Pathway crosstalk between Ras/Raf and PI3K in promotion of M-CSF-induced MEK/ERK-mediated osteoclast survival

While M-CSF-mediated MEK/ERK activation promotes osteoclast survival, the signaling pathway by which M-CSF activates MEK/ERK is unresolved. Functions for PI3K, Ras, and Raf have been implicated in support of osteoclast survival, although interaction between these signaling components has not been examined. Therefore, the interplay between PI3K, Ras and Raf in M-CSF-promoted MEK/ERK activation and osteoclast survival was investigated. M-CSF activates Ras to coordinate activation of PI3K and Raf/MEK/ERK, since Ras inhibition decreased PI3K activation and PI3K inhibition did not block M-CSF-mediated Ras activation. As further support for Ras-mediated signaling, constitutively active (ca) Ras promoted MEK/ERK activation and osteoclast survival, which was blocked by inhibition of PI3K or Raf. Moreover, PI3K-selective or Raf-selective caRas were only partially able to promote osteoclast survival when compared to parental caRas. We then examined whether PI3K and Raf function linearly or in parallel downstream of Ras. Expression of caPI3K increased MEK/ERK activation and promoted osteoclast survival downstream of M-CSF, supporting this hypothesis. Blocking Raf did not decrease osteoclast survival and MEK/ERK activation promoted by caPI3K. In addition, PI3K-selective Ras-mediated survival was not blocked by Raf inhibition. Taken together, our data support that Raf signaling is separate from Ras/PI3K signaling and PI3K signaling is separate from Ras/Raf signaling. These data therefore support a role for Ras in coordinate activation of PI3K and Raf acting in parallel to mediate MEK/ERK-promoted osteoclast survival induced by M-CSF.     

Inhibition of glycolytic metabolism in glioblastoma cells by Pt3glc combinated with PI3K inhibitor via SIRT3-mediated mitochondrial and PI3K/Akt–MAPK pathway

Glioblastoma multiforme (GBM) is the most malignant and aggressive glioma with abnormal expression of genes that mediate glycolytic metabolism and tumor cell growth. Petunidin-3-O-glucoside (Pt3glc) is a kind of anthocyanin in the red grape and derived beverages, representing the most common naturally occurring anthocyanins with a reduced incidence of cancer and heart diseases. In this study, whether Pt3glc could effectively regulate glycolysis to inhibit GBM cell was investigated by using the DBTRG-05MG cell lines. Notably, Pt3glc displayed potent antiproliferative activity and significantly changed the protein levels related to both glycolytic metabolism and GBM cell survival. The expression of the proapoptotic protein Bcl-2-associated X protein was increased with concomitant reduction on the levels of the antiapoptotic protein B-cell lymphoma 2 and caspase-3 activity. Furthermore, the levels of survival signaling proteins, such as protein kinase B (Akt) and phospho-Akt (Scr473), extracellular signal-regulated kinase (ERK) and phospho-ERK, were significantly decreased by Pt3glc in combination with the phosphoinositide 3-kinase (PI3K) inhibitor of LY294002. Most importantly, the levels of Sirtuin 3 (SIRT3) and phosphorylated p53 were also downregulated, indicating that Pt3glc combinated with PI3K inhibitor could induce GBM cell death may act via the SIRT3/p53-mediated mitochondrial and PI3K/Akt-ERK pathways. Our findings thus provide rational evidence that the combination of Pt3glc with PI3K inhibitor, which target alternative pathways in GBM cells, may be a useful adjuvant therapy in glioblastoma treatment.     

PI3K is required for insulin-stimulated but not EGF-stimulated ERK1/2 activation

The Ras/Raf/extracellular signal-regulated kinase 1 and 2 (ERK1/2) signaling pathway is known to cross-talk with other signaling pathways, including phosphatidylinositol 3-kinase (PI3K)/Akt pathway. However, the role of PI3K in ERK-1/2 activation induced by tyrosine kinase receptors was not fully understood. Here, we report that two structurally distinct PI3K inhibitors, wortmannin and LY294002, inhibited insulin-induced activation of ERK1/2 but had no effect on EGF-induced activation of ERK1/2 in hepatocellular carcinoma BEL-7402 and SMMC-7721 cells, breast cancer MCF-7 cells, and prostate cancer LNCaP cells. Although protein kinase C could act as a mediator between PI3K and ERK1/2, protein kinase C inhibitor chelerythrine chloride did not inhibit insulin-induced ERK1/2 activation. Both insulin- and EGF-induced ERK1/2 activation are strictly dependent on Ras activation, however, wortmannin only inhibited insulin-induced, but not EGF-induced Ras activation. These results indicate that PI3K plays different roles in the activation of Ras/ERK1/2 signaling by insulin and EGF, and that insulin-stimulated, but not EGF-stimulated, ERK1/2 and Akt signalings diverge at PI3K.     

TIMP-1 stimulates proliferation of human aortic smooth muscle cells and Ras effector pathways

Tissue inhibitor of metalloproteinases-1 (TIMP-1) is a multifunctional protein, which is found in most tissues and body fluids. Here, we demonstrated that recombinant TIMP-1 but not the synthetic matrix metalloproteinase inhibitor, GM6001, stimulated proliferation of human aortic smooth muscle cells (AoSMC) in a dose-dependent manner. The mitogenic effect was associated with activation of Ras, increased phosphorylation of ERK, and stimulation of cyclin D1 expression. The phosphatidylinositol 3-kinase (PI3K) signaling pathway was also involved since the PI3K inhibitor, LY294002, abolished the TIMP-1-mediated growth stimulation. These data suggest that TIMP-1 activates Ras, which then turns on the ERK and PI3K signaling pathways to promote cell cycle progression of the AoSMC.     

Interactions of opioid and chemokine receptors: oligomerization of mu,kappa, and delta with CCR5 on immune cells

In this study, we examined the signaling pathways for extracellular signal-related protein kinase (ERK) activation by three structurally different peroxisome proliferator activated receptor-gamma (PPARgamma) agonists. In murine C2C12 myoblasts, treatment with 15-deoxy-Delta(12,14)-prostaglandin J(2) (15d-PGJ(2)), ciglitazone, and GW1929 leads to ERK1/2 phosphorylation in a time- and concentration-dependent manner. Consistent with ERK phosphorylation, mitogen activated protein/ERK kinase (MEK) phosphorylation as well as Raf-1 kinase activity are also accordingly stimulated, while the constitutive Ser259 phosphorylation of Raf-1 is decreased. The ERK phosphorylation induced by PPARgamma agonists is not blocked by the PKC inhibitors GF109203X and Ro31-8220, the PI3K inhibitor wortmannin, the Ras inhibitor FPTI, the negative mutant of Ras, or the PPARgamma antagonist bisphenol A diglycidil ether. Expression of PPARgamma2 without DNA binding domain or with a nonphosphorylatable mutant (S112A) fails to change ERK phosphorylation by 15d-PGJ(2). On the contrary, the ERK phosphorylation by PPARgamma agonists is inhibited by the MEK inhibitor PD98059, GSH, and permeable SOD mimetic MnTBAP. Chemiluminescence study reveals that these three PPARgamma agonists are able to induce superoxide anion production, with an efficacy similar to their action on ERK phosphorylation. Consistent with this notion, we also show that superoxide anion donor 2,3-dimethoxy-1,4-naphoquinone elicits ERK phosphorylation. In this study, we for the first time demonstrate a novel mechanism, independent of Ras activation but initiated by superoxide anion production, for PPARgamma agonists to trigger the Raf-MEK-ERK1/2 signaling pathway.     

Phosphatidylinositol 3-kinase regulation of gastrin-releasing peptide-induced cell cycle progression in neuroblastoma cells

Gastrin-releasing peptide (GRP), the mammalian equivalent of bombesin (BBS), is an autocrine growth factor for neuroblastoma; its receptor is up-regulated in undifferentiated neuroblastomas. Phosphatidylinositol 3-kinase (PI3K) is a critical cell survival pathway; it is negatively regulated by the PTEN tumor suppressor gene. We have recently found that poorly differentiated neuroblastomas express decreased PTEN protein levels. Moreover, overexpression of the GRP receptor, a member of the G-protein coupled receptor family, down-regulates PTEN expression, resulting in increased neuroblastoma cell growth. Therefore, we sought to determine whether GRP or BBS activates PI3K in neuroblastoma cells (BE(2)-C, LAN-1, SK-N-SH). GRP or BBS treatment rapidly increased phosphorylation of Akt and GSK-3beta in neuroblastoma cells. Inhibition of GRP receptor, with antagonist GRP-H2756 or siRNA, attenuated BBS-induced phosphorylation of Akt. LY294002, a PI3K inhibitor, also abrogated BBS-stimulated phospho-Akt as well as its cell cycle targets. GRP increased G1/S phase progression in SK-N-SH cells. BBS-mediated BrdU incorporation was blocked by LY294002. Our findings identify PI3K as an important signaling pathway for GRP-mediated neuroblastoma cell growth. A novel therapy targeted at GRP/GRP receptor may prove to be an effective treatment option to inhibit PI3K in neuroblastomas.     

Akt/PKB activity is required for Ha-Ras-mediated transformation of intestinal epithelial cells

Phosphatidylinositol 3-kinase (PI3K)/protein kinase B (PKB/Akt) is thought to serve as an oncogenic signaling pathway which can be activated by Ras. The role of PI3K/Akt in Ras-mediated transformation of intestinal epithelial cells is currently not clear. Here we demonstrate that inducible expression of oncogenic Ha-Ras results in activation of PKB/Akt in rat intestinal epithelial cells (RIE-iHa-Ras), which was blocked by treatment with inhibitors of PI3K activity. The PI3K inhibitor, LY-294002, partially reversed the morphological transformation induced by Ha-Ras and resulted in a modest stimulation of apoptosis. The most pronounced phenotypic alteration following inhibition of PI3K was induction of G(1) phase cell cycle arrest. LY-294002 blocked the Ha-Ras-induced expression of cyclin D1, cyclin-dependent kinase (CDK) 2, and increased the levels of p27(kip). Both LY-294002 and wortmannin significantly reduced anchorage-independent growth of RIE-iHa-Ras cells. Forced expression of both the constitutively active forms of Raf (DeltaRaf-22W or Raf BXB) and Akt (Akt-myr) resulted in transformation of RIE cells that was not achieved by transfection with either the Raf mutant construct or Akt-myr alone. These findings delineate an important role for PI3K/Akt in Ras-mediated transformation of intestinal epithelial cells.     

RasGRPs Are Targets of the Anti-Cancer Agent Ingenol-3-Angelate

Ingenol-3–angelate (I3A) is a non-tumor promoting phorbol ester-like compound identified in the sap of Euphoria peplus. Similar to tumor promoting phorbol esters, I3A is a diacylglycerol (DAG) analogue that binds with high affinity to the C1 domains of PKCs, recruits PKCs to cellular membranes and promotes enzyme activation. Numerous anti-cancer activities have been attributed to I3A and ascribed to I3A’s effects on PKCs. We show here that I3A also binds to and activates members of the RasGRP family of Ras activators leading to robust elevation of Ras-GTP and engagement of the Raf-Mek-Erk kinase cascade. In response to I3A, recombinant proteins consisting of GFP fused separately to full-length RasGRP1 and RasGRP3 were rapidly recruited to cell membranes, consistent with direct binding of the compound to RasGRP’s C1 domain. In the case of RasGRP3, IA3 treatment led to positive regulatory phosphorylation on T133 and activation of the candidate regulatory kinase PKCδ. I3A treatment of select B non-Hodgkin’s lymphoma cell lines resulted in quantitative and qualitative changes in Bcl-2 family member proteins and induction of apoptosis, as previously demonstrated with the DAG analogue bryostatin 1 and its synthetic analogue pico. Our results offer further insights into the anticancer properties of I3A, support the idea that RasGRPs represent potential cancer therapeutic targets along with PKC, and expand the known range of ligands for RasGRP regulation.     

Ligand-independent regulation of ErbB4 receptor phosphorylation by activated Ras

The ErbB family of receptor tyrosine kinases regulates cell growth, differentiation and survival. Activation of the receptors is induced by specific growth factors in an autocrine, paracrine or juxtacrine manner. The activated ErbB receptors turn on a large variety of signaling cascades, including the prominent Ras-dependent signaling pathways. The activated Ras can induce secretion of growth factors such as EGF and neuregulin, which activate their respective receptors. In the present study, we demonstrate for the first time that activated Ras can activate ErbB4 receptor in a ligand-independent manner. Expression of constitutively active H-Ras(12V), K-Ras(12V) or N-Ras(13V) in PC12-ErbB4 cells induced ErbB4-receptor phosphorylation, indicating that each of the most abundant Ras isoforms can induce receptor activation. NRG-induced phosphorylation of ErbB4 receptor was blocked by the soluble ErbB4 receptor, which had no effect on the Ras-induced receptor phosphorylation. Moreover, conditioned medium from H-Ras(12V)-transfected PC12-ErbB4 cells had no effect on receptor phosphorylation. It thus indicates that Ras induces ErbB4 phosphorylation in a ligand-independent manner. Each of the Ras effector domain mutants, H-Ras(12V)S35, H-Ras(12V)C40, and H-Ras(12V)G37, which respectively activate Raf1, PI3K, and RalGEF, induced a small but significant receptor phosphorylation. The PI3K inhibitor LY294002 and the MEK inhibitor PD98059 caused a partial inhibition of the Ras-induced ErbB4 receptor phosphorylation. Using a mutant ErbB4 receptor, which lacks kinase activity, we demonstrated that the Ras-mediated ErbB4 phosphorylation depends on the kinase activity of the receptor and facilitates ligand-independent neurite outgrowth in PC12-ErbB4 cells. These experiments demonstrate a novel mechanism controlling ErbB receptor activation. Ras induces ErbB4 receptor phosphorylation in a non-autocrine manner and this activation depends on multiple Ras effector pathways and on ErbB4 kinase activity.     

Effect of constitutively active Ras overexpression on cell growth in recombinant Chinese hamster ovary cells

Constitutively active Ras (CA-Ras) is known to enhance cell growth through the induction of various signaling cascades including the phosphoinositide 3-kinase (PI3K)/Akt and mitogen-activated protein kinase (MAPK)/ERK signaling pathways, although the cellular response is highly dependent on the cell type. To evaluate the effect of CA-Ras overexpression on cell growth in recombinant Chinese hamster ovary (rCHO) cells, an erythropoietin (EPO)-producing rCHO cell line with regulated CA-Ras overexpression (EPO-off-CA-Ras) was established using the Tet-off system. The CA-Ras expression level in EPO-off-CA-Ras cells was tightly regulated by doxycycline addition. Although CA-Ras overexpression slightly increased the viable cell concentration during the late exponential phase, it did not increase the maximum viable cell concentration or specific growth rate to a significant degree. Unexpectedly, CA-Ras overexpression in rCHO cells led only to the enhancement in the activation of the MAPK/ERK signaling pathway and not the PI3K/Akt signaling pathway. Taken together, CA-Ras overexpression in rCHO cells did not significantly affect cell growth; it also had no critical impact on viable cell concentration or EPO production, possibly due to a failure to activate the PI3K/Akt signaling pathway.     

Activation of PI3K and R‐ras signaling promotes the extension of sensory axons on inhibitory chondroitin sulfate proteoglycans

Chondroitin sulfate proteoglycans (CSPGs) are extracellular inhibitors of axon extension and plasticity, and cause growth cones to exhibit dystrophic behaviors. Phosphoinositide 3‐kinase (PI3K) is a lipid kinase activated by axon growth promoting signals. In this study, we used embryonic chicken dorsal root ganglion neurons to determine if CSPGs impair signaling through PI3K. We report that CSPGs inhibit PI3K signaling in axons and growth cones, as evidenced by decreased levels of phosphorylated downstream kinases (Akt and S6). Direct activation of PI3K signaling, using a cell permeable phosphopeptide (PI3Kpep), countered the effects of CSPGs on growth cones and axon extension. Both overnight and acute treatment with PI3Kpep promoted axon extension on CSPG‐coated substrates. The R‐Ras GTPase is an upstream positive regulator of PI3K signaling. Expression of constitutively active R‐Ras promoted axon extension and growth cone elaboration on CSPGs and permissive substrata. In contrast, an N‐terminus‐deleted constitutively active R‐Ras, deficient in PI3K activation, promoted axon extension but not growth cone elaboration on CSPGs and permissive substrata. These data indicate that activation of R‐Ras‐PI3K signaling may be a viable approach for manipulating axon extension on CSPGs. © 2014 Wiley Periodicals, Inc. Develop Neurobiol 74: 918–933, 2014     

Homocysteine induces smooth muscle cell proliferation through differential regulation of cyclins A and D1 expression

The mechanism of homocysteine‐induced cell proliferation in human vascular smooth muscle cells (SMCs) remains unclear. We investigated the molecular mechanisms by which homocysteine affects the expression of cyclins A and D1 in human umbilical artery SMCs (HUASMCs). Homocysteine treatment induced proliferation of HUASMCs and increased the expression levels of cyclins A and D1. Knocking down either cyclin A or cyclin D1 by small interfering RNA (siRNA) inhibited homocysteine‐induced cell proliferation. Furthermore, treatment with extracellular signal‐related kinase (ERK) inhibitor (PD98059) and dominant negative Ras (RasN17) abolished homocysteine‐induced cyclin A expression; and treatment with phosphatidylinositol 3‐kinase (PI3K) inhibitor (LY294002) and mammalian target of rapamycin (mTOR) inhibitor (rapamycin) attenuated the homocysteine‐induced cyclin D1 expression. Homocysteine also induced transient phosphorylation of ERK, Akt, and p70 ribosomal S6 kinase (p70S6K). Neutralizing antibody and siRNA for β1 integrin blocked cell proliferation, expression of cyclins A and D1, and phosphorylation of ERK and Akt. In conclusion, homocysteine‐induced differential activation of Ras/ERK and PI3K/Akt/p70S6K signaling pathways and consequent expression of cyclins A and D1 are dependent on β1 integrin. Homocysteine may accelerate progression of atherosclerotic lesions by promoting SMC proliferation. J. Cell. Physiol. 226: 1017–1026, 2011. © 2010 Wiley‐Liss, Inc.     

Increased sensitivity to the platelet-derived growth factor (PDGF) receptor inhibitor STI571 in chemoresistant glioma cells is associated with enhanced PDGF-BB-mediated signaling and STI571-induced Akt inactivation

The platelet-derived growth factor receptor (PDGFR) is a tyrosine kinase, implicated in the development and progression of different tumors, including gliomas. Chemoresistance is a common feature of malignant gliomas. Since receptor tyrosine kinases contribute to chemoresistance in tumors, we addressed whether PDGFR signaling might confer selective growth advantage to chemoresistant cells. The effects of the PDGFR inhibitor STI571 on proliferation and PDGFR signaling were compared in chemosensitive and cisplatin-selected, chemoresistant sublines derived from glioma and from two other PDGFR-expressing tumors (ovarian carcinoma and neuroblastoma). The chemoresistant glioma U87/Pt cells were twofold more sensitive to STI571 growth-inhibitory effects than the chemosensitive U87 cells, and two- to threefold more sensitive than five unrelated glioma cell lines. The other two paired cell lines were equally responsive. Sensitization of U87/Pt cells correlated with upregulation of the PDGF-B isoform and with PDGF-BB-induced Akt overactivation, which was prevented by STI571. STI571 specifically inhibited PDGF-BB-, but not PDGF-AA- or stem cell factor-mediated signaling. In serum-containing medium, STI571 decreased phospho-Akt in U87/Pt cells, but not in U87, while activating extracellular signal-regulated kinase (Erk) in both. STI571 antiproliferative effects were partially reverted by constitutively active Akt. Cotreatment with inhibitors of phosphatidylinositol 3'-kinase (PI3K) or mitogen-activated protein kinase kinase (MEK) resulted in enhanced growth inhibition in glioma cells. Our results suggest that increased PDGF-BB signaling may sensitize chemoresistant glioma cells to STI571, suggesting a therapeutic potential for STI571 in patients with malignant gliomas refractory to chemotherapy. Simultaneous blockade of PDGFR and PI3K or Erk pathway may enhance therapeutic targeting in gliomas.     

Regulation of the phosphatidylinositol 3-kinase-Akt and the mitogen-activated protein kinase pathways by ursolic acid in human endometrial cancer cells

The phosphatidylinositol 3-kinase-Akt (PI3K-Akt) pathway and the mitogen activated protein kinase (MAPK) pathway are important in the development and proliferation of various human cancers. It has been found recently that ursolic acid treatment affects growth and apoptosis in cancer cells. We sought to determine whether prominent signaling pathways, including the PI3K-Akt pathway and the MAPK (JNK, P38, and P44/42) pathway mediate these effects. Endometrial cancer cells often have high levels of phosphorylated Akt seen in conjunction with a PTEN mutation or deletion. Elevation in Akt protects the cancer cell from apoptosis. Ursolic acid treatment moderately decreased PI3K levels in SNG-II cells. Treatment also decreased phospho-Akt and phospho-P44/42 in a dose- and time-dependent fashion, dramatically in SNG-II cells and moderately in HEC108 cells. This effect was most pronounced following treatment with 50 mum ursolic acid for 72 h. Our study found inhibition of both the PI3K-Akt pathway and the MAPK pathway in two endometrial cancer cell lines, SNG-II and the poorly differentiated HEC108 cell line.     

Modulation of amino acid uptake by TGF-beta in lung myofibroblasts

Hormones such as insulin, growth factors, and cell stress stimulate system A amino acid transporter. Transforming growth factor-beta (TGF-beta) stimulates amino acid uptake thereby inducing cell proliferation, cellular hypertrophy, and matrix synthesis. Insulin appears to activate amino acid in smooth muscle cells via a phosphatidylinositol 3-kinase (PI3-kinase)-dependent pathway. We examine the effect and interaction of TGF-beta, insulin, and PI3-kinase activity on amino acid uptake in human lung myofibroblasts. TGF-beta treatment induced large increases in system A activity and a small delayed increase in the phosphorylation of protein kinase B, also termed phospho-Akt. In contrast, insulin induced small increases in system A activity and large increases in phospho-Akt levels. LY294002, a PI3-kinase inhibitor, blocked the TGF-beta-induced amino acid uptake only partially, but completely blocked TGF-beta-induced Akt phosphorylation. Moreover, the level of phospho-Smad3 was found to be high even when LY294002 blocked TGF-beta-induced phospho-Akt levels. Inhibition of PI3-kinase activity resulted in increase in Km, consistent with a major change in transporter activity without change in transporter number. The PI3-kinase inhibitor also did not change the amino acid transporter 2 (ATA2) mRNA levels. Taken together, these results suggest that TGF-beta induced Smad-3 and amino acid uptake through a PI3-kinase independent pathway.     

Pertussis toxin activates tyrosine kinase signaling cascade in myelomonocytic cells: a mechanism for cell adhesion

Pertussis toxin (PTX) has recently been shown to specifically bind to CD14 to promote myelomonocytic cell adhesion to serum. The present study investigated the signaling mechanisms responsible for PTX-induced differentiated U937 cell adhesion. PTX-induced myelomonocytic cell adhesion was blocked by genistein or tyrphostin-47 (two protein tyrosine kinase inhibitors), LY294002 (a phosphatidylinositol 3-kinase (PI3K) inhibitor), or PD098059 (a mitogen-activated protein kinase (MAPK)/extracellular signal-regulated kinase (ERK) kinase (MEK) inhibitor). PTX induced a rapid tyrosine phosphorylation of several discrete cytoplasmic proteins, which could be inhibited by genistein or tyrphostin 47. In addition, PTX induced phosphorylation of Akt and of ERK2, which could be completely blocked by LY294002 and PD098059, respectively, and by genistein or tyrphostin 47 as well. All of these PTX-induced signaling events could be reproduced using purified PTX B-oligomer (PTX-B) alone. Our data show that PTX can activate tyrosine kinase signaling cascade, including the downstream PI3K and ERK/MAPK pathways, in myelomonocytic cells to induce cell adhesion to serum.     

Activity-dependent NMDA receptor-mediated activation of protein kinase B/Akt in cortical neuronal cultures

The serine/threonine protein kinase B (PKB)/Akt is a phosphoinositide 3-kinase (PI3K) effector that is thought to play an important roll in a wide variety of cellular events. The present study examined whether PKB activation in cortical neuronal cultures is coupled with synaptic activity. A 1-h incubation of neuronal cultures with tetrodotoxin (TTX), the PI3K inhibitor wortmannin, the NMDA receptor antagonist MK-801 or removal of extracellular calcium significantly reduced basal levels of phospho(Ser473)-PKB, indicating that activity-dependent glutamate release maintains PKB activation through an NMDA receptor-PI3K pathway. A 5-min exposure to NMDA (50 micro m) in the presence of TTX increased phospho-PKB back to levels observed in the absence of TTX. NMDA stimulation of phospho-PKB was blocked by wortmannin, the CaMKII inhibitor KN-93, MK-801, and removal of extracellular calcium. We have previously shown that NMDA receptors can bi-directionally regulate activation of extracellular-signal regulated kinase (ERK), and NMDA receptor stimulation of PKB in the present study appeared to mirror activation of ERK. These results suggest that in cultured cortical neurons, PKB activity is dynamically regulated by synaptic activity and is coupled to NMDA receptor activation. In addition, NMDA receptor activation of ERK and PKB may occur through overlapping signaling pathways that bifurcate at the level of Ras.     

AND-34 activates phosphatidylinositol 3-kinase and induces anti-estrogen resistance in a SH2 and GDP exchange factor-like domain-dependent manner

AND-34, a 95-kDa protein with modest homology to Ras GDP exchange factors, associates with the focal adhesion protein p130Cas. Overexpression of AND-34 confers anti-estrogen resistance in breast cancer cell lines, a property linked to its ability to activate Rac. Here, we show that both the GDP exchange factor-like domain and the SH2 domain of AND-34 are required for Rac activation and for resistance to the estrogen receptor (ER) antagonist ICI 182,780. As phosphatidylinositol 3-kinase (PI3K) signaling can regulate Rac activation, we examined the effects of AND-34 on PI3K. Overexpression of AND-34 in MCF-7 cells increased PI3K activity and augmented Akt Ser(473) phosphorylation and kinase activity. Inhibition of PI3K with LY294002 or a dominant-negative p85 construct blocked AND-34-mediated Rac and Akt activation. Although R-Ras can activate PI3K, transfection with constitutively active R-Ras failed to induce Rac activation and AND-34 overexpression failed to induce R-Ras activation. Treatment of either vector-only or AND-34-transfected ZR-75-1 cells with ICI 182,780 markedly diminished ERalpha levels, suggesting that AND-34-induced anti-estrogen resistance is likely to occur by an ERalpha-independent mechanism. Treatment of a ZR-75-1 breast cancer cell line stably transfected with AND-34 plus 2 micromol/L LY294002 or 10 micromol/L NSC23766, a Rac-specific inhibitor, abrogated AND-34-induced resistance to ICI 182,780. Our studies suggest that AND-34-mediated PI3K activation induces Rac activation and anti-estrogen resistance in human breast cancer cell lines.     

Regulation of alpha3 nicotinic acetylcholine receptor subunit mRNA levels by nerve growth factor and cyclic AMP in PC12 cells

To investigate the effects of nerve growth factor (NGF) and cyclic AMP (cAMP) on the level of the nicotinic acetylcholine receptor subunit alpha3 mRNA, we used PC12h cells, PC12 cells expressing dominant-negative Ras protein, and the parental PC12 cells. PC12h cells have NGF-responsive tyrosine hydroxylase activity. Expression of dominant-negative Ras protein prevents the signaling through the Ras-mitogen-activated protein kinase cascade. The morphological changes of the parental PC12 cells in response to NGF and 8-(4-chlorophenylthio)adenosine 3',5'-cyclic monophosphate (CPTcAMP), a cell-penetrating cAMP analogue, were similar to those of PC12h cells. NGF up-regulated the alpha3 mRNA level in PC12h cells and down-regulated the alpha3 mRNA level in the parental PC12 cells. Expression of dominant-negative Ras protein and an inhibitor of mitogen-activated protein kinase kinase inhibited the effects of NGF on alpha3 mRNA level. CPTcAMP down-regulated the alpha3 mRNA level in all three PC12 cell lines. An inhibitor of protein kinase A inhibited the CPTcAMP-induced down-regulation of alpha3 mRNA. The alpha3 mRNA down-regulation required prolonged treatment with CPTcAMP even after cAMP response element binding protein phosphorylation was decreased. Membrane depolarization with high K+ had no effect on the alpha3 mRNA level in PC12h cells. Based on these results, we propose that at least two unknown effectors regulate alpha3 mRNA levels in PC12 cells.