The role of individual SH2 domains in mediating association of phospholipase C-gamma1 with the activated EGF receptor

The impact of nitric oxide on HER family post-translational modification and downstream signaling in cancer

The human epidermal growth factor receptor (HER) family consists of four members, activated by two families of ligands. They are known for mediating cell-cell interactions in organogenesis, and their deregulation has been associated with various cancers, including breast and esophageal cancers. In particular, aberrant epidermal growth factor receptor (EGFR) and HER2 signaling drive disease progression and result in poorer patient outcomes. Nitric oxide (NO) has been proposed as an alternative activator of the HER family and may play a role in this aberrant activation due to its ability to induce s-nitrosation and phosphorylation of the EGFR. This review discusses the potential impact of NO on HER family activation and downstream signaling, along with its role in the efficacy of therapeutics targeting the family.

8-Br-cGMP suppresses tumor progression through EGFR/PLC γ1 pathway in epithelial ovarian cancer

BACKGROUND

Cyclic guanosine monophosphate (cGMP)-dependent protein kinase I (PKG-I), a serine/threonine kinase, is important in tumor development. The present study determines that the cGMP/PKG I pathway is essential for promoting cell proliferation and survival in human ovarian cancer cells, whereas cGMP analog has been shown to lead to growth inhibition and apoptosis of various cancer cells. The role of cGMP/PKG I pathway in epithelial ovarian cancer (EOC), therefore, remains controversial. We investigated the effect of cGMP/PKG I pathway and the underlying mechanism in EOC.

METHODS AND RESULTS

The results showed that exogenous 8-Bromoguanosine-3', 5'-cyclic monophosphate (8-Br-cGMP) (cGMP analog) could antagonize the effects by EGF, including suppressing proliferation, invasion and migration of EOC cells. In vivo, 8-Br-cGMP hampered the growth of the xenograft tumor. Additionally, the expressions of epidermal growth factor receptor (EGFR), matrix metallopeptidase 9 (MMP9), proliferating cell nuclear antigen and Ki67 in xenograft tumor were decreased after 8-Br-cGMP intervention. Further research demonstrated that 8-Br-cGMP decreased the phosphorylation of EGFR (Y992) and downstream proteins phospholipase Cγ1 (PLC γ1) (Y783), calmodulin kinase II (T286) and inhibited cytoplasmic Ca2+ release as well as PKC transferring to cell membrane. It's worth noting that the inhibition was 8-Br-cGMP dose-dependent and 8-Br-cGMP showed similar inhibitory effect on EOC cells compared with U-73122, a specific inhibitor of PLC γ1.

CONCLUSIONS

The activation of endogenous PKG I by addition of exogenous 8-Br-cGMP could inhibit EOC development probably via EGFR/PLCγ1 signaling pathway. 8-Br-cGMP/PKG I provide a new insight and strategy for EOC treatment.

The ErbB Signaling Network and Its Potential Role in Endometrial Cancer

Endometrial cancer (EC) is the second most common malignancy of the female reproductive system worldwide. The updated EC classification emphasizes the significant role of various signaling pathways such as PIK3CA-PIK3R1-PTEN and RTK/RAS/β-catenin in EC pathogenesis. Some of these pathways are part of the EGF system signaling network, which becomes hyperactivated by various mechanisms and participates in cancer pathogenesis. In EC, the expression of ErbB receptors is significantly different, compared with the premenopausal and postmenopausal endometrium, mainly because of the increased transcriptional activity of ErbB encoding genes in EC cells. Moreover, there are some differences in ErbB-2 receptor profile among EC subgroups that could be explained by the alterations in pathophysiology and clinical behavior of various EC histologic subtypes. The fact that ErbB-2 receptor expression is more common in aggressive EC histologic subtypes (papillary serous and clear cell) could indicate a future role of ErbB-targeted therapies in well-defined EC subgroups with overexpression of ErbB receptors.

WSD-0922, a novel brain-penetrant inhibitor of epidermal growth factor receptor, promotes survival in glioblastoma mouse models

Background

Although the epidermal growth factor receptor (EGFR) is a frequent oncogenic driver in glioblastoma (GBM), efforts to therapeutically target this protein have been largely unsuccessful. The present preclinical study evaluated the novel EGFR inhibitor WSD-0922.

Methods

We employed flank and orthotopic patient-derived xenograft models to characterize WSD-0922 and compare its efficacy to erlotinib, a potent EGFR inhibitor that failed to provide benefit for GBM patients. We performed long-term survival studies and collected short-term tumor, plasma, and whole-brain samples from mice treated with each drug. We utilized mass spectrometry to measure drug concentrations and spatial distribution and to assess the impact of each drug on receptor activity and cellular signaling networks.

Results

WSD-0922 inhibited EGFR signaling as effectively as erlotinib in in vitro and in vivo models. While WSD-0922 was more CNS penetrant than erlotinib in terms of total concentration, comparable concentrations of both drugs were measured at the tumor site in orthotopic models, and the concentration of free WSD-0922 in the brain was significantly less than the concentration of free erlotinib. WSD-0922 treatment provided a clear survival advantage compared to erlotinib in the GBM39 model, with marked suppression of tumor growth and most mice surviving until the end of the study. WSD-0922 treatment preferentially inhibited phosphorylation of several proteins, including those associated with EGFR inhibitor resistance and cell metabolism.

Conclusions

WSD-0922 is a highly potent inhibitor of EGFR in GBM, and warrants further evaluation in clinical studies.

It Takes Two to Tango: IGF-I and TSH Receptors in Thyroid Eye Disease

CONTEXT

Thyroid eye disease (TED) is a complex autoimmune disease process. Orbital fibroblasts represent the central orbital immune target. Involvement of the TSH receptor (TSHR) in TED is not fully understood. IGF-I receptor (IGF-IR) is overexpressed in several cell types in TED, including fibrocytes and orbital fibroblasts. IGF-IR may form a physical and functional complex with TSHR.

OBJECTIVE

Review literature relevant to autoantibody generation in TED and whether these induce orbital fibroblast responses directly through TSHR, IGF-IR, or both.

EVIDENCE

IGF-IR has traditionally been considered a typical tyrosine kinase receptor in which tyrosine residues become phosphorylated following IGF-I binding. Evidence has emerged that IGF-IR possesses kinase-independent activities and can be considered a functional receptor tyrosine kinase/G-protein-coupled receptor hybrid, using the G-protein receptor kinase/β-arrestin system. Teprotumumab, a monoclonal IGF-IR antibody, effectively reduces TED disease activity, proptosis, and diplopia. In addition, the drug attenuates in vitro actions of both IGF-I and TSH in fibrocytes and orbital fibroblasts, including induction of proinflammatory cytokines by TSH and TED IgGs.

CONCLUSIONS

Although teprotumumab has been proven effective and relatively safe in the treatment of TED, many questions remain pertaining to IGF-IR, its relationship with TSHR, and how the drug might be disrupting these receptor protein/protein interactions. Here, we propose 4 possible IGF-IR activation models that could underlie clinical responses to teprotumumab observed in patients with TED. Teprotumumab is associated with several adverse events, including hyperglycemia and hearing abnormalities. Underpinning mechanisms of these are being investigated. Patients undergoing treatment with drug must be monitored for these and managed with best medical practices.

Dynamics of allosteric regulation of the phospholipase C-γ isozymes upon recruitment to membranes

Numerous receptor tyrosine kinases and immune receptors activate phospholipase C-γ (PLC-γ) isozymes at membranes to control diverse cellular processes including phagocytosis, migration, proliferation, and differentiation. The molecular details of this process are not well understood. Using hydrogen-deuterium exchange mass spectrometry, we show that PLC-γ1 is relatively inert to lipid vesicles that contain its substrate, phosphatidylinositol 4,5-bisphosphate (PIP₂), unless first bound to the kinase domain of the fibroblast growth factor receptor (FGFR1). Exchange occurs throughout PLC-γ1 and is exaggerated in PLC-γ1 containing an oncogenic substitution (D1165H) that allosterically activates the lipase. These data support a model whereby initial complex formation shifts the conformational equilibrium of PLC-γ1 to favor activation. This receptor-induced priming of PLC-γ1 also explains the capacity of a kinase-inactive fragment of FGFR1 to modestly enhance the lipase activity of PLC-γ1 operating on lipid vesicles but not a soluble analog of PIP₂ and highlights potential cooperativity between receptor engagement and membrane proximity. Priming is expected to be greatly enhanced for receptors embedded in membranes and nearly universal for the myriad of receptors and co-receptors that bind the PLC-γ isozymes.

Recruitment of phospholipase Cγ1 to the non-structural membrane protein pK15 of Kaposi Sarcoma-associated herpesvirus promotes its Src-dependent phosphorylation

Kaposi Sarcoma-associated herpesvirus (KSHV) causes three human malignancies, Kaposi Sarcoma (KS), Primary Effusion Lymphoma (PEL) and the plasma cell variant of multicentric Castleman’s Disease (MCD), as well as an inflammatory cytokine syndrome (KICS). Its non-structural membrane protein, pK15, is among a limited set of viral proteins expressed in KSHV-infected KS tumor cells. Following its phosphorylation by Src family tyrosine kinases, pK15 recruits phospholipase C gamma 1 (PLCγ1) to activate downstream signaling cascades such as the MEK/ERK, NFkB and PI3K pathway, and thereby contributes to the increased proliferation and migration as well as the spindle cell morphology of KSHV-infected endothelial cells. Here, we show that a phosphorylated Y⁴⁸¹EEVL motif in pK15 preferentially binds into the PLCγ1 C-terminal SH2 domain (cSH2), which is involved in conformational changes occurring during the activation of PLCγ1 by receptor tyrosine kinases. We determined the crystal structure of a pK15 12mer peptide containing the phosphorylated pK15 Y⁴⁸¹EEVL motif in complex with a shortened PLCγ1 tandem SH2 (tSH2) domain. This structure demonstrates that the pK15 peptide binds to the PLCγ1 cSH2 domain in a position that is normally occupied by the linker region connecting the PLCγ1 cSH2 and SH3 domains. We also show that longer pK15 peptides containing the phosphorylated pK15 Y⁴⁸¹EEVL motif can increase the Src-mediated phosphorylation of the PLCγ1 tSH2 region in vitro. This pK15-induced increase in Src-mediated phosphorylation of PLCγ1 can be inhibited with the small pK15-derived peptide which occupies the PLCγ1 cSH2 domain. Our findings thus suggest that pK15 may act as a scaffold protein to promote PLCγ1 activation in a manner similar to the cellular scaffold protein SLP-76, which has been shown to promote PLCγ1 activation in the context of T-cell receptor signaling. Reminiscent of its positional homologue in Epstein-Barr Virus, LMP2A, pK15 may therefore mimic aspects of antigen-receptor signaling. Our findings also suggest that it may be possible to inhibit the recruitment and activation of PLCγ1 pharmacologically.

Kaposi’s Sarcoma-Associated Herpesvirus (KSHV) causes three human malignancies (Kaposi Sarcoma, Primary Effusion Lymphoma, Multicentric Castleman’s Disease) and an inflammatory condition, KICS. One of its non-structural membrane proteins, pK15, is expressed in tumor cells and has previously been shown to contribute to its ability to reactivate from latency and to its pathogenetic properties in endothelial cells by recruiting the cellular signaling enzyme phospholipase Cγ1 (PLCγ1). Here we investigate the interaction of pK15 with PLCγ1, report the structure of a PLCγ1 domain in complex with a pK15 peptide and show that pK15 primes PLCγ1 for phosphorylation by the cellular kinase Src. We also show that the pK15-dependent activation of PLCγ1 can be inhibited with a small peptide. Our findings therefore identify the pK15-PLCγ1 interaction as a putative druggable target and provide the basis for the development of small molecule inhibitors that could perhaps serve to inhibit KSHV replication and pathogenesis.

mTOR-Rictor-EGFR axis in oncogenesis and diagnosis of glioblastoma multiforme

Glioblastoma multiforme (GBM) is one of the aggressive brain cancers with patients having less survival period upto 12-15 months. Mammalian target of rapamycin (mTOR) is a serine/threonine kinase, belongs to the phosphatidylinositol 3-kinases (PI3K) pathway and is involved in various cellular processes of cancer cells. Cancer metabolism is regulated by mTOR and its components. mTOR forms two complexes as mTORC1 and mTORC2. Studies have identified the key component of the mTORC2 complex, Rapamycin-insensitive companion of mammalian target of rapamycin (Rictor) plays a prominent role in the regulation of cancer cell proliferation and metabolism. Apart, growth factor receptor signaling such as epidermal growth factor signaling mediated by epidermal growth factor receptor (EGFR) regulates cancer-related processes. In EGFR signaling various other signaling cascades such as phosphatidyl-inositol 3-kinase (PI3K)/protein kinase B (Akt)/mammalian target of rapamycin (mTOR pathway) and Ras/Raf/mitogen-activated protein kinase/ERK kinase (MEK)/extracellular-signal-regulated kinase (ERK) -dependent signaling cross-talk each other. From various studies about GBM, it is very well established that Rictor and EGFR mediated signaling pathways majorly playing a pivotal role in chemoresistance and tumor aggressiveness. Recent studies have shown that non-coding RNAs such as microRNAs (miRs) and long non-coding RNAs (lncRNAs) regulate the EGFR and Rictor and sensitize the cells towards chemotherapeutic agents. Thus, understanding of microRNA mediated regulation of EGFR and Rictor will help in cancer prevention and management as well as a future therapy.

Identification of SH2 Domain-Mediated Protein Interactions that Operate at Fertilization in the Sea Star Patiria miniata

The signaling mechanisms controlling internal calcium release at fertilization in animals are still largely unknown. Echinoderms, such as the sea star Patiria miniata, produce abundant and easily accessible sperm and eggs. In addition, eggs are naturally synchronized at the same cell cycle stage, collectively making these animals an attractive model to study the signaling proteins controlling fertilization. However, the lack of antibodies to identify proteins in this model system has slowed progress in identifying key signaling molecules. With the advances in mass spectrometry, we present a method for identifying tyrosine phosphorylated proteins binding to GST-tagged SH2 domains in sea star cell lysates for downstream mass spectrometry analysis.

Mechanisms of Oocyte Maturation and Related Epigenetic Regulation

Meiosis is the basis of sexual reproduction. In female mammals, meiosis of oocytes starts before birth and sustains at the dictyate stage of meiotic prophase I before gonadotropins-induced ovulation happens. Once meiosis gets started, the oocytes undergo the leptotene, zygotene, and pachytene stages, and then arrest at the dictyate stage. During each estrus cycle in mammals, or menstrual cycle in humans, a small portion of oocytes within preovulatory follicles may resume meiosis. It is crucial for females to supply high quality mature oocytes for sustaining fertility, which is generally achieved by fine-tuning oocyte meiotic arrest and resumption progression. Anything that disturbs the process may result in failure of oogenesis and seriously affect both the fertility and the health of females. Therefore, uncovering the regulatory network of oocyte meiosis progression illuminates not only how the foundations of mammalian reproduction are laid, but how mis-regulation of these steps result in infertility. In order to provide an overview of the recently uncovered cellular and molecular mechanism during oocyte maturation, especially epigenetic modification, the progress of the regulatory network of oocyte meiosis progression including meiosis arrest and meiosis resumption induced by gonadotropins is summarized. Then, advances in the epigenetic aspects, such as histone acetylation, phosphorylation, methylation, glycosylation, ubiquitination, and SUMOylation related to the quality of oocyte maturation are reviewed.

Autophosphorylation of EGFR at Y954 Facilitated Homodimerization and Enhanced Downstream Signals

Asymmetric dimer formation of epidermal growth factor receptor (EGFR) is crucial for EGF-induced receptor activation. Even though autophosphorylation is important for activation, its role remains elusive in the context of regulating dimers. In this study, employing overlapping time series analysis to raster image correlation spectroscopy (RICS), we observed time-dependent transient dynamics of EGFR dimerization and found EGFR kinase activity to be essential for dimerization. As a result of which, we hypothesized that phosphorylation could influence dimerization. Evaluating this point, we observed that one of the tyrosine residues (Y954) located in the C-terminal lobe of the activator kinase domain was important to potentiate dimerization. Functional imaging to monitor Ca²⁺ and ERK signals revealed a significant role of Y954 in influencing downstream signaling cascade. Crucial for stabilization of EGFR asymmetric dimer is a "latch" formed between kinase domains of the binding partners. Because Y954 is positioned adjacent to the latch binding region on the kinase domain, we propose that phosphorylation strengthened the latch interaction. On the contrary, we identified that threonine phosphorylation (T669) in the latch domain negatively regulated EGFR dimerization and the downstream signals. Overall, we have delineated the previously anonymous role of phosphorylation at the latch interface of kinase domains in regulating EGFR dimerization.

Targeting PKCδ as a Therapeutic Strategy against Heterogeneous Mechanisms of EGFR Inhibitor Resistance in EGFR-Mutant Lung Cancer

Multiple mechanisms of resistance to epidermal growth factor receptor (EGFR) tyrosine kinase inhibitors (TKIs) have been identified in EGFR-mutant non-small cell lung cancer (NSCLC); however, recurrent resistance to EGFR TKIs due to the heterogeneous mechanisms underlying resistance within a single patient remains a major challenge in the clinic. Here, we report a role of nuclear protein kinase Cδ (PKCδ) as a common axis across multiple known TKI-resistance mechanisms. Specifically, we demonstrate that TKI-inactivated EGFR dimerizes with other membrane receptors implicated in TKI resistance to promote PKCδ nuclear translocation. Moreover, the level of nuclear PKCδ is associated with TKI response in patients. The combined inhibition of PKCδ and EGFR induces marked regression of resistant NSCLC tumors with EGFR mutations.

β-Heregulin impairs EGF induced PLC-γ1 signalling in human breast cancer cells

The interplay of ErbB receptor homo- and heterodimers plays a crucial role in the pathology of breast cancer since activated signal transduction cascades coordinate proliferation, survival and migration of cells. EGF and β-Heregulin are well characterised ligands known to induce ErbB homo- and heterodimerisation, which have been associated with disease progression. In the present study, we investigated the impact of both factors on the migration of MDA-NEO and MDA-HER2 human breast cancer cells. MDA-NEO cells are positive for EGFR and HER3, while MDA-HER2 cells express EGFR, HER2 and HER3. Cell migration analysis revealed that β-Heregulin potently impaired EGF induced migration in both cell lines. Western blot studies showed that both ErbB receptor and PLC-γ1 tyrosine phosphorylation levels were diminished in EGF and β-Heregulin co-treated MDA-NEO and MDA-HER2 cells, which was further correlated to a significantly impaired calcium influx. Our data indicate that EGF and HRG may interfere with each other for receptor binding and dimerisation, which ultimately has an impact on signalling outcome.

Molecular Mechanisms of Prophase I Meiotic Arrest Maintenance and Meiotic Resumption in Mammalian Oocytes

Mechanisms of meiotic prophase I arrest maintenance (germinal vesicle [GV] stage) and meiotic resumption (germinal vesicle breakdown [GVBD] stage) in mammalian oocytes seem to be very complicated. These processes are regulated via multiple molecular cascades at transcriptional, translational, and posttranslational levels, and many of them are interrelated. There are many molecular cascades of meiosis maintaining and meiotic resumption in oocyte which are orchestrated by multiple molecules produced by pituitary gland and follicular cells. Furthermore, many of these molecular cascades are duplicated, thus ensuring the stability of the entire system. Understanding mechanisms of oocyte maturation is essential to assess the oocyte status, develop effective protocols of oocyte in vitro maturation, and design novel contraceptive drugs. Mechanisms of meiotic arrest maintenance at prophase I and meiotic resumption in mammalian oocytes are covered in the present article.

Epidermal Growth Factor Receptor Cell Proliferation Signaling Pathways

The epidermal growth factor receptor (EGFR) is a receptor tyrosine kinase that is commonly upregulated in cancers such as in non-small-cell lung cancer, metastatic colorectal cancer, glioblastoma, head and neck cancer, pancreatic cancer, and breast cancer. Various mechanisms mediate the upregulation of EGFR activity, including common mutations and truncations to its extracellular domain, such as in the EGFRvIII truncations, as well as to its kinase domain, such as the L858R and T790M mutations, or the exon 19 truncation. These EGFR aberrations over-activate downstream pro-oncogenic signaling pathways, including the RAS-RAF-MEK-ERK MAPK and AKT-PI3K-mTOR pathways. These pathways then activate many biological outputs that are beneficial to cancer cell proliferation, including their chronic initiation and progression through the cell cycle. Here, we review the molecular mechanisms that regulate EGFR signal transduction, including the EGFR structure and its mutations, ligand binding and EGFR dimerization, as well as the signaling pathways that lead to G1 cell cycle progression. We focus on the induction of CYCLIN D expression, CDK4/6 activation, and the repression of cyclin-dependent kinase inhibitor proteins (CDKi) by EGFR signaling pathways. We also discuss the successes and challenges of EGFR-targeted therapies, and the potential for their use in combination with CDK4/6 inhibitors.

Epidermal Growth Factor Receptor Cell Proliferation Signaling Pathways

The epidermal growth factor receptor (EGFR) is a receptor tyrosine kinase that is commonly upregulated in cancers such as in non-small-cell lung cancer, metastatic colorectal cancer, glioblastoma, head and neck cancer, pancreatic cancer, and breast cancer. Various mechanisms mediate the upregulation of EGFR activity, including common mutations and truncations to its extracellular domain, such as in the EGFRvIII truncations, as well as to its kinase domain, such as the L858R and T790M mutations, or the exon 19 truncation. These EGFR aberrations over-activate downstream pro-oncogenic signaling pathways, including the RAS-RAF-MEK-ERK MAPK and AKT-PI3K-mTOR pathways. These pathways then activate many biological outputs that are beneficial to cancer cell proliferation, including their chronic initiation and progression through the cell cycle. Here, we review the molecular mechanisms that regulate EGFR signal transduction, including the EGFR structure and its mutations, ligand binding and EGFR dimerization, as well as the signaling pathways that lead to G1 cell cycle progression. We focus on the induction of CYCLIN D expression, CDK4/6 activation, and the repression of cyclin-dependent kinase inhibitor proteins (CDKi) by EGFR signaling pathways. We also discuss the successes and challenges of EGFR-targeted therapies, and the potential for their use in combination with CDK4/6 inhibitors.

Oocyte activation and latent HIV-1 reactivation: AMPK as a common mechanism of action linking the beginnings of life and the potential eradication of HIV-1

In all mammalian species studied to date, the initiation of oocyte activation is orchestrated through alterations in intracellular calcium (Ca(2+)) signaling. Upon sperm binding to the oocyte plasma membrane, a sperm-associated phospholipase C (PLC) isoform, PLC zeta (PLCζ), is released into the oocyte cytoplasm. PLCζ hydrolyzes phosphatidylinositol 4,5-bisphosphate (PIP2) to produce diacylglycerol (DAG), which activates protein kinase C (PKC), and inositol 1,4,5-trisphosphate (IP3), which induces the release of Ca(2+) from endoplasmic reticulum (ER) Ca(2+) stores. Subsequent Ca(2+) oscillations are generated that drive oocyte activation to completion. Ca(2+) ionophores such as ionomycin have been successfully used to induce artificial human oocyte activation, facilitating fertilization during intra-cytoplasmic sperm injection (ICSI) procedures. Early studies have also demonstrated that the PKC activator phorbol 12-myristate 13-acetate (PMA) acts synergistically with Ca(2+) ionophores to induce parthenogenetic activation of mouse oocytes. Interestingly, the Ca(2+)-induced signaling cascade characterizing sperm or chemically-induced oocyte activation, i.e. the "shock and live" approach, bears a striking resemblance to the reactivation of latently infected HIV-1 viral reservoirs via the so called "shock and kill" approach, a method currently being pursued to eradicate HIV-1 from infected individuals. PMA and ionomycin combined, used as positive controls in HIV-1 latency reversal studies, have been shown to be extremely efficient in reactivating latent HIV-1 in CD4(+) memory T cells by inducing T cell activation. Similar to oocyte activation, T cell activation by PMA and ionomycin induces an increase in intracellular Ca(2+) concentrations and activation of DAG, PKC, and downstream Ca(2+)-dependent signaling pathways necessary for proviral transcription. Interestingly, AMPK, a master regulator of cell metabolism that is activated thorough the induction of cellular stress (e.g. increase in Ca(2+) concentration, reactive oxygen species generation, increase in AMP/ATP ratio) is essential for oocyte maturation, T cell activation, and mitochondrial function. In addition to the AMPK kinase LKB1, CaMKK2, a Ca(2+)/calmodulin-dependent kinase that also activates AMPK, is present in and activated on T cell activation and is also present in mouse oocytes and persists until the zygote and two-cell stages. It is our hypothesis that AMPK activation represents a central node linking T cell activation-induced latent HIV-1 reactivation and both physiological and artificial oocyte activation. We further propose the novel observation that various compounds that have been shown to reactivate latent HIV-1 (e.g. PMA, ionomycin, metformin, bryostatin, resveratrol, etc.) or activate oocytes (PMA, ionomycin, ethanol, puromycin, etc.) either alone or in combination likely do so via stress-induced activation of AMPK.

Carcinoma cells induce lumen filling and EMT in epithelial cells through soluble E-cadherin-mediated activation of EGFR

In epithelial cancers, carcinoma cells coexist with normal cells. Although it is known that the tumor microenvironment (TME) plays a pivotal role in cancer progression, it is not completely understood how the tumor influences adjacent normal epithelial cells. In this study, a three-dimensional co-culture system comprising non-transformed epithelial cells (MDCK) and transformed carcinoma cells (MSV-MDCK) was used to demonstrate that carcinoma cells sequentially induce preneoplastic lumen filling and epithelial-mesenchymal transition (EMT) in epithelial cysts. MMP-9 secreted by carcinoma cells cleaves cellular E-cadherin (encoded by CDH1) from epithelial cells to generate soluble E-cadherin (sE-cad), a pro-oncogenic protein. We show that sE-cad induces EGFR activation, resulting in lumen filling in MDCK cysts. Long-term sE-cad treatment induced EMT. sE-cad caused lumen filling by induction of the ERK signaling pathway and triggered EMT through the sustained activation of the AKT pathway. Although it is known that sE-cad induces MMP-9 release and consequent EGFR activation in tumor cells, our results, for the first time, demonstrate that carcinoma cells can induce sE-cad shedding in adjacent epithelial cells, which leads to EGFR activation and the eventual transdifferentiation of the normal epithelial cells.

Inhibition of Receptor Dimerization as a Novel Negative Feedback Mechanism of EGFR Signaling

Dimerization of the epidermal growth factor receptor (EGFR) is crucial for initiating signal transduction. We employed raster image correlation spectroscopy to continuously monitor the EGFR monomer-dimer equilibrium in living cells. EGFR dimer formation upon addition of EGF showed oscillatory behavior with a periodicity of about 2.5 min, suggesting the presence of a negative feedback loop to monomerize the receptor. We demonstrated that monomerization of EGFR relies on phospholipase Cγ, protein kinase C, and protein kinase D (PKD), while being independent of Ca2+ signaling and endocytosis. Phosphorylation of the juxtamembrane threonine residues of EGFR (T654/T669) by PKD was identified as the factor that shifts the monomer-dimer equilibrium of ligand bound EGFR towards the monomeric state. The dimerization state of the receptor correlated with the activity of an extracellular signal-regulated kinase, downstream of the EGFR. Based on these observations, we propose a novel, negative feedback mechanism that regulates EGFR signaling via receptor monomerization.

Inhibiting the Recruitment of PLCγ1 to Kaposi's Sarcoma Herpesvirus K15 Protein Reduces the Invasiveness and Angiogenesis of Infected Endothelial Cells

Kaposi’s sarcoma (KS), caused by Kaposi’s sarcoma herpesvirus (KSHV), is a highly vascularised tumour of endothelial origin. KSHV infected endothelial cells show increased invasiveness and angiogenesis. Here, we report that the KSHV K15 protein, which we showed previously to contribute to KSHV-induced angiogenesis, is also involved in KSHV-mediated invasiveness in a PLCγ1-dependent manner. We identified βPIX, GIT1 and cdc42, downstream effectors of PLCγ1 in cell migration, as K15 interacting partners and as contributors to KSHV-triggered invasiveness. We mapped the interaction between PLCγ1, PLCγ2 and their individual domains with two K15 alleles, P and M. We found that the PLCγ2 cSH2 domain, by binding to K15P, can be used as dominant negative inhibitor of the K15P-PLCγ1 interaction, K15P-dependent PLCγ1 phosphorylation, NFAT-dependent promoter activation and the increased invasiveness and angiogenic properties of KSHV infected endothelial cells. We increased the binding of the PLCγ2 cSH2 domain for K15P by substituting two amino acids, thereby creating an improved dominant negative inhibitor of the K15P-dependent PLCγ1 activation. Taken together, these results demonstrate a necessary role of K15 in the increased invasiveness and angiogenesis of KSHV infected endothelial cells and suggest the K15-PLCγ1 interaction as a possible new target for inhibiting the angiogenic and invasive properties of KSHV.

Kaposi’s Sarcoma (KS), etiologically linked to Kaposi’s sarcoma herpesvirus (KSHV), is a tumour of endothelial origin characterised by angiogenesis and invasiveness. In vitro, KSHV infected endothelial cells display an increased invasiveness and high angiogenicity. Here we report that the KSHV protein K15, which increases the angiogenicity of endothelial cells, contributes to KSHV-mediated invasiveness by the recruitment and activation of the cellular protein PLCγ1 and its downstream effectors βPIX, GIT1 and cdc42. We explored the functional consequences of disrupting the K15-PLCγ1 interaction by using an isolated PLCγ2 cSH2 domain as a dominant negative inhibitor. This protein fragment, by interacting with K15, reduces K15-driven recruitment and activation of PLCγ1 in a dose-dependent manner. Moreover, the PCLγ2 cSH2 domain, when overexpressed in KSHV infected endothelial cells, reduces the angiogenesis and invasiveness induced by the virus. These findings highlight the role of the K15-PLCγ1 interaction in KSHV-mediated invasiveness and identify it as a possible therapeutic target.

AXL mediates resistance to PI3Kα inhibition by activating the EGFR/PKC/mTOR axis in head and neck and esophageal squamous cell carcinomas

Phosphoinositide-3-kinase (PI3K)-α inhibitors have shown clinical activity in squamous cell carcinomas (SCCs) of head and neck (H&N) bearing PIK3CA mutations or amplification. Studying models of therapeutic resistance, we have observed that SCC cells that become refractory to PI3Kα inhibition maintain PI3K-independent activation of the mammalian target of rapamycin (mTOR). This persistent mTOR activation is mediated by the tyrosine kinase receptor AXL. AXL is overexpressed in resistant tumors from both laboratory models and patients treated with the PI3Kα inhibitor BYL719. AXL dimerizes with and phosphorylates epidermal growth factor receptor (EGFR), resulting in activation of phospholipase Cγ (PLCγ)-protein kinase C (PKC), which, in turn, activates mTOR. Combined treatment with PI3Kα and either EGFR, AXL, or PKC inhibitors reverts this resistance.

Extracellular signal-regulated kinases 1/2 and Akt contribute to triclosan-stimulated proliferation of JB6 Cl 41-5a cells

Triclosan is a broad spectrum anti-bacterial agent widely used in many personal care products, household items, medical devices, and clinical settings. Human exposure to triclosan is mainly through oral and dermal routes. In previous studies, we found that sub-chronic dermal exposure of B6C3F1 mice to triclosan induced epidermal hyperplasia and focal necrosis; however, the mechanisms for these responses remain elusive. In this study, using mouse epidermis-derived JB6 Cl 41-5a cells, we found that triclosan stimulated cell growth in a concentration- and time-dependent manner. Enhanced cell proliferation was demonstrated by a substantial increase in the percentage of BrdU-positive cells, an elevation in the protein levels of cyclin D1 and cyclin A, and a reduction in the protein level of p27(Kip1). Western blotting analysis revealed that triclosan induced the activation of extracellular signal-regulated kinases 1/2 (ERK1/2), c-Jun N-terminal kinases (JNK), p38, and Akt. Pre-treatment of the cells with PD184352, an inhibitor of the upstream kinase MEK1/2, or with wortmannin, an inhibitor of phosphoinositide 3-kinase, blocked triclosan-mediated phosphorylation of ERK1/2 and Akt, respectively, and substantially suppressed triclosan-stimulated cell proliferation, whereas the JNK inhibitor SP600125 or the p38 inhibitor SB203580 had little to no effect on triclosan-stimulated cell proliferation. The phosphorylation activation of ERK1/2 and Akt was further confirmed on the skin of mice dermally administered triclosan. These data suggest that the activation of ERK1/2 and Akt is involved in triclosan-stimulated proliferation of JB6 Cl 41-5a cells.

Epidermal growth factor receptor signaling-dependent calcium elevation in cumulus cells is required for NPR2 inhibition and meiotic resumption in mouse oocytes

In preovulatory ovarian follicles, the oocyte is maintained in meiotic prophase arrest by natriuretic peptide precursor C (NPPC) and its receptor natriuretic peptide receptor 2 (NPR2). LH treatment results in the decrease of NPR2 guanylyl cyclase activity that promotes resumption of meiosis. We investigated the regulatory mechanism of LH-activated epidermal growth factor (EGF) receptor signaling on NPR2 function. Cumulus cell-oocyte complex is cultured in the medium with 30 nM NPPC to prevent oocyte spontaneous maturation. In this system, EGF could stimulate oocyte meiotic resumption after 4 hours of incubation. Further study showed that EGF elevated intracellular calcium concentrations of cumulus cells and decreased cGMP levels in cumulus cells and oocytes, and calcium-elevating reagents ionomycin and sphingosine-1-phosphate mimicked the effects of EGF on oocyte maturation and cGMP levels. EGF-mediated cGMP levels and meiotic resumption could be reversed by EGF receptor inhibitor AG1478 and the calcium chelator bis-(o-aminophenoxy)-ethane-N,N,N',N'-tetraacetic acid, tetra(acetoxymethyl)-ester. EGF also decreased the expression of Npr2 mRNA in cumulus cells, which may not be involved in meiotic resumption, because the block of NPR2 protein de novo synthesis by cycloheximide had no effect on NPPC and EGF-mediated oocyte maturation. However, EGF had no effect on oocyte maturation when meiotic arrest was maintained in the present of cGMP analog 8-bromoadenosine-cGMP. These results suggest that EGF receptor signaling induces meiotic resumption by elevating calcium concentrations of cumulus cells to decrease NPR2 guanylyl cyclase activity.

Profiling pathway-specific novel therapeutics in preclinical assessment for central nervous system atypical teratoid rhabdoid tumors (CNS ATRT): favorable activity of targeting EGFR- ErbB2 signaling with lapatinib

Despite intensifying multimodal treatments, children with central nervous system atypical teratoid/rhabdoid tumor (CNS ATRT) continue to endure unacceptably high mortality rates. At present, concerted efforts are focusing on understanding the characteristic INI1 mutation and its implications for the growth and survival of these tumors. Additionally, pharmaceutical pipeline libraries constitute a significant source of potential agents that can be taken to clinical trials in a timely manner. However, this process requires efficient target validation and relevant preclinical studies. As an initial screening approach, a panel of 129 small molecule inhibitors from multiple pharmaceutical pipeline libraries was tested against three ATRT cell lines by in vitro cytotoxicity assays. Based on these data, agents that have strong activity and corresponding susceptible cellular pathways were identified. Target modulation, antibody array analysis, drug combination and in vivo xenograft studies were performed on one of the pathway inhibitors found in this screening. Approximately 20% of agents in the library showed activity with IC(50) values of 1 μM or less and many showed IC(50) values less than 0.05 μM. Intra cell line variability was also noted among some of the drugs. However, it was determined that agents capable of affecting pathways constituting ErbB2, mTOR, proteasomes, Hsp90, Polo like kinases and Aurora kinases were universally effective against the three ATRT cell lines. The first target selected for further analysis, the inhibition of ErbB2-EGFR pathway by the small molecule inhibitor lapatinib, indicated inhibition of cell migration properties and the initiation of apoptosis. Synergy between lapatinib and IGF-IR inhibition was also demonstrated by combination index (CI) values. Xenograft studies showed effective antitumor activity of lapatinib in vivo. We present an experimental approach to identifying agents and drug combinations for future clinical trials and provide evidence for the potential of lapatinib as an effective agent in the context of the biology and heterogeneity of its targets in ATRT.

Phosphorylated EGFR expression may predict outcome of EGFR-TKIs therapy for the advanced NSCLC patients with wild-type EGFR

Background

EGFR mutation is a strong predictive factor of EGFR-TKIs therapy. However, at least 10% of patients with EGFR wild-type are responsive to TKIs, suggesting that other determinants of outcome besides EGFR mutation might exist. We hypothesized that activation of phosphorylated EGFR could be a potential predictive biomarker to EGFR-TKIs treatment among patients in wild-type EGFR.

Method

Total of 205 stage IIIb and IV NSCLC patients, tissue samples of whom were available for molecular analysis, were enrolled in this study. The phosphorylation of EGFR at tyrosine 1068 (pTyr1068) and 1173 (pTyr1173) were assessed by immunohistochemistry, and EGFR mutations were detected by denaturing high performance liquid chromatograph (DHPLC).

Results

Among 205 patients assessable for EGFR mutation and phosphorylation analysis, 92 (44.9%) were EGFR mutant and 165 patients (57.6%) had pTyr1173 expression. Superior progression-free survival (PFS) was seen after EGFR-TKIs therapy in patients with pTyr1068 expression compared to pTyr1068 negative ones (median PFS 7.0 months vs. 1.2 months, P < 0.001). Inversely, patients with pTyr1173 had a shorter PFS (4.8 months VS. 7.7 months, P = 0.016). In subgroup of patients with wild-type EGFR, pTyr1068 expression positive ones had a significantly prolonged PFS (4.2 months vs.1.2 months P < 0.001) compared with those without pTyr1068 expression. Sixteen patients with both wild-type EGFR and pTyr1068 who responded to EGFR-TKIs had median PFS of 15.6 months (95%CI: 7.28-23.9).

Conclusion

pTyr1068 may be a predictive biomarker for screening the population for clinical response to EGFR-TKIs treatment; especially for patients with wild-type EGFR.

Migfilin protein promotes migration and invasion in human glioma through epidermal growth factor receptor-mediated phospholipase C-γ and STAT3 protein signaling pathways

Migfilin is critical for cell shape and motile regulation. However, its pathological role in glioma is unknown. Using an immunohistochemical staining assay, we demonstrate that there is a significant correlation between expression of Migfilin and pathological tumor grade in 217 clinical glioma samples. High Migfilin expression is associated with poor prognosis for patients with glioma. Investigation of the molecular mechanism shows that Migfilin promotes migration and invasion in glioma cells. Moreover, Migfilin positively modulates the expression and activity of epidermal growth factor receptor, and Migfilin-mediated migration and invasion depend on epidermal growth factor receptor-induced PLC-γ and STAT3-signaling pathways. Our results may provide significant clinical application, including use of Migfilin as a molecular marker in glioma for early diagnosis and as an indicator of prognosis.

Phosphorylation of epidermal growth factor receptor and chromosome 7 polysomy in gastric adenocarcinoma

OBJECTIVE

To investigate the phosphorylation of epidermal growth factor receptor (EGFR) and its potentially associated chromosomal aberrations in gastric adenocarcinoma.

METHODS

Phosphorylated EGFR (pEGFR) was detected by immunohistochemistry on 145 specimens including 60 tumoral, 60 non-tumoral, 12 tumor-adjacent intramucosal dysplasia from patients with gastric adenocarcinoma and 13 mucosae from cancer-free patients. EGFR gene amplification and chromosome 7 (Chr-7) polysomy were detected by fluorescence in situ hybridization.

RESULTS

Positivity of pEGFR was found in 50 tumoral (83.3%) and 42 non-tumoral specimens (70.0%). There was an association between tumoral and non-tumoral zones on immunostains of pEGFR (r = 0.353, P = 0.006). Nuclear pEGFR usually presented in mucosae with Helicobacter pylori infection, stromal reaction or vascular invasion. Cytoplasmic pEGFR was correlated with local cancer extension (r = 0.337, P = 0.014) and inversely related with gastrokine 2, which had been previously detected in the same specimens. Eleven intramucosal dysplastic specimens were also positive for pEGFR while 13 mucosae from cancer-free patients were all negative. No EGFR gene amplification was observed. However, seven tumor specimens showed Chr-7 polysomy (11.7%) in which 5 were strongly positive for pEGFR.

CONCLUSIONS

EGFR phosphorylation may be one of the mechanisms that promote tumor initiation and expansion in gastric adenocarcinoma. Detection of pEGFR with analysis of its nuclear or cytoplasmic patterns could be clinicopathologically valuable. Chr-7 polysomy may partially contribute to EGFR activation in gastric adenocarcinoma, although its role does not predominate.

Diacylglycerol kinase θ counteracts protein kinase C-mediated inactivation of the EGF receptor

Epidermal growth factor receptor (EGFR) activation is negatively regulated by protein kinase C (PKC) signaling. Stimulation of A431 cells with EGF, bradykinin or UTP increased EGFR phosphorylation at Thr654 in a PKC-dependent manner. Inhibition of PKC signaling enhanced EGFR activation, as assessed by increased phosphorylation of Tyr845 and Tyr1068 residues of the EGFR. Diacylglycerol is a physiological activator of PKC that can be removed by diacylglycerol kinase (DGK) activity. We found, in A431 and HEK293 cells, that the DGKθ isozyme translocated from the cytosol to the plasma membrane, where it co-localized with the EGFR and subsequently moved into EGFR-containing intracellular vesicles. This translocation was dependent on both activation of EGFR and PKC signaling. Furthermore, DGKθ physically interacted with the EGFR and became tyrosine-phosphorylated upon EGFR stimulation. Overexpression of DGKθ attenuated the bradykinin-stimulated, PKC-mediated EGFR phosphorylation at Thr654, and enhanced the phosphorylation at Tyr845 and Tyr1068. SiRNA-induced DGKθ downregulation enhanced this PKC-mediated Thr654 phosphorylation. Our data indicate that DGKθ translocation and activity is regulated by the concerted activity of EGFR and PKC and that DGKθ attenuates PKC-mediated Thr654 phosphorylation that is linked to desensitisation of EGFR signaling.

Luteinizing hormone reduces the activity of the NPR2 guanylyl cyclase in mouse ovarian follicles, contributing to the cyclic GMP decrease that promotes resumption of meiosis in oocytes

In preovulatory ovarian follicles of mice, meiotic prophase arrest in the oocyte is maintained by cyclic GMP from the surrounding granulosa cells that diffuses into the oocyte through gap junctions. The cGMP is synthesized in the granulosa cells by the transmembrane guanylyl cyclase natriuretic peptide receptor 2 (NPR2) in response to the agonist C-type natriuretic peptide (CNP). In response to luteinizing hormone (LH), cGMP in the granulosa cells decreases, and as a consequence, oocyte cGMP decreases and meiosis resumes. Here we report that within 20 min, LH treatment results in decreased guanylyl cyclase activity of NPR2, as determined in the presence of a maximally activating concentration of CNP. This occurs by a process that does not reduce the amount of NPR2 protein. We also show that by a slower process, first detected at 2h, LH decreases the amount of CNP available to bind to the receptor. Both of these LH actions contribute to decreasing cGMP in the follicle, thus signaling meiotic resumption in the oocyte.

Insulin receptor-mediated signaling via phospholipase C-γ regulates growth and differentiation in Drosophila

Coordination between growth and patterning/differentiation is critical if appropriate final organ structure and size is to be achieved. Understanding how these two processes are regulated is therefore a fundamental and as yet incompletely answered question. Here we show through genetic analysis that the phospholipase C-γ (PLC-γ) encoded by small wing (sl) acts as such a link between growth and patterning/differentiation by modulating some MAPK outputs once activated by the insulin pathway; particularly, sl promotes growth and suppresses ectopic differentiation in the developing eye and wing, allowing cells to attain a normal size and differentiate properly. sl mutants have previously been shown to have a combination of both growth and patterning/differentiation phenotypes: small wings, ectopic wing veins, and extra R7 photoreceptor cells. We show here that PLC-γ activated by the insulin pathway participates broadly and positively during cell growth modulating EGF pathway activity, whereas in cell differentiation PLC-γ activated by the insulin receptor negatively regulates the EGF pathway. These roles require different SH2 domains of PLC-γ, and act via classic PLC-γ signaling and EGF ligand processing. By means of PLC-γ, the insulin receptor therefore modulates differentiation as well as growth. Overall, our results provide evidence that PLC-γ acts during development at a time when growth ends and differentiation begins, and is important for proper coordination of these two processes.

Specific epidermal growth factor receptor autophosphorylation sites promote mouse colon epithelial cell chemotaxis and restitution

Upon ligand binding, epidermal growth factor (EGF) receptor (R) autophosphorylates on COOH-terminal tyrosines, generating docking sites for signaling partners that stimulate proliferation, restitution, and chemotaxis. Specificity for individual EGFR tyrosines in cellular responses has been hypothesized but not well documented. Here we tested the requirement for particular tyrosines, and associated downstream pathways, in mouse colon epithelial cell chemotactic migration. We compared these requirements to those for the phenotypically distinct restitution (wound healing) migration. Wild-type, Y992/1173F, Y1045F, Y1068F, and Y1086F EGFR constructs were expressed in EGFR(-/-) cells; EGF-induced chemotaxis or restitution were determined by Boyden chamber or modified scratch wound assay, respectively. Pharmacological inhibitors of p38, phospholipase C (PLC), Src, MEK, JNK/SAPK, phosphatidylinositol 3-kinase (PI 3-kinase), and protein kinase C (PKC) were used to block EGF-stimulated signaling. Pathway activation was determined by immunoblot analysis. Unlike wild-type EGFR, Y992/1173F and Y1086F EGFR did not stimulate colon epithelial cell chemotaxis toward EGF; Y1045F and Y1068F EGFR partially stimulated chemotaxis. Only wild-type EGFR promoted colonocyte restitution. Inhibition of p38, PLC, and Src, or Grb2 knockdown, blocked chemotaxis; JNK, PI 3-kinase, and PKC inhibitors or c-Cbl knockdown blocked restitution but not chemotaxis. All four EGFR mutants stimulated downstream signaling in response to EGF, but Y992/1173F EGFR was partially defective in PLCγ activation whereas both Y1068F and Y1086F EGFR failed to activate Src. We conclude that specific EGFR tyrosines play key roles in determining cellular responses to ligand. Chemotaxis and restitution, which have different migration phenotypes and physiological consequences, have overlapping but not identical EGFR signaling requirements.

Diverse injurious stimuli reduce protein tyrosine phosphatase-μ expression and enhance epidermal growth factor receptor signaling in human airway epithelia

In response to injury, airway epithelia utilize an epidermal growth factor (EGF) receptor (EGFR) signaling program to institute repair and restitution. Protein tyrosine phosphatases (PTPs) counterregulate EGFR autophosphorylation and downstream signaling. PTPμ is highly expressed in lung epithelia and can be localized to intercellular junctions where its ectodomain homophilically interacts with PTPμ ectodomain expressed on neighboring cells. We asked whether PTPμ expression might be altered in response to epithelial injury and whether altered PTPμ expression might influence EGFR signaling. In A549 cells, diverse injurious stimuli dramatically reduced PTPμ protein expression. Under basal conditions, small interfering RNA (siRNA)-induced silencing of PTPμ increased EGFR Y992 and Y1068 phosphorylation. In the presence of EGF, PTPμ knockdown increased EGFR Y845, Y992, Y1045, Y1068, Y1086, and Y1173 but not Y1148 phosphorylation. Reduced PTPμ expression increased EGF-stimulated phosphorylation of Y992, a docking site for phospholipase C (PLC)γ(1), activation of PLCγ(1) itself, and increased cell migration in both wounding and chemotaxis assays. In contrast, overexpression of PTPμ decreased EGF-stimulated EGFR Y992 and Y1068 phosphorylation. Therefore, airway epithelial injury profoundly reduces PTPμ expression, and PTPμ depletion selectively increases phosphorylation of specific EGFR tyrosine residues, PLCγ(1) activation, and cell migration, providing a novel mechanism through which epithelial integrity may be restored.

Multicolor protein labeling in living cells using mutant β-lactamase-tag technology

Protein labeling techniques using small molecule probes have become important as practical alternatives to the use of fluorescent proteins (FPs) in live cell imaging. These labeling techniques can be applied to more sophisticated fluorescence imaging studies such as pulse-chase imaging. Previously, we reported a novel protein labeling system based on the combination of a mutant β-lactamase (BL-tag) with coumarin-derivatized probes and its application to specific protein labeling on cell membranes. In this paper, we demonstrated the broad applicability of our BL-tag technology to live cell imaging by the development of a series of fluorescence labeling probes for this technology, and the examination of the functions of target proteins. These new probes have a fluorescein or rhodamine chromophore, each of which provides enhanced photophysical properties relative to coumarins for the purpose of cellular imaging. These probes were used to specifically label the BL-tag protein and could be used with other small molecule fluorescent probes. Simultaneous labeling using our new probes with another protein labeling technology was found to be effective. In addition, it was also confirmed that this technology has a low interference with respect to the functions of target proteins in comparison to GFP. Highly specific and fast covalent labeling properties of this labeling technology is expected to provide robust tools for investigating protein functions in living cells, and future applications can be improved by combining the BL-tag technology with conventional imaging techniques. The combination of probe synthesis and molecular biology techniques provides the advantages of both techniques and can enable the design of experiments that cannot currently be performed using existing tools.

Involvement of the epidermal growth factor receptor in Pb²+-induced activation of cPLA₂/COX-2 genes and PGE₂ production in vascular smooth muscle cells

Lead (Pb²+) is one of the most common heavy metal pollutants, which can cause chronic cardiovascular diseases. To clarify the mechanism by which Pb²+ induces inflammatory reactions, we examined the expression of inflammatory genes including encoding cyclooxygenase-2 (COX-2), cytosolic phospholipase A₂ (cPLA₂), and their down stream product prostaglandin E₂ (PGE₂) in CRL1999 cells that is a vascular smooth muscle cell line from human aorta. The expression of COX-2/cPLA₂ genes and PGE₂ secretion was increased markedly after cells were exposed to 1 μM Pb²+. PD098059, a MEK inhibitor, suppressed Pb²+-mediated inflammatory reactions; this indicates the involvement of the phosphorylation of extracellular signal-regulated kinases 1 and 2 (ERK1/2). Furthermore, Pb²+-induced activation of the COX-2/cPLA₂ genes was inhibited by both epidermal growth factor receptor (EGFR) inhibitors (AG1478 and PD153035) and EGFR siRNA. Short-term stimulation with Pb²+ induced EGFR phosphorylation at the Tyr residue (position, 1173). Importantly, overexpression of EGFR resulted in a significant potentiation effect on Pb²+-induced gene expression. Taken together, our results indicate that 1 μM Pb²+ can induce PGE₂ secretion by upregulating the transcription of COX-2/cPLA₂ genes. EGFR is the key target in the plasma membrane responsible for transmitting Pb²+ signals in order to trigger downstream inflammatory cascades.

Norepinephrine modulates the zonally different hepatocyte proliferation through the regulation of transglutaminase activity

A neurotransmitter, norepinephrine (NE), amplifies the mitogenic effect of epidermal growth factor (EGF) in the liver by acting on the alpha(1)-adrenergic receptor coupled with G protein, Galpha(h). However, the molecular mechanism is not well understood. Galpha(h) is known as a transglutaminase 2 (TG2), a cross-linking enzyme implicated in hepatocyte proliferation. We investigated the effect of NE on EGF-induced cell proliferation and TG2 activity using hepatocytes isolated in periportal and perivenous regions of the liver, which differ in proliferative capacity. Periportal hepatocytes (PPH) and perivenous hepatocytes (PVH) were isolated by the digitonin-collagenase perfusion technique. EGF or NE receptor binding was analyzed by Scatchard analysis. Changes in NE-induced DNA synthesis, EGF receptor (EGFR) dimerization and phosphorylation, and TG2 activity were measured. NE enhanced EGF-induced DNA synthesis, EGF-induced EGFR dimerization, and its phosphorylation in PVH but not in PPH. [(3)H]NE binding studies indicated that PVH was found to have a greater affinity and number of receptors than PPH. Furthermore, NE treatment decreased TG2 activity and increased phospholipase C activity in PVH although TG2 level showed no change. These results suggest that NE-induced amplification of EGF-induced DNA synthesis especially in PVH is caused by upregulation of EGFR activation through the switching of function from TG2 to Galpha(h).

Spatio-temporal modeling of signaling protein recruitment to EGFR

Background

A stochastic simulator was implemented to study EGFR signal initiation in 3D with single molecule detail. The model considers previously unexplored contributions to receptor-adaptor coupling, such as receptor clustering and diffusive properties of both receptors and binding partners. The agent-based and rule-based approach permits consideration of combinatorial complexity, a problem associated with multiple phosphorylation sites and the potential for simultaneous binding of adaptors.

Results

The model was used to simulate recruitment of four different signaling molecules (Grb2, PLCγ1, Stat5, Shc) to the phosphorylated EGFR tail, with rules based on coarse-grained prediction of spatial constraints. Parameters were derived in part from quantitative immunoblotting, immunoprecipitation and electron microscopy data. Results demonstrate that receptor clustering increases the efficiency of individual adaptor retainment on activated EGFR, an effect that is overridden if crowding is imposed by receptor overexpression. Simultaneous docking of multiple proteins is highly dependent on receptor-adaptor stability and independent of clustering.

Conclusions

Overall, we propose that receptor density, reaction kinetics and membrane spatial organization all contribute to signaling efficiency and influence the carcinogenesis process.

[Molecular diagnostics in lung carcinoma for therapy stratification]

Lung cancer is the most common tumor-related cause of death in western industrialized countries, despite continuous improvement in both diagnostic and therapeutic approaches. Since epidermal growth factor receptor (EGFR) is overexpressed in 80% of cases of non-small cell lung carcinoma, mediating important carcinogenic properties such as cell-cycle progression, apoptosis, angiogenesis and metastasis, it is considered a relevant target in novel specific therapies. This has lead to the development of the low-molecular EGFR tyrosine kinase inhibitors (EGFR-TKI) Gefitinib and Erlotinib. Predicting which patients will respond to an EGFR-targeted therapy is of particular clinical interest. Recent studies show a significantly better response and prolonged progression-free survival in patients with EGFR-mutated tumors, even when used as first-line therapy. Moreover, genetic mutations which correlate to primary EGFR-TKI resistance (e.g. KRAS) or produce secondary resistance to known TKI (e.g. EGFR mutation T790 M or MET amplification) have meanwhile been explained. Predictive diagnosis of these mutations using histological material is becoming increasingly important for patient stratification and will soon be indispensable not only for lung cancer.

Prognostic effect of activated EGFR expression in human colon carcinomas: comparison with EGFR status

BACKGROUND

Evidence suggests that epidermal growth factor receptor (EGFR)-activation status may better predict the clinical behaviour of colon cancers than does EGFR expression. However, the prognostic effect of phospho-EGFR in primary colon cancer remains undefined.

METHODS

Phospho-EGFR (Tyr-1173) and EGFR expression were analysed by immunohistochemistry (IHC) in tissue microarrays of TNM stage II and III colon cancers from completed adjuvant therapy trials (n=388). Staining intensity was scored and correlated with clinicopathological variables, DNA mismatch repair (MMR) status, rates of cell proliferation (Ki-67), apoptosis (caspase-3), and patient survival.

RESULTS

Phospho-EGFR expression was detected in 157 of 388 (40%) tumours, whereas EGFR was found in 214 of 361 (59%). Although phospho-EGFR was unrelated to clinicopathological variables, strong EGFR intensity was associated with higher tumour stage (P=0.03). Tumours overexpressing EGFR (P=0.0002) or phospho-EGFR (P=0.015) showed increased Ki-67, but not caspase-3 expression. Phospho-EGFR was not prognostic. EGFR intensity was associated with worse disease-free survival (DFS) (hazard ratio (HR): 1.21 (1.03, 1.41); P=0.019) and overall survival (OS) (HR: 1.19 (1.02, 1.39); P=0.028). Tumours expressing both EGFR and phospho-EGFR had similar survival as EGFR alone. Stage and lymph node number were prognostic for DFS and OS, and histological grade for OS. EGFR was an independent predictor of DFS (P=0.042) after adjustment for stage, histological grade, age, and MMR status.

CONCLUSION

Phospho-EGFR and EGFR expression were associated with tumour cell hyperproliferation. Phospho-EGFR was not prognostic, whereas increased EGFR intensity was independently associated with poor DFS.

Semaphorin 4D signaling requires the recruitment of phospholipase C gamma into the plexin-B1 receptor complex

The semaphorin 4D (Sema4D) receptor plexin-B1 constitutively interacts with particular Rho guanine nucleotide exchange factors (RhoGEFs) and thereby mediates Sema4D-induced RhoA activation, a process which involves the tyrosine phosphorylation of plexin-B1 by ErbB-2. It is, however, unknown how plexin-B1 phosphorylation regulates RhoGEF activity. We show here that activation of plexin-B1 by Sema4D and its subsequent tyrosine phosphorylation creates docking sites for the SH2 domains of phospholipase Cgamma (PLCgamma). PLCgamma is thereby recruited into the plexin-B1 receptor complex and via its SH3 domain activates the Rho guanine nucleotide exchange factor PDZ-RhoGEF. PLCgamma-dependent RhoGEF activation is independent of its lipase activity. The recruitment of PLCgamma has no effect on the R-Ras GTPase-activating protein activity of plexin-B1 but is required for Sema4D-induced axonal growth cone collapse as well as for the promigratory effects of Sema4D on cancer cells. These data demonstrate a novel nonenzymatic function of PLCgamma as an important mechanism of plexin-mediated signaling which links tyrosine phosphorylation of plexin-B1 to the regulation of a RhoGEF protein and downstream cellular processes.