Signal strength dictates phosphoinositide 3-kinase contribution to Ras/extracellular signal-regulated kinase 1 and 2 activation via differential Gab1/Shp2 recruitment: consequences for resistance to epidermal growth factor receptor inhibition

SIK2: A Novel Negative Feedback Regulator of FGF2 Signaling

A wide range of cells respond to fibroblast growth factor 2 (FGF2) by proliferation via activation of the Ras/ERK1/2 pathway. In this study, the potential involvement of salt inducible kinase SIK2) in this cascade within retinal Müller glia is explored. It is found that SIK2 phosphorylation status and activity are modulated in an FGF2-dependent manner, possibly via ERK1/2. With SIK2 downregulation, enhanced ERK1/2 activation with delayed attenuation and increased cell proliferation is observed, while SIK2 overexpression hampers FGF2-dependent ERK1/2 activation. In vitro kinase and site-directed mutagenesis studies indicate that SIK2 targets the pathway element GRB2-associated-binding protein 1 (Gab1) on Ser266. This phosphorylation event weakens Gab1 interactions with its partners growth factor receptor-bound protein 2 (Grb2) and Src homology region 2 domain containing phosphatase 2 (Shp2). Collectively, these results suggest that during FGF2-dependent proliferation process ERK1/2-mediated activation of SIK2 targets Gab1, resulting in downregulation of the Ras/ERK1/2 cascade in a feedback loop.

Phosphatidylinositol 3,4-bisphosphate: Out of the shadows and into the spotlight

Phosphoinositide 3-kinases regulate many cellular functions, including migration, growth, proliferation, and cell survival. Early studies equated the inhibition of Class I PI3Ks with loss of; phosphatidylinositol 3,4,5-trisphosphate (PIP3), but over time, it was realised that these; treatments also depleted phosphatidylinositol 3,4-bisphosphate (PI(3,4)P2). In recent years, the; use of better tools and an improved understanding of its metabolism have allowed for the; identification of specific roles of PI(3,4)P2. This includes the production of PI(3,4)P2 and the; activation of its effector Akt2 in response to growth factor signalling. In contrast, a lysosomal pool of PI(3,4)P2 is a negative regulator of mTORC1 during growth factor deprivation. A growing body of literature also demonstrates that PI(3,4)P2 controls many dynamic plasmalemmal processes. The significance of PI(3,4)P2 in cell biology is increasingly evident.

A Phosphoproteomics Data Resource for Systems-level Modeling of Kinase Signaling Networks

Building mechanistic models of kinase-driven signaling pathways requires quantitative measurements of protein phosphorylation across physiologically relevant conditions, but this is rarely done because of the insensitivity of traditional technologies. By using a multiplexed deep phosphoproteome profiling workflow, we were able to generate a deep phosphoproteomics dataset of the EGFR-MAPK pathway in non-transformed MCF10A cells across physiological ligand concentrations with a time resolution of <12 min and in the presence and absence of multiple kinase inhibitors. An improved phosphosite mapping technique allowed us to reliably identify >46,000 phosphorylation sites on >6600 proteins, of which >4500 sites from 2110 proteins displayed a >2-fold increase in phosphorylation in response to EGF. This data was then placed into a cellular context by linking it to 15 previously published protein databases. We found that our results were consistent with much, but not all previously reported data regarding the activation and negative feedback phosphorylation of core EGFR-ERK pathway proteins. We also found that EGFR signaling is biphasic with substrates downstream of RAS/MAPK activation showing a maximum response at <3ng/ml EGF while direct substrates, such as HGS and STAT5B, showing no saturation. We found that RAS activation is mediated by at least 3 parallel pathways, two of which depend on PTPN11. There appears to be an approximately 4-minute delay in pathway activation at the step between RAS and RAF, but subsequent pathway phosphorylation was extremely rapid. Approximately 80 proteins showed a >2-fold increase in phosphorylation across all experiments and these proteins had a significantly higher median number of phosphorylation sites (~18) relative to total cellular phosphoproteins (~4). Over 60% of EGF-stimulated phosphoproteins were downstream of MAPK and included mediators of cellular processes such as gene transcription, transport, signal transduction and cytoskeletal arrangement. Their phosphorylation was either linear with respect to MAPK activation or biphasic, corresponding to the biphasic signaling seen at the level of the EGFR. This deep, integrated phosphoproteomics data resource should be useful in building mechanistic models of EGFR and MAPK signaling and for understanding how downstream responses are regulated.

Pharmacologic Inhibition of SHP2 Blocks Both PI3K and MEK Signaling in Low-epiregulin HNSCC via GAB1

Preclinical and clinical studies have evidenced that effective targeted therapy treatment against receptor tyrosine kinases (RTKs) in different solid tumor paradigms is predicated on simultaneous inhibition of both the PI3K and MEK intracellular signaling pathways. Indeed, re-activation of either pathway results in resistance to these therapies. Recently, oncogenic phosphatase SHP2 inhibitors have been developed with some now reaching clinical trials. To expand on possible indications for SHP099, we screened over 800 cancer cell lines covering over 25 subsets of cancer. We found HNSCC was the most sensitive adult subtype of cancer to SHP099. We found that, in addition to the MEK pathway, SHP2 inhibition blocks the PI3K pathway in sensitive HNSCC, resulting in downregulation of mTORC signaling and anti-tumor effects across several HNSCC mouse models, including an HPV+ patient-derived xenograft (PDX). Importantly, we found low levels of the RTK ligand epiregulin identified HNSCCs that were sensitive to SHP2 inhibitor, and, adding exogenous epiregulin mitigated SHP099 efficacy. Mechanistically, epiregulin maintained SHP2-GAB1 complexes in the presence of SHP2 inhibition, preventing downregulation of the MEK and PI3K pathways. We demonstrate HNSCCs were highly dependent on GAB1 for their survival and knockdown of GAB1 is sufficient to block the ability of epiregulin to rescue MEK and PI3K signaling. These data connect the sensitivity of HNSCC to SHP2 inhibitors and to a broad reliance on GAB1-SHP2, revealing an important and druggable signaling axis. Overall, SHP2 inhibitors are being heavily developed and may have activity in HNSCCs, and in particular those with low levels of epiregulin.

PI3K/AKT Signaling Tips the Balance of Cytoskeletal Forces for Cancer Progression

The PI3K/AKT signaling pathway plays essential roles in multiple cellular processes, which include cell growth, survival, metabolism, and motility. In response to internal and external stimuli, the PI3K/AKT signaling pathway co-opts other signaling pathways, cellular components, and cytoskeletal proteins to reshape individual cells. The cytoskeletal network comprises three main components, which are namely the microfilaments, microtubules, and intermediate filaments. Collectively, they are essential for many fundamental structures and cellular processes. In cancer, aberrant activation of the PI3K/AKT signaling cascade and alteration of cytoskeletal structures have been observed to be highly prevalent, and eventually contribute to many cancer hallmarks. Due to their critical roles in tumor progression, pharmacological agents targeting PI3K/AKT, along with cytoskeletal components, have been developed for better intervention strategies against cancer. In our review, we first discuss existing evidence in-depth and then build on recent advances to propose new directions for therapeutic intervention.

Macromolecular crowding induces a binding competent transient structure in intrinsically disordered Gab1

Intrinsically disordered proteins (IDPs) are an important class of proteins which lack tertiary structure elements. Their dynamic properties can depend on reversible post-translational modifications and the complex cellular milieu, which provides a crowded environment. Both influences the thermodynamic stability and folding of globular proteins as well as the conformational plasticity of IDPs. Here we investigate the intrinsically disordered C-terminal region (amino acids 613-694) of human Grb2-associated binding protein 1 (Gab1), which binds to the disease-relevant Src homolog region2 (SH2) domain-containing protein tyrosine phosphatase SHP2 (PTPN11). This binding is mediated by phosphorylation at Tyr 627 and Tyr 659 in Gab1. We characterize induced structure in Gab1_613-694 and binding to SHP2 by NMR, CD and ITC under non-crowding and crowding conditions, employing chemical and biological crowding agents and compare the results of the non-phosphorylated and tyrosine phosphorylated C-terminal Gab1 fragment. Our results show that under crowding conditions pre-structured motifs in two distinct regions of Gab1 are formed whereas phosphorylation has no impact on the dynamics and IDP character. These structured regions are identical to the binding regions towards SHP2. Therefore, biological crowders could induce some SHP2 binding capacity. Our results therefore indicate that high concentrations of macromolecules stabilize the preformed or excited binding state in the C-terminal Gab1 region and foster the binding to the SH2 tandem motif of SHP2, even in the absence of tyrosine phosphorylation.

FARP1, ARHGEF39, and TIAM2 are essential receptor tyrosine kinase effectors for Rac1-dependent cell motility in human lung adenocarcinoma

Despite the undisputable role of the small GTPase Rac1 in the regulation of actin cytoskeleton reorganization, the Rac guanine-nucleotide exchange factors (Rac-GEFs) involved in Rac1-mediated motility and invasion in human lung adenocarcinoma cells remain largely unknown. Here, we identify FARP1, ARHGEF39, and TIAM2 as essential Rac-GEFs responsible for Rac1-mediated lung cancer cell migration upon EGFR and c-Met activation. Noteworthily, these Rac-GEFs operate in a non-redundant manner by controlling distinctive aspects of ruffle dynamics formation. Mechanistic analysis reveals a leading role of the AXL-Gab1-PI3K axis in conferring pro-motility traits downstream of EGFR. Along with the positive association between the overexpression of Rac-GEFs and poor lung adenocarcinoma patient survival, we show that FARP1 and ARHGEF39 are upregulated in EpCam⁺ cells sorted from primary human lung adenocarcinomas. Overall, our study reveals fundamental insights into the complex intricacies underlying Rac-GEF-mediated cancer cell motility signaling, hence underscoring promising targets for metastatic lung cancer therapy.

Evidence for functional selectivity in TUDC- and norUDCA-induced signal transduction via α5β1 integrin towards choleresis

Functional selectivity is the ligand-specific activation of certain signal transduction pathways at a receptor and has been described for G protein-coupled receptors. However, it has not yet been described for ligands interacting with integrins without αI domain. Here, we show by molecular dynamics simulations that four side chain-modified derivatives of tauroursodeoxycholic acid (TUDC), an agonist of α₅β₁ integrin, differentially shift the conformational equilibrium of α₅β₁ integrin towards the active state, in line with the extent of β₁ integrin activation from immunostaining. Unlike TUDC, 24-nor-ursodeoxycholic acid (norUDCA)-induced β₁ integrin activation triggered only transient activation of extracellular signal-regulated kinases and p38 mitogen-activated protein kinase and, consequently, only transient insertion of the bile acid transporter Bsep into the canalicular membrane, and did not involve activation of epidermal growth factor receptor. These results provide evidence that TUDC and norUDCA exert a functional selectivity at α₅β₁ integrin and may provide a rationale for differential therapeutic use of UDCA and norUDCA.

The Upstream Pathway of mTOR-Mediated Autophagy in Liver Diseases

Autophagy, originally found in liver experiments, is a cellular process that degrades damaged organelle or protein aggregation. This process frees cells from various stress states is a cell survival mechanism under stress stimulation. It is now known that dysregulation of autophagy can cause many liver diseases. Therefore, how to properly regulate autophagy is the key to the treatment of liver injury. mechanistic target of rapamycin (mTOR)is the core hub regulating autophagy, which is subject to different upstream signaling pathways to regulate autophagy. This review summarizes three upstream pathways of mTOR: the phosphoinositide 3-kinase (PI3K)/protein kinase (AKT) signaling pathway, the adenosine monophosphate-activated protein kinase (AMPK) signaling pathway, and the rat sarcoma (Ras)/rapidly accelerated fibrosarcoma (Raf)/mitogen-extracellular activated protein kinase kinase (MEK)/ extracellular-signal-regulated kinase (ERK) signaling pathway, specifically explored their role in liver fibrosis, hepatitis B, non-alcoholic fatty liver, liver cancer, hepatic ischemia reperfusion and other liver diseases through the regulation of mTOR-mediated autophagy. Moreover, we also analyzed the crosstalk between these three pathways, aiming to find new targets for the treatment of human liver disease based on autophagy.

The multi-site docking protein Grb2-associated binder 1 (Gab1) enhances interleukin-6-induced MAPK-pathway activation in an SHP2-, Grb2-, and time-dependent manner

Background

Cytokine-dependent activation of signalling pathways is tightly orchestrated. The spatiotemporal activation of signalling pathways dictates the specific physiological responses to cytokines. Dysregulated signalling accounts for neoplastic, developmental, and inflammatory diseases. Grb2-associated binder (Gab) family proteins are multi-site docking proteins, which expand cytokine-induced signal transduction in a spatial- and time-dependent manner by coordinating the recruitment of proteins involved in mitogen activated protein kinase (MAPK)/extracellular-signal regulated kinase (ERK) and phosphatidyl-inositol-3-kinase (PI3K) signalling. Interaction of Gab family proteins with these signalling proteins determines strength, duration and localization of active signalling cascades. However, the underlying molecular mechanisms of signal orchestration by Gab family proteins in IL-6-induced signalling are only scarcely understood.

Methods

We performed kinetic analyses of interleukin-6 (IL-6)-induced MAPK activation and analysed downstream responses. We compared signalling in wild-type cells, Gab1 knock-out cells, those reconstituted to express Gab1 mutants, and cells expressing gp130 receptors or receptor mutants.

Results

Interleukin-6-induced MAPK pathway activation can be sub-divided into an early Gab1-independent and a subsequent Gab1-dependent phase. Early Gab1-independent MAPK activation is critical for the subsequent initiation of Gab1-dependent amplification of MAPK pathway activation and requires binding of SH2 domain-containing phosphatase 2 (SHP2) to the interleukin-6 receptor complex. Subsequent and coordinated recruitment of Grb2 and SHP2 to Gab1 is essential for Gab1-dependent amplification of IL-6-induced late MAPK pathway activation and subsequent gene expression.

Conclusions

Overall, we elaborated the molecular requirements for Gab1-dependent, spatiotemporal orchestration of interleukin-6-dependent MAPK signalling. We discriminated IL-6-induced Gab1-independent, early activation of MAPK signalling and Gab1-dependent, sustained activation of MAPK signalling.

CRF1 Receptor Signaling via the ERK1/2-MAP and Akt Kinase Cascades: Roles of Src, EGF Receptor, and PI3-Kinase Mechanisms

In the present study, we determined the cellular regulators of ERK1/2 and Akt signaling pathways in response to human CRF₁ receptor (CRF₁R) activation in transfected COS-7 cells. We found that Pertussis Toxin (PTX) treatment or sequestering Gβγ reduced CRF₁R-mediated activation of ERK1/2, suggesting the involvement of a G_i-linked cascade. Neither G_s/PKA nor G_q/PKC were associated with ERK1/2 activation. Besides, CRF induced EGF receptor (EGFR) phosphorylation at Tyr¹⁰⁶⁸, and selective inhibition of EGFR kinase activity by AG1478 strongly inhibited the CRF₁R-mediated phosphorylation of ERK1/2, indicating the participation of EGFR transactivation. Furthermore, CRF-induced ERK1/2 phosphorylation was not altered by pretreatment with batimastat, GM6001, or an HB-EGF antibody indicating that metalloproteinase processing of HB-EGF ligands is not required for the CRF-mediated EGFR transactivation. We also observed that CRF induced Src and PYK2 phosphorylation in a Gβγ-dependent manner. Additionally, using the specific Src kinase inhibitor PP2 and the dominant-negative-SrcYF-KM, it was revealed that CRF-stimulated ERK1/2 phosphorylation depends on Src activation. PP2 also blocked the effect of CRF on Src and EGFR (Tyr⁸⁴⁵) phosphorylation, further demonstrating the centrality of Src. We identified the formation of a protein complex consisting of CRF₁R, Src, and EGFR facilitates EGFR transactivation and CRF₁R-mediated signaling. CRF stimulated Akt phosphorylation, which was dependent on G_i/βγ subunits, and Src activation, however, was only slightly dependent on EGFR transactivation. Moreover, PI3K inhibitors were able to inhibit not only the CRF-induced phosphorylation of Akt, as expected, but also ERK1/2 activation by CRF suggesting a PI3K dependency in the CRF₁R ERK signaling. Finally, CRF-stimulated ERK1/2 activation was similar in the wild-type CRF₁R and the phosphorylation-deficient CRF₁R-Δ386 mutant, which has impaired agonist-dependent β-arrestin-2 recruitment; however, this situation may have resulted from the low β-arrestin expression in the COS-7 cells. When β-arrestin-2 was overexpressed in COS-7 cells, CRF-stimulated ERK1/2 phosphorylation was markedly upregulated. These findings indicate that on the base of a constitutive CRF₁R/EGFR interaction, the G_i/βγ subunits upstream activation of Src, PYK2, PI3K, and transactivation of the EGFR are required for CRF₁R signaling via the ERK1/2-MAP kinase pathway. In contrast, Akt activation via CRF₁R is mediated by the Src/PI3K pathway with little contribution of EGFR transactivation.

Survival of pancreatic cancer cells lacking KRAS function

Activating mutations in the proto-oncogene KRAS are a hallmark of pancreatic ductal adenocarcinoma (PDAC), an aggressive malignancy with few effective therapeutic options. Despite efforts to develop KRAS-targeted drugs, the absolute dependence of PDAC cells on KRAS remains incompletely understood. Here we model complete KRAS inhibition using CRISPR/Cas-mediated genome editing and demonstrate that KRAS is dispensable in a subset of human and mouse PDAC cells. Remarkably, nearly all KRAS deficient cells exhibit phosphoinositide 3-kinase (PI3K)-dependent mitogen-activated protein kinase (MAPK) signaling and induced sensitivity to PI3K inhibitors. Furthermore, comparison of gene expression profiles of PDAC cells retaining or lacking KRAS reveal a role of KRAS in the suppression of metastasis-related genes. Collectively, these data underscore the potential for PDAC resistance to even the very best KRAS inhibitors and provide insights into mechanisms of response and resistance to KRAS inhibition.

Pancreatic cancer cells may develop resistance to KRAS inhibitors due to activation of compensatory pathways. In this study, the authors demonstrate that KRAS is dispensable in a subset of pancreatic cancer and that PI3K signalling may have an important role in mediating tumor growth following KRAS inhibition.

The multi-site docking protein Gab1 is constitutively phosphorylated independent from its recruitment to the plasma membrane in Jak2-V617F-positive cells and mediates proliferation of human erythroleukaemia cells

The constitutively active Janus kinase 2 mutant Jak2-V617F is responsible for cytokine-independent growth of hematopoietic cells and the development of myeloproliferative neoplasms, such as polycythaemia vera and essential thrombocythaemia. Cells expressing Jak2-V617F exhibit constitutive STAT, MAPK, and PI3K signalling, and constitutive association of the multi-site docking protein Gab1 to PIP3 at the plasma membrane. Here, we demonstrate the crucial role of Gab1 for the proliferation of Jak2-V617F-positive human erythroleukaemia (HEL) cells. In Jak2-V617F-expressing cells Gab1 is constitutively phosphorylated by Erk1/2 on serine residue 552, which regulates binding to PIP3. Additionally, Gab1 is constitutively phosphorylated on tyrosine residue 627. Tyrosine 627 is a SHP2 binding site and required for Gab1-dependent Erk1/2 activation. As previously shown, Jak2-V617F-dependent Erk1/2 and PI3K activation act synergistically on the proliferation of Jak2-V617F-positive cells. Here, we examined whether constitutive membrane association of Gab1 explains cytokine-independent Gab1 phosphorylation in Jak2-V617F-expressing cells. Although we could demonstrate Jak2-V617F-dependent constitutive serine 552 and tyrosine 627 phosphorylation of Gab1, interestingly, both phosphorylations do not require binding of Gab1 to PIP3 at the plasma membrane. Instead, we observed a constitutive interaction of Gab1 with the erythropoietin receptor in Jak2-V617F-expressing cells, which depends on Janus kinase activity. Thus, constitutive Gab1-dependent signalling in Jak2-V617F-expressing cells does not occur due to the constitutive association of Gab1 with PIP3 at the plasma membrane.

Integration of Receptor Tyrosine Kinases Determines Sensitivity to PI3Kα-selective Inhibitors in Breast Cancer

PI3Kα-selective inhibitor BYL719 is currently in phase II/III clinical trial for the treatment of breast cancer, but highly variable response has been observed among patients. We sought to discover predictive biomarker for the efficacy of BYL719 by dissecting the proliferative signaling pathway mediated by PI3K in breast cancer. BYL719 concurrently inhibited the phosphorylation of AKT and ERK in PIK3CA-mutated human breast cancer cells. PI3K-regulated ERK phosphorylation was independent of canonical PDK1/AKT/mTOR pathway, while it was associated with RAF/MEK. Hyper-activation of EGFR or RAS abrogated inhibition of ERK phosphorylation by BYL719. Furthermore, hyper-activation of receptor tyrosine kinases (RTKs) including EGFR, c-MET, FGFR and HER3 but not IGF-1R restored ERK phosphorylation and cell viability suppressed by BYL719, suggesting the discriminative functions of RTKs in cell signaling and proliferation. By profiling 22 breast cancer cell lines, we found that BYL719 was more potent in cell lines where phosphorylation of both AKT and ERK was attenuated than those where only AKT phosphorylation was inhibited. The potency of BYL719 was further found to be significantly correlated with the expression profile of RTKs in breast cancer cells. Specifically, overexpression of EGFR, c-MET and/or FGFR1 forecasted resistance, while overexpression of IGF-1R and/or HER2 predicted sensitivity to BYL719 in breast cancer cells. Similar correlation between BYL719 efficacy and expression profile of RTKs was found in patient-derived xenograft models of breast cancer. Thus, inhibition of ERK phosphorylation by PI3Kα inhibitor BYL719 contributes to its antitumor efficacy and is determined by the converged signaling from RTKs. The expression profile of RTKs in breast cancer tissue could be potentially developed as a predictive biomarker for the efficacy of PI3Kα inhibitors.

PI3K is required for both basal and LPA-induced DNA synthesis in oral carcinoma cells

BACKGROUND

The glycerophospholipid lysophosphatidic acid (LPA), which is present in most tissues and in high concentrations in saliva, may exert profound effects on oral cancer cells. We have investigated mitogenic signalling induced by LPA in the two oral carcinoma cell lines, D2 and E10, focusing on the role of EGFR transactivation and downstream pathways.

METHODS

Two oral squamous carcinoma cell lines, D2 and E10, were analysed for effects of LPA on signalling pathways and induction of DNA synthesis. Pathway activation was investigated by examining phosphorylation of signalling proteins and by the use of specific pathway inhibitors.

RESULTS

The D2 cells had higher levels of activated signalling proteins and higher DNA synthesis activity in the basal condition than E10 cells. EGF did not induce proliferation in D2 cells, whereas LPA induced proliferation in both cell lines, by mechanisms depending on EGFR transactivation. Release of EGFR ligands was involved in basal and LPA-induced proliferation in both D2 and E10 cells. The proliferation in D2 cells was dependent on the PI3K/Akt pathway, but not the MEK/ERK pathway. In E10 cells, the PI3K/Akt, MEK/ERK and p38 pathways were all involved in the proliferation.

CONCLUSION

Transactivation of EGFR is required for LPA-induced DNA synthesis in D2 and E10 cells. Our results also show that although proliferation of oral carcinoma cells is regulated by several pathways, and differentially in E10 and D2 cells, the PI3K pathway has a crucial role in both cell lines.

Dual PI3K/mTOR inhibitor BEZ235 exerts extensive antitumor activity in HER2-positive gastric cancer

Background

To investigate the in vitro and in vivo antitumor activity of dual PI3K/mTOR inhibitor BEZ235 (NVP-BEZ235) in HER2-positive gastric cancer.

Methods

HER2-positive breast cancer cell line (BT474), HER2-positive (NCI-N87 and SNU216), and HER2-negative (MKN45) gastric cancer cell lines were used in this study. Cell viability, cell cycle, and HER2 downstream signaling pathways were analyzed using the MTS assay, flow cytometry, and western blotting, respectively. For the in vivo experiments, HER2-positive gastric cancer patient-derived xenografts were treated with BEZ235 to assess its antitumor activity.

Results

The sensitivity of trastuzumab in BT474 cells was higher than that for NCI-N87 and SNU216 cells, which may be partially attributed to continuously active HER2 downstream signaling pathway. BEZ235 inhibited the proliferation of NCI-N87 and SNU216 cells in vitro in a dose-dependent manner by inducing the cell cycle arrest at the G1 phase. BEZ235 demonstrated greater inhibitory effects than trastuzumab, a unique targeted drug, in both the in vitro and in vivo set of experiments. Additionally, our results indicate that BEZ235 displayed some synergism with trastuzumab. BEZ235 exhibited its antitumor activity in gastric cancer by inhibiting important HER2 downstream signaling pathways, as indicated by the inhibition of phosphorylated AKT and S6.

Conclusion

The present study has demonstrated, for the first time, the antitumor activity of BEZ235 against HER2-positive gastric cancer in patient-derived xenografts, as well its synergistic interaction with trastuzumab. These important findings can be utilized to facilitate the design of future clinical trials.

Electronic supplementary material

The online version of this article (doi:10.1186/s12885-015-1900-y) contains supplementary material, which is available to authorized users.

Simultaneous targeting of PI3Kδ and a PI3Kδ-dependent MEK1/2-Erk1/2 pathway for therapy in pediatric B-cell acute lymphoblastic leukemia

B cell acute lymphoblastic leukemia (B-ALL) is the most common hematological malignancy diagnosed in children, and blockade of the abnormally activated PI3Kδ displayed promising outcomes in B cell acute or chronic leukemias, but the mechanisms are not well understood. Here we report a novel PI3Kδ selective inhibitor X-370, which displays distinct binding mode with p110δ and blocks constitutively active or stimulus-induced PI3Kδ signaling. X-370 significantly inhibited survival of human B cell leukemia cells in vitro, with associated induction of G1 phase arrest and apoptosis. X-370 abrogated both Akt and Erk1/2 signaling via blockade of PDK1 binding to and/or phosphorylation of MEK1/2. Forced expression of a constitutively active MEK1 attenuated the antiproliferative activity of X-370. X-370 preferentially inhibited the survival of primary pediatric B-ALL cells displaying PI3Kδ-dependent Erk1/2 phosphorylation, while combined inhibition of PI3Kδ and MEK1/2 displayed enhanced activity. We conclude that PI3Kδ inhibition led to abrogation of both Akt and Erk1/2 signaling via a novel PI3K-PDK1/MEK1/2-Erk1/2 signaling cascade, which contributed to its efficacy against B-ALL. These findings support the rationale for clinical testing of PI3Kδ inhibitors in pediatric B-ALL and provide insights needed to optimize the therapeutic strategy.

Gab1 amplifies signaling in response to low-intensity stimulation by HGF

The receptor tyrosine kinases EGFR and Met induce phosphorylation of the docking protein Gab1, and there is evidence that Gab1 may have a role in the signaling from these receptors. Studying hepatocytes, we previously found that although Gab1 mechanistically interacted in different ways with EGFR and Met, it was involved in mitogenic signaling induced by both EGF and HGF. It has been reported that in EGFR, Gab1 is required particularly at a low dose of EGF. Whether this also applies to HGF/Met signaling has not been investigated. We have studied the role of Gab1 in activation of the Akt and ERK pathways at low- and high-intensity stimulation with EGF and HGF in cultured hepatocytes. In cells where Gab1 was depleted by a specific Gab1-directed siRNA, the EGF-induced phosphorylation of ERK was lowered and HGF-induced phosphorylation of both ERK and Akt was substantially reduced. These effects were more marked at low-dose HGF stimulation. The inhibitory consequence of Gab1 depletion was particularly pronounced for HGF-induced Akt phosphorylation. The results suggest that Gab1 is an important signal amplifier for low-intensity stimulation by HGF.

Inhibition of triple-negative and Herceptin-resistant breast cancer cell proliferation and migration by Annexin A2 antibodies

Background:

Annexin A2 (AnxA2), a calcium-dependent phospholipid binding protein, is abundantly present at the surface of triple-negative and Herceptin-resistant breast cancer cells. Interactions between cell-surface AnxA2 and tyrosine kinase receptors have an important role in the tumour microenvironment and act together to enhance tumour growth. The mechanism supporting this role is still unknown.

Methods:

The membrane function of AnxA2 was blocked by incubating cells with anti-AnxA2 antibodies. Western blotting, immunoprecipitation, immunofluorescence, 1-(4,5-Dimethylthiazol-2-yl)-3,5-diphenylformazan (MTT), flow cytometry, Clonogenic, and wound-healing assays were performed in this study.

Results:

We demonstrate that AnxA2 interacts with epidermal growth factor receptor (EGFR) at the cell surface and has an important role in cancer cell proliferation and migration by modulating EGFR functions. Blocking AnxA2 function at the cell surface by anti-AnxA2 antibody suppressed the EGF-induced EGFR tyrosine phosphorylation and internalisation by blocking its homodimerisation. Furthermore, addition of AnxA2 antibody significantly inhibited the EGFR-dependent PI3K-AKT and Raf-MEK-ERK downstream pathways under both EGF-induced and basal growth conditions, resulting in lower cell proliferation and migration.

Conclusions:

These findings suggest that cell-surface AnxA2 has an important regulatory role in EGFR-mediated oncogenic processes by keeping EGFR signalling events in an activated state. Therefore, AnxA2 could potentially be used as a therapeutic target in triple-negative and Herceptin-resistant breast cancers.

PLC-γ and PI3K link cytokines to ERK activation in hematopoietic cells with normal and oncogenic Kras

Oncogenic K-Ras proteins, such as K-Ras(G12D), accumulate in the active, guanosine triphosphate (GTP)-bound conformation and stimulate signaling through effector kinases. The presence of the K-Ras(G12D) oncoprotein at a similar abundance to that of endogenous wild-type K-Ras results in only minimal phosphorylation and activation of the canonical Raf-mitogen-activated or extracellular signal-regulated protein kinase kinase (MEK)-extracellular signal-regulated kinase (ERK) and phosphoinositide 3-kinase (PI3K)-Akt-mammalian target of rapamycin (mTOR) signaling cascades in primary hematopoietic cells, and these pathways remain dependent on growth factors for efficient activation. We showed that phospholipase C-γ (PLC-γ), PI3K, and their generated second messengers link activated cytokine receptors to Ras and ERK signaling in differentiated bone marrow cells and in a cell population enriched for leukemia stem cells. Cells expressing endogenous oncogenic K-Ras(G12D) remained dependent on the second messenger diacylglycerol for the efficient activation of Ras-ERK signaling. These data raise the unexpected possibility of therapeutically targeting proteins that function upstream of oncogenic Ras in cancer.

The involvement of the docking protein Gab1 in mitogenic signalling induced by EGF and HGF in rat hepatocytes

Grb2-associated binder (Gab) family proteins are docking molecules that can interact with receptor tyrosine kinases (RTKs) and cytokine receptors and bind several downstream signalling proteins. Studies in several cell types have shown that Gab1 may have a role in signalling mediated by the two RTKs epidermal growth factor (EGF) receptor (EGFR) and Met, the receptor for hepatocyte growth factor (HGF), but the involvement of Gab1 in EGFR and Met signalling has not been directly compared in the same cell. We have studied mechanisms of activation and role in mitogenic signalling of Gab1 in response to EGF and HGF in cultured rat hepatocytes. Gab1, but not Gab2, was expressed in the hepatocytes and was phosphorylated upon stimulation with EGF or HGF. Depletion of Gab1, using siRNA, decreased the ERK and Akt activation, cyclin D1 expression, and DNA synthesis in response to both EGF and HGF. Studies of mechanisms of recruitment to the receptors showed that HGF induced co-precipitation of Gab1 and Met while EGF induced binding of Gab1 to Grb2 but not to EGFR. Gab1 activation in response to both EGF and HGF was dependent on PI3K. While EGF activated Gab1 and Shc equally, within the same concentration range, HGF very potently and almost exclusively activated Gab1, having only a minimal effect on Shc. Collectively, our results strongly suggest that although Gab1 interacts differently with EGFR and Met, it is involved in mitogenic signalling mediated by both these growth factor receptors in hepatocytes.

Receptor tyrosine kinase (RTK) signalling in the control of neural stem and progenitor cell (NSPC) development

Important developmental responses are elicited in neural stem and progenitor cells (NSPC) by activation of the receptor tyrosine kinases (RTK), including the fibroblast growth factor receptors, epidermal growth factor receptor, platelet-derived growth factor receptors and insulin-like growth factor receptor (IGF1R). Signalling through these RTK is necessary and sufficient for driving a number of developmental processes in the central nervous system. Within each of the four RTK families discussed here, receptors are activated by sets of ligands that do not cross-activate receptors of the other three families, and therefore, their activation can be independently regulated by ligand availability. These RTK pathways converge on a conserved core of signalling molecules, but differences between the receptors in utilisation of signalling molecules and molecular adaptors for intracellular signal propagation become increasingly apparent. Intracellular inhibitors of RTK signalling are widely involved in the regulation of developmental signalling in NSPC and often determine developmental outcomes of RTK activation. In addition, cellular responses of NSPC to the activation of a given RTK may be significantly modulated by signal strength. Cellular propensity to respond also plays a role in developmental outcomes of RTK signalling. In combination, these mechanisms regulate the balance between NSPC maintenance and differentiation during development and in adulthood. Attribution of particular developmental responses of NSPC to specific pathways of RTK signalling becomes increasingly elucidated. Co-activation of several RTK in developing NSPC is common, and analysis of co-operation between their signalling pathways may advance knowledge of RTK role in NSPC development.

Modelling reveals novel roles of two parallel signalling pathways and homeostatic feedbacks in yeast

Ensemble modelling is used to study the yeast high osmolarity glycerol (HOG) pathway, a prototype for eukaryotic mitogen-activated kinase signalling systems. The best fit model provides new insights into the function of this system, some of which are then experimentally validated.

The main mechanism for osmo-adaptation is a fast and transient non-transcriptional Hog1-mediated activation of glycerol production.

The transcriptional response rather serves to maintain an increased steady-state glycerol production with low steady-state Hog1 activity after adaptation.

A fast negative feedback of activated Hog1 on the upstream signalling branches serves to stabilise the adaptation response by preventing oscillatory behaviour.

Two parallel redundant signalling branches elicit a more robust and swifter adaptation than a single branch alone, at least for low osmotic shock. This notion could be corroborated by dedicated measurements of single-cell volume recovery for the wild-type and single-branch mutants.

The high osmolarity glycerol (HOG) pathway in yeast serves as a prototype signalling system for eukaryotes. We used an unprecedented amount of data to parameterise 192 models capturing different hypotheses about molecular mechanisms underlying osmo-adaptation and selected a best approximating model. This model implied novel mechanisms regulating osmo-adaptation in yeast. The model suggested that (i) the main mechanism for osmo-adaptation is a fast and transient non-transcriptional Hog1-mediated activation of glycerol production, (ii) the transcriptional response serves to maintain an increased steady-state glycerol production with low steady-state Hog1 activity, and (iii) fast negative feedbacks of activated Hog1 on upstream signalling branches serves to stabilise adaptation response. The best approximating model also indicated that homoeostatic adaptive systems with two parallel redundant signalling branches show a more robust and faster response than single-branch systems. We corroborated this notion to a large extent by dedicated measurements of volume recovery in single cells. Our study also demonstrates that systematically testing a model ensemble against data has the potential to achieve a better and unbiased understanding of molecular mechanisms.

Brain-derived neurotrophic factor and glucocorticoids: reciprocal influence on the central nervous system

Brain-derived neurotrophic factor (BDNF) has multiple roles in the central nervous system (CNS), including maintaining cell survival and regulation of synaptic function. In CNS neurons, BDNF triggers activation of phospholipase Cγ (PLCγ), mitogen-activated protein/extracellular signal-regulated kinase (MAPK/ERK), and phosphoinositide 3-kinase (PI3K)/Akt pathways, influencing neuronal cells beneficially through these intracellular signaling cascades. There is evidence to suggest that decreased BDNF expression or function is related to the pathophysiology of brain diseases including psychiatric disorders. Additionally, glucocorticoids, which are critical stress hormones, also influence neuronal function in the CNS, and are putatively involved in the onset of depression when levels are abnormally high. In animal models of depression, changes in glucocorticoid levels, expression of glucocorticoid receptor (GR), and alterations in BDNF signaling are observed. Interestingly, several studies using in vivo and in vitro systems suggest that glucocorticoids interact with BDNF to ultimately affect CNS function. In the present review, we provide an overview of recent evidence concerning the interaction between BDNF and glucocorticoids.

A phase I/II, non-randomized, feasibility/safety and efficacy study of the combination of everolimus, cetuximab and capecitabine in patients with advanced pancreatic cancer

BACKGROUND

Improvements in knowledge of molecular mechanisms in cancer are the basis for new studies combining chemotherapy with targeted drugs. Inhibition of the epidermal growth factor receptor (EGFR) by erlotinib or cetuximab has limited or no activity, respectively, in pancreatic cancer. The crosstalk between EGFR and mammalian target of rapamycin (mTOR) pathways is a potential mechanism of resistance; therefore we conducted a study to explore safety and efficacy of multiple pathway inhibition by cetuximab and everolimus in combination with capecitabine.

METHODS

Safety and efficacy of fixed standard dose cetuximab in combination with various dose levels of everolimus (5-10 mg/day) and capecitabine (600-800 mg/m(2) bid, 2 weeks every 3 weeks) were investigated in a phase I/II study in patients with advanced pancreatic cancer. The primary endpoint was objective response.

RESULTS

Sixteen patients were treated in the phase I part at two dose levels. Mucositis, rash and hand-foot syndrome were dose-limiting toxicities. Dose level 1 (everolimus 5 mg/day, capecitabine 600 mg/m(2) bid for 2 weeks every 3 weeks and cetuximab 250 mg/m(2) weekly) was considered the maximum tolerated dose (MTD). Of 31 patients in the phase II part, partial response was documented in two patients (6.5%) and five (16.1%) had stable disease. Median overall survival was 5.0 months (CI 3.1-6.8).

CONCLUSION

The schedule of capecitabine, everolimus and cetuximab resulted in considerable epidermal and mucosal toxicities and prevented escalation to optimal dose levels. Because of toxicity and low efficacy this treatment combination cannot be recommended for treatment in pancreatic cancer patients.

HER1 signaling mediates extravillous trophoblast differentiation in humans

This study examines the role of HER1 signaling in the differentiation of proliferative extravillous trophoblast (EVT) into invasive EVT. Using the JAR choriocarcinoma cell line and placental villous explants as experimental models and immunohistochemical assessment of protein markers of EVT differentiation (downregulation of HER1 and Cx40 and upregulation of HER2 and alpha1 integrin), we show that the ability of decidual conditioned medium (DCM) to induce HER1/2 switching was abrogated in the presence of the HER1 antagonist, AG1478. Similarly, epidermal growth factor (EGF) treatment resulted in the downregulation of HER1 and an upregulation of HER2 expression, whereas co-incubation of EGF with AG1478 inhibited this response. However, EGF did not downregulate Cx40 or induce migration of EVT. In contrast, heparin-binding epidermal-like growth factor (HBEGF) stimulated dose-dependent JAR cell migration, which was inhibited by both AG1478 and AG825 (HER2 antagonist). Western blot analysis of HER1 activation demonstrated that HBEGF-mediated phosphorylation of the HER1 Tyr992 and Tyr1068 sites, while EGF activated the Tyr1045 site. Moreover, HBEGF induced a stronger and more sustained activation of both the mitogen-activated protein kinase and phosphoinositol 3 kinase (PIK3) signaling pathways. Migration assays using a panel of signaling pathway inhibitors demonstrated that the HBEGF-mediated migration was dependent on the PIK3 pathway. These results demonstrate that HBEGF-mediated HER1 signaling through PIK3 is an important component of EVT invasion.

SIRPalpha1 receptors interfere with the EGFRvIII signalosome to inhibit glioblastoma cell transformation and migration

EGFRvIII, a frequent genetic alteration of the epidermal growth factor receptor (EGFR), has been shown to increase the migratory potential of tumor cells and normal fibroblasts. Previously, we showed that signal regulatory protein alpha1 (SIRPalpha1) receptors interact with SHP-2 to inhibit wild-type (wt) EGFR-mediated tumor migration, survival and cell transformation. However, the effects of SIRPalpha1 inhibitory receptors on EGFRvIII-mediated phenotypes are unclear. The aim of this study was to investigate the effect of SIRPalpha1 receptor on the EGFRvIII signalosome and phenotypes. Overexpression of SIRPalpha1 in U87MG.EGFRvIII cells inhibited transformation and migration in a MAPK-dependent manner, and is independent of the phosphatidylinositol 3-kinase (PI3-K)/Akt pathway. We observed reduced EGFRvIII/SHP-2/Gab1/Grb2/Sos-1 interaction and enhanced SIRP/SHP-2 association in U87MG.EGFRvIII/SIRPalpha1 cells when compared with empty vector control cells. Interestingly, SIRPalpha1 overexpression differentially modulated SHP-2 phosphorylation at tyrosyl 542 and 580 residues, which may regulate Erk1/2 activity and the EGFRvIII phenotype. In addition, SIRPalpha1-expressing cells exhibited reduced focal adhesion kinase (FAK) phosphorylation and its recruitment to the EGFRvIII/Grb2/Sos-1/Gab1/SHP-2 complex. Collectively, our data indicate that SIRPalpha1 specifically affects the SHP-2/FAK/Grb2/Sos-1/MAPK activation loop to downmodulate EGFRvIII-mediated migration and transformation. Further understanding of the molecular interactions between the SIRPalpha1 inhibitory receptor and the EGFRvIII signalosome may facilitate the identification of novel targets to inhibit the EGFRvIII glioblastoma phenotype.

Functional effects of PTPN11 (SHP2) mutations causing LEOPARD syndrome on epidermal growth factor-induced phosphoinositide 3-kinase/AKT/glycogen synthase kinase 3beta signaling

LEOPARD syndrome (LS), a disorder with multiple developmental abnormalities, is mainly due to mutations that impair the activity of the tyrosine phosphatase SHP2 (PTPN11). How these alterations cause the disease remains unknown. We report here that fibroblasts isolated from LS patients displayed stronger epidermal growth factor (EGF)-induced phosphorylation of both AKT and glycogen synthase kinase 3beta (GSK-3beta) than fibroblasts from control patients. Similar results were obtained in HEK293 cells expressing LS mutants of SHP2. We found that the GAB1/phosphoinositide 3-kinase (PI3K) complex was more abundant in fibroblasts from LS than control subjects and that both AKT and GSK-3beta hyperphosphorylation were prevented by reducing GAB1 expression or by overexpressing a GAB1 mutant unable to bind to PI3K. Consistently, purified recombinant LS mutants failed to dephosphorylate GAB1 PI3K-binding sites. These mutants induced PI3K-dependent increase in cell size in a model of chicken embryo cardiac explants and in transcriptional activity of the atrial natriuretic factor (ANF) gene in neonate rat cardiomyocytes. In conclusion, SHP2 mutations causing LS facilitate EGF-induced PI3K/AKT/GSK-3beta stimulation through impaired GAB1 dephosphorylation, resulting in deregulation of a novel signaling pathway that could be involved in LS pathology.

Function, regulation and pathological roles of the Gab/DOS docking proteins

Since their discovery a little more than a decade ago, the docking proteins of the Gab/DOS family have emerged as important signalling elements in metazoans. Gab/DOS proteins integrate and amplify signals from a wide variety of sources including growth factor, cytokine and antigen receptors as well as cell adhesion molecules. They also contribute to signal diversification by channelling the information from activated receptors into signalling pathways with distinct biological functions. Recent approaches in protein biochemistry and systems biology have revealed that Gab proteins are subject to complex regulation by feed-forward and feedback phosphorylation events as well as protein-protein interactions. Thus, Gab/DOS docking proteins are at the centre of entire signalling subsystems and fulfil an important if not essential role in many physiological processes. Furthermore, aberrant signalling by Gab proteins has been increasingly linked to human diseases from various forms of neoplasia to Alzheimer's disease.

In this review, we provide a detailed overview of the structure, effector functions, regulation and evolution of the Gab/DOS family. We also summarize recent findings implicating Gab proteins, in particular the Gab2 isoform, in leukaemia, solid tumours and other human diseases.

Activation of a novel estrogen receptor, GPER, is cardioprotective in male and female rats

Premenopausal females have a lower incidence of cardiovascular disease than their male counterparts, but the mechanism is unclear. Estrogen has been thought to signal through two nuclear receptors: estrogen receptor-alpha or estrogen receptor-beta; however, a third, membrane-bound receptor G protein-coupled estrogen receptor (GPER), has been identified and shown to bind estrogen with high affinity. To date, there is little information on GPER in the heart and no study has looked at the effect of GPER activation during myocardial ischemia-reperfusion (I/R). Therefore, the goal of this study was to determine whether activation of GPER is cardioprotective in rats. A highly specific GPER agonist, G-1, was administered to Sprague-Dawley (200-350 g) rat hearts 10 min before 20 min of ischemic followed by 120 min of reperfusion using a Langendorff model. Similar levels of GPER were found in both male and female rat hearts. With administration of 110 nM of G-1, postischemic contractile dysfunction was significantly reduced compared with untreated controls (43.8 + or - 4.3% vs. 26.9 + or - 2.1% of preischemic rate pressure product; P < 0.05). Additionally, infarct size was reduced in the G-1-treated animals when compared with control (18.8 + or - 2.7% vs. 32.4 + or - 2.1%; P < 0.05). These observations were demonstrated in both male and intact female rat hearts. Through Western blot analysis, it was demonstrated that G-1 induces the activation of both Akt and ERK1/2. Furthermore, the protection afforded by G-1 was blocked by coadministration of a phosphatidylinositol 3-kinase (PI3K) inhibitor (wortmannin, 100 nM). Taken together, the data show that G-1 activation of GPER improves functional recovery and reduces infarct size in isolated rat hearts following I/R through a PI3K-dependent, gender-independent mechanism.

Cell type-specific importance of ras-c-raf complex association rate constants for MAPK signaling

We generated 17 c-Raf (RAF proto-oncogene serine-threonine protein kinase) mutants with altered Ras-Raf association and dissociation rates to investigate the role of electrostatically driven Ras-Raf association rates on epidermal growth factor (EGF)-activated mitogen-activated protein kinase (MAPK) signal transduction. Some of these mutants had compensating changes in association and dissociation rates, enabling the effects of changes in association rate to be distinguished from those of changes in affinity. In rabbit kidney (RK13) cells, these mutants affected downstream signaling, with changes in Ras-c-Raf association rates having a greater effect on MAPK signaling than did similar changes in dissociation rates. Mutants with compensating decreases in both association and dissociation rates stimulated less extracellular signal-regulated kinase (ERK)-dependent reporter activity than did wild-type c-Raf, whereas the converse was true for mutants with increased association and dissociation rates. In marked contrast, the mutants had little or no effect on signaling in human embryonic kidney (HEK) 293 cells. These two cell lines also showed distinct patterns of EGF-dependent ERK phosphorylation and signaling: ERK activation and signaling were transient in HEK293 cells and sustained in RK13 cells, with the difference resulting from the lack of negative feedback from ERK to Sos (Son of Sevenless) in the latter. Computer simulation revealed that, in the presence of negative feedback, changes in the rate of Ras-c-Raf binding have little effect on ERK activation. Thus, EGF-MAPK activation kinetics and feedback regulation is cell type specific and depends on the network topology.

Phosphorylation-dependent binding of 14-3-3 terminates signalling by the Gab2 docking protein

Grb2-associated binder (Gab)2 functions downstream of a variety of receptor and cytoplasmic tyrosine kinases as a docking platform for specific signal transducers and performs important functions in both normal physiology and oncogenesis. Gab2 signalling is promoted by its association with specific receptors through the adaptor Grb2. However, the molecular mechanisms that attenuate Gab2 signals have remained unclear. We now demonstrate that growth factor-induced phosphorylation of Gab2 on two residues, S210 and T391, leads to recruitment of 14-3-3 proteins. Together, these events mediate negative-feedback regulation, as Gab2(S210A/T391A) exhibits sustained receptor association and signalling and promotes cell proliferation and transformation. Importantly, introduction of constitutive 14-3-3-binding sites into Gab2 renders it refractory to receptor activation, demonstrating that site-selective binding of 14-3-3 proteins is sufficient to terminate Gab2 signalling. Furthermore, this is associated with reduced binding of Grb2. This leads to a model where signal attenuation occurs because 14-3-3 promotes dissociation of Gab2 from Grb2, and thereby uncouples Gab2 from the receptor complex. This represents a novel regulatory mechanism with implications for diverse tyrosine kinase signalling systems.

Genomic-wide analysis of lymphatic metastasis-associated genes in human hepatocellular carcinoma

AIM: To identify the genes related to lymph node metastasis in human hepatocellular carcinoma (HCC), 32 HCC patients with or without lymph node metastasis were investigated by high-throughput microarray comprising 886 genes.

METHODS: The samples of cancerous and non-cancerous paired tissue were taken from 32 patients with HCC who underwent hepatectomy with lymph node dissection. Total RNA was extracted from the cells obtained by means of laser microdissection (LCM) and was amplified by the T7-based amplification system. Then, the amplified samples were applied in the cDNA microarray comprising of 886 genes.

RESULTS: The results demonstrated that 25 up-regulated genes such as cell membrane receptor, intracellular signaling and cell adhesion related genes, and 48 down-regulated genes such as intracellular signaling and cell cycle regulator-related genes, were correlated with lymph node metastasis in HCC. Amongst them were included some interesting genes, such as MET, EPHA2, CCND1, MMP2, MMP13, CASP3, CDH1, and PTPN2. Expression of 16 genes (MET, CCND1, CCND2, VEGF, KRT18, RFC4, BIRC5, CDC6, MMP2, BCL2A1, CDH1, VIM, PDGFRA, PTPN2, SLC25A5 and DSP) were further confirmed by real-time quantitative reverse transcriptional polymerase chain reaction (RT-PCR).

CONCLUSION: Tumor metastasis is an important biological characteristic, which involves multiple genetic changes and cumulation. This genome-wide information contributes to an improved understanding of molecular alterations during lymph node metastasis in HCC. It may help clinicians to predict metastasis of lymph nodes and assist researchers in identifying novel therapeutic targets for metastatic HCC patients.

Multiple mechanisms are responsible for transactivation of the epidermal growth factor receptor in mammary epithelial cells

The number of distinct signaling pathways that can transactivate the epidermal growth factor receptor (EGFR) in a single cell type is unclear. Using a single strain of human mammary epithelial cells, we found that a wide variety of agonists, such as lysophosphatidic acid (LPA), uridine triphosphate, growth hormone, vascular endothelial growth factor, insulin-like growth factor-1 (IGF-1), and tumor necrosis factor-alpha, require EGFR activity to induce ERK phosphorylation. In contrast, hepatocyte growth factor can stimulate ERK phosphorylation independent of the EGFR. EGFR transactivation also correlated with an increase in cell proliferation and could be inhibited with metalloprotease inhibitors. However, there were significant differences with respect to transactivation kinetics and sensitivity to different inhibitors. In particular, IGF-1 displayed relatively slow transactivation kinetics and was resistant to inhibition by the selective ADAM-17 inhibitor WAY-022 compared with LPA-induced transactivation. Studies using anti-ligand antibodies showed that IGF-1 transactivation required amphiregulin production, whereas LPA was dependent on multiple ligands. Direct measurement of ligand shedding confirmed that LPA treatment stimulated shedding of multiple EGFR ligands, but paradoxically, IGF-1 had little effect on the shedding rate of any ligand, including amphiregulin. Instead, IGF-1 appeared to work by enhancing EGFR activation of Ras in response to constitutively produced amphiregulin. This enhancement of EGFR signaling was independent of both receptor phosphorylation and PI-3-kinase activity, suggestive of a novel mechanism. Our studies demonstrate that within a single cell type, the EGFR autocrine system can couple multiple signaling pathways to ERK activation and that this modulation of EGFR autocrine signaling can be accomplished at multiple regulatory steps.

The PTEN-PI3K pathway: of feedbacks and cross-talks

The tumor suppressor PTEN was originally identified as a negative regulator of the phosphoinositide 3-kinase (PI3K) signaling, a main regulator of cell growth, metabolism and survival. Yet this function of PTEN is extremely relevant for its tumor-suppressive ability, albeit the recent characterization of many PI3K-independent tumor-suppressive activities. PI3K-mediated PIP(3) production leads to the activation of the canonical AKT-mTORC1 pathway. The implications of this signaling cascade in health and disease have been underscored by the high number of regulators within the pathway whose alterations give rise to different malignancies, including familiar syndromes, metabolic dysfunctions and cancer. Moreover, PI3K is tightly buffered at multiple levels by downstream components, which have turned this signaling pathway literally upside down. PI3K and its downstream components in turn cross-talk with a number of other pathways, thereby leading to a complex network of signals that may have dramatic consequences when perturbed. Here, we review the current status of the PTEN-PI3K signaling pathway with special emphasis on the most recent data on targets and regulation of the PTEN-PI3K axis. This provides novel provocative therapeutic implications based on the targeted modulation of PI3K-cross-talking signals.

Inhibition of mTORC1 leads to MAPK pathway activation through a PI3K-dependent feedback loop in human cancer

Numerous studies have established a causal link between aberrant mammalian target of rapamycin (mTOR) activation and tumorigenesis, indicating that mTOR inhibition may have therapeutic potential. In this study, we show that rapamycin and its analogs activate the MAPK pathway in human cancer, in what represents a novel mTORC1-MAPK feedback loop. We found that tumor samples from patients with biopsy-accessible solid tumors of advanced disease treated with RAD001, a rapamycin derivative, showed an administration schedule-dependent increase in activation of the MAPK pathway. RAD001 treatment also led to MAPK activation in a mouse model of prostate cancer. We further show that rapamycin-induced MAPK activation occurs in both normal cells and cancer cells lines and that this feedback loop depends on an S6K-PI3K-Ras pathway. Significantly, pharmacological inhibition of the MAPK pathway enhanced the antitumoral effect of mTORC1 inhibition by rapamycin in cancer cells in vitro and in a xenograft mouse model. Taken together, our findings identify MAPK activation as a consequence of mTORC1 inhibition and underscore the potential of a combined therapeutic approach with mTORC1 and MAPK inhibitors, currently employed as single agents in the clinic, for the treatment of human cancers.

Inhibition of mTORC1 leads to MAPK pathway activation through a PI3K-dependent feedback loop in human cancer

Numerous studies have established a causal link between aberrant mammalian target of rapamycin (mTOR) activation and tumorigenesis, indicating that mTOR inhibition may have therapeutic potential. In this study, we show that rapamycin and its analogs activate the MAPK pathway in human cancer, in what represents a novel mTORC1-MAPK feedback loop. We found that tumor samples from patients with biopsy-accessible solid tumors of advanced disease treated with RAD001, a rapamycin derivative, showed an administration schedule-dependent increase in activation of the MAPK pathway. RAD001 treatment also led to MAPK activation in a mouse model of prostate cancer. We further show that rapamycin-induced MAPK activation occurs in both normal cells and cancer cells lines and that this feedback loop depends on an S6K-PI3K-Ras pathway. Significantly, pharmacological inhibition of the MAPK pathway enhanced the antitumoral effect of mTORC1 inhibition by rapamycin in cancer cells in vitro and in a xenograft mouse model. Taken together, our findings identify MAPK activation as a consequence of mTORC1 inhibition and underscore the potential of a combined therapeutic approach with mTORC1 and MAPK inhibitors, currently employed as single agents in the clinic, for the treatment of human cancers.

Epidermal growth factor receptor and glioblastoma multiforme: molecular basis for a new approach

High-grade gliomas are the most common primary malignant brain tumours. Surgery, radiotherapy and chemotherapy are the cornerstone of actual treatment. In spite of large therapeutic efforts, overall survival is still poor. New molecular data allow a new molecular classification for high-grade gliomas and open a therapeutic window for targeted therapy. Molecular diagnostic tools may provide a basis for receptor-based therapies and enough information to personalise future treatments. In this regard, epidermal growth factor receptor (EGFR) is a target that will play a critical role in the management of glioma patients. This review summarises basic and preclinical data that support future use of therapies against EGFR.