Tyrphostin A9 and wortmannin perturb the Golgi complex and block proliferation of vascular smooth muscle cells

Tyrphostin A9 attenuates glioblastoma growth by suppressing PYK2/EGFR-ERK signaling pathway

PURPOSE

Glioblastoma (GBM) is a fatal primary brain tumor with extremely poor clinical outcomes. The anticancer efficiency of tyrosine kinase inhibitors (TKIs) has been shown in GBM and other cancer, with limited therapeutic outcomes. In the current study, we aimed to investigate the clinical impact of active proline-rich tyrosine kinase-2 (PYK2) and epidermal growth factor receptor (EGFR) in GBM and evaluate its druggability by a synthetic TKI-Tyrphostin A9 (TYR A9).

METHODS

The expression profile of PYK2 and EGFR in astrocytoma biopsies (n = 48) and GBM cell lines were evaluated through quantitative PCR, western blots, and immunohistochemistry. The clinical association of phospho-PYK2 and EGFR was analyzed with various clinicopathological features and the Kaplan-Meier survival curve. The phospho-PYK2 and EGFR druggability and subsequent anticancer efficacy of TYR A9 was evaluated in GBM cell lines and intracranial C6 glioma model.

RESULTS

Our expression data revealed an increased phospho-PYK2, and EGFR expression aggravates astrocytoma malignancy and is associated with patients' poor survival. The mRNA and protein correlation analysis showed a positive association between phospho-PYK2 and EGFR in GBM tissues. The in-vitro studies demonstrated that TYR A9 reduced GBM cell growth, cell migration, and induced apoptosis by attenuating PYK2/EGFR-ERK signaling. The in-vivo data showed TYR A9 treatment dramatically reduced glioma growth with augmented animal survival by repressing PYK2/EGFR-ERK signaling.

CONCLUSION

Altogether, this study report that increased phospho-PYK2 and EGFR expression in astrocytoma was associated with poor prognosis. The in-vitro and in-vivo evidence underlined translational implication of TYR A9 by suppressing PYK2/EGFR-ERK modulated signaling pathway. The schematic diagram displayed proof of concept of the current study indicating activated PYK2 either through the Ca2+/Calmodulin-dependent protein kinase II (CAMKII) signaling pathway or autophosphorylation at Tyr402 induces association to the SH2 domain of c-Src that leads to c-Src activation. Activated c-Src in turn activates PYK2 at other tyrosine residues that recruit Grb2/SOS complex and trigger ERK½ activation. Besides, PYK2 interaction with c-Src acts as an upstream of EGFR transactivator that can activate the ERK½ signaling pathway, which induces cell proliferation and cell survival by increasing anti-apoptotic proteins or inhibiting pro-apoptotic proteins. TYR A9 treatment attenuate GBM cell proliferation and migration; and induce GBM cell death by inhibiting PYK2 and EGFR-induced ERK activation.

Kinase inhibitors tyrphostin 9 and rottlerin block early steps of rabies virus cycle

Rabies virus (RABV) is a neurotropic virus that causes fatal encephalitis in humans and animals and still kills up to 59,000 people worldwide every year. To date, only preventive or post-exposure vaccination protects against the disease but therapeutics are missing. After screening a library of 80 kinases inhibitors, we identified two compounds as potent inhibitors of RABV infection: tyrphostin 9 and rottlerin. Mechanism of action studies show that both inhibitors interfere with an early step of viral cycle and can prevent viral replication. In presence of tyrphostin 9, the viral entry through endocytosis is disturbed leading to improper delivery of viral particles in cytoplasm, whereas rottlerin is inhibiting the transcription, most likely by decreasing intracellular ATP concentration, and therefore the replication of the viral genome.

Calcium around the Golgi apparatus: implications for intracellular membrane trafficking

As with other complex cellular functions, intracellular membrane transport involves the coordinated engagement of a series of organelles and machineries; in the last couple of decades more importance has been given to the role of calcium (Ca(2+)) in the regulation of membrane trafficking, which is directly involved in coordinating the endoplasmic reticulum-to-Golgi-to-plasma membrane delivery of cargo. Consequently, the Golgi apparatus (GA) is now considered not just the place proteins mature in as they move to their final destination(s), but it is increasingly viewed as an intracellular Ca(2+) store. In the last few years the mechanisms regulating the homeostasis of Ca(2+) in the GA and its role in membrane trafficking have begun to be elucidated. Here, these recent discoveries that shed light on the role Ca(2+) plays as of trigger of different steps during membrane trafficking has been reviewed. This includes recruitment of proteins and SNARE cofactors to the Golgi membranes, which are both fundamental for the membrane remodeling and the regulation of fusion/fission events occurring during the passage of cargo across the GA. I conclude by focusing attention on Ca(2+) homeostasis dysfunctions in the GA and their related pathological implications.

Changes in expression and activity of the secretory pathway Ca2+ ATPase 1 (SPCA1) in A7r5 vascular smooth muscle cells cultured at different glucose concentrations

Diabetes mellitus-related vascular disease is often associated with both a dysregulation of Ca2+ homoeostasis and enhanced secretory activity in VSMCs (vascular smooth muscle cells). Here, we employ a commonly used rat cell line for VSMCs (A7r5 cells) to investigate the effects of glucose on the expression and activity of the SPCA1 (secretory pathway Ca2+-ATPase 1; also known as ATP2C1), which is a P-type Ca2+ pump located in the Golgi apparatus that plays a key role in the secretory pathway. Our results show that mRNA expression levels of SPCA1 are significantly increased in A7r5 cells cultured in high glucose (25.0 mM)-supplemented medium compared with normal glucose (5.55 mM)-supplemented medium. SPCA1 protein expression levels and thapsigargin-insensitive Ca2+-dependent ATPase activity were also consistent with a higher than normal expression level of SPCA1 in high-glucose-cultured A7r5 cells. Analysis of AVP (arginine-vasopressin)-induced cytosolic Ca2+ transients in A7r5 cells (after pre-treatment with thapsigargin) showed faster rise and decay phases in cells grown in high glucose medium compared with cells grown in normal glucose medium, supporting the observation of increased SPCA expression/activity. The significant levels of both Ca2+-ATPase activity and AVP-induced Ca2+ transients, in the presence of thapsigargin, indicate that SPCA must play a significant role in Ca2+ uptake within VSMCs. We therefore propose that, if such increases in SPCA expression and activity also occur in primary VSMCs, this may play a substantial role in the aetiology of diabetes mellitus-associated vascular disease, due to alterations in Ca2+ homoeostasis within the Golgi apparatus.

Identification of novel small-molecule compounds that inhibit the proproliferative Kruppel-like factor 5 in colorectal cancer cells by high-throughput screening

Colorectal cancer is one of the leading causes of cancer mortality and morbidity worldwide. Previous studies indicate that the zinc finger-containing transcription factor Krüppel-like factor 5 (KLF5) positively regulates proliferation of intestinal epithelial cells and colorectal cancer cells. Importantly, inhibition of KLF5 expression in intestinal epithelial cells and colorectal cancer cells by pharmacologic or genetic means reduces their rate of proliferation. To identify additional and novel small molecules that inhibit KLF5 expression and thus colorectal cancer proliferation, we developed a reporter assay using colorectal cancer cell line (DLD-1) that stably expressed a luciferase reporter gene directed by 1,959 bp of the human KLF5 promoter upstream of the ATG start codon and performed a cell-based high-throughput screen with the Library of Pharmacologically Active Compounds that contains 1,280 biologically active compounds. The screen identified 8 potential inhibitors and 6 potential activators of the KLF5 promoter. Three potential inhibitors, wortmannin, AG17, and AG879, were further evaluated by secondary analyses. All three significantly reduced both KLF5 promoter-luciferase activity and protein level in DLD-1 cells in a dose- and time-dependent manner when compared with controls. They also significantly reduced the rate of proliferation of DLD-1 and two other colorectal cancer cell lines, HCT116 and HT29. Our results show the principle of using high-throughput screening to identify small-molecule compounds that modulate KLF5 activity and consequently inhibit colorectal cancer proliferation.

Effects of different magnitudes of cyclic stretch on Na+-K+-ATPase in skeletal muscle cells in vitro

The Na(+)-K(+)-ATPase, which plays a major role in modulation of skeletal muscle excitability and contractility, is one of the marker enzymes that senses the mechanical strain and adapts to the stimuli. Although many papers had been published on the effects of mechanical stress on Na(+)-K(+)-ATPase in aortic smooth muscle cells, little was known about the effects of different magnitudes of mechanical stretch on Na(+)-K(+)-ATPase in skeletal muscle cells. In the present study, we determined the effect of different magnitudes(6%, 12%, or 25% elongation) of cyclic stretch on the activity of the Na(+)-K(+)-ATPase and investigated possible mechanisms that might be involved in the action of stretch. The results showed the application of different magnitudes of cyclic stretch induced a magnitude-dependent increase of Na(+)-K(+)-ATPase activity in cultured skeletal muscle cells. Furthermore, inhibition of ionic fluxes through SACs prevented the action of stretch on Na(+)-K(+)-ATPase activity. The stretch-induced increase in Na(+)-K(+)-ATPase activity was not blocked by Actinomycin D. No significant changes in mRNA and total cell protein levels of Na(+)-K(+)-ATPase were detected after stretched continuous for 24 h. However, cyclic stretch increased cell surface expression of Na(+)-K(+)-ATPase alpha(1)- and alpha(2)-subunit proteins by 1.3- and 1.75-fold, respectively, and the increases in Na(+)-K(+)-ATPase activity and cell surface expression were abolished by LY-294002. These data indicated that cyclic stretch induced a "magnitude-dependent" increase of Na(+)-K(+)-ATPase activity in cultured skeletal muscle cells in vitro. The upregulation involved translocation of Na(+)-K(+)-ATPase alpha(1)- and alpha(2)-subunits to plasma membrane, not increased gene transcription. These results suggested a novel nontranscriptional mechanism for regulation of Na(+)-K(+)-ATPase in skeletal muscle cells by cyclic stretch.

Cyclic stretch translocates the alpha2-subunit of the Na pump to plasma membrane in skeletal muscle cells in vitro

The Na+-K+-ATPase and its regulation is important for maintaining membrane potential and transmembrane Na(+) gradient in all skeletal muscle cells and thus is essential for cell survival and function. In our previous study, cyclic stretch activated the Na pump in cultured skeletal muscle cells. Presently, we investigated whether this stimulation was the result of translocation of Na+-K+-ATPase from endosomes to the plasma membrane, and also evaluated the role of phosphatidylinositol 3-kinase (PI 3-kinase), the activation of which initiated vesicular trafficking and targeting of proteins to specific cell compartments. Skeletal muscle cells were stretched at 25% elongation continuous for 24h using the Flexercell Strain Unit. The plasma membrane and endosome fractions were isolated and Western blotted to localize the Na+-K+-ATPase alpha1- and alpha2-subunit protein. The results showed stretch increased Na+-K+-ATPase alpha1- and alpha2-subunit protein expression in plasma membrane fractions and decreased it in endosomes. The alpha2-subunit had a more dynamic response to mechanical stretch. PI 3-kinase inhibitors (LY294002) blocked the stretch-induced translocation of the Na+-K+-ATPase alpha2-subunit, while LY294002 had no effect on the transfer of alpha1-subunit. We concluded that cyclic stretch mainly stimulated the translocation of the alpha2-subunit of Na+-K+-ATPase from endosomes to the plasma membrane via a PI 3-kinase-dependent mechanism in cultured skeletal muscle cells in vitro, which in turn increased the activity of the Na pump.

TbVps34, the trypanosome orthologue of Vps34, is required for Golgi complex segregation

Phosphoinositides are important regulators of numerous cellular functions. The yeast class III phosphatidylinositol 3-kinase Vps34p, and its human orthologue hVPS34, are implicated in control of several key pathways, including endosome to lysosome transport, retrograde endosome to Golgi traffic, multivesicular body formation, and autophagy. We have identified the Vps34p orthologue in the African trypanosome, TbVps34. Knockdown of TbVps34 expression by RNA interference induces a severe growth defect, with a post-mitotic block to cytokinesis accompanied by a variety of morphological abnormalities. GFP2xFYVE, a chimeric protein that specifically binds phosphatidylinositol 3-phosphate, localizes to the trypanosome endosomal system and is delocalized under TbVps34 RNA interference (RNAi), confirming that TbVps34 is an authentic phosphatidylinositol 3-kinase. Expression of GFP2xFYVE enhances the TbVps34 RNAi-associated growth defect, suggesting a synthetic interaction via competition for phosphatidylinositol 3-phosphate-binding sites with endogenous FYVE domain proteins. Endocytosis of a fluid phase marker is unaffected by TbVps34 RNAi, but receptor-mediated endocytosis of transferrin and transport of concanavalin A to the lysosome are both impaired, confirming a role in membranous endocytic trafficking for TbVps34. TbVps34 knockdown inhibits export of variant surface glycoprotein, indicating a function in exocytic transport. Ultrastructural analysis revealed a highly extended Golgi apparatus following TbVps34 RNAi, whereas expression of the Golgi marker red fluorescent protein-GRASP (Grp1 (general receptor for phosphoinositides-1)-associated scaffold protein) demonstrated that trypanosomes are able to duplicate the Golgi complex but failed to complete segregation during mitosis, despite faithful replication and segregation of basal bodies and the kinetoplast. These observations implicate TbVps34 as having a role in coordinating segregation of the Golgi complex at cell division.

Involvement of glycogen synthase kinase-3beta and tau phosphorylation in neuronal Golgi disassembly

The dissociation of the neuronal Golgi complex is a classical feature observed in neurodegenerative disorders including Alzheimer's disease. The goal of this study is to determine if the phosphorylation of tau protein is involved in neuronal Golgi disassembly. Primary cortical cultures were exposed to two Golgi toxins, brefeldin A (BFA) or nordihydroguaiaretic acid (NDGA). Immunocytochemical studies using the anti58 k antibody revealed that Golgi disassembly started in exposed neurons a few minutes after treatment. BFA and NDGA induced a rapid and transient increase in tau phosphorylation in a site-specific manner on immunoblots. In addition, the increase in tau phosphorylation directly correlated with a transient dissociation of tau from the cytoskeleton and a decrease of the acetylated tubulin. Furthermore, the activity of glycogen synthase kinase-3beta (GSK-3beta) increased transiently, as demonstrated by the kinase activity assay and by immunoblottings of serine-9 and tyrosine-216 phosphorylated of GSK-3beta. A decrease of the Akt phosphorylated form was also shown. The increase in tau phosphorylation was inhibited by the GSK-3beta inhibitor, lithium. Finally, morphometric studies showed that lithium partially blocked the Golgi disassembly caused by BFA or NDGA. Together these findings indicate that GSK-3beta activity and tau phosphorylation state are involved in the maintenance of the neuronal Golgi organization.

Glucosamine enhances platelet-derived growth factor-induced DNA synthesis via phosphatidylinositol 3-kinase pathway in rat aortic smooth muscle cells

Vascular smooth muscle cells play a key role in the development of atherosclerosis. Culture of vascular smooth muscle A10 cells with high glucose for 4 weeks enhanced platelet-derived growth factor (PDGF)-induced BrdU incorporation. Since a long period of high glucose incubation was required for the effect, and it was inhibited by co-incubation with azaserine, the role of hexosamine biosynthesis in the development of atherosclerosis in diabetes was studied in A10 cells. Addition of glucosamine to the culture media enhanced PDGF-stimulated BrdU incorporation, and PDGF-induced tyrosine phosphorylation of the PDGF beta-receptor was increased by glucosamine treatment. Of the subsequent intracellular signaling pathways, PDGF-induced PDGF beta-receptor association with PLC gamma was not affected, whereas tyrosine phosphorylation of Shc, subsequent association of Shc with Grb2, and MAP kinase activation were relatively decreased. In contrast, PDGF-induced PDGF beta-receptor association with the p85 regulatory subunit of PI3-kinase and PI3-kinase activation were increased by 20% (P<0.01) and 36% (P<0.01), respectively. The intracellular signaling molecules responsible for the glucosamine effect were further examined using pharmacological inhibitors. Pretreatment with PLC inhibitor (U73122) had negligible effects, and MEK1 inhibitor (PD98059) showed only a slight inhibitory effect on the PDGF-induced BrdU incorporation. In contrast, pretreatment with PI3-kinase inhibitor (LY294002) significantly inhibited glucosamine enhancement of PDGF-induced BrdU incorporation. These findings suggest that glucosamine is involved in the development of atherosclerosis by enhancing PDGF-induced mitogenesis specifically via the PI3-kinase pathway.

Regulation of Na(+) pump expression by vascular smooth muscle cells

The Na(+) pump and its regulation is important for maintaining membrane potential and transmembrane Na(+) gradient in all mammalian cells and thus is essential for cell survival and function. Vascular smooth muscle cells (VSMC) have a relatively low number of pump sites on their membrane compared with other cells. We wished to determine the mechanisms for regulating the number of pump sites in these cells. We used canine saphenous vein VSMC cultured in 10% serum and passaged one time. These cells were subcultured in 5% serum media with low K(+) (1 mM vs. control of 5 mM), and their pump expression was assessed. These VSMC upregulated their pump sites as early as 4 h after treatment (measured by [(3)H]ouabain binding). At this early time point, there was no detectable increase in protein expression of either alpha(1)- or beta(1)-subunits of the pump shown by Western blots. When the cells were treated with the phosphoinositide 3-kinase (PI-3-K) inhibitor LY-294002 (which is known to inhibit cytoplasmic transport processes) in low-K(+) media, the pump site upregulation was inhibited. These data suggest that the low-K(+)-induced upregulation of Na(+) pump number can occur by translocation of preformed pumps from intracellular stores.

Phenotypic modulation of arterial smooth muscle cells is associated with prolonged activation of ERK1/2

Arterial smooth muscle cells grown in primary culture on a substrate of fibronectin in serum-free medium are converted from a contractile to a synthetic phenotype. This process is dependent on integrin signaling and includes a major structural reorganization with loss of myofilaments and formation of a large secretory apparatus. Functionally, the cells lose their contractility and become competent to migrate, secrete extracellular matrix components, and proliferate in response to growth factor stimulation. Here, it is demonstrated that the mitogen-activated protein kinases ERK1/2 play a vital role in the fibronectin-mediated modification of rat aortic smooth muscle cells. Immunoblotting showed that phosphorylated ERK1/2 (p44/p42) were expressed throughout the period when the change in phenotypic properties of the cells took place. Moreover, phosphorylated ERK1/2 accumulated in the nucleus as revealed by immunocytochemical staining. Additional support for an active role of ERK1/2 in the shift in smooth muscle phenotype was obtained by the finding that PD98059, an inhibitor of the upstream kinase MEK1, potently suppressed both the expression of phosphorylated ERK1/2 and the fine structural rebuilding of the cells. In conclusion, the observations point to an important and multifaceted role of ERK1/2 in the regulation of differentiated properties and growth of vascular smooth muscle cells.

Distinct classes of phosphatidylinositol 3'-kinases are involved in signaling pathways that control macroautophagy in HT-29 cells

3-Methyladenine which stops macroautophagy at the sequestration step in mammalian cells also inhibits the phosphoinositide 3-kinase (PI3K) activity raising the possibility that PI3K signaling controls the macroautophagic pathway (Blommaart, E. F. C., Krause, U., Schellens, J. P. M., Vreeling-Sindelárová, H., and Meijer, A. J. (1997) Eur. J. Biochem. 243, 240-246). The aim of this study was to identify PI3Ks involved in the control of macroautophagic sequestration in human colon cancer HT-29 cells. An increase of class I PI3K products (phosphatidylinositol 3,4-bisphosphate and phosphatidylinositol 3,4,5-triphosphate) caused by either feeding cells with synthetic lipids (dipalmitoyl phosphatidylinositol 3, 4-bisphosphate and dipalmitoyl phosphatidylinositol 3,4, 5-triphosphate) or by stimulating the enzymatic activity by interleukin-13 reduced macroautophagy. In contrast, an increase in the class III PI3K product (phosphatidylinositol 3-phosphate), either by feeding cells with a synthetic lipid or by overexpressing the p150 adaptor, stimulates macroautophagy. Transfection of a specific class III PI3K antisense oligonucleotide greatly inhibited the rate of macroautophagy. In accordance with a role of class III PI3K, wortmannin (an inhibitor of PI3Ks) inhibits macroautophagic sequestration and protein degradation in the low nanomolar range (IC(50) 5-15 nM). Further in vitro enzymatic assay showed that 3-methyladenine inhibits the class III PI3K activity. Dipalmitoyl phosphatidylinositol 3-phosphate supplementation or p150 overexpression rescued the macroautophagic pathway in HT-29 cells overexpressing a GTPase-deficient mutant of the Galpha(i3) protein suggesting that both class III PI3K and trimeric G(i3) protein signaling are required in the control macroautophagy in HT-29 cells. In conclusion, our results demonstrate that distinct classes of PI3K control the macroautophagic pathway in opposite directions. The roles of PI3Ks in macroautophagy are discussed in the context of membrane recycling.

Differential mRNA expression and subcellular locations of PI3-kinase isoforms in sympathetic and sensory neurons

Phosphatidylinositol 3-kinase (PI3-kinase) enzymes are key signalling molecules in the PC12 and neuronal cell survival pathway and are also involved in the regulation of retrograde axonal transport of nerve growth factor (NGF), with sympathetic neurons more sensitive to the effects of wortmannin/LY294002 than sensory neurons (Bartlett et al. [1997]; Brain Res. 761:257-262; Reynolds et al. [1998] Brain Res. 798:67-74). In this article, we characterized the mRNA expression of PI3-kinase isoforms in mouse sympathetic superior cervical ganglia (SCG) and sensory trigeminal ganglia (TGG) and examined the subcellular locations of immunoreactivity of the PI3-kinase isoforms in mouse cultured SCG and dorsal root ganglion (DRG) neurons. Both the SCG and the TGG express mRNA for the p110alpha, beta, gamma, delta, and vps34p PI3-kinase isoforms, but the TGG and not the SCG express mRNA for the p170 PI3-kinase isoform. In cultured SCG and DRG neurons, p110alpha, beta, and gamma immunoreactivity is in the SCG and DRG growth cones, and predominantly in puncta throughout the growth cone varicosity. However, in the cell bodies immunoreactivity varied, p110alpha is localized predominantly at the plasma membrane, while p110beta and gamma is localized in the perinuclear region of the cells. In addition, unlike other cell types, wortmannin has little effect on actin filament polymerization in either mouse cultured SCG or DRG neurons.