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PubMed1997

Cripto-1 inhibits beta-casein expression in mammary epithelial cells through a p21ras-and phosphatidylinositol 3'-kinase-dependent pathway.

Cripto-1 (CR-1) is a recently discovered protein of the epidermal growth factor family that does not directly activate any of the known erbB type 1 tyrosine kinase receptors. Also, CR-1 stimulates the growth of HC-11 mouse mammary epithelial cells. We found that prior treatment of HC-11 cells with exogenous CR-1 induced a competency response to the lactogenic hormones dexamethasone, insulin, and prolactin (DIP) with respect to the induction of the milk protein beta-casein. In contrast, simultaneous treatment of mouse HC-11 cells with CR-1 in the presence of DIP inhibited beta-casein expression. The inhibitory effects of CR-1 on beta-casein expression in response to DIP were not unique to this mouse mammary epithelial cell line, because beta-casein and whey acidic protein expression in primary mouse mammary explant cultures established from midpregnant mice were also differentially inhibited by several epidermal growth factor-related peptides including CR-1. The mitogenic and differentiation effects of CR-1 are mediated by the binding of CR-1 to a cell surface receptor that is known to activate the ras/raf/mitogen-activated protein kinase (MAPK)/MAPK kinase pathway. The inhibitory response of CR-1 in HC-11 cells on beta-casein expression after treatment with DIP can be attenuated by B581, a peptidomimetic farnesyltransferase inhibitor that blocks p21ras farnesylation and activation, and by the phosphatidylinositol 3'-kinase (PI3k) inhibitor LY 294002 but not by PD 98059, a MAPK kinase inhibitor that blocks MAPK activation. These data suggest that the ability of CR-1 to block lactogenic hormone-induced expression of beta-casein is mediated through a p21ras-dependent, PI3k-mediated pathway. This is further substantiated by the observation that CR-1 is able to stimulate the tyrosine phosphorylation of the p85 PI3k regulatory subunit and to increase the activity of PI3k in HC-11 cells.

Animals↗
PubMed1998

Analysis of signal transduction pathways regulating cytokine-mediated Fc receptor activation on human eosinophils.

Igs can be potent stimulants of eosinophil activation since interaction with IgA or IgG-coated particles can lead to eosinophil degranulation. We have investigated the comparative roles of mitogen-activated protein (MAP) kinases (MAPKs; ERK1/2 and p38) and phosphatidylinositol-3 kinase (PI3K) in the priming and regulation of Fc receptor functioning on human eosinophils utilizing a MAPK kinase (MEK) inhibitor (PD98059), a p38 inhibitor SB203580, and the widely used PI3K inhibitors wortmannin and LY294002. We demonstrate that priming of human eosinophils with Th2-derived cytokines, IL-4 and IL-5, differentially activate phosphotyrosine-associated PI3K and ERK and p38 MAP kinases. This activation can be inhibited by pre-incubation with wortmannin or LY294002, PD98059, and SB203580, respectively. Analysis of the effects of the inhibitors on rosette formation between human eosinophils and IgA- or IgG-coated beads revealed that activation of MEK was not required for IgA binding after priming with IL-4 or IL-5. However, inhibition of MEK did inhibit IL-5-primed binding of IgG-beads. The rosette formation of primed eosinophils with IgA-beads could be completely inhibited by wortmannin and LY294002 treatment, demonstrating a critical role for PI3K. Interestingly, inhibition of the p38 pathway also resulted in a complete blockade of IgA rosette formation. This work demonstrates regulatory control by inside-out signaling of Fc receptors by various cytokines on human eosinophils. Thus in vivo the local production of Th2-derived cytokines will regulate the effector functions of Fc receptors.

Androstadienes↗
PubMed2026

Crosstalk between the Wnt pathway and other signaling pathways.

The Wnt/β-catenin signaling pathway is a deeply conserved regulatory network that governs embryonic development, stem cell maintenance, and tissue homeostasis. Aberrant activation of the Wingless/Integrated protein (Wnt) signaling is a hallmark of numerous human diseases, most prominently in colorectal cancer, where it cooperates with additional oncogenic pathways to drive tumor initiation, progression, and therapeutic resistance (See Supplementary Table 1 for a list of the abbreviations used in this manuscript and their definitions.). Increasing evidence indicates that Wnt signaling does not function as an isolated linear cascade but rather as an integrative signaling hub that dynamically interfaces with major signaling pathways, including the RAS-RAF-MAPK and PI3K-AKT-mTOR pathways. Rat Sarcoma protein (RAS)- Rapidly Accelerated Fibrosarcoma protein (RAF)- Mitogen-Activated Protein Kinase (MAPK) and Phosphoinositide 3-Kinase (PI3K)- Ak strain transforming protein (AKT)- Mechanistic Target of Rapamycin (mTOR) pathways. These interactions occur at multiple molecular levels, encompassing shared kinases, transcriptional regulators, metabolic nodes, and cytoskeletal components, thereby coordinating proliferative, metabolic, and migratory programs. In this review, we synthesize current mechanistic and clinical insights into the crosstalk between Wnt signaling and the RAS-RAF-MAPK and PI3K-AKT-mTOR pathways, with particular emphasis on colorectal cancer. We discuss how these signaling networks converge to regulate β-catenin stability, transcriptional activity, cell adhesion, and metabolic reprogramming, thereby generating oncogenic phenotypes that cannot be explained by activation of individual pathways alone. To illustrate the evolutionary conservation and biological significance of these interactions, we integrate developmental paradigms from early Xenopus embryogenesis, where Wnt signaling governs zygotic genome activation, body axis formation, and the regulation of cell growth, protein stability, and biomass accumulation. Finally, we examine how an improved understanding of Wnt-centered signaling networks is informing emerging therapeutic strategies, including combinatorial pathway inhibition and nanoparticle-based drug delivery. Collectively, this review highlights Wnt signaling as a central integrator of developmental and oncogenic programs, providing a conceptual framework for understanding signaling network crosstalk and identifying new therapeutic opportunities in cancer.

Humans↗
PubMed2025

Pathway-specific genomic alterations in pancreatic cancer across diverse cohorts.

BACKGROUND/OBJECTIVES: Pancreatic cancer (PC) is an aggressive malignancy with rising incidence and poor survival rates. While Hispanic/Latino (H/L) patients have a lower overall incidence compared to Non-Hispanic White (NHW) patients, they are diagnosed at younger ages, often present with more advanced disease, and experience worse survival outcomes. The molecular drivers underlying these disparities remain poorly understood. Key oncogenic pathways, including TP53, WNT, PI3K, TGF-Beta, and RTK/RAS, play crucial roles in tumor progression, therapy resistance, and response to targeted treatments. However, their ethnicity-specific alterations and prognostic implications in PC remain largely unexplored. This study aims to characterize pathway-specific mutations in PC among H/L and NHW patients, assess tumor mutation burden, and identify ethnicity-specific oncogenic drivers using publicly available datasets. The findings may provide critical insights to optimize precision medicine strategies and enhance targeted therapies for underrepresented populations. METHODS: A bioinformatics analysis was performed using publicly available PC datasets to evaluate mutation frequencies in genes associated with the TGF-Beta, RTK/RAS, WNT, PI3K, and TP53 pathways. The study included 4,248 patients, with 407 identified as H/L and 3,841 as NHW. Patients were stratified by ethnicity to assess differences in mutation prevalence. Chi-squared tests were conducted to compare mutation rates between groups, while Kaplan-Meier survival analysis was performed to evaluate overall survival differences based on pathway-specific alterations. RESULTS: Significant differences were observed in the TGF-Beta pathway between H/L and NHW patients. TGF-Beta mutations were less prevalent in H/L patients (18.4% vs. 24.4%, p = 8.6e-3). Additionally, genes related to the TGF-Beta pathway showed significant alterations, with SMAD2 (1.5% vs. 0.4%, p = 6.3e-3) and SMAD4 (15% vs. 19.9%, p = 0.02) exhibiting notable differences. Although RTK/RAS, WNT, PI3K, and TP53 pathway mutations were not statistically significant overall, borderline significance was observed in genes associated with these pathways, including ERBB4 (3.4% vs. 1.8%, p = 0.03), ALK (2.7% vs. 1.1%, p = 0.01), HRAS (1.2% vs. 0.1%, p = 1.3e-4), and RIT1 (0.7% vs. 0.1%, p = 0.03) in the RTK/RAS pathway, as well as CTNNB1 (2.9% vs. 1.3%, p = 0.01) in the WNT pathway. Survival analysis revealed no significant differences in overall survival among H/L patients. However, NHW patients with TP53 pathway alterations exhibited borderline significant differences in survival outcomes.

PI3K pathway↗
PubMed1999

An IL-2 receptor beta subdomain that controls Bcl-X(L) expression and cell survival.

IL-2 binding to its high-affinity receptor regulates signaling events that control both lymphocyte cell survival and cell cycle progression. Although many studies have examined the mechanisms by which IL-2 regulates cell growth, few studies have dissected the pathways involved in promoting cell survival or the coupling of these pathways to the receptor. In the present study, using the pre-B cell line Baf-B03 transfected with a truncated form of the IL-2 receptor (IL-2R) beta chain, we demonstrate that IL-2-dependent cell survival requires only the N-terminal 350 amino acids of the IL-2Rbeta chain. IL-2-dependent survival of cells expressing the truncated receptor correlates with increases in receptor-associated phosphatidylinositol 3-kinase (PI3K) activity and expression of Bcl-X(L), but not with changes in c-Myc expression or proliferation. Inhibition of the PI3K pathway in these cells, but not in cells expressing the wild-type receptor, has a marked effect on the capacity of IL-2 to prevent cell death and diminishes the Bcl-X(L) response. The requirement for IL-2-induced PI3K activity in suppressing the onset of apoptotic cell death is discussed.

Apoptosis↗
PubMed2000

Interactions of phosphatidylinositol 3-kinase Src homology 3 domain with its ligand peptide studied by absorption, circular dichroism, and UV resonance raman spectroscopies.

Absorption, circular dichroism (CD), and UV resonance Raman (UVRR) spectroscopies were applied to selectively examine the environmental and structural changes of Trp and Tyr residues in the phosphatidylinositol 3-kinase (PI3K) SH3 domain induced by ligand association. Comparison of the spectra of PI3K SH3 in the presence or absence of its ligand peptide RLP1 (RKLPPRPSK) indicated that RLP1 binding changed the environment of Trp55 of the SH3 to be more hydrophilic and its H bonding weaker and that of Tyr residues to be more hydrophobic. The D21N mutant (Asp21 --> Asn) of the SH3 yielded a UV CD distinct from that of the wild type, and its spectral changes induced by RLP1 binding were smaller and different from those of the wild type in absorption, CD, and UVRR spectra, suggesting that the mutation of conserved Asp21 affected the conformation of the ligand binding cleft and thus might lead to the decrease in the ligand affinity. These data provide direct evidence for the occurrence of environmental and structural changes of PI3K SH3 by the association of a ligand and the D21N mutation.

Absorption↗
PubMed2000

Perturbation of EGF-activated MEK1 and PKB signal pathways by TGF-beta1 correlates with perturbation of EGF-induced cyclin D1 and DNA synthesis by TGF-beta1 in C3H 10T1/2 cells.

In mouse C3H 10T1/2 cells, we previously reported that TGF-beta1 first delays and later potentiates EGF-induced DNA synthesis corresponding to an inhibition of EGF-induced cyclin D1 expression at t = 13 h. We report here that in accord with DNA synthesis kinetics, TGF-beta1 initially suppresses EGF-induced cyclin D1 expression then later releases the inhibition. Furthermore, TGF-beta1 also first decreases and later potentiates the levels of EGF-activated MEK1/MAPK and PKB, indicating the existence of cross talk between TGF-beta 1- and EGF-activated signal transduction pathways. PD98059, the specific inhibitor of MEK1, significantly blocks EGF-induced DNA synthesis, whereas wortmannin, the PI3K inhibitor, exerts a modest inhibitory effect, which suggests that the activation of MEK1-MAPK pathway plays a major role in EGF-induced DNA synthesis and the activation of PI3K-PKB pathway plays a minor role. Upon examination of mechanisms underlying the cross talk, it was discovered that application of TGF-beta1 triggers a rapid association between Raf-1 and catalytic subunits of PKA, which are reported to be able to inactivate Raf-1 upon activation. Therefore, TGF-beta1 may activate PKA to inhibit the EGF-activated MEK1-MAPK pathway. The wortmannin-sensitive phosphorylation at the thr(389) site is necessary for activation of p70s6K, an important kinase involved in mitogen-stimulated protein synthesis. Although we found that EGF-stimulated p70s6K phosphorylates through a MAPK-dependent and a MAPK-independent (wortmannin-sensitive) pathway, TGF-beta1 failed to block EGF-triggered phosphorylation of p70s6K at thr(389) and thr(421)/ser(424) sites, implying that PKB inhibition by TGF-beta1 may result from inhibition of PDK1 activity instead of inhibition of PI3K activity. These data also suggest that TGF-beta1 may selectively perturb certain EGF-activated MAPK pools.

Animals↗
PubMed2001

Pleiotrophin induces angiogenesis: involvement of the phosphoinositide-3 kinase but not the nitric oxide synthase pathways.

Pleiotrophin (PTN) is a developmentally regulated protein that has been shown to be involved in tumor growth and metastasis presumably by activating tumor angiogenesis. To clarify the potential angiogenic activity of PTN and to analyze the signaling pathways involved in this process, we used an in vitro model of Human Umbilical Vein Endothelial Cells (HUVEC). We show that PTN was mitogenic toward a variety of endothelial cells including HUVEC, stimulated HUVEC migration across a reconstituted basement membrane and induced the formation of capillary-like structures by HUVEC grown as 3D-cultures in Matrigel or collagen. The signaling pathways triggered following endothelial cell stimulation by PTN were studied by using pharmacological inhibitors of the Phosphoinositide-3 kinase (PI3K) and endothelial Nitric Oxide Synthase (eNOS), two enzymes that have been shown to be crucial in the angiogenic response to Vascular Endothelial Growth Factor (VEGF). Whereas wortmannin (a PI3K inhibitor) and L-NAME (an eNOS inhibitor) dramatically reduced HUVEC growth induced by VEGF, only the former inhibitor reduced the growth induced by PTN and to a lesser extent that stimulated by basic Fibroblast Growth Factor. Thus, our results indicate that PTN induces angiogenesis and utilizes PI3K- but not eNOS-dependent pathways for its angiogenic activity.

Androstadienes↗
PubMed2000

CD19 signal transduction in normal human B cells: linkage to downstream pathways requires phosphatidylinositol 3-kinase, protein kinase C and Ca2+.

CD19 is required for normal antibody responses in mice. We have shown that CD19 enhances the activation of extracellular signal-regulated kinase (ERK) 2 by membrane (m) IgM but otherwise little is known of CD19 signaling in primary human cells. We now ask which pathways link CD19 with ERK2 in human tonsillar B cells. In analyses of signaling intermediates, the phosphatidylinositol 3-kinase (PI3K) inhibitor wortmannin partially suppressed the release of Ca2+ induced by coligation of CD19 and mIgM but the selective PKC inhibitor bisindolylmaleimide I (BIM-I) did not. The Ca2+ chelator 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid, BIM-I and wortmannin each had only a small effect on ERK2 activation induced by surface IgM alone but blocked the enhancement of that activation by CD1 9/mIgM coligation. To analyze the mitogen-activated protein kinase (MAPK) cascade, we measured activation of Raf, MAPK- or ERK kinase (MEK) 1 and ERK2. CD19 consistently enhanced activation of ERK2 and MEK1. However, synergistic activation of Raf was variably observed. In subpopulation analyses, synergistic activation of Raf1 was consistently observed in the IgDlow but not in the IgDhigh cells. Thus, in normal human B cells, PI3K is upstream of the Ca2+ response while PI3K, Ca2+ release and protein kinase C are all required for ERK2 activation, and CD19 enhances the MAPK cascade at multiple levels, depending on the state of differentiation.

Adolescent↗
PubMed2005

Leukocytes on the move with phosphoinositide 3-kinase and its downstream effectors.

Cell signalling mediators derived from membrane phospholipids are frequent participants in biological processes. The family of phosphoinositide 3-kinases (PI3Ks) phosphorylate the membrane lipid phosphatidylinositol, generating second messengers that direct diverse responses. These PI3K products are fundamental for leukocyte migration or chemotaxis, a pivotal event during the immune response. This system is therefore of significant biomedical interest. This review focuses on the biochemistry and signalling pathways of PI3K, with particular emphasis on chemokine (chemotactic cytokine)-directed responses. The key objectives of chemotaxis are motility and direction. The latter--direction--requires distinct events at the front and back of a cell. In light of this, the coordinated localisation of signalling factors, an event choreographed by a sharp intracellular gradient of PI3K-derived products, is a common theme.

Amino Acid Motifs↗
PubMed2007

Mechanisms of endothelin 1-stimulated proliferation in colorectal cancer cell lines.

BACKGROUND: The peptide endothelin (ET) 1 promotes proliferation in a number of epithelial cancers. The aim of this study was to identify the mechanism of ET-1-stimulated proliferation in colorectal cancer cells in vitro. METHODS: The effects of ET-1 on colorectal cancer cell lines HT29, LIM1215 and SW620 were studied. Cells were cultured with ET-1 plus antagonists/inhibitors to ET(A) or ET(B) receptors, G protein subtypes, phosphoinositide 3-kinase (PI3K) or protein kinase C (PKC). DNA replication and apoptosis were investigated by 5-bromo-2'-deoxyuridine incorporation and Annexin V staining. Transactivation of the epidermal growth factor (EGF) receptor was investigated by blockade of the receptor in the presence of ET-1, measurement of levels of phosphorylated EGF receptor in the presence of ET-1, and comparing the effects of ET-1 and EGF on cell proliferation. RESULTS: ET-1 significantly stimulated growth of all cell lines via ET(A) receptors. ET-1 stimulated DNA replication, not apoptosis. ET-1-stimulated growth was inhibited by antagonism of pertussis toxin-sensitive G proteins, PI3K and PKC. Inhibition of the EGF receptor reduced the effect of ET-1. ET-1 increased levels of phosphorylated EGF receptor via the ET(A) receptor. CONCLUSION: ET-1 increased DNA replication in colorectal cancer cells via the ET(A) receptor. This mitogenic action was mediated via pertussis toxin-sensitive G proteins, PI3K, PKC and transactivation of the EGF receptor.

Analysis of Variance↗
PubMed2002

Phosphorylation of Akt/PKB is required for suppression of cancer cell apoptosis and tumor progression in human colorectal carcinoma.

BACKGROUND: Akt/protein kinase B (PKB), which is included in phosphatidyl inositol-3-OH kinase (PI3K) signaling, controls many intracellular processes, such as the suppression of apoptosis and the promotion of the cell cycle. Therefore, the authors investigated phosphorylated Akt (Ser473) in colorectal carcinomas to reveal the role of PI3K signaling during the development of colorectal carcinoma. METHODS: Expression of phosphorylated Akt (Ser473) in two colon carcinoma cell lines (DLD-1 and Colo205) and 65 human colorectal carcinomas was analyzed using western blotting and immunohistochemistry, respectively. Growth inhibition and induction of apoptosis caused by LY294002, a specific inhibitor of PI3K, were also examined in these cell lines. In tumor samples, the level of cell proliferation activity (Ki-67) and number of apoptotic bodies (single stranded DNA) were determined by counting positive cells. RESULTS: LY294002 significantly affected the proliferation and apoptosis of Colo205 cells, suggesting an association with the low phosphorylation level of Akt protein. Immunohistochemic analysis showed that 46% of the tumors had a high level of expression of phosphorylated Akt with a close association with Ki-67 proliferative activity (P < 0.001) and the number of apoptotic bodies (P < 0.001). Akt phosphorylation was also correlated with some clinicopathologic parameters of the malignancies, including depth of invasion, infiltration to venous vessels, lymph node metastasis, and clinicopathologic stage. CONCLUSIONS: The phosphorylated Akt level can monitor cell growth and resistance to apoptosis, indicating that activation of Akt plays an important role during the progression of colorectal carcinomas by helping promote cell growth and rescue cells from apoptosis. These findings also suggest the possibility of using LY294002 for treatment of colorectal carcinoma.

Adult↗
PubMed2004

Enhanced cathepsin L expression is mediated by different Ras effector pathways in fibroblasts and epithelial cells.

Ras expression induces increased expression and altered targeting of lysosomal proteases in multiple cell types, but the specific downstream cytoplasmic signaling pathways mediating these changes have not been identified. In this study, we compared the involvement of 3 major Ras effectors, Raf, phosphatidylinositol 3-kinase (PI3K) and Ral guanine nucleotide exchange factor (RalGEF) in the Ras-mediated alteration of lysosomal protease protein expression and targeting in rat 208F fibroblasts and rat ovarian surface epithelial (ROSE) cells. Effector domain mutants of Ras, constitutively activated variants of Raf, PI3K and RalGEF and pharmacologic inhibitors of MEK and PI3K were utilized to determine the role of these downstream pathways in mediating fibroblast transformation and lysosomal protease regulation in the fibroblasts and epithelial cells. We found that Raf activation of the ERK mitogen-activated protein kinase pathway alone was sufficient to cause morphologic and growth transformation of the fibroblasts and was necessary and sufficient to alter cathepsin L expression and targeting. In contrast, transformation and upregulation of cathepsin L expression in the epithelial cells required the activity of all 3 Ras effectors. Increased protease secretion from the epithelial cells was not observed on ectopic expression of Ras, as it was from the fibroblasts, consistent with the utilization of different signaling pathways in the 2 cell types. In neither cell type did Ras expression increase the expression, processing or secretion of 2 other major lysosomal proteases, cathepsin B and cathepsin D. Thus, Ras utilizes different effectors to mediate transformation and to deregulate cathepsin L expression and secretion in fibroblast and epithelial cells.

Animals↗
PubMed2006

Role of Rac1 and Cdc42 in hypoxia induced p53 and von Hippel-Lindau suppression and HIF1alpha activation.

Low oxygen tension can influence tumor progression by enhancing angiogenesis, a process that may involve Rho GTPases whose activities have been implicated in tumorigenesis and metastasis. In the present study, we show that hypoxia can increase the mRNA levels and intracellular activities of Rac1 and Cdc42 in a time-dependent manner. The hypoxia-stimulated activities of Rac1 and Cdc42 could be blocked by the phosphatidylinositol 3'-kinase (PI3K) inhibitor LY294002 and the protein tyrosine kinase (PTK) inhibitor genistein but were not affected by the p38MAPK inhibitor SB203580 or the MEK-1 inhibitor PD98059, suggesting that the hypoxia-mediated signals were through PI3K and PTK. Correlating with the increased activities of Rac1 and Cdc42, the expression of the pro-angiogenesis factors HIF-1alpha and vascular endothelial growth factor (VEGF) was upregulated by hypoxia, whereas the expression of the tumor suppressors von Hippel-Lindau and p53 was down-regulated. Dominant negative N17Rac1 and N17Cdc42 could upregulate the expression of p53 and pVHL but downregulate that of HIF-1alpha and VEGF under hypoxia. Furthermore, the preconditioned medium from N17Rac1 or N17Cdc42-expressing gastric cancer cells was able to inhibit the proliferation of HUVECs. Our results indicate that PI3K and PTK-mediated activations of Rac1 and Cdc42 are involved in the hypoxia-induced production of angiogenesis-promoting factors and tumor suppressors, and suggest that the Rho family GTPases Rac1 and Cdc42 may contribute to the hypoxia-mediated angiogenesis.

Blotting, Western↗
PubMed2002

Frequent activation of AKT2 kinase in human pancreatic carcinomas.

Activation of AKT/protein kinase B promotes a variety of biological activities important in tumorigenesis, such as cell survival and cell cycle progression. We previously demonstrated amplification and overexpression of the AKT2 gene in a subset of human pancreatic carcinomas. In this investigation, we assessed AKT2 catalytic activity in 50 frozen pancreatic tissues (37 carcinomas, four benign tumors and nine normal pancreata) by in vitro kinase assay. Twelve of 37 (32%) pancreatic carcinomas showed markedly elevated levels of AKT2 activity compared to normal pancreata and begin pancreatic tumors. To delineate mechanisms contributing to AKT2 activation in malignant pancreatic tumors, we examined the status of upstream components of the phosphatilydlinositol 3-kinase (PI3K)/AKT pathway. Western blot analysis revealed loss of PTEN protein expression in two of the 12 pancreatic carcinomas with activated AKT2. In vitro PI3K assays demonstrated high levels of PI3K activity in seven carcinoma specimens that showed AKT2 activation. Immunohistochemical staining confirmed high levels of phosphorylated (active) AKT in malignant pancreatic tumors compared to normal pancreata. Overall, these data suggest that upstream perturbations of the PI3K/AKT pathway contribute to frequent activation of AKT2 in pancreatic cancer, which may contribute to the pathogenesis of this highly aggressive form of human malignancy.

Adenocarcinoma↗
PubMed2004

Transforming growth factor-beta1-dependent activation of Smad2/3 and up-regulation of PAI-1 expression is negatively regulated by Src in SKOV-3 human ovarian cancer cells.

The net balance between urokinase-type plasminogen activator (uPA) and plasminogen activator inhibitor type-1 (PAI-1) has been implicated in tumor cell invasion and metastasis. To elucidate the mechanism of the transforming growth factor-beta1 (TGF-beta1)-dependent up-regulation of PAI-1 expression, we investigated which signaling pathway transduced by TGF-beta1 is responsible for this effect. Here, we show (1) nontoxic concentrations of TGF-beta1 up-regulates uPA expression in HRA and SKOV-3 human ovarian cancer cells, (2) TGF-beta1 activates Smads (phosphorylation of Smad2 and nuclear translocation of Smad3) and subsequently up-regulates PAI-1 expression in HRA cells, whereas TGF-beta1 neither activates Smads nor up-regulates PAI-1 in SKOV-3 cells, (3) pharmacological Src inhibitor PP2 or antisense (AS) c-Src oligodeoxynucleotide (ODN) treatment significantly induces TGF-beta1-dependent activation of Smads, leading to PAI-1 synthesis, compared with controls, in SKOV-3 cells, (4) combination of TGF-beta1 and PP2, which activates PAI-1 expression and reduces uPA expression in SKOV-3, results in decreased invasiveness, (5) pharmacological inhibitors for mitogen-activated protein kinase (MAPK) (PD98059) and phosphoinositide-3-kinase (PI3K) (LY294002 and wortmannin) or AS-PI3K ODN transfection do not affect TGF-beta1-induced Smad signaling and up-regulation of PAI-1 expression in SKOV-3 cells pretreated with PP2, and (6) the induction of PAI-1 protein was partially inhibited by an inhibitor of Sp1-DNA binding, mithramycin, implicating, at least in part, Sp1 in the regulation of this gene by TGF-beta1. In conclusion, TGF-beta1-dependent activation of Smad2/3, leading to PAI-1 synthesis, may be negatively regulated by Src, but not its downstream targets MAPK and PI3K in SKOV-3 cells. These data also reflect the complex biological effect of uPA-PAI-1 system.

DNA-Binding Proteins↗
PubMed2004

Involvement of phosphoinositide 3-kinase signaling pathway in chondrocytic differentiation of ATDC5 cells: application of a gene-trap mutagenesis.

Gene-trap mutagenesis is based on the notion that the random insertion of a trapping vector may disturb the function of inserted genes. Here, we applied this method to murine mesenchymal ATDC5 cells, which differentiate into mature chondrocytes in the presence of insulin. As the trap vector we used pPT1-geo, which lacks its own promoter and enhancer, but contains a lacZ-neo fusion gene as a reporter and selection marker driven by the promoter of the trapped gene. After pPT1-geo was introduced into ATDC5 cells by electroporation, the neomycin-resistant clones were screened for beta-galactosidase activity. The selected clones were cultured in differentiation medium to evaluate the chondrogenic phenotype. The clones no. 6-30 and 6-175, which exhibited impaired and accelerated mineralization, respectively, were subjected to further analysis. In clone no. 6-30 in which the gene coding for the p85alpha subunit of phosphoinositide 3-kinase (PI3K) was trapped, the expression of marker genes of early chondrocytes including collagen type II, aggrecan, and PTH/PTHrP receptor was delayed. The insulin-induced stimulation of growth was reduced in clone no. 6-30 compared with the parental ATDC5 cells. Moreover, treatment of parental ATDC5 cells with a specific inhibitor of PI3K, LY294002, phenocopied clone no. 6-30, suggesting the involvement of PI3K signaling in the chondrogenic differentiation of ATDC5 cells. Clone no. 6-175 with accelerated mineralization was revealed to have a gene homologous to human KIAA0312 trapped, whose function remains unclear. Taken together, the gene-trap in ATDC5 cells might be useful to identify the molecules involved in chondrogenic differentiation.

Animals↗
PubMed2007

Phosphatase PTEN is inactivated in bovine aortic endothelial cells exposed to cyclic strain.

Hemodynamic forces, including cyclic strain (CS) and shear stress (SS), have been recognized as important modulators of vascular cell morphology and function. PTEN (also known as MMAC1/TEP1) is a lipid phosphatase that leads to a decrease in intracellular phosphatidylinositol 3,4,5 trisphosphate (PIP3) and therefore can modulate the stimulating effect of phosphatidylinositol 3-kinase (PI3K). In this study, we focused on the upstream regulators of the PI3K-Akt pathway by assessing Akt, PTEN, casein kinase 2 (CK2) (a kinase that catalyzes phosphorylation of PTEN), and PI3K activity in endothelial cells (EC) exposed to CS. The activity of phospho-PTEN (n = 4) and phospho-CK2 (n = 4) increased in a time-dependent fashion, reaching maximal activity by 10 min of CS stimulation. The peak of phospho-Akt activity (n = 4) occurred later, at 60 min. Akt activity was altered by transfection of EC with dominant negative PTEN plasmids. Furthermore, CS increased PIP3 immunoreactivity in a time-dependent manner, reaching maximal activity after 60 min of CS stimulation, and these effects were affected by transfection of EC with dominant negative PTEN plasmids. Inhibition of PTEN activity had no effect on CS-mediated cell proliferation but inhibited CS-mediated suppression of apoptosis.

Animals↗