference with PDGFR signaling was demonstrated using imatinib, an inhibitor of PDGFR tyrosine kinase. The anti-proliferative effect of imatinib observed in control preadipocytes was not significant in SHIP2 PDR/AAA-expressing preadipocytes, indicating a pre-existing impairment of PDGFR-dependent mitogenesis in these cells. The inhibition of PDGF-activated mitogenic pathways by SHIP2 PDR/AAA was consistent with a decrease in PDGFR phosphorylation caused by a drop in receptor levels in SHIP2 PDR/AAA-expressing cells. SHIP2 PDR/AAA promoted ubiquitination of the PDGFR and its degradation via the lysosomal pathway independently of the association between the E3 ubiquitin ligase c-Cbl and PDGFR. Overall, our findings indicate that SHIP2 PDR/AAA reduces preadipocyte proliferation by attenuating PDGFR signaling.

Inhibition of gluconeogenesis in primary hepatocytes by stromal cell-derived factor-1 (SDF-1) through a c-Src/Akt-dependent signaling pathway

Hepatic gluconeogenesis is elevated in diabetes and a major contributor to hyperglycemia. Stromal cell-derived factor-1 (SDF-1) is a chemokine and an activator of Akt. In this study, we tested the hypothesis that SDF-1 suppresses hepatic gluconeogenesis through Akt. Our results from isolated primary hepatocytes show that SDF-1alpha and SDF-1beta inhibited glucose production via gluconeogenesis and reduced transcript levels of key gluconeogenic genes glucose-6-phosphatase (G6Pase) and phosphoenolpyruvate carboxykinase (PEPCK). Additionally, SDF-1alpha and SDF-1beta both inhibited activation of the PEPCK promoter. In examining the mechanism by which SDF-1 inhibits gluconeogenesis, we found that SDF-1 promoted phosphorylation of Akt, FoxO1, and c-Src, but did not activate insulin receptor substrate-1-like insulin. Blockade of Akt activation by LY294002, FoxO1 translocation by constitutively nuclear FoxO1 mutant, or c-Src activation by the chemical inhibitor PP2, respectively, blunted SDF-1 suppression of gluconeogenesis. Finally, our results show that knocking down the level of SDF-1 receptor CXCR4 mRNA blocked SDF-1 suppression of gluconeogenesis. Together, our results demonstrate that SDF-1 is capable of inhibiting gluconeogenesis in primary hepatocytes through a signaling pathway distinct from the insulin signaling.

Resveratrol inhibits PDGF receptor mitogenic signaling in mesangial cells: role of PTP1B

Mesangioproliferative glomerulonephritis is associated with overactive PDGF receptor signal transduction. We show that the phytoalexin resveratrol dose dependently inhibits PDGF-induced DNA synthesis in mesangial cells with an IC(50) of 10 microM without inducing apoptosis. Remarkably, the increased SIRT1 deacetylase activity induced by resveratrol was not necessary for this inhibitory effect. Resveratrol significantly blocked PDGF-stimulated c-Src and Akt kinase activation, resulting in reduced cyclin D1 expression and attenuated pRb phosphorylation and cyclin-dependent kinase-2 (CDK2) activity. Furthermore, resveratrol inhibited PDGFR phosphorylation at the PI 3 kinase and Grb-2 binding sites tyrosine-751 and tyrosine-716, respectively. This deficiency in PDGFR phosphorylation resulted in significant inhibition of PI 3 kinase and Erk1/2 MAPK activity. Interestingly, resveratrol increased the activity of protein tyrosine phosphatase PTP1B, which dephosphorylates PDGF-stimulated phosphorylation at tyrosine-751 and tyrosine-716 on PDGFR with concomitant reduction in Akt and Erk1/2 kinase activity. PTP1B significantly inhibited PDGF-induced DNA synthesis without inducing apoptosis. These results for the first time provide evidence that the stilbene resveratrol targets PTP1B to inhibit PDGFR mitogenic signaling.

Targeting alpha-fetoprotein represses the proliferation of hepatoma cells via regulation of the cell cycle

BACKGROUND

AFP is a biomarker for primary liver cancer, yet little is known about its effect in the pathogenesis of hepatoma. We examined how AFP modulates the proliferation of hepatoma cells.

METHODS

Recombinant adenovirus expressing siRNA against AFP was created. The repression of cell proliferation in vitro and growth of hepatoma in vivo were examined by colony formation assay and tumor xenograft in SCID mice, respectively. Cell cycle was assayed by flow cytometry. Expression profile was determined by microarrays.

RESULTS

siRNA targeting reduced expression of AFP specifically and markedly inhibited the proliferation of hepatoma cells. Local treatment using Adv-AFPsiRNA caused significant repression of the growth of hepatoma derived HepG2 cells in xenograft in SCID mice. Knockdown of AFP resulted in an obvious delay in the G(1)/S transition of cell cycle, but did not affect apoptosis in HepG2 cells. Some genes related to the cell cycle, including SKP2, Cyclin D1, Csk and EBAG9 were identified.

CONCLUSIONS

The endogenous AFP is a critical determinant of the growth of hepatoma cells, which functions by regulating the cell cycle. This study suggests that targeting of AFP with siRNA could be a potential therapeutic approach for hepatoma.

Suppression of hepatic glucose production by human neutrophil alpha-defensins through a signaling pathway distinct from insulin

In this study, we tested the hypothesis that human neutrophil alpha-defensins (HNPs) inhibit hepatic glucose production through a signaling pathway distinct from insulin. The effect of HNP-1 on fasting blood glucose levels and the expression of hepatic gluconeogenic genes was first examined. Using hyperinsulinemic-euglycemic clamps, we determined the effect of HNP-1 on endogenous glucose production, hepatic expression of key gluconeogenic genes and glucose uptake in skeletal muscle in Zucker diabetic fatty rats. In isolated primary hepatocytes, we studied the effect of HNP-1 and -2 on glucose production, expression of gluconeogenic genes, and phosphorylation of Akt, c-Src, and FoxO1. Our results show that HNP-1 reduced blood glucose levels of both normal mice and Zucker diabetic fatty rats predominantly through suppression of hepatic glucose production. HNPs inhibited glycogenolysis and gluconeogenesis in isolated hepatocytes. HNPs also suppressed expression of key gluconeogenic genes including phosphoenoylpyruvate carboxyl kinase and glucose-6-phosphatase. To investigate the mechanism, we found that HNPs stimulated phosphorylation of Akt and FoxO1 without activating IRS1. Nevertheless, HNPs activated c-Src. Blockade of c-Src activity with either a chemical inhibitor PP2 or an alternative inhibitor CSK prevented the inhibitory effect of HNPs on gluconeogenesis. Together, our results support the hypothesis that HNPs can suppress hepatic glucose production through an intracellular mechanism distinct from the classical insulin signaling pathway.

Raptor-rictor axis in TGFbeta-induced protein synthesis

Transforming growth factor-beta (TGFbeta) stimulates pathological renal cell hypertrophy for which increased protein synthesis is critical. The mechanism of TGFbeta-induced protein synthesis is not known, but PI 3 kinase-dependent Akt kinase activity is necessary. We investigated the contribution of downstream effectors of Akt in TGFbeta-stimulated protein synthesis. TGFbeta increased inactivating phosphorylation of Akt substrate tuberin in a PI 3 kinase/Akt dependent manner, resulting in activation of mTOR kinase. mTOR activity increased phosphorylation of S6 kinase and the translation repressor 4EBP-1, which were sensitive to inhibition of both PI 3 kinase and Akt. mTOR inhibitor rapamycin and a dominant negative mutant of mTOR suppressed TGFbeta-induced phosphorylation of S6 kinase and 4EBP-1. PI 3 kinase/Akt and mTOR regulated dissociation of 4EBP-1 from eIF4E to make the latter available for binding to eIF4G. mTOR and 4EBP-1 modulated TGFbeta-induced protein synthesis. mTOR is present in two multi protein complexes, mTORC1 and mTORC2. Raptor and rictor are part of mTORC1 and mTORC2, respectively. shRNA-mediated downregulation of raptor inhibited TGFbeta-stimulated mTOR kinase activity, resulting in inhibition of phosphorylation of S6 kinase and 4EBP-1. Raptor shRNA also prevented protein synthesis in response to TGFbeta. Downregulation of rictor inhibited serine 473 phosphorylation of Akt without any effect on phosphorylation of its substrate, tuberin. Furthermore, rictor shRNA increased phosphorylation of S6 kinase and 4EBP-1 in TGFbeta-independent manner, resulting in increased protein synthesis. Thus mTORC1 function is essential for TGFbeta-induced protein synthesis. Our data also provide novel evidence that rictor negatively regulates TORC1 activity to control basal protein synthesis, thus conferring tight control on cellular hypertrophy.

Nitric oxide inactivates the retinoblastoma pathway in chronic inflammation

Patients with chronic inflammatory bowel disease have a high risk of colon cancer. The molecules that initiate and promote colon cancer and the cancer pathways altered remain undefined. Here, using in vitro models and a mouse model of colitis, we show that nitric oxide (NO) species induce retinoblastoma protein (pRb) hyperphosphorylation and inactivation, resulting in increased proliferation through the pRb-E2F1 pathway. NO-driven pRb hyperphosphorylation occurs through soluble guanylyl cyclase/guanosine 3',5'-cyclic monophosphate signaling and is dependent on the mitogen-activated protein kinase/extracellular signal-regulated kinase kinase MEK/ERK and phosphatidylinositol 3-kinase/AKT pathways. Our results reveal a link between NO and pRb inactivation and provide insight into molecules that can be targeted in the prevention of the inflammation-to-cancer sequence.

TGFbeta intercepts nuclear glycogen synthase kinase 3beta to inhibit PDGF-induced DNA synthesis in mesangial cells

Here, we demonstrate a mechanism of TGFbeta-mediated inhibition of PDGF-induced DNA synthesis in mesangial cells. TGFbeta significantly inhibited nuclear Akt phosphorylation without any effect on PDGF-stimulated phosphorylation of PDGFR at PI 3 kinase binding site (Tyr-751). Remarkably, TGFbeta inhibited cyclin D1 and cyclin E expression with concomitant decrease in CDK2 activity induced by PDGF. More importantly, we demonstrate that TGFbeta significantly abolished Akt-mediated serine-9 phosphorylation of glycogen synthase kinase 3beta (GSK3beta), thus prevented its inactivation. Expression of inactive GSK3betaK85R mutant increased cyclin D1 expression and DNA synthesis similar to PDGF. These results provide the first evidence that TGFbeta intercepts Akt kinase activity in the nucleus to block inactivation of GSK3beta, leading to attenuation of PDGF-induced CDK2 activity and DNA synthesis.

A novel signaling pathway for β-adrenergic receptor-mediated activation of phosphoinositide 3-kinase in H9c2 cardiomyocytes

Stimulation of cardiac β-adrenergic receptors (β-AR) activates both the Gs- and Gi-coupled signaling cascades, including the phosphoinositide 3 kinase (PI3K) pathway, that have important physiological implications. Multiple isoforms of PI3K exist in the heart. The goals of this study were to examine the intracellular signaling pathways linking β-AR to PI3K and to identify the PI3K isoform mediating this transactivation in a cardiac context. Acute β-AR stimulation with isoproterenol resulted in increased tyrosine kinase-associated PI3K activity and phosphorylation of Akt and p70S6K in H9c2 cardiomyocytes. Cotreatment with ICI-118,551, but not CGP-20712, abolished the increase in PI3K activity, suggesting a β2-AR-mediated event. PI3K activation was also abrogated by cotreatment with pertussis toxin, 4-amino-5-(4-chlorophenyl)-7-( t-butyl)pyrazolol[3,4-d]pyrimidine (PP2, a selective Src-family tyrosine kinases inhibitor), or AG-1296 [selective platelet-derived growth factor receptor (PDGFR) inhibitor] but not with an inhibitor for protein kinase A, protein kinase C, Ras, adenylyl cyclase, epidermal growth factor receptor, or insulin-like growth factor-1 receptor. β-AR stimulation induced an increase in tyrosine phosphorylation of PDGFR, which was abolished by inhibition of Src either by PP2 or small interfering RNA. Moreover, H9c2 cardiomyocytes stably transfected with a vector expressing a Gβγ sequestrant peptide derived from the COOH-terminus of β-AR kinase-1 failed to activate PI3K after β-AR stimulation, suggesting Gβγ is required for the transactivation. Furthermore, acute β-AR stimulation in vivo resulted in increases in PDGFR-associated PI3K and PI3Kα isoform activities but not the activities of other isoforms (PI3Kβ, -δ, -γ) in adult mouse heart. Taken together, these data provide in vitro and in vivo evidence for a novel mechanism of β-AR-mediated transactivation of cardiac PI3Kα via sequential involvement of Gαi/Gβγ, Src, and PDGFR.

The 5-HT transporter transactivates the PDGFbeta receptor in pulmonary artery smooth muscle cells

Serotonin (5-HT) stimulates smooth muscle cell growth through 5-HT receptors and the 5-HT transporter (5-HTT), and has been associated with pulmonary hypertension (PH). Platelet-derived growth factor receptors (PDGFR) have also been associated with PH. We present evidence for the first time that 5-HT transactivates PDGFRbeta through the 5-HTT in pulmonary artery (PA) SMCs. Inhibition of PDGFR kinase with imatinib or AG1296 blocks 5-HT-stimulated PDGFRbeta phosphorylation. 5-HTT inhibitors and the Na+/K+-ATPase inhibitor ouabain, but not 5-HT2 and 5-HT1B/1D receptor inhibitors, block PDGFRbeta activation by 5-HT. Notably, 5-HTT binds the PDGFRbeta upon 5-HT stimulation and the 5-HTT inhibitor fluoxetine blocks both the binding and PDGDRbeta activation. Activation of PDGFRbeta may occur through oxidation of a catalytic cysteine of tyrosine phosphatase. 5-HT-activated PDGFRbeta phosphorylation is blocked by the antioxidant N-acetyl-L-cysteine and the NADPH oxidase inhibitor, DPI. Inhibition of PDGFR kinase with imatinib or AG1296 significantly inhibits SMC proliferation and migration induced by 5-HT in vitro. Infusion of 5-HT by miniosmotic pumps enhances PDGFRbeta activation in mouse lung in vivo. In summary, these results demonstrate that 5-HT transactivates PDGFRbeta in PASMCs leading to SMC proliferation and migration, and may be an important signaling pathway in the production of PH in vivo.

Statin-induced Ras activation integrates the phosphatidylinositol 3-kinase signal to Akt and MAPK for bone morphogenetic protein-2 expression in osteoblast differentiation

Lovastatin promotes osteoblast differentiation by increasing bone morphogenetic protein-2 (BMP-2) expression. We demonstrate that lovastatin stimulates tyrosine phosphorylation of the p85 regulatory subunit of phosphatidylinositol 3-kinase (PI3K), leading to an increase in its kinase activity in osteoblast cells. Inhibition of PI3K ameliorated expression of the osteogenic markers alkaline phosphatase, type I collagen, osteopontin, and BMP-2. Expression of dominant-negative PI3K and PTEN, an inhibitor of PI3K signaling, significantly attenuated lovastatin-induced transcription of BMP-2. Akt kinase was also activated in a PI3K-dependent manner. However, our data suggest involvement of an additional signaling pathway. Lovastatin-induced Erk1/2 activity contributed to BMP-2 transcription. Inhibition of PI3K abrogated Erk1/2 activity in response to lovastatin, indicating the presence of a signal relay between them. We provide, as a mechanism of this cross-talk, the first evidence that lovastatin stimulates rapid activation of Ras, which associates with and activates PI3K in the plasma membrane, which in turn regulates Akt and Erk1/2 to induce BMP-2 expression for osteoblast differentiation.