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  • Academic
    nkalogri@stanford.edu
    University - Academic staff Department: Genetics Position: Basic Life Research Scientist

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  • Mail Code: 5120

All Publications

  • Structural basis for GPCR-independent activation of heterotrimeric Gi proteins. Proceedings of the National Academy of Sciences of the United States of America Kalogriopoulos, N. A., Rees, S. D., Ngo, T., Kopcho, N. J., Ilatovskiy, A. V., Sun, N., Komives, E. A., Chang, G., Ghosh, P., Kufareva, I. 2019; 116 (33): 16394-16403

    Abstract

    Heterotrimeric G proteins are key molecular switches that control cell behavior. The canonical activation of G proteins by agonist-occupied G protein-coupled receptors (GPCRs) has recently been elucidated from the structural perspective. In contrast, the structural basis for GPCR-independent G protein activation by a novel family of guanine-nucleotide exchange modulators (GEMs) remains unknown. Here, we present a 2.0-Å crystal structure of Gαi in complex with the GEM motif of GIV/Girdin. Nucleotide exchange assays, molecular dynamics simulations, and hydrogen-deuterium exchange experiments demonstrate that GEM binding to the conformational switch II causes structural changes that allosterically propagate to the hydrophobic core of the Gαi GTPase domain. Rearrangement of the hydrophobic core appears to be a common mechanism by which GPCRs and GEMs activate G proteins, although with different efficiency. Atomic-level insights presented here will aid structure-based efforts to selectively target the noncanonical G protein activation.

    View details for DOI 10.1073/pnas.1906658116

    View details for PubMedID 31363053

    View details for PubMedCentralID PMC6697900

  • Convergence of Wnt, growth factor, and heterotrimeric G protein signals on the guanine nucleotide exchange factor Daple. Science signaling Aznar, N., Ear, J., Dunkel, Y., Sun, N., Satterfield, K., He, F., Kalogriopoulos, N. A., Lopez-Sanchez, I., Ghassemian, M., Sahoo, D., Kufareva, I., Ghosh, P. 2018; 11 (519)

    Abstract

    Cellular proliferation, differentiation, and morphogenesis are shaped by multiple signaling cascades, and their dysregulation plays an integral role in cancer progression. Three cascades that contribute to oncogenic potential are those mediated by Wnt proteins and the receptor Frizzled (FZD), growth factor receptor tyrosine kinases (RTKs), and heterotrimeric G proteins and associated GPCRs. Daple is a guanine nucleotide exchange factor (GEF) for the G protein Gαi Daple also binds to FZD and the Wnt/FZD mediator Dishevelled (Dvl), and it enhances β-catenin-independent Wnt signaling in response to Wnt5a-FZD7 signaling. We identified Daple as a substrate of multiple RTKs and non-RTKs and, hence, as a point of convergence for the three cascades. We found that phosphorylation near the Dvl-binding motif in Daple by both RTKs and non-RTKs caused Daple/Dvl complex dissociation and augmented the ability of Daple to bind to and activate Gαi, which potentiated β-catenin-independent Wnt signals and stimulated epithelial-mesenchymal transition (EMT) similarly to Wnt5a/FZD7 signaling. Although Daple acts as a tumor suppressor in the healthy colon, the concurrent increased abundance of Daple and epidermal growth factor receptor (EGFR) in colorectal tumors was associated with poor patient prognosis. Thus, the Daple-dependent activation of Gαi and the Daple-dependent enhancement of β-catenin-independent Wnt signals are not only stimulated by Wnt5a/FZD7 to suppress tumorigenesis but also hijacked by growth factor-activated RTKs to enhance tumor progression. These findings identify a cross-talk paradigm among growth factor RTKs, heterotrimeric G proteins, and the Wnt/FZD pathway in cancer.

    View details for DOI 10.1126/scisignal.aao4220

    View details for PubMedID 29487190

    View details for PubMedCentralID PMC5862031

  • Biochemical, Biophysical and Cellular Techniques to Study the Guanine Nucleotide Exchange Factor, GIV/Girdin. Current protocols in chemical biology Ghosh, P., Aznar, N., Swanson, L., Lo, I. C., Lopez-Sanchez, I., Ear, J., Rohena, C., Kalogriopoulos, N., Joosen, L., Dunkel, Y., Sun, N., Nguyen, P., Bhandari, D. 2016; 8 (4): 265-298

    Abstract

    Canonical signal transduction via heterotrimeric G proteins is spatiotemporally restricted, i.e., triggered exclusively at the plasma membrane, only by agonist activation of G protein-coupled receptors via a finite process that is terminated within a few hundred milliseconds. Recently, a rapidly emerging paradigm has revealed a noncanonical pathway for activation of heterotrimeric G proteins via the nonreceptor guanidine-nucleotide exchange factor, GIV/Girdin. Biochemical, biophysical, and functional studies evaluating this pathway have unraveled its unique properties and distinctive spatiotemporal features. As in the case of any new pathway/paradigm, these studies first required an in-depth optimization of tools/techniques and protocols, governed by rationale and fundamentals unique to the pathway, and more specifically to the large multimodular GIV protein. Here we provide the most up-to-date overview of protocols that have generated most of what we know today about noncanonical G protein activation by GIV and its relevance in health and disease. © 2016 by John Wiley & Sons, Inc.

    View details for DOI 10.1002/cpch.13

    View details for PubMedID 27925669

    View details for PubMedCentralID PMC5154557

  • Heterotrimeric G protein signaling via GIV/Girdin: Breaking the rules of engagement, space, and time. BioEssays : news and reviews in molecular, cellular and developmental biology Aznar, N., Kalogriopoulos, N., Midde, K. K., Ghosh, P. 2016; 38 (4): 379-93

    Abstract

    Canonical signal transduction via heterotrimeric G proteins is spatially and temporally restricted, that is, triggered exclusively at the plasma membrane (PM), only by agonist activation of G protein-coupled receptors (GPCRs) via a process that completes within a few hundred milliseconds. Recently, a rapidly emerging paradigm has revealed a non-canonical pathway for activation of heterotrimeric G proteins by the non-receptor guanidine-nucleotide exchange factor (GEF), GIV/Girdin. This pathway has distinctive temporal and spatial features and an unusual profile of receptor engagement: diverse classes of receptors, not just GPCRs can engage with GIV to trigger such activation. Such activation is spatially and temporally unrestricted, that is, can occur both at the PM and on internal membranes discontinuous with the PM, and can continue for prolonged periods of time. Here, we provide the most complete up-to-date review of the molecular mechanisms that govern the unique spatiotemporal aspects of non-canonical G protein activation by GIV and the relevance of this new paradigm in health and disease.

    View details for DOI 10.1002/bies.201500133

    View details for PubMedID 26879989

    View details for PubMedCentralID PMC5123561

  • Focal adhesions are foci for tyrosine-based signal transduction via GIV/Girdin and G proteins. Molecular biology of the cell Lopez-Sanchez, I., Kalogriopoulos, N., Lo, I. C., Kabir, F., Midde, K. K., Wang, H., Ghosh, P. 2015; 26 (24): 4313-24

    Abstract

    GIV/Girdin is a multimodular signal transducer and a bona fide metastasis-related protein. As a guanidine exchange factor (GEF), GIV modulates signals initiated by growth factors (chemical signals) by activating the G protein Gαi. Here we report that mechanical signals triggered by the extracellular matrix (ECM) also converge on GIV-GEF via β1 integrins and that focal adhesions (FAs) serve as the major hubs for mechanochemical signaling via GIV. GIV interacts with focal adhesion kinase (FAK) and ligand-activated β1 integrins. Phosphorylation of GIV by FAK enhances PI3K-Akt signaling, the integrity of FAs, increases cell-ECM adhesion, and triggers ECM-induced cell motility. Activation of Gαi by GIV-GEF further potentiates FAK-GIV-PI3K-Akt signaling at the FAs. Spatially restricted signaling via tyrosine phosphorylated GIV at the FAs is enhanced during cancer metastasis. Thus GIV-GEF serves as a unifying platform for integration and amplification of adhesion (mechanical) and growth factor (chemical) signals during cancer progression.

    View details for DOI 10.1091/mbc.E15-07-0496

    View details for PubMedID 26446841

    View details for PubMedCentralID PMC4666128

  • Activation of G proteins by GIV-GEF is a pivot point for insulin resistance and sensitivity. Molecular biology of the cell Ma, G. S., Lopez-Sanchez, I., Aznar, N., Kalogriopoulos, N., Pedram, S., Midde, K., Ciaraldi, T. P., Henry, R. R., Ghosh, P. 2015; 26 (23): 4209-23

    Abstract

    Insulin resistance (IR) is a metabolic disorder characterized by impaired insulin signaling and cellular glucose uptake. The current paradigm for insulin signaling centers upon the insulin receptor (InsR) and its substrate IRS1; the latter is believed to be the sole conduit for postreceptor signaling. Here we challenge that paradigm and show that GIV/Girdin, a guanidine exchange factor (GEF) for the trimeric G protein Gαi, is another major hierarchical conduit for the metabolic insulin response. By virtue of its ability to directly bind InsR, IRS1, and phosphoinositide 3-kinase, GIV serves as a key hub in the immediate postreceptor level, which coordinately enhances the metabolic insulin response and glucose uptake in myotubes via its GEF function. Site-directed mutagenesis or phosphoinhibition of GIV-GEF by the fatty acid/protein kinase C-theta pathway triggers IR. Insulin sensitizers reverse phosphoinhibition of GIV and reinstate insulin sensitivity. We also provide evidence for such reversible regulation of GIV-GEF in skeletal muscles from patients with IR. Thus GIV is an essential upstream component that couples InsR to G-protein signaling to enhance the metabolic insulin response, and impairment of such coupling triggers IR. We also provide evidence that GIV-GEF serves as therapeutic target for exogenous manipulation of physiological insulin response and reversal of IR in skeletal muscles.

    View details for DOI 10.1091/mbc.E15-08-0553

    View details for PubMedID 26378251

    View details for PubMedCentralID PMC4642855

  • GIV/girdin binds exocyst subunit-Exo70 and regulates exocytosis of GLUT4 storage vesicles. Biochemical and biophysical research communications Lopez-Sanchez, I., Ma, G. S., Pedram, S., Kalogriopoulos, N., Ghosh, P. 2015; 468 (1-2): 287-93

    Abstract

    Insulin resistance (IR) is a metabolic disorder characterized by impaired glucose uptake in response to insulin. The current paradigm for insulin signaling centers upon the insulin receptor (InsR) and its substrate IRS1; the latter is believed to be the chief conduit for post-receptor signaling. We recently demonstrated that GIV, a Guanidine Exchange Factor (GEF) for the trimeric G protein, Gαi, is a major hierarchical conduit for the metabolic insulin response. By virtue of its ability to directly bind the InsR, IRS1 and PI3K, GIV enhances the InsR-IRS1-Akt-AS160 (RabGAP) signaling cascade and cellular glucose uptake via its GEF function. Phosphoinhibition of GIV-GEF by the fatty-acid/PKCθ pathway inhibits the cascade and impairs glucose uptake. Here we show that GIV directly and constitutively binds the exocyst complex subunit Exo-70 and also associates with GLUT4-storage vesicles (GSVs) exclusively upon insulin stimulation. Without GIV or its GEF function, membrane association of Exo-70 as well as exocytosis of GSVs in response to insulin are impaired. Thus, GIV is an essential component within the insulin signaling cascade that couples upstream signal transducers within the InsR and G-Protein signaling cascade to downstream vesicular trafficking events within the exocytic pathway. These findings suggest a role of GIV in coordinating key signaling and trafficking events of metabolic insulin response.

    View details for DOI 10.1016/j.bbrc.2015.10.111

    View details for PubMedID 26514725

    View details for PubMedCentralID PMC4659757

  • Therapeutic effects of cell-permeant peptides that activate G proteins downstream of growth factors. Proceedings of the National Academy of Sciences of the United States of America Ma, G. S., Aznar, N., Kalogriopoulos, N., Midde, K. K., Lopez-Sanchez, I., Sato, E., Dunkel, Y., Gallo, R. L., Ghosh, P. 2015; 112 (20): E2602-10

    Abstract

    In eukaryotes, receptor tyrosine kinases (RTKs) and trimeric G proteins are two major signaling hubs. Signal transduction via trimeric G proteins has long been believed to be triggered exclusively by G protein-coupled receptors (GPCRs). This paradigm has recently been challenged by several studies on a multimodular signal transducer, Gα-Interacting Vesicle associated protein (GIV/Girdin). We recently demonstrated that GIV's C terminus (CT) serves as a platform for dynamic association of ligand-activated RTKs with Gαi, and for noncanonical transactivation of G proteins. However, exogenous manipulation of this platform has remained beyond reach. Here we developed cell-permeable GIV-CT peptides by fusing a TAT-peptide transduction domain (TAT-PTD) to the minimal modular elements of GIV that are necessary and sufficient for activation of Gi downstream of RTKs, and used them to engineer signaling networks and alter cell behavior. In the presence of an intact GEF motif, TAT-GIV-CT peptides enhanced diverse processes in which GIV's GEF function has previously been implicated, e.g., 2D cell migration after scratch-wounding, invasion of cancer cells, and finally, myofibroblast activation and collagen production. Furthermore, topical application of TAT-GIV-CT peptides enhanced the complex, multireceptor-driven process of wound repair in mice in a GEF-dependent manner. Thus, TAT-GIV peptides provide a novel and versatile tool to manipulate Gαi activation downstream of growth factors in a diverse array of pathophysiologic conditions.

    View details for DOI 10.1073/pnas.1505543112

    View details for PubMedID 25926659

    View details for PubMedCentralID PMC4443320

  • Intratumoral treatment of smaller mouse neuroblastoma tumors with a recombinant protein consisting of IL-2 linked to the hu14.18 antibody increases intratumoral CD8+ T and NK cells and improves survival. Cancer immunology, immunotherapy : CII Yang, R. K., Kalogriopoulos, N. A., Rakhmilevich, A. L., Ranheim, E. A., Seo, S., Kim, K., Alderson, K. L., Gan, J., Reisfeld, R. A., Gillies, S. D., Hank, J. A., Sondel, P. M. 2013; 62 (8): 1303-13

    Abstract

    Hu14.18-IL2 is an immunocytokine (IC) consisting of human IL-2 linked to hu14.18 mAb, which recognizes GD2 disialoganglioside. Phase II clinical trials of intravenous-hu14.18-IL2 (IV-IC) in neuroblastoma and melanoma are underway, and have already demonstrated activity in neuroblastoma. In our Phase II trial, lower neuroblastoma burden at the time of treatment was associated with a greater likelihood of clinical response to IV-IC. We have previously shown that intratumoral-hu14.18-IL2 (IT-IC) compared to IV-IC results in enhanced local and systemic antitumor activity in tumor-bearing mice. We utilized a mouse model to investigate the impact of tumor burden on hu14.18-IL2 treatment efficacy in IV- versus IT-treated animals. Studies presented here describe the analyses of tumor burden at the initiation of treatment and its effects on treatment efficacy, survival, and tumor-infiltrating leukocytes in A/J mice bearing subcutaneous NXS2 neuroblastoma. We show that smaller tumor burden at treatment initiation is associated with increased infiltration of NK and CD8+ T cells and increased overall survival. NXS2 tumor shrinkage shortly after completion of the 3 days of hu14.18-IL2 treatment is necessary for long-term survival. This model demonstrates that tumor size is a strong predictor of hu14.18-IL2-induced lymphocyte infiltration and treatment outcome.

    View details for DOI 10.1007/s00262-013-1430-x

    View details for PubMedID 23661160

    View details for PubMedCentralID PMC3720701

  • Tumor-associated myeloid cells can be activated in vitro and in vivo to mediate antitumor effects. Cancer immunology, immunotherapy : CII Rakhmilevich, A. L., Baldeshwiler, M. J., Van De Voort, T. J., Felder, M. A., Yang, R. K., Kalogriopoulos, N. A., Koslov, D. S., Van Rooijen, N., Sondel, P. M. 2012; 61 (10): 1683-97

    Abstract

    Tumor growth is often accompanied by the accumulation of myeloid cells in the tumors and lymphoid organs. These cells can suppress T cell immunity, thereby posing an obstacle to T cell-targeted cancer immunotherapy. In this study, we tested the possibility of activating tumor-associated myeloid cells to mediate antitumor effects. Using the peritoneal model of B16 melanoma, we show that peritoneal cells (PEC) in tumor-bearing mice (TBM) had reduced ability to secrete nitric oxide (NO) following in vitro stimulation with interferon gamma and lipopolysaccharide, as compared to PEC from control mice. This reduced function of PEC was accompanied by the influx of CD11b(+) Gr-1(+) myeloid cells to the peritoneal cavity. Nonadherent PEC were responsible for most of the NO production in TBM, whereas in naïve mice NO was mainly secreted by adherent CD11b(+) F4/80(+) macrophages. Sorted CD11b(+) Gr-1(-) monocytic and CD11b(+) Gr-1(+) granulocytic PEC from TBM had a reduced ability to secrete NO following in vitro stimulation (compared to naïve PEC), but effectively suppressed proliferation of tumor cells in vitro. In vivo, treatment of mice bearing established peritoneal B16 tumors with anti-CD40 and CpG resulted in activation of tumor-associated PEC, reduction in local tumor burden and prolongation of mouse survival. Inhibition of NO did not abrogate the antitumor effects of stimulated myeloid cells. Taken together, the results indicate that in tumor-bearing hosts, tumor-associated myeloid cells can be activated to mediate antitumor effects.

    View details for DOI 10.1007/s00262-012-1236-2

    View details for PubMedID 22392192

    View details for PubMedCentralID PMC3572779

  • Intratumoral hu14.18-IL-2 (IC) induces local and systemic antitumor effects that involve both activated T and NK cells as well as enhanced IC retention. Journal of immunology (Baltimore, Md. : 1950) Yang, R. K., Kalogriopoulos, N. A., Rakhmilevich, A. L., Ranheim, E. A., Seo, S., Kim, K., Alderson, K. L., Gan, J., Reisfeld, R. A., Gillies, S. D., Hank, J. A., Sondel, P. M. 2012; 189 (5): 2656-64

    Abstract

    hu14.18-IL-2 (IC) is an immunocytokine consisting of human IL-2 linked to hu14.18 mAb, which recognizes the GD2 disialoganglioside. Phase 2 clinical trials of i.v. hu14.18-IL-2 (i.v.-IC) in neuroblastoma and melanoma are underway and have already demonstrated activity in neuroblastoma. We showed previously that intratumoral hu14.18-IL-2 (IT-IC) results in enhanced antitumor activity in mouse models compared with i.v.-IC. The studies presented in this article were designed to determine the mechanisms involved in this enhanced activity and to support the future clinical testing of intratumoral administration of immunocytokines. Improved survival and inhibition of growth of both local and distant tumors were observed in A/J mice bearing s.c. NXS2 neuroblastomas treated with IT-IC compared with those treated with i.v.-IC or control mice. The local and systemic antitumor effects of IT-IC were inhibited by depletion of NK cells or T cells. IT-IC resulted in increased NKG2D receptors on intratumoral NKG2A/C/E⁺ NKp46⁺ NK cells and NKG2A/C/E⁺ CD8⁺ T cells compared with control mice or mice treated with i.v.-IC. NKG2D levels were augmented more in tumor-infiltrating lymphocytes compared with splenocytes, supporting the localized nature of the intratumoral changes induced by IT-IC treatment. Prolonged retention of IC at the tumor site was seen with IT-IC compared with i.v.-IC. Overall, IT-IC resulted in increased numbers of activated T and NK cells within tumors, better IC retention in the tumor, enhanced inhibition of tumor growth, and improved survival compared with i.v.-IC.

    View details for DOI 10.4049/jimmunol.1200934

    View details for PubMedID 22844125

    View details for PubMedCentralID PMC3424361