High-efficiency expression/cloning of epidermal growth factor-receptor-binding proteins with Src homology 2 domains

Adapting to change: resolving the dynamic and dual roles of NCK1 and NCK2

Adaptor proteins play central roles in the assembly of molecular complexes and co-ordinated activation of specific pathways. Through their modular domain structure, the NCK family of adaptor proteins (NCK1 and NCK2) link protein targets via their single SRC Homology (SH) 2 and three SH3 domains. Classically, their SH2 domain binds to phosphotyrosine motif-containing receptors (e.g. receptor tyrosine kinases), while their SH3 domains bind polyproline motif-containing cytoplasmic effectors. Due to these functions being established for both NCK1 and NCK2, their roles were inaccurately assumed to be redundant. However, in contrast with this previously held view, NCK1 and NCK2 now have a growing list of paralog-specific functions, which underscores the need to further explore their differences. Here we review current evidence detailing how these two paralogs are unique, including differences in their gene/protein regulation, binding partners and overall contributions to cellular functions. To help explain these contrasting characteristics, we then discuss SH2/SH3 structural features, disordered interdomain linker regions and post-translational modifications. Together, this review seeks to highlight the importance of distinguishing NCK1 and NCK2 in research and to pave the way for investigations into the origins of their interaction specificity.

Grb7, Grb10 and Grb14, encoding the growth factor receptor-bound 7 family of signalling adaptor proteins have overlapping functions in the regulation of fetal growth and post-natal glucose metabolism

BACKGROUND

The growth factor receptor bound protein 7 (Grb7) family of signalling adaptor proteins comprises Grb7, Grb10 and Grb14. Each can interact with the insulin receptor and other receptor tyrosine kinases, where Grb10 and Grb14 inhibit insulin receptor activity. In cell culture studies they mediate functions including cell survival, proliferation, and migration. Mouse knockout (KO) studies have revealed physiological roles for Grb10 and Grb14 in glucose-regulated energy homeostasis. Both Grb10 KO and Grb14 KO mice exhibit increased insulin signalling in peripheral tissues, with increased glucose and insulin sensitivity and a modestly increased ability to clear a glucose load. In addition, Grb10 strongly inhibits fetal growth such that at birth Grb10 KO mice are 30% larger by weight than wild type littermates.

RESULTS

Here, we generate a Grb7 KO mouse model. We show that during fetal development the expression patterns of Grb7 and Grb14 each overlap with that of Grb10. Despite this, Grb7 and Grb14 did not have a major role in influencing fetal growth, either alone or in combination with Grb10. At birth, in most respects both Grb7 KO and Grb14 KO single mutants were indistinguishable from wild type, while Grb7:Grb10 double knockout (DKO) were near identical to Grb10 KO single mutants and Grb10:Grb14 DKO mutants were slightly smaller than Grb10 KO single mutants. In the developing kidney Grb7 had a subtle positive influence on growth. An initial characterisation of Grb7 KO adult mice revealed sexually dimorphic effects on energy homeostasis, with females having a significantly smaller renal white adipose tissue depot and an enhanced ability to clear glucose from the circulation, compared to wild type littermates. Males had elevated fasted glucose levels with a trend towards smaller white adipose depots, without improved glucose clearance.

CONCLUSIONS

Grb7 and Grb14 do not have significant roles as inhibitors of fetal growth, unlike Grb10, and instead Grb7 may promote growth of the developing kidney. In adulthood, Grb7 contributes subtly to glucose mediated energy homeostasis, raising the possibility of redundancy between all three adaptors in physiological regulation of insulin signalling and glucose handling.

Grb7 knockout mice develop normally but litters born to knockout females fail to thrive

BACKGROUND

Growth factor receptor-bound 7 (Grb7) is an adaptor protein involved in signal transduction downstream of multiple receptor tyrosine kinases, including ERBB, FGFR, and PDGFR pathways. Experimental studies have implicated Grb7 in regulating cell proliferation, survival, migration, and invasion through its large repertoire of protein-protein interactions.

RESULTS

Here, we describe the generation and characterization of a Grb7 knockout mouse. These mice are viable and fertile. A lacZ knock-in reporter was used to visualize Grb7 promoter activity patterns in adult tissues, indicating widespread Grb7 expression in glandular epithelium, the central nervous system, and other tissues. The sole defect observed in these animals was a failure of Grb7 knockout females to successfully raise pups to weaning age, a phenotype that was independent of both paternal and pup genotypes.

CONCLUSIONS

These data suggest a regulatory role for Grb7 in mammary lactational physiology.

Follicular cells protect Xenopus oocyte from abnormal maturation via integrin signaling downregulation and O-GlcNAcylation control

Xenopus oocytes are encompassed by a layer of follicular cells that contribute to oocyte growth and meiosis in relation to oocyte maturation. However, the effects of the interaction between follicular cells and the oocyte surface on meiotic processes are unclear. Here, we investigated Xenopus follicular cell function using oocyte signaling and heterologous-expressing capabilities. We found that oocytes deprotected from their surrounding layer of follicular cells and expressing the epidermal growth factor (EGF) receptor (EGFR) and the Grb7 adaptor undergo accelerated prophase I to metaphase II meiosis progression upon stimulation by EGF. This unusual maturation unravels atypical spindle formation but is rescued by inhibiting integrin β1 or Grb7 binding to the EGFR. In addition, we determined that oocytes surrounded by their follicular cells expressing EGFR-Grb7 exhibit normal meiotic resumption. These oocytes are protected from abnormal meiotic spindle formation through the recruitment of O-GlcNAcylated Grb7, and OGT (O-GlcNAc transferase), the enzyme responsible for O-GlcNAcylation processes, in the integrin β1-EGFR complex. Folliculated oocytes can be forced to adopt an abnormal phenotype and exclusive Grb7 Y338 and Y188 phosphorylation instead of O-GlcNAcylation under integrin activation. Furthermore, an O-GlcNAcylation increase (by inhibition of O-GlcNAcase), the glycosidase that removes O-GlcNAc moieties, or decrease (by inhibition of OGT) amplifies oocyte spindle defects when follicular cells are absent highlighting a control of the meiotic spindle by the OGT-O-GlcNAcase duo. In summary, our study provides further insight into the role of the follicular cell layer in oocyte meiosis progression.

Real role of growth factor receptor-binding protein 10: Linking lipid metabolism to diabetes cardiovascular complications

Cardiovascular complications of patients with type 2 diabetes mellitus (T2DM) threaten the health and life of numerous individuals. Recently, growth factor receptor-binding protein 10 (GRB10) was found to play a pivotal role in vascular complications of T2DM, which participates in the regulation of lipid metabolism of T2DM patients. The genetic variation of GRB10 rs1800504 is closely related to the risk of coronary heart disease in patients with T2DM. The development of GRB10 as a key mediator in the association of lipid metabolism with cardiovascular complications in T2DM is detailed in and may provide new potential concerns for the study of cardiovascular complications in T2DM patients.

Enhancing the Bioactivity of Bicyclic Peptides Targeted to Grb7-SH2 by Restoring Cell Permeability

The development of peptide inhibitors against intracellular targets depends upon the dual challenge of achieving a high affinity and specificity for the target and maintaining cellular permeability for biological activity. Previous efforts to develop bicyclic peptides targeted to the Grb7 signalling protein implicated in HER2+ve cancer progression have resulted in improved affinity. However, these same peptides demonstrated a lowered activity due to their decreased ability to penetrate cell membranes. Here, we report the testing of a new series of bicyclic G7 peptides designed to possess improved bioactivity. We discovered that the incorporation of two amino acids (Phe-Pro, Phe-Trp or Phe-Arg) within the bicyclic peptide framework maintains an enhanced binding affinity for the Grb7-SH2 domain compared to that of the first-generation monocyclic peptide G7-18NATE. Structure determination using X-ray crystallography revealed that the mode of binding by the expanded bicyclic G7 peptide is analogous to that of G7-18NATE. Interestingly, while the bicyclic peptide containing Phe-Trp did not display the highest affinity for Grb7-SH2 in the series, it was the most potent inhibitor of HER2+ve SKBR3 breast cancer cell migration when coupled to Penetratin. Together, this demonstrates that peptide flexibility as well as the amino acid tryptophan can play important roles in the uptake of peptides into the cell.

Grb7, a Critical Mediator of EGFR/ErbB Signaling, in Cancer Development and as a Potential Therapeutic Target

The partner of activated epidermal growth factor receptor (EGFR), growth factor receptor bound protein-7 (Grb7), a functionally multidomain adaptor protein, has been demonstrated to be a pivotal regulator for varied physiological and pathological processes by interacting with phospho-tyrosine-related signaling molecules to affect the transmission through a number of signaling pathways. In particular, critical roles of Grb7 in erythroblastic leukemia viral oncogene homolog (ERBB) family-mediated cancer development and malignancy have been intensively evaluated. The overexpression of Grb7 or the coamplification/cooverexpression of Grb7 and members of the ERBB family play essential roles in advanced human cancers and are associated with decreased survival and recurrence of cancers, emphasizing Grb7's value as a prognostic marker and a therapeutic target. Peptide inhibitors of Grb7 are being tested in preclinical trials for their possible therapeutic effects. Here, we review the molecular, functional, and clinical aspects of Grb7 in ERBB family-mediated cancer development and malignancy with the aim to reveal alternative and effective therapeutic strategies.

The role of small adaptor proteins in the control of oncogenic signalingr driven by tyrosine kinases in human cancer

Protein phosphorylation on tyrosine (Tyr) residues has evolved as an important mechanism to coordinate cell communication in multicellular organisms. The importance of this process has been revealed by the discovery of the prominent oncogenic properties of tyrosine kinases (TK) upon deregulation of their physiological activities, often due to protein overexpression and/or somatic mutation. Recent reports suggest that TK oncogenic signaling is also under the control of small adaptor proteins. These cytosolic proteins lack intrinsic catalytic activity and signal by linking two functional members of a catalytic pathway. While most adaptors display positive regulatory functions, a small group of this family exerts negative regulatory functions by targeting several components of the TK signaling cascade. Here, we review how these less studied adaptor proteins negatively control TK activities and how their loss of function induces abnormal TK signaling, promoting tumor formation. We also discuss the therapeutic consequences of this novel regulatory mechanism in human oncology.

The adaptors Grb10 and Grb14 are calmodulin-binding proteins

We identified the Grb7 family members, Grb10 and Grb14, as Ca²⁺ -dependent CaM-binding proteins using Ca²⁺ -dependent CaM-affinity chromatography as we previously did with Grb7. The potential CaM-binding sites were identified and experimentally tested using fluorescent-labeled peptides corresponding to these sites. The apparent affinity constant of these peptides for CaM, and the minimum number of calcium ions bound to CaM that are required for effective binding to these peptides were also determined. We prepared deletion mutants of the three adaptor proteins lacking the identified sites and determined that they lost or strongly diminished their CaM-binding capacity following the sequence Grb7 > > Grb14 > Grb10. More than one CaM-binding site and/or accessory CaM-binding sites appear to exist in Grb10 and Grb14, as compared to a single one present in Grb7.

Grb7 and Hax1 may colocalize partially to mitochondria in EGF-treated SKBR3 cells and their interaction can affect Caspase3 cleavage of Hax1

Growth factor receptor bound protein 7 (Grb7) is a signal-transducing adaptor protein that mediates specific protein-protein interactions in multiple signaling pathways. Grb7, with Grb10 and Grb14, is members of the Grb7 protein family. The topology of the Grb7 family members contains several protein-binding domains that facilitate the formation of protein complexes, and high signal transduction efficiency. Grb7 has been found overexpressed in several types of cancers and cancer cell lines and is presumed involved in cancer progression through promotion of cell proliferation and migration via interactions with the erythroblastosis oncogene B 2 (human epidermal growth factor receptor 2) receptor, focal adhesion kinase, Ras-GTPases, and other signaling partners. We previously reported Grb7 binds to Hax1 (HS1 associated protein X1) isoform 1, an anti-apoptotic protein also involved in cell proliferation and calcium homeostasis. In this study, we confirm that the in vitro Grb7/Hax1 interaction is exclusive to these two proteins and their interaction does not depend on Grb7 dimerization state. In addition, we report Grb7 and Hax1 isoform 1 may colocalize partially to mitochondria in epidermal growth factor-treated SKBR3 cells and growth conditions can affect this colocalization. Moreover, Grb7 can affect Caspase3 cleavage of Hax1 isoform 1 in vitro, and Grb7 expression may slow Caspase3 cleavage of Hax1 isoform 1 in apoptotic HeLa cells. Finally, Grb7 is shown to increase cell viability in apoptotic HeLa cells in a time-dependent manner. Taken together, these discoveries provide clues for the role of a Grb7/Hax1 protein interaction in apoptosis pathways involving Hax1. Copyright © 2016 John Wiley & Sons, Ltd.

Non-HER2 signaling pathways activated in resistance to anti-HER2 therapy in breast cancer

HER2 receptor is overexpressed approximately in 20 % of human breast cancer (BC) and is a poor prognostic factor. Although therapies targeting this receptor have improved the prognosis of this cancer, up to 62 % patients treated with these drugs experiment progression during the first year of treatment. Some molecular mechanisms have been proposed to be responsible for this resistance, such as activation of alternative signaling pathways (through ERBB receptors and non-ERBB receptors or increased expression of ligands and alterations in HER2 signaling components). In this article, we will review the influence of genetic markers in non-HER2 signaling pathways investigated to date as cause of resistance to HER2-targeted drugs in HER2-positive BC patients. GRB7, included in the 17q12 amplicon, has been associated to poor prognosis in BC patients. Biomarkers like EPHAR and SRC, have demonstrated clinical relevance and prognostic value in HER2-positive BC patients. Non-invasive biomarkers, such as elevated IGF1 serum levels have been revealed as interesting biomarkers to be considered as predictors of trastuzumab clinical outcomes in BC patients. However, the prognostic value of most of the biomarkers investigated to date, such as HER3, IGF1R, PIK3CA, or AKT1 cannot be fully established yet, since results have not been conclusive.

Grb7 gene amplification and protein expression by FISH and IHC in ovarian cancer

OBJECTIVE

Overexpression of growth factor receptor-bound protein 7 (Grb7) has been found in numerous human cancers. The aim of this study was to evaluate the correlation between Grb7 gene amplification and protein expression in ovarian cancer (OC).

METHODS

We use Tissue Microarray (TMA) respectively to detect the gene amplification and protein expression of Grb7 in 90 cases OC and 10 control specimens of normal ovarian tissues by IHC and FISH.

RESULTS

The Grb7 protein expression by IHC analysis was observed in 52/90 (57.8%) OC with 3 cases (3.3%) scored 3(+) and 9 cases (10%) scored 2(+) Grb7 gene amplification by FISH analysis was successfully detectable in 6 specimens with a positive rate of 6.8% (6/88) in which immunostaining 3(+), 2(+) and negative (1(+)/0) expressions of Grb7 were 100.0% (3/3), 11.1% (1/9) and 2.6% (2/76), respectively. Our data exhibited that the IHC and FISH results had a good consistency between Grb7 gene amplification and Grb7 protein expression (Kappa = 0.651, P < 0.001). Both the results of IHC and FISH revealed that Grb7 did not seem to have a role in OC clinicopathology.

CONCLUSION

There is a close relationship between Grb7 gene amplification and GRB7 protein overexpression in human OC. IHC might have limited diagnostic value especially in these tumors and especially in characterizing genetically diverse borderline cases, FISH could be superior to IHC.

Preparation of crystals for characterizing the Grb7 SH2 domain before and after complex formation with a bicyclic peptide antagonist

Human growth factor receptor-bound protein 7 (Grb7) is an adapter protein involved in cell growth, migration and proliferation. It is now recognized that Grb7 is an emerging therapeutic target in specific cancer subtypes. Recently, the discovery of a bicyclic peptide inhibitor that targets the Grb7 SH2 domain, named G7-B1, was reported. In an attempt to probe the foundation of its interaction with Grb7, the crystallization and preliminary data collection of both the apo and G7-B1-bound forms of the Grb7 SH2 domain are reported here. Diffraction-quality crystals were obtained using the hanging-drop vapour-diffusion method. After several rounds of microseeding, crystals of the apo Grb7 SH2 domain were obtained that diffracted to 1.8 Å resolution, while those of the G7-B1-Grb7 SH2 domain complex diffracted to 2.2 Å resolution. The apo Grb7 SH2 domain crystallized in the trigonal space group P63, whereas the G7-B1-Grb7 SH2 domain complex crystallized in the monoclinic space group P21. The experimental aspects of crystallization, crystal optimization and data collection and the preliminary data are reported.

Context-dependent role of Grb7 in HER2+ve and triple-negative breast cancer cell lines

Grb7 is an adapter protein, aberrantly co-overexpressed with HER2 and identified as an independent prognostic marker in breast cancer. It has been established that Grb7 exacerbates the cellular growth and migratory behaviour of HER2+ve breast cancer cells. Less is known about Grb7's role in the context of HER2-ve cells. Here we directly compare the effect of stable Grb7 knockdown in oestrogen sensitive (T47D), HER2+ve (SKBR3) and triple-negative (MDA-MB-468 and MDA-MB-231) breast cancer cell lines on anchorage dependent and independent cell growth, wound healing and chemotaxis. All cell lines showed reduced ability to migrate upon Grb7 knockdown, despite their greatly varied endogenous levels of Grb7. Decreased cell proliferation was not observed in any of the cell lines upon Grb7 knockdown; however, decreased ability to form colonies was observed for all but the oestrogen sensitive cell line, depending upon the stringency of the growth conditions. The data reveal that Grb7 plays an important role in breast cancer progression, beyond the context of HER2+ve cell types.

Dissecting GRB7-mediated signals for proliferation and migration in HER2 overexpressing breast tumor cells: GTP-ase rules

Amplification of human Her2 and its aberrant signaling in 20-30% of early breast cancer patients is responsible for highly aggressive tumors with poor outcome. Grb7 is reported to be co-amplified with Her2. We report a concurrent high expression of mRNA (from FFPE tumor samples; mRNA correlation, Pearson r(2)= 0.806), and high levels of GRB7 protein (immunoblot) in HER2+ breast cancer cell lines. We demonstrated the signaling mechanism of HER2 and downstream effectors that contributes to proliferation and migration. Using HER2+ and trastuzumab-resistant breast cancer cell lines, we identified the interaction between GRB7 and HER2 in the control of HER2+ cell proliferation. Our co-IP data show that GRB7 recruits SHC into the HER2-GRB7 signaling complex. This complex formation leads to activation of RAS-GTP. We also observed that following integrin engagement, GRB7 is phosphorylated at tyrosine in a p-FAK (Y397) dependent manner. This FAK-GRB7 complex leads to downstream activation of RAC1-GTP (responsible for migration) probably through the recruitment of VAV2. Our CO-IP data demonstrate that GRB7 directly binds with VAV2 following fibronectin engagement in HER2+ cells. To address whether GRB7 could serve as a pathway specific therapeutic target, we used siRNA to suppress GRB7 expression. Knockdown of GRB7 expression in the HER2+ breast cancer cell lines decreases RAS activation, cell proliferation, 2D and 3D colony formation and also blocked integrin-mediated RAC1 activation along with integrin-directed cell migration. These findings dissected the HER2-mediated signaling cascade into (1) HER2+ cell proliferation (HER2-GRB7-SHC-RAS) and (2) HER2+ cell migration (alpha5 beta1/alpha4 beta1-FAK-GRB7-VAV2-RAC1). Our data clearly demonstrate that a coupling of GRB7 with HER2 is required for the proliferative and migratory signals in HER2+ breast tumor cells.

The discovery of phenylbenzamide derivatives as Grb7-based antitumor agents

Grb7 is a non-catalytic protein, the overexpression of which has been associated with the proliferative and migratory potentials of cancer cells. Virtual screening strategies involving a shape-based similarity search, molecular docking, and 2D-similarity searches complemented by experimental binding studies (Thermofluor and isothermal titration calorimetry) resulted in the identification of nine novel phenylbenzamide-based antagonists of the Grb7 SH2 domain. Moderate binding affinities were observed, ranging from K(d)=32.3 μM for lead phenylbenzamide NSC 104999 (1) to K(d)=1.1 μM for a structurally related compound, NSC 57148 (2). Deconvolution of the affinity data into its components revealed differences in lead binding, from being entropy based (lead 1) to enthalpically driven (NSC 100874 (3), NSC 55158 (4), and compound 2). Finally, the lead compound 1 was found to decrease the growth of MDA-MB-468 breast cancer cells, with an IC(50) value of 39.9 μM. It is expected that these structures will serve as novel leads in the development of Grb7-based anticancer therapeutics.

Molecular profiles of pre- and postoperative breast cancer tumours reveal differentially expressed genes

Gene expression studies on breast cancer have generally been performed on tissue obtained at the time of surgery. In this study, we have compared the gene expression profiles in preoperative tissue (core needle biopsies) while tumor is still in its normal milieu to postoperative tissue from the same tumor obtained during surgery. Thirteen patients were included of which eleven had undergone sentinel node diagnosis procedure before operation. Microarray gene expression analysis was performed using total RNA from all the samples. Paired significance analysis of microarrays revealed 228 differently expressed genes, including several early response stress-related genes such as members of the fos and jun families as well as genes of which the expression has previously been associated with cancer. The expression profiles found in the analyses of breast cancer tissue must be evaluated with caution. Different profiles may simply be the result of differences in the surgical trauma and timing of when samples are taken and not necessarily associated with tumor biology.

Eph family receptors and ligands in vascular cell targeting and assembly

Members of the Eph family of receptor tyrosine kinases determine neural cell aggregation and targeting behavior, functions that are also critical in vascular assembly and remodeling. Among this class of diverse receptors, EphA2 (Eck) and EphB1 (ELK) represent prototypes for two receptor subfamilies distinguished by high-affinity interaction with either glycerophosphatidylinositol (GPI)-linked or transmembrane ligands, respectively. EphA2 participates in angiogenic responses to tumor necrosis factor (TNF) through an autocrine loop affecting endothelial cell migration. EphB1 and its ligand Ephrin-B1 (LERK-2) are important determinants of assembly of endothelial cells from the microvasculature of the kidney, where both are expressed in endothelial progenitors and in glomerular microvascular endothelial cells. Ephrin-B1 activation of EphB1 promotes assembly of these cells into capillary-like structures. Interaction trap approaches have identified downstream signaling proteins that complex with ligand-activated EphA2 or EphB1, including nonreceptor tyrosine kinases and SH2 domain-containing adapter proteins. The Grb 10 adapter is one of a subset that binds activated EphB1, but not EphA2, defining distinct signaling mechanisms for these related endothelial receptors. On the basis of observations in vascular endothelial cells and recent results defining Eph receptor and ligand roles in neural cell targeting, we propose that these receptors direct cell-cell recognition events that are critical in vasculogenesis and angiogenesis. (Trends Cardiovasc Med 1997;7:329-334). © 1997, Elsevier Science Inc.

[A uNick protein]

Nck is an adaptor protein composed of three N-terminal Src Homology (SH) 3 domains followed by a unique C‑terminal SH2 domain. Like other SH2/SH3 domains-containing adaptor proteins, Nck mediates signal transduction from activated cell surface receptors by directing the flow of information to elicit properly orchestrated cell responses. In this way, Nck appears to be unique in its contribution to a wide variety of cellular processes. Moreover, in addition to the typical signal/pY-SH2/SH3-effectors mode of signaling, Nck also transduces signals through an inverse mode of -signaling (signal-SH3/SH2-pY/effectors) and from various cell compartments. Since Nck contributes to important morphogenic and mitogenic processes, deregulated expression of Nck could be detrimental to cellular homeostasis. In agreement, Nck expression has been found upregulated in numerous types of cancer. In this paper we delineate the main molecular -signaling -complexes associated with Nck, focusing on those involved in cancer progression.

Genomic organization and control of the grb7 gene family

Grb7 and their related family members Grb10 and Grb14 are adaptor proteins, which participate in the functionality of multiple signal transduction pathways under the control of a variety of activated tyrosine kinase receptors and other tyrosine-phosphorylated proteins. They are involved in the modulation of important cellular and organismal functions such as cell migration, cell proliferation, apoptosis, gene expression, protein degradation, protein phosphorylation, angiogenesis, embryonic development and metabolic control. In this short review we shall describe the organization of the genes encoding the Grb7 protein family, their transcriptional products and the regulatory mechanisms implicated in the control of their expression. Finally, the alterations found in these genes and the mechanisms affecting their expression under pathological conditions such as cancer, diabetes and some congenital disorders will be highlighted.

A chemical and phosphoproteomic characterization of dasatinib action in lung cancer

We describe a strategy to comprehend signaling pathways active in lung cancer cells and targeted by dasatinib employing chemical proteomics to identify direct interacting proteins combined with immunoaffinity purification of tyrosine phosphorylated peptides corresponding to activated tyrosine kinases. We identified nearly 40 different kinase targets of dasatinib. These include SFK members (LYN, SRC, FYN, LCK, YES), non-receptor tyrosine kinases (FRK, BRK, ACK), and receptor tyrosine kinases (Ephrin receptors, DDR1, EGFR). Using quantitative phosphoproteomics we identified peptides corresponding to autophosphorylation sites of these tyrosine kinases that are inhibited in a concentration-dependent manner by dasatinib. Using drug resistant gatekeeper mutants, we show that SFK kinases, particularly SRC and FYN, as well as EGFR are relevant targets for dasatinib action. The combined mass spectrometry based approach described here provides a system-level view of dasatinib action in cancer cells and suggests both functional targets and rationale combinatorial therapeutic strategies.

Grb7 upregulation is a molecular adaptation to HER2 signaling inhibition due to removal of Akt-mediated gene repression

The efficacy of anti-HER2 therapeutics, such as lapatinib and trastuzumab, is limited by primary and acquired resistance. Cellular adaptations that allow breast cancer cell to survive prolonged HER2 inhibition include de-repression of the transcription factor FOXO3A with consequent estrogen receptor activation, and/or increased HER3 signaling. Here, we used low-density arrays, quantitative PCR, and western blotting to determine how HER2 signaling inhibition with lapatinib or PI3K inhibitors affects the expression of genes involved in breast cancer metastatic spread and overall prognosis. Retroviral transgenesis was used to express constitutively active forms of Akt in the HER2⁺ breast cancer cell line SKBR3, and Grb7 in MCF7 cells. Specific gene silencing was obtained by siRNAs transfection. A murine BT474 xenograft cancer model was used to assess the effect of lapatinib on gene expression in vivo. We found that lapatinib induces upregulation of Grb7, an adaptor protein involved in receptor tyrosine kinase signaling and promoting cell survival and cell migration. Grb7 upregulation induced by lapatinib was found to occur in cancer cells in vitro and in vivo. We demonstrate that Grb7 upregulation is recreated by PI3K inhibitors while being prevented by constitutively active Akt. Thus, Grb7 is repressed by PI3K signaling and lapatinib-mediated Akt inhibition is responsible for Grb7 de-repression. Finally, we show that Grb7 removal by RNA-interference reduces breast cancer cell viability and increases the activity of lapatinib. In conclusion, Grb7 upregulation is a potentially adverse consequence of HER2 signaling inhibition. Preventing Grb7 accumulation and/or its interaction with receptor tyrosine kinases may increase the benefit of HER2-targeting drugs.

Identification of the early VIP-regulated transcriptome and its associated, interactome in resting and activated murine CD4 T cells

More than 40 years after the discovery of vasoactive intestinal peptide (VIP), its transcriptome in the immune system has still not been completely elucidated. In an attempt to understand the biological role of this neuropeptide in immunity, we chose CD4 T cells as a cellular system. Agilent Mouse Whole Genome microarrays were hybridized with fluorescently labeled total RNA isolated from resting CD4 T cells cultured +/-10(-7)M VIP for 5h or PMA/ionomycin activated CD4 T cells cultured +/-10(-7)M VIP for 5h. These VIP-regulated transcriptomes were analyzed by Significance Analysis of Microarrays (SAM) and Ingenuity Pathway Analysis (IPA) software to identify relevant signaling pathways modulated by VIP in the absence and presence of T cell activation. In resting CD4 T cells, VIP-modulated 368 genes, ranging from 3.49 to -4.78-fold. In the PMA/ionomycin activated CD4 T cells, 326 gene expression levels were changed by VIP, ranging from 2.94 to -1.66-fold. IPA analysis revealed that VIP exposure alters cellular function through EGFR signaling in resting CD4 T cells, and modulates immediate early genes, Fos and CREM/ICER, in activated CD4 T cells. These gene expression changes are suggested to explain at a molecular level how VIP can regulate T cell homing to the gut and induce regulatory T cell generation.

Growth factor receptor-bound protein-7 (Grb7) as a prognostic marker and therapeutic target in breast cancer

BACKGROUND

Growth factor receptor-bound protein-7 (Grb7) is an adapter-type signaling protein recruited to various tyrosine kinases, including HER2/neu. Grb7-specific inhibitors are in early development. As with other targeted therapies, response to therapy might be associated with target expression.

MATERIALS AND METHODS

Tissue microarrays containing 638 primary breast cancer specimens with 15-year patient follow-up were employed to assess Grb7 expression using our Automated QUantitative Analysis method; cytokeratin defines pixels as breast cancer (tumor mask) within the histospot, and Grb7 expression within the mask is measured with Cy5-conjugated antibodies.

RESULTS

High Grb7 expression was strongly associated with decreased survival in the entire cohort and in the node-positive subset (P = 0.0034 and P = 0.0019, respectively). On multivariable analysis, it remained an independent prognostic marker (P = 0.01). High Grb7 was strongly associated with high HER2/neu, and coexpression of these molecules was associated with worse prognosis than HER2/neu overexpression alone.

CONCLUSIONS

High Grb7 defines a subset of breast cancer patients with decreased survival, indicating that Grb7 might be a valuable prognostic marker and drug target. Coexpression with HER2/neu indicates that cotargeting these molecules might be an effective approach for treating HER2/neu-positive breast cancers. Future studies using Grb7-targeting agents should include assessment of Grb7 levels.

Tyrosine phosphorylation of growth factor receptor-bound protein-7 by focal adhesion kinase in the regulation of cell migration, proliferation, and tumorigenesis

We have previously reported that growth factor receptor-bound protein-7 (Grb7), an Src-homology 2 (SH2)-containing adaptor protein, enables interaction with focal adhesion kinase (FAK) to regulate cell migration in response to integrin activation. To further elucidate the signaling events mediated by FAK*Grb7 complexes in promoting cell migration and other cellular functions, we firstly examined the phosphorylated tyrosine site(s) of Grb7 by FAK using an in vivo mutagenesis. We found that FAK was capable of phosphorylating at least 2 of 12 tyrosine residues within Grb7, Tyr-188 and Tyr-338. Moreover, mutations converting the identified Tyr to Phe inhibited integrin-dependent cell migration as well as impaired cell proliferation but not survival compared with the wild-type control. Interestingly, the above inhibitory effects caused by the tyrosine phosphorylation-deficient mutants are probably attributed to their down-regulation of phospho-Tyr-397 of FAK, thereby implying a mechanism by competing with wild-type Grb7 for binding to FAK. Consequently, these tyrosine phosphorylation-deficient mutants evidently altered the phospho-Tyr-118 of paxillin and phosphorylation of ERK1/2 but less on phospho-Ser-473 of AKT, implying their involvement in the FAK*Grb7-mediated cellular functions. Additionally, we also illustrated that the formation of FAK*Grb7 complexes and Grb7 phosphorylation by FAK in an integrin-dependent manner were essential for cell migration, proliferation and anchorage-independent growth in A431 epidermal carcinoma cells, indicating the importance of FAK*Grb7 complexes in tumorigenesis. Our data provide a better understanding on the signal transduction event for FAK*Grb7-mediated cellular functions as well as to shed light on a potential therapeutic in cancers.

Development of Binding Assays for the SH2 Domain of Grb7 and Grb2 Using Fluorescence Polarization

Adaptor proteins Grb7 and Grb2 have been implicated as being 2 potential therapeutic targets in several human cancers, especially those that overexpress ErbB2. These 2 proteins contain both a SH2 domain (Src homology 2) that binds to phosphorylated tyrosine residues contained within ErbB2 and other specific protein targets. Two assays based on enzyme-linked immunosorbent assay and fluorescence polarization methods have been developed and validated to find and rank inhibitors for both proteins binding to the pY1139. Fluorescence polarization assays allowed the authors to determine quickly and reproducibly affinities of peptides from low nanomolar to high micromolar range and to compare them directly for Grb7 and Grb2. As a result, the assays have identified a known peptidomimetic Grb2 SH2 inhibitor (mAZ-pTyr-(αMe)pTyr-Asn-NH2) that exhibits the most potent affinity for the Grb7 SH2 domain described to date. ( Journal of Biomolecular Screening 2008:112-119)

Activation of growth factor receptors in esophageal cancer--implications for therapy

Esophageal cancer is a highly aggressive disease and is the seventh most common cause of cancer-related death in the western world. Worldwide, it ranks as the sixth most frequent cause of cancer death. Despite advances in surgical techniques and treatment, the prognosis of esophageal cancer remains poor, with very few long-term survivors. The need for novel strategies to detect esophageal cancer earlier and to improve current therapy is urgent. It is well established that growth factors and growth factor receptor-mediated signaling pathways are important components of the transformation process in many forms of cancer, including esophageal cancer. With the recent advances in drug development, there are emerging possibilities to use growth factor signal transduction pathways in targeted therapy. This review provides a summary of the role of growth factors and their receptors in esophageal cancer and discusses their potential roles as biomarkers and as targets in therapy.

Calorimetric investigation of phosphorylated and non-phosphorylated peptide ligand binding to the human Grb7-SH2 domain

Grb7 is a member of the Grb7 family of proteins, which also includes Grb10 and Grb14. All three proteins have been found to be overexpressed in certain cancers and cancer cell lines. In particular, Grb7 (along with the receptor tyrosine kinase erbB2) is overexpressed in 20-30% of breast cancers. In general, growth factor receptor bound (Grb) proteins bind to activated membrane-bound receptor tyrosine kinases (RTKs; e.g., the epidermal growth factor receptor, EGFR) through their Src homology 2 (SH2) domains. In particular, Grb7 binds to erbB2 (a.k.a. EGFR2) and may be involved in cell signaling pathways that promote the formation of metastases and inflammatory responses. In previous studies, we reported the solution structure and the backbone relaxation behavior of the Grb7-SH2/erbB2 peptide complex. In this study, isothermal titration calorimetry studies have been completed by measuring the thermodynamic binding parameters of several phosphorylated and non-phosphorylated peptides representative of natural Grb7 receptor ligands as well as ligands developed through combinatorial peptide screening methods. The entirety of these calorimetric studies is interpreted in an effort to describe the specific ligand binding characteristics of the Grb7 protein.

Role of Growth Factor Receptor–Bound Protein 7 in Hepatocellular Carcinoma

The human growth factor receptor-bound protein 7 (Grb7) is an adaptor molecule and is related to cell invasion. In this present study, we investigated the clinical and biological significance of Grb7 expression in human hepatocellular carcinoma (HCC). We reviewed 64 consecutive patients who had undergone liver resection for HCC, and we investigated the correlation between Grb7 expression and clinical outcome. To analyze the biological behavior of Grb7 in vitro and in vivo, we established Grb7 stable knockdown HCC cells using RNA interference technology. The positive staining of Grb7 protein was correlated with portal venous invasion (P < 0.01), hepatic venous invasion (P < 0.01), and intrahepatic metastasis (P < 0.05). Positive expression of Grb7 was significantly correlated with focal adhesion kinase (FAK) protein levels in HCC (P < 0.01). The Grb7- and FAK-positive group showed a significantly poorer prognosis as compared with the Grb7- and FAK-negative group (P < 0.05). Grb7 knockdown HCC cells exhibited significantly lower levels of invasion potential (P < 0.05) and motility (P < 0.05) than the control cells in vitro; moreover, Grb7 knockdown HCC cells showed delayed onset of the tumors compared with the control cells in vivo. Grb7 expression can modulate the invasive phenotype of HCC. Grb7 plays an important role in HCC progression and is strongly associated with expression of FAK. Grb7 could be a therapeutic target in HCC.

Peripheral disruption of the Grb10 gene enhances insulin signaling and sensitivity in vivo

Grb10 is a pleckstrin homology and Src homology 2 domain-containing protein that interacts with a number of phosphorylated receptor tyrosine kinases, including the insulin receptor. In mice, Grb10 gene expression is imprinted with maternal expression in all tissues except the brain. While the interaction between Grb10 and the insulin receptor has been extensively investigated in cultured cells, whether this adaptor protein plays a positive or negative role in insulin signaling and action remains controversial. In order to investigate the in vivo role of Grb10 in insulin signaling and action in the periphery, we generated Grb10 knockout mice by the gene trap technique and analyzed mice with maternal inheritance of the knockout allele. Disruption of Grb10 gene expression in peripheral tissues had no significant effect on fasting glucose and insulin levels. On the other hand, peripheral-tissue-specific knockout of Grb10 led to significant overgrowth of the mice, consistent with a role for endogenous Grb10 as a growth suppressor. Loss of Grb10 expression in insulin target tissues, such as skeletal muscle and fat, resulted in enhanced insulin-stimulated Akt and mitogen-activated protein kinase phosphorylation. Hyperinsulinemic-euglycemic clamp studies revealed that disruption of Grb10 gene expression in peripheral tissues led to increased insulin sensitivity. Taken together, our results provide strong evidence that Grb10 is a negative regulator of insulin signaling and action in vivo.

Grb10 and active Raf-1 kinase promote Bad-dependent cell survival

The proapoptotic protein Bad is a key player in cell survival decisions, and is regulated post-translationally by several signaling networks. We expressed Bad in mouse embryonic fibroblasts to sensitize them to apoptosis, and tested cell lines derived from knock-out mice to establish the significance of the interaction between the adaptor protein Grb10 and the Raf-1 protein kinase in anti-apoptotic signaling pathways targeting Bad. When compared with wild-type cells, both Grb10 and Raf-1-deficient cells exhibit greatly enhanced sensitivity to apoptosis in response to Bad expression. Structure-function analysis demonstrates that, in this cellular model, the SH2, proline-rich, and pleckstrin homology domains of Grb10, as well as its Akt phosphorylation site and consequent binding by 14-3-3, are all necessary for its anti-apoptotic functions. As for Raf-1, its kinase activity, its ability to be phosphorylated by Src on Tyr-340/341 and the binding of its Ras-associated domain to the Grb10 SH2 domain are all necessary to promote cell survival. Silencing the expression of either Grb10 or Raf-1 by small interfering RNAs as well as mutagenesis of specific serine residues on Bad, coupled with signaling inhibitor studies, all indicate that Raf-1 and Grb10 are required for the ability of both the phosphatidylinositol 3-kinase/Akt and MAP kinase pathways to modulate the phosphorylation and inactivation of Bad. Because total Raf-1, ERK, and Akt kinase activities are not impaired in the absence of Grb10, we propose that this adapter protein creates a subpopulation of Raf-1 with specific anti-apoptotic activity.

Transduced PEP-1-Grb7 fusion protein suppressed LPS-induced COX-2 expression

Although the incidence and severity of atopic dermatitis (AD) is steadily increasing at an alarming rate, its pathogenic mechanisms remain poorly understood yet. Recently, we found that the expression of Grb7 protein was markedly decreased in AD patients using proteomic analysis. In the present study, human Grb7 gene was fused with PEP-1 peptide in a bacterial expression vector to produce a genetic in-frame PEP-1-Grb7 fusion protein. The expressed and purified PEP-1-Grb7 fusion proteins transduced efficiently into skin cells in a time- and dose-dependent manner when added exogenously in culture media. Once inside the cells, the transduced PEP-1-Grb7 protein was stable for 48 h. In addition, transduced PEP-1-Grb7 fusion protein markedly increased cell viability in macrophage RAW 264.7 cells treated with LPS by inhibition of the COX-2 expression level. These results suggest that the PEP-1-Grb7 fusion protein can be used in protein therapy for inflammatory skin disorders, including AD.

Combination treatment with Grb7 peptide and Doxorubicin or Trastuzumab (Herceptin) results in cooperative cell growth inhibition in breast cancer cells

Grb7 has potential importance in the progression of cancer. We have previously identified a novel peptide that binds to the SH2 domain of Grb7 and inhibits its association with several different receptor tyrosine kinases. We have synthesised the Grb7 peptide, G7-18NATE, with two different cell penetrating peptides, Penetratin and Tat. In this study, we have shown that both Penetratin- and Tat-conjugated G7-18NATE peptides are able to inhibit the proliferation of SK-BR-3, ZR-75-30, MDA-MB-361 and MDA-MB-231 breast cancer cells. There was no significant effects on breast cancer MCF-7cells, non-malignant MCF 10A or 3T3 cells. In addition, there was no significant inhibition of proliferation by Penetratin or Tat alone or by their conjugates with arbitrary peptide sequence in any of the cell lines tested. We determined the EC₅₀ of G7-18NATE-P peptide for SK-BR-3 cell proliferation to be 7.663 × 10⁻⁶ M. Co-treatment of G7-18NATE-P peptide plus Doxorubicin in SK-BR-3 breast cancer cells resulted in an additional inhibition of proliferation, resulting in 56 and 84% decreases in the Doxorubicin EC₅₀ value in the presence of 5 × 10⁻⁶ and 1.0 × 10⁻⁵ M G7-18NATE-P peptide, respectively. Importantly, the co-treatment with Doxorubicin and the delivery peptide did not change the Doxorubicin EC₅₀. Since Grb7 associates with ErbB2, we assessed whether the peptide inhibitor would have a combined effect with a molecule that targets ErbB2, Herceptin. Co-treatment of Herceptin plus 1.0 × 10⁻⁵ M G7-18NATE-P peptide in SK-BR-3 cells resulted in a 46% decrease in the Herceptin EC₅₀ value and no decrease following the co-treatment with Herceptin and penetratin alone. This Grb7 peptide has potential to be developed as a therapeutic agent alone, in combination with traditional chemotherapy, or in combination with other targeting molecules.

The adaptor Grb7 links netrin-1 signaling to regulation of mRNA translation

We previously reported a novel biological activity of Netrin-1 in translational stimulation of kappa opioid receptor (KOR). We now identify Grb7 as a new RNA-binding protein that serves as the molecular adaptor for transmitting Netrin-1 signals, through focal adhesion kinase (FAK), to the translation machinery. Grb7 binds specifically to the first stem loop of kor mRNA 5'-UTR through a new RNA-binding domain located in its amino terminus. Upon binding to its capped, target mRNA, Grb7 blocks the recruitment of eIF4E, rendering mRNA untranslatable. The RNA-binding and translation-repressive activity is reduced by FAK-mediated hyperphosphorylation on two tyrosine residues of its carboxyl terminus. This study reports an adaptor protein Grb7 that transmits the stimulating signals of Netrin-1 to the translational machinery to rapidly regulate mRNA translation.

Tissue-specific expression of Clec2g in mice

Estrogens regulate the proliferation and differentiation of mouse vaginal epithelial cells. We examined the temporal and spatial expression of DDV10, a novel C-type lectin during stratification and cornification of the vaginal epithelium. DDV10 was expressed in vagina but not uterus in ovariectomized mice treated with 17beta-estradiol (E2). In mouse stomach, the expression of DDV10 was detected in pars proventricularis but not in pars glandularis. Furthermore, the DDV10 gene was found to possess two transcripts, a long form (DDV10) and a short form (OCILrP1, osteoclast inhibitory lectin-related protein 1). DDV10 mRNA but not OCILrP1 mRNA was expressed in the stratified and cornified epithelial tissues. DDV10 mRNA was first detected between 12 and 18 h after E2 treatment in the vaginal epithelium, and was detected in the vagina of the neonatally diethylstilbestrol (DES)-treated mouse. Recently, a unified name was registered in GenBank (C-type lectin domain family 2, member g; Clec2 g). Taken together, these data suggest that DDV10 is the long form of Clec2 g (Clec2g-L), and DDV10/Clec2g-L may play a role in the stratification and/or cornification of epithelial cells during differentiation.

Specific Peptide Ligand for Grb7 Signal Transduction Protein and Pancreatic Cancer Metastasis

BACKGROUND

Pancreatic cancer is one of the most aggressive malignancies, with high rates of invasion and metastasis and with generally poor prognosis. We previously found that metastasis was strongly associated with the expression of growth factor receptor-bound protein 7 (Grb7), which contains a Src homology 2 (SH2) domain. In this study, we evaluated Grb7 protein as a molecular target of therapy for metastatic pancreatic cancer.

METHODS

Grb7 protein expression was measured by immunohistochemistry in 36 human pancreatic cancer specimens and adjacent normal pancreatic tissue. We synthesized a nonphosphorylated peptide inhibitor that binds specifically to the SH2 domain of Grb7. Intracellular signaling was assessed by immunoprecipitation and immunoblot assays in cultured human pancreatic cancer cells. Cell migration was measured with a modified Boyden chamber method. Peritoneal metastasis of the pancreatic cancer cells was measured with a mouse model. All statistical tests were two-sided.

RESULTS

We found that 22 (61%) of 36 pancreatic cancer specimens had higher levels of Grb7 protein than their corresponding normal pancreatic tissue specimens. Grb7 expression was statistically significantly different between specimens from patients without lymph node metastasis (stage N0; two of the 10 patients) and patients with lymph node metastasis (stages N1 + N2; 20 of the 26 patients) (P = .006). The Grb7 peptide inhibitor selectively blocked the interaction between Grb7 and focal adhesion kinase and blocked the phosphorylation of Grb7 protein. In vivo Grb7 peptide inhibitor statistically significantly attenuated cell migration (for control peptide, 87.5 cells migrated, 95% confidence interval [CI] = 82.6 to 92.4 cells; for Grb7 peptide, 5.7 cells migrated, 95% CI = 2.3 to 9.0 cells; P < .001) and peritoneal metastasis of the pancreatic cancer cells in a mouse model, as assessed by the number of nodules (control = 72.6 nodules, 95% CI = 55.8 to 89.4 nodules; and for Grb7 peptide = 3.2 nodules, 95% CI = 1.6 to 4.8 nodules; P < .001, t test) and their weight (control = 4.13 g, 95% CI = 3.40 to 4.86 g; Grb7 peptide = 0.19 g, 95% CI = 0.06 to 0.32 g; P < .001, t test).

CONCLUSIONS

The Grb7 peptide inhibitor appears to be a promising molecularly targeted therapeutic agent against metastatic pancreatic cancer.

Expression of HER2 and the coamplified genes GRB7 and MLN64 in human breast cancer: quantitative real-time reverse transcription-PCR as a diagnostic alternative to immunohistochemistry and fluorescence in situ hybridization

PURPOSE

Accurate testing of HER2 is centrally important for breast cancer therapy and prognosis. Immunohistochemistry (IHC) and fluorescence in situ hybridization (FISH) are current standard testing methods. As a potential alternative for assessment of HER2, we explored quantitative real-time reverse transcription-PCR (RT-PCR), a fast and inexpensive method yielding quantitative results insensitive to interobserver variability and amenable to standardized scoring.

EXPERIMENTAL DESIGN

We assessed HER2 status at the DNA, mRNA, and protein levels with FISH, quantitative RT-PCR, and IHC in 136 tumor samples from 85 breast cancer patients. Expression of GRB7, MLN64, and p21, genes coregulated with HER2, was also quantified with quantitative RT-PCR and correlated with the overall survival (OS) and disease-free survival (DFS) individually and in combination with HER2.

RESULTS

Twenty-nine percent and 19% of the patients scored HER2 positive with IHC and quantitative RT-PCR, respectively. In 18 of 19 cases, HER2 statuses in tumors and lymph node metastases were identical. HER2 status significantly correlated with DFS when determined by IHC (P < 0.01), quantitative RT-PCR (P < 0.003), but not with FISH (P = 0.09). The combination of HER2 with MLN64, but not with GRB7 or p21, enhanced the prognostic power for the DFS (P < 0.00005) and OS (P < 0.0008).

CONCLUSIONS

Quantitative RT-PCR seems to be clinically as useful in the assessment of HER2 status as IHC and FISH, yielding comparable correlations of HER2 status with the OS and DFS. Thus, quantitative RT-PCR analysis of HER2 or HER2 plus MLN64 is a promising complement or alternative to current methods for HER2 testing, particularly in laboratories lacking FISH or IHC technology.

Grb10 and Grb14: enigmatic regulators of insulin action--and more?

The Grb proteins (growth factor receptor-bound proteins) Grb7, Grb10 and Grb14 constitute a family of structurally related multidomain adapters with diverse cellular functions. Grb10 and Grb14, in particular, have been implicated in the regulation of insulin receptor signalling, whereas Grb7 appears predominantly to be involved in focal adhesion kinase-mediated cell migration. However, at least in vitro, these adapters can bind to a variety of growth factor receptors. The highest identity within the Grb7/10/14 family occurs in the C-terminal SH2 (Src homology 2) domain, which mediates binding to activated receptors. A second well-conserved binding domain, BPS [between the PH (pleckstrin homology) and SH2 domains], can act to enhance binding to the IR (insulin receptor). Consistent with a putative adapter function, some non-receptor-binding partners, including protein kinases, have also been identified. Grb10 and Grb14 are widely, but not uniformly, expressed in mammalian tissues, and there are various isoforms of Grb10. Binding of Grb10 or Grb14 to autophosphorylated IR in vitro inhibits tyrosine kinase activity towards other substrates, but studies on cultured cell lines have been conflicting as to whether Grb10 plays a positive or negative role in insulin signalling. Recent gene knockouts in mice have established that Grb10 and Grb14 act as inhibitors of intracellular signalling pathways regulating growth and metabolism, although the phenotypes of the two knockouts are distinct. Ablation of Grb14 enhances insulin action in liver and skeletal muscle and improves whole-body tolerance, with little effect on embryonic growth. Ablation of Grb10 results in disproportionate overgrowth of the embryo and placenta involving unidentified pathways, and also impacts on hepatic glycogen synthesis, and probably on glucose homoeostasis. This review discusses the extent to which previous studies in vitro can account for the observed phenotype of knockout animals, and considers evidence that aberrant function of Grb10 or Grb14 may contribute to disorders of growth and metabolism in humans.

Biochemistry and biomechanics of cell motility

Cell motility is an essential cellular process for a variety of biological events. The process of cell migration requires the integration and coordination of complex biochemical and biomechanical signals. The protrusion force at the leading edge of a cell is generated by the cytoskeleton, and this force generation is controlled by multiple signaling cascades. The formation of new adhesions at the front and the release of adhesions at the rear involve the outside-in and inside-out signaling mediated by integrins and other adhesion receptors. The traction force generated by the cell on the extracellular matrix (ECM) regulates cell-ECM adhesions, and the counter force exerted by ECM on the cell drives the migration. The polarity of cell migration can be amplified and maintained by the feedback loop between the cytoskeleton and cell-ECM adhesions. Cell migration in three-dimensional ECM has characteristics distinct from that on two-dimensional ECM. The migration of cells is initiated and modulated by external chemical and mechanical factors, such as chemoattractants and the mechanical forces acting on the cells and ECM, as well as the surface density, distribution, topography, and rigidity of the ECM.

Backbone nuclear relaxation characteristics and calorimetric investigation of the human Grb7-SH2/erbB2 peptide complex

Grb7 is a member of the Grb7 family of proteins, which also includes Grb10 and Grb14. All three proteins have been found to be overexpressed in certain cancers and cancer cell lines. In particular, Grb7 (along with the receptor tyrosine kinase erbB2) is overexpressed in 20%-30% of breast cancers. Grb7 binds to erbB2 and may be involved in cell signaling pathways that promote the formation of metastases and inflammatory responses. In a prior study, we reported the solution structure of the Grb7-SH2/erbB2 peptide complex. In this study, T(1), T(2), and steady-state NOE measurements were performed on the Grb7-SH2 domain, and the backbone relaxation behavior of the domain is discussed with respect to the potential function of an insert region present in all three members of this protein family. Isothermal titration calorimetry (ITC) studies were completed measuring the thermodynamic parameters of the binding of a 10-residue phosphorylated peptide representative of erbB2 to the SH2 domain. These measurements are compared to calorimetric studies performed on other SH2 domain/phosphorylated peptide complexes available in the literature.

The adaptor Grb7 is a novel calmodulin-binding protein: functional implications of the interaction of calmodulin with Grb7

We demonstrate using Ca2+-dependent calmodulin (CaM)-affinity chromatography and overlay with biotinylated CaM that the adaptor proteins growth factor receptor bound (Grb)7 and Grb7V (a naturally occurring variant lacking the Src homology 2 (SH2) domain) are CaM-binding proteins. Deletion of an amphiphilic basic amino-acid sequence (residues 243-256) predicted to form an alpha-helix located in the proximal region of its pleckstrin homology (PH) domain demonstrates the location of the CaM-binding domain. This site is identical in human and rodents Grb7, and shares great homology with similar regions of Grb10 and Grb14, and the Mig10 protein from Caenorhabditis elegans. We show that Grb7 and Grb7V are present in the cytosol and bound to membranes, while the deletion mutants (Grb7Delta and Grb7VDelta) have less capacity to be associated to membranes. Grb7Delta maintains in part the capacity to bind phosphoinositides, and CaM competes for phosphoinositide binding. Activation of ErbB2 by heregulin beta1 decreases the pool of Grb7 associated to membranes. The cell-permeable CaM antagonist W7 (N-(6-aminohexyl)-5-chloro-1-naphthalenesulfonamide), but not the CaM-dependent protein kinase II inhibitor KN93, prevents this effect. Highly specific cell-permeable CaM inhibitory peptides decrease the association of Grb7 to membranes. This suggests that CaM regulates the intracellular mobilization of Grb7 in living cells. Direct interaction between enhanced yellow fluorescent protein (EYFP)-Grb7 and enhanced cyan fluorescent protein (ECFP)-CaM chimeras at the plasma membrane of living cells was demonstrated by fluorescence resonance energy transfer (FRET). The FRET signal dramatically decreased in cells loaded with a cell-permeable Ca2+ chelator, and was significantly attenuated when enhanced yellow fluorescent protein-Grb7 chimera (EYFP-Grb7)Delta instead of EYFP-Grb7 was used. Finally, we show that conditioned media from cells transiently transfected with Grb7Delta and Grb7VDelta lost its angiogenic activity, in contrast to those from cells transiently transfected with their wild-type counterparts.

Grb7-SH2 domain dimerisation is affected by a single point mutation

Growth factor receptor bound protein 7 (Grb7) is an adaptor protein that is co-overexpressed and forms a tight complex with the ErbB2 receptor in a number of breast tumours and breast cancer cell lines. The interaction of Grb7 with the ErbB2 receptor is mediated via its Src homology 2 (SH2) domain. Whilst most SH2 domains exist as monomers, recently reported studies have suggested that the Grb7-SH2 domain exists as a homodimer. The self-association properties of the Grb7-SH2 domain were therefore studied using sedimentation equilibrium ultracentrifugation. Analysis of the data demonstrated that the Grb7-SH2 domain is dimeric with a dissociation constant of approximately 11 muM. We also demonstrate, using size-exclusion chromatography, that mutation of phenylalanine 511 to an arginine produces a monomeric form of the Grb7-SH2 domain. This mutation represents the first step in the engineering of a Grb7-SH2 domain with good solution properties for further biophysical and structural investigation.

Solution structure of the human Grb14-SH2 domain and comparison with the structures of the human Grb7-SH2/erbB2 peptide complex and human Grb10-SH2 domain

Grb14 is an adapter protein that is known to be overexpressed in estrogen receptor positive breast cancers, and in a number of prostate cancer cell lines. Grb14 has been demonstrated to bind to a number of activated receptor tyrosine kinases (RTKs) and to modulate signals transduced through these receptors. The RTKs to which Grb14 binds include the insulin receptor (IR), the fibroblast growth factor receptor (FGFR), the platelet-derived growth factor receptor (PDGFR), and the tunica endothelial kinase (Tek/Tie2) receptor. Grb14 has been shown to bind to these activated RTKs through its Src homology 2 (SH2) domain, with the exception of the insulin receptor, where the primary binding interaction is via a small domain adjacent to the SH2 domain (the BPS or PIR domain). Grb14 is a member of the Grb7 family of proteins, which also includes Grb7 and Grb10. We have solved the solution structure of the human Grb14-SH2 domain and compared it with the recently determined Grb7-SH2 and Grb10-SH2 domain structures.

Coamplification and coexpression of GRB7 and ERBB2 is found in high grade intraepithelial neoplasia and in invasive Barrett's carcinoma

The human growth factor receptor-bound protein 7 gene (GRB7), the founding member of a family of adaptor molecules has been shown to regulate cell migration and has been implicated in tumor progression. GRB7 is localized in close proximity to the ERBB2 gene within an amplicon previously identified in Barrett's adenocarcinoma (BCA). We evaluated gene amplification and mRNA expression of GRB7 and ERBB2 in Barrett's carcinoma and its associated precursor lesions to assess their possible role in Barrett's malignant transformation. Copy number and expression levels were analyzed by Q-PCR (GRB7, ERBB2) and QRT-PCR (GRB7, ERBB2) using TaqMan technology and fluorescence in situ hybridization (ERBB2) in a series of 24 laser-microdissected samples of Barrett's carcinomas and 32 samples of associated premalignant lesions. Parallel analysis of gene copy number changes and expression levels demonstrated that GRB7 and ERBB2 displayed concomitant elevated expression levels and increased copy numbers in 32% of Barrett's carcinomas. There was a correlation between GRB7 and ERBB2 in BCA at the DNA level (r(s) = 0.76, p < 0.001) and the mRNA level (r(s) = 0.89, p < 0.001). Moreover, coamplification (r(s) = 0.97, p < 0.001) and coexpression (r(s) = 0.81, p < 0.001) of GRB7 and ERBB2 are shown to be already present in a subset of BCA associated high-grade intraepithelial neoplasia (HGIN), possibly reflecting a role of a concerted expression of GRB7 and ERBB2. No alterations, neither gene amplification nor overexpression were detected in Barrett's carcinoma associated low grade intraepithelial neoplasia (LGIN), intestinal metaplasia (IM) and squamous epithelium, indicating that alterations of GRB7 and ERBB2 are late events in the carcinogenesis of Barrett's esophagus. These findings may be of particular interest because the transition from high grade intraepithelial neoplasia to invasive carcinoma is a crucial step in malignant transformation in Barrett's carcinogenesis and might underline the putative role of GRB7 and ERBB2 in cell migration and tumor invasion.

Purification and identification of protein-tyrosine kinase-binding proteins using synthetic phosphopeptides as affinity reagents

Protein-tyrosine kinases are known regulators of cell division that have been implicated in the onset of a variety of malignancies. They act through cellular signaling proteins that bind to specific autophosphorylation sites. To find out whether these autophosphorylation sites can be used to identify downstream signaling proteins, synthetic peptides based on an autophosphorylation site in the colony-stimulating factor-1 (CSF-1) receptor were linked to agarose beads and incubated with lysates from macrophages. Bound proteins were analyzed by MS, leading to the identification of both known and novel CSF-1 receptor-interacting proteins. The approach presented here can be applied to phosphorylation sites in a wide variety of proteins. It will lead to the identification of novel protein-protein interactions and provide new insights into the mechanics of signal transduction. Novel protein-protein interactions may provide useful targets for the development of drugs that interfere with the activation of signaling cascades used by protein-tyrosine kinases to turn on cell division.

Solution structure of the human Grb7-SH2 domain/erbB2 peptide complex and structural basis for Grb7 binding to ErbB2

The solution structure of the hGrb7-SH2 domain in complex with a ten amino acid phosphorylated peptide ligand representative of the erbB2 receptor tyrosine kinase (pY1139) is presented as determined by nuclear magnetic resonance methods. The hGrb7-SH2 domain structure reveals the Src homology 2 domain topology consisting of a central beta-sheet capped at each end by an alpha-helix. The presence of a four residue insertion in the region between beta-strand E and the EF loop and resulting influences on the SH2 domain/peptide complex structure are discussed. The binding conformation of the erbB2 peptide is in a beta-turn similar to that found in phosphorylated tyrosine peptides bound to the Grb2-SH2 domain. To our knowledge this is only the second example of an SH2 domain binding its naturally occurring ligands in a turn, instead of extended, conformation. Close contacts between residues responsible for binding specificity in hGrb7-SH2 and the erbB2 peptide are characterized and the potential effect of mutation of these residues on the hGrb7-SH2 domain structure is discussed.

Developmental markers of B cells are superior to those of T cells for identification of stages with distinct gene expression profiles

B and T lymphocytes develop through a series of cellular stages, which are defined by recombination status of the immunoglobulin and T cell receptor loci and can be separated by analysis of cell-surface markers. We evaluated how well 26 and 41 samples from five and eight developmental stages of B and T cell development, respectively, could be correctly assigned to their lineage of origin and developmental stage by analysis of the expression of 13,026 genes and expressed sequence tags (ESTs). The RNA expression patterns of eight genes correctly classified all 67 samples as belonging to the B cell or to the T cell lineage. Ninety-two to 100% of B-lineage samples could be correctly assigned to the protein-defined developmental stage by the RNA expression pattern of 29 genes. By contrast, RNA expression patterns of 39 genes were necessary to correctly assign 85-100% of T-lineage samples to the correct developmental stage. The sets of genes used for these classifications contain ESTs as well as known genes that have not previously been associated with lymphocyte development. Graphical display of the classifications shows that B-lineage samples are well separated from T-lineage samples, and samples from the five stages of B cell development are well separated from each other. By contrast, samples from the eight stages of T cell development cannot be separated precisely. We conclude that the protein markers currently widely used for separating stages of B cell development better identify molecularly distinct stages than those used for separating stages of T cell development.